Article

The Nested Assembly of Plant Facilitation Networks Prevents Species Extinctions

February 2008
The American Naturalist 172(6):751-60

February 2008
172(6):751-60

DOI:10.1086/593003

Source
PubMed

Authors:

Alfonso Valiente-Banuet

Universidad Nacional Autónoma de México

Facilitation is a positive interaction assembling ecological communities and preserving global biodiversity. Although communities acquire emerging properties when many species interact, most of our knowledge about facilitation is based on studies between pairs of species. To understand how plant facilitation preserves biodiversity in complex ecological communities, we propose to move from the study of pairwise interactions to the network approach. We show that facilitation networks behave as mutualistic networks do, characterized by a nonrandom, nested structure of plant-plant interactions in which a few generalist nurses facilitate a large number of species while the rest of the nurses facilitate only a subset of them. Consequently, generalist nurses shape a dense and highly connected network. Interestingly, such generalist nurses are the most abundant species in the community, making facilitation-shaped communities strongly resistant to extinction, as revealed by coextinction simulations. The nested structure of facilitative networks explains why facilitation, by preventing extinction, preserves biodiversity.

Phylogenetic and functional constraints of plant facilitation rewiring

Article

Full-text available

Jan 2023
ECOLOGY

Facilitative interactions bind community species in intricate ecological networks, preserving species that would otherwise be lost. The traditional understanding of ecological networks as static components of biological communities overlooks the fact that species interactions in a network can fluctuate. Analyzing the patterns that cause those shifts can reveal the principles that govern the identity of pairwise interactions and whether they are predictable based on the traits of the interacting species and the local environmental contexts in which they occur. Here we explore how abiotic stress and phylogenetic and functional affinities constrain those shifts. Specifically, we hypothesize that rewiring the facilitative interactions is more limited in stressful than in mild environments. We present evidence of a distinct pattern in the rewiring of facilitation‐driven communities at different stress levels. In highly stressful environments with a firm reliance on facilitation, rewiring is limited to growing beneath nurse species with traits to overcome harsh stressful conditions. However, when environments are milder, rewiring is more flexible, although it is still constrained to nurses that are close relatives. Understanding the ability of species to rewire their interactions is crucial for predicting how communities may respond to the unprecedented rate of perturbations on Earth.

RecruitNet: A global database of plant recruitment networks

Article

Full-text available

Jan 2023
ECOLOGY

Plant recruitment interactions (i.e., what recruits under what) shape the composition, diversity, and structure of plant communities. Despite the huge body of knowledge on the mechanisms underlying recruitment interactions among species, we still know little about the structure of the recruitment networks emerging in ecological communities. Modeling and analyzing the community‐level structure of plant recruitment interactions as a complex network can provide relevant information on ecological and evolutionary processes acting both at the species and ecosystem levels. We report a data set containing 143 plant recruitment networks in 23 countries across five continents, including temperate and tropical ecosystems. Each network identifies the species under which another species recruits. All networks report the number of recruits (i.e., individuals) per species. The data set includes >850,000 recruiting individuals involved in 118,411 paired interactions among 3318 vascular plant species across the globe. The cover of canopy species and open ground is also provided. Three sampling protocols were used: (1) The Recruitment Network (RN) protocol (106 networks) focuses on interactions among established plants (“canopy species”) and plants in their early stages of recruitment (“recruit species”). A series of plots was delimited within a locality, and all the individuals recruiting and their canopy species were identified; (2) The paired Canopy‐Open (pCO) protocol (26 networks) consists in locating a potential canopy plant and identifying recruiting individuals under the canopy and in a nearby open space of the same area; (3) The Georeferenced plot (GP) protocol (11 networks) consists in using information from georeferenced individual plants in large plots to infer canopy‐recruit interactions. Some networks incorporate data for both herbs and woody species, whereas others focus exclusively on woody species. The location of each study site, geographical coordinates, country, locality, responsible author, sampling dates, sampling method, and life habits of both canopy and recruit species are provided. This database will allow researchers to test ecological, biogeographical, and evolutionary hypotheses related to plant recruitment interactions. There are no copyright restrictions on the data set; please cite this data paper when using these data in publications.

Outcomes of facilitative plant interactions in shrublands of NW Patagonia, Argentina

Article

Full-text available

May 2021

Question The study examined the plant-plant interaction networks and we analyzed to what extent different nurse species groups with different traits (evergreen and deciduous) mediate the outcomes of the facilitated species composition Location Four shrublands located in Nahuel Huapi National Park, in Northern Patagonia, Argentina (41°11'55.34" S and 71°19'43.07" W). Methods We selected ten woody species as nurse species: five evergreens and five deciduous species. We recorded species composition and total cover below nurse species and in open spaces during two consecutive years, with different inter-annual precipitation variability. We determined the facilitated species with RII index, constructed facilitation networks, and analyzed the species composition below nurses and in open spaces Results In our networks, nurse and facilitated species are generalist species. The species composition below the nurse canopies and open areas varied between years. The structure and parameters of networks built on two consecutive years were similar. However, we found changes on plant species interactions between the studied years. The species composition of the facilitated species growing below deciduous and evergreen nurse species groups was similar. Conclusions Our findings provide insights into the facilitation networks knowledge in Patagonian shrublands. We found that networks were not nested and had many generalist species (nurses and facilitated). It implies that the disappearance of any nurse species would not change the community maintenance.

Evaluación de sistemas agroforestales dinámicos en el semiárido de Cochabamba. Diez estudios de caso de las comunidades de Rodeo (Sacaba), La Maica (Tarata), Aramasí (Tapacarí) y Combuyo y Pairumani (Vinto)

Book

Full-text available

Nov 2018

Mauricio Azero

Relationships between productive trees and accompanying trees in dynamic agroforestry systems of xeric bioclimate (Spanish)

Chapter

Full-text available

Nov 2020

Desafios cientificos. Ciencia aplicada e innovación social. El caso de sistemas agroforestales dinámicos en Cochabamba, Bolivia

Book

Full-text available

Oct 2020

Este libro tende un puente entre la Geografa Aplicada, una ciencia que busca solución a problemas actuales desde una perspectva holístca, y una propuesta concreta de innovación social, que permite una producción agrícola que mitga el impacto del cambio climátco e inicia procesos de restauración de suelos. Tomando en cuenta perspectvas europeas y latnoamericanas son desarrollados conocimientos multdisciplinarios que ofrecen solución a problemas actuales complejos, como son los ecosistemas degradados. Desde la Geografa Aplicada y su mirada novedosa hacia conocimientos locales innovadores, es apuntada la Agroforestería Dinámica. El lector podrá informase sobre algunos argumentos a favor de esta técnica productva que, aún en suelos en proceso de desertfcación, permite la producción al mismo tempo que la restauración del medio ambiente. Los resultados dan la esperanza de que los sistemas agroforestales dinámicos pueden ser aplicados en otras regiones que sufren los impactos del cambio climátco, tales como la sequía creciente, las temperaturas extremas y la perdida de la biodiversidad.

Uncovering structural features that underlie coexistence in an invaded woody plant community with interaction networks at multiple life stages

Article

Full-text available

Sep 2020
J ECOL

Nicole L. Kinlock

Understanding the patterns of competitive and facilitative interactions within and among species in plant communities is a central goal of plant ecology, because these patterns determine species coexistence and community dynamics. Network theory provides tools that allow these patterns to be quantified, and can provide greater understanding of important community properties, including community stability, than can documenting pairwise species interactions. I characterized the interactions of multiple, co‐occurring invasive and native species in an old field woody plant community to build plant interaction networks at two different life stages. With the goal of identifying structural features that may operate to maintain species coexistence, I characterized the architecture of these networks at multiple scales: the entire network, the substructures that compose the network and species' roles within substructures. I found that species‐level pairwise interactions alone did not provide an accurate or sufficiently detailed picture of community structure. Rather, using a network approach, I identified substructures that have the potential to promote and hinder species coexistence in interactions among seedlings. Characterizing the nuances of network substructures was illuminating, as the size of the substructures and the pattern of interaction intensities within substructures influence the expected effects on species coexistence. Including interactions at multiple life stages was also important; the seedling species that benefited most from the nested structure of facilitative interactions with adults occupied subordinate roles in substructures with other seedlings. This role reversal at different life stages is a potential factor promoting coexistence in the community. Last, the network framework was useful for comparing species' roles between native and invasive members of the community, and the three invasive species in this system had different, life stage‐dependent strategies in interactions with co‐occurring plants. Synthesis. The interplay of network architecture and substructures within plant communities and among plants at different life stages is important for understanding species coexistence. In the plant community characterized in this study, there were several features that may promote coexistence, and these features were not observable in interactions within a single life stage or when considering pairwise interactions independently.

Unifying facilitation and recruitment networks

Article

Jul 2019

Ecological network studies are providing important advances about the organization, stability and dynamics of ecological systems. However, the ecological networks approach is being integrated very slowly in plant community ecology, even though the first studies on plant facilitation networks were published more than a decade ago. The study of interaction networks between established plants and plants recruiting beneath them, which we call Recruitment Networks (RNs), can provide new insights on mechanisms driving plant community structure and dynamics. RNs basically describe which plants recruit under which others, so they can be seen as a generalisation of the classic Facilitation Networks (FNs) since they do not imply any particular effect (positive, negative or neutral) of the established plants on recruiting ones. RNs summarise information on the structure of sapling banks. More importantly, the information included in RNs can be incorporated into models of replacement dynamics to evaluate how different aspects of network structure, or different mechanisms of network assembly, may affect plant community stability and species coexistence. To allow an efficient development of the study of FNs and RNs, here we unify concepts, synthesise current knowledge, clarify some conceptual issues, and propose basic methodological guidelines to standardise sampling methods that could make future studies of these networks directly comparable.

Contextualizing the ecology of plant–plant interactions and constructive networks

Article

Full-text available

Jul 2023

Gianalberto Losapio

Botanical concepts have traditionally viewed the environment as a static box containing plants. In this box, plants compete with one another and act as passive resource consumers subjected to the environment in a top-down manner. This entails that plants have only negative effects on other plants and have no influence on the environment. By contrast, there is increasing evidence that plants have positive, bottom-up engineering effects and diversity effects on other plants and on the environment. Here, to overcome limitations of top-down environmental control, antagonistic-only, and pairwise interactions, I propose the concept of constructive networks. Constructive networks unify niche construction and network theory recognizing that (i) plants have manifold ecological functions and impacts on their neighbors, and (ii) the environment shapes and is shaped by diverse organisms, primarily plants. Constructive networks integrate both plant–environment and plant–plant interactions in a relational context. It is addressed how plants influence the environment and support or inhibit other plant species by physically, biochemically, and ecologically shaping environmental conditions. Constructive networks acknowledge the fact that diverse plants change and create novel environmental conditions as well as co-produce, share, and transform resources, thereby influencing biological communities and the environment in constructive ways. Different interaction types are considered simultaneously in constructive networks. Yet, the understanding of constructive networks is mainly limited by identifying plant links. This barrier may be overcame by applying complexity theory and statistical mechanics to comparative data and experimental field botany. Considering multiple interaction types and feedbacks between plants and the environment may improve our understanding of mechanisms responsible for biodiversity maintenance and help us to better anticipate the response of plant systems to global change.

Drivers and consequences of structure in plant–lemur ecological networks

Article

Full-text available

Sep 2022
J ANIM ECOL

Species interactions shape the diversity and resilience of ecological networks. Plant and animal traits, as well as phylogeny, affect interaction likelihood, driving variation in network structure and tolerance to disturbance. We investigated how traits and phylogenetic effects influenced network‐wide interaction probabilities and examined the consequences of extinction on the structure and robustness of ecological networks. We combined both mutualistic and antagonistic interactions of animals (55 species, Infraorder Lemuriformes, Order Primates) and their food plants (590 genera) throughout Madagascar to generate ecological networks. We tested the effects of both lemur and plant traits, biogeographic factors and phylogenetic relatedness on interaction probability in these networks using exponential random graph models. Next, we simulated animal and plant extinction to analyse the effects of extinction on network structure (connectance, nestedness and modularity) and robustness for mutualistic, antagonistic and combined plant–animal networks. Both animal and plant traits affected their interaction probabilities. Large, frugivorous lemurs with a short gestation length, occurring in arid habitats, and with a Least Concern threat level had a high interaction probability in the network, given all other variables. Closely related plants were more likely to interact with the same lemur species than distantly related plants, but closely related lemurs were not more likely to interact with the same plant genus. Simulated lemur extinction tended to increase connectance and modularity, but decrease nestedness and robustness, compared to pre‐extinction networks. Networks were more tolerant to plant than lemur extinctions. Lemur–plant interactions were highly trait structured and the loss of both lemurs and plants threatened the tolerance of mutualistic, antagonistic and combined networks to future disturbance.

Positive heterospecific interactions can increase long‐term diversity of plant communities more than negative conspecific interactions alone

Article

Full-text available

Nov 2021
FUNCT ECOL

Negative conspecific interactions have been shown to promote diversity in plant communities, as have some heterospecific interactions such as intransitive competition and facilitation. However, it is unclear whether combinations of conspecific and other heterospecific interactions can also promote diversity in plant communities. We therefore investigated the effects of heterospecific plant interaction network architecture with and without conspecific interactions on alpha diversity, beta diversity and long‐term diversity. We simulated long‐term plant community dynamics for theoretical plant interaction scenarios with modular, ring and nested networks of positive or negative heterospecific interactions and conspecific interactions, using a spatially explicit cellular automaton model that accounted for stochastic effects. Throughout the simulations several measures of diversity were recorded. The way that heterospecific interactions affected diversity depended strongly on various characteristics of the architecture of the interaction network. Negative conspecific interactions generally promoted alpha diversity and reduced beta diversity, with a few key exceptions. Positive heterospecific ring interactions that resulted in cyclic appearance and disappearance of species groups led to the greatest long‐term diversity (a measure of the total diversity over time). This study provides new theoretical insights into how the network architecture of heterospecific plant interactions can affect the diversity of plant communities over time and provides the first evidence that heterospecific plant interactions can increase long‐term diversity more than negative conspecific interactions alone. A free Plain Language Summary can be found within the Supporting Information of this article.

Positive interactions support complex networks

Preprint

Jun 2017

Ecologists have recognised the effects of biotic interactions on the spatial distribution of living organisms. Yet, the spatial structure of plant interaction networks in real-world ecosystems has remained elusive so far. Using spatial pattern and network analyses, we found that alpine plant communities are organised in spatially variable and complex networks. Specifically, the cohesiveness of complex networks is promoted by short-distance positive plant interactions. At fine spatial scale, where positive mutual interactions prevailed, networks were characterised by a large connected component. With increasing scale, when negative interactions took over, network architecture became more hierarchical with many detached components that show a network collapse. This study highlights the crucial role of positive interactions for maintaining species diversity and the resistance of communities in the face of environmental perturbations.

The assembly of plant–patch networks in Mediterranean alpine grasslands

Article

Full-text available

Jun 2020
J PLANT ECOL-UK

Aims Harsh environmental conditions in alpine ecosystems shape vegetation structure into patches, where many different plant species cluster and grow together. Yet, which factors are important for the structure and dynamics of such plant–patch networks remains poorly understood. We aim to assess which and how environmental and biotic factors predict the assembly of plant–patch networks along a mountain range. Methods We examined the distribution of plant species in more than 5500 vegetation patches in 37 Mediterranean alpine grasslands distributed along a 500 m altitudinal gradient (National Park of Sierra Guadarrama, Spain). We established a plant–patch network for each grassland community and analyzed how nestedness and modularity vary with environmental (altitude, insolation and soil conditions) and biotic factors (number of species per plot, mean patch area and total pasture area). Important Findings Plant–patch networks showed consistent, non-random patterns characterized by a nested, but not modular, structure, which suggests that positive associations among co-occurring specialists promote their growth within patches as subsets of a pool with more generalist species. Both nestedness and modularity of plant–patch networks varied among grasslands. Specifically, nestedness decreased with increasing species per plot and increased with mean patch area, while it was independent of environmental variables; modularity increased with increasing pasture area and species per plot. The negative relationship between species per plot and nested patterns may be linked to the restricted number of species that can coexist within the same patch at a given size. Moreover, the positive relationship between patch size and nestedness indicates that the growth of rare plant species within vegetation patches occupied by more abundant species is facilitated in bigger rather than smaller patches. Furthermore, these results indicate that the nested assembly of vegetation patches may be independent of abiotic conditions. These findings suggest that large and unfragmented vegetation patches are fundamental for the maintenance of plant diversity in alpine grasslands. Looking at species distribution at fine spatial scales may shed new light on the biotic processes underlying plant network assembly and provide novel ways for conserving biodiversity.

Septoglomus mexicanum , a new species of arbuscular mycorrhizal fungi from semiarid regions in Mexico

Article

Nov 2019

Septoglomus mexicanum is here described as a new species of arbuscular mycorrhizal fungi (AMF; Glomeromycota) based on morphological and phylogenetic analyses. It was isolated from rhizospheric soil of two endemic Mexican legumes: Prosopis laevigata and Mimosa luisana, which grow in semiarid regions of central Mexico. Septoglomus mexicanum is characterized by forming globose spores of (154.5–)202.8(–228.9) µm diam and a spore wall consisting of four layers (SWL1–SWL4): outer wall layer (SWL1) hyaline, evanescent, (1.7–)3.2(–4.3) µm thick; SWL2 laminate and smooth, orange to reddish orange, (3.1–)4.5(–6.1) µm thick; SWL3 laminate, smooth, reddish orange to reddish brown, (4.1–)5.1(–5.7) µm thick; and SWL4 hyaline, semiflexible, (0.93–)1.2(–1.4) µm thick. None of the spore wall layers stain with Melzer’s reagent. The subtending hypha has a color from yellowish to golden and presents a septum on spore base. Septoglomus mexicanum can be distinguished from all other Septoglomus species by spore size and color, by spore wall structure (four layers), and by color change of the subtending hypha. Phylogenetic analysis based on the AMF extended DNA barcode covering a 1.5-kb fragment of the small subunit (SSU), internal transcribed spacer region (ITS1-5.8S-ITS2), and the large subunit (LSU) of rRNA genes places S. mexicanum in the genus Septoglomus, separated from other described Septoglomus species, especially S. turnauae, with whom it could be confused morphologically. All available sequences in public databases suggest that this new fungal species has not yet been previously detected. Thus, there are currently 149 Glomeromycota species registered in Mexico, representing 47.4% of the known species worldwide.

Plant interactions can lead to emergent relationships between plant community diversity, productivity and vulnerability to invasion

Article

Full-text available

Jun 2024

Understanding what makes a community vulnerable to invasion is integral to the successful management of invasive species. Our understanding of how characteristics of resident plant interactions, such as the network architecture of interactions, can affect the invasibility of plant communities is limited. Using a simulation model, we tested how successfully a new plant invader established in communities with different network architectures of species interactions. We also investigated whether species interaction networks lead to relationships between invasibility and other community properties also affected by species interaction networks, such as diversity, species dominance, compositional stability and the productivity of the resident community. We found that higher invasibility strongly related with a lower productivity of the resident community. Plant interaction networks influenced diversity and invasibility in ways that led to complex but clear relationships between the two. Heterospecific interactions that increased diversity tended to decrease invasibility. Negative conspecific interactions always increased diversity and invasibility, but increased invasibility more when they increased diversity less. This study provides new theoretical insights into the effects of plant interaction networks on community invasibility and relationships between diversity and invasibility. Combined with increasing empirical evidence, these insights could have useful implications for the management of invasive plant species.

Análisis del conocimiento actual de la ecología, evolución y manejo del género Bursera (Burseraceae) en México

Article

Full-text available

May 2024
ACTA BOT MEX

Antecedentes y Objetivos: El género Bursera es altamente diverso y alcanza su mayor riqueza en México. Dada su relevancia, usos actuales y potenciales y el reciente aumento en las publicaciones en torno a él, es necesario analizar los avances en su conocimiento. Presentamos una revisión de las publicaciones sobre ecología, historia natural, evolución, usos y manejo del género en México, con el fin de analizar las tendencias generales en el conocimiento y detectar las áreas que requieren más investigación.Métodos: Se consultaron las bases de datos Scopus y Lens; el periodo abarcó desde la primera publicación (1965) hasta 2022. Los datos se depuraron e integraron y se realizó un análisis en la librería bibliometrix de R; las publicaciones se clasificaron en 19 categorías. Adicionalmente, se analizó la distribución de las especies en función de un gradiente de aridez, para establecer en qué intervalo se encuentran las especies más (y menos) estudiadas.Resultados clave: La base de datos consta de 216 publicaciones producidas entre 1965 y 2022. A partir de 2000 se registra un claro incremento en el número de publicaciones. Destacan las palabras clave Burseraceae, México y Bursera, seguidas por bosque seco y filogenia. Los estudios de composición y estructura de la vegetación y los relativos a usos fueron los más abundantes, seguidos por los de florística, distribución, evolución, sucesión e interacciones. Entre los tópicos emergentes destacan rasgos funcionales, ecología de poblaciones y restauración ecológica. Solo 16 especies cuentan con ≥10 publicaciones; las del intervalo más seco son las menos estudiadas.Conclusiones: A pesar de los avances recientes, aún hay un conjunto amplio de temas y de especies que no han sido estudiadas; es necesario incrementar sustancialmente las investigaciones en ellas. Los análisis de genética y dinámica de poblaciones han estado casi ausentes, y algunas interacciones han recibido poca atención.

Homogeneous microenvironmental conditions under nurses promote facilitation

Article

Full-text available

Dec 2023
FUNCT ECOL

Biotic interactions are highly affected by species traits and micro‐environmental variability. Research on facilitation has primarily focused on how nurse species alleviate abiotic stress for beneficiary species, while the impact of the micro‐environmental variability generated by nurse plants in shaping facilitation outcomes is poorly understood. This study has two objectives: (i) To evaluate which traits define beneficiary species and (ii) to evaluate whether nurse and non‐nurse species differ in their ability to reduce abiotic stress and its variability under their canopy. We sampled recruits in two arid and stressful environments to assess (i) which species accumulate more juveniles beneath their canopy controlling for their coverage (nurse vs. non‐nurse species) and (ii) which species benefited from facilitation by determining whether they tend to recruit more beneath other species or on the bare ground (beneficiary/non‐beneficiary). First, we compared how nurse and non‐nurse species modify the physical and chemical microenvironments underneath their canopy, both in terms of magnitude and variation. Second, we compared root growth, water retention and nutrient accumulation in juvenile plants of beneficiary and non‐beneficiary species. We found that facilitation is enhanced by species that provide a more homogeneous microenvironment rather than an intense reduction of microenvironmental stress under their canopy. In addition, the juveniles of beneficiary species invest more in root development, accumulate Ca and S in their shoot tissues, and show a higher water content than non‐beneficiary species. Our findings indicate that the homogeneity of microenvironments plays a crucial role in facilitative interactions, and the juveniles of beneficiary species show a less conservative strategy, investing more in resource acquisition than juveniles of non‐beneficiary species. Read the free Plain Language Summary for this article on the Journal blog.

Multiple interaction networks reveal that Lepidoptera larvae and adults prefer various host plants for diet and pollination

Article

Full-text available

Jul 2023
Integr Zool

Plant-Lepidoptera interactions are often studied using the pollination or herbivore networks only. Lepidoptera species are involved in two types of plant-insect interactions because they are herbivores as larvae and pollinators as adults. The study of entangled networks is critical, since the interaction of different networks can affect the overall network and community stability. Here, we studied the interaction of plants and Lepidoptera on the Yongxing Island, South China Sea. A plant-lepidopteran pollination network and a plant-lepidopteran herbivore network were built by using data from flower-pollinator and leaf-herbivore interactions. We then combined the two networks into a single network. We measured plant composition similarity within each sub-network and across sub-networks for Lepidoptera species. Our findings indicate that the plant-Lepidoptera pollination network and the herbivory network share significant proportions of Lepidoptera but small proportions of plant assemblages. The pollination network had higher nestedness and connectance than the herbivore network. Agrius convolvuli was the most specialized species, while Zizina otis had the highest species strength in the pollination network. Most Lepidoptera species were highly specialized in the herbivore network and their importance positively correlated across the two networks. Furthermore, there was no dietary composition similarity between the two networks for most Lepidoptera species. Our findings highlight the visible structural difference between the pollination and the herbivore networks. Adult Lepidoptera selects different plants for oviposition and feeding, a strategy that may benefit their reproduction and survival by sustaining adequate resources for their two life stages and the diversity of both plants and insects in oceanic island communities.

Removing flowers of a generalist plant changes pollinator visitation, composition, and interaction network structure

Article

Full-text available

Jul 2022

Pollination is essential for ecosystem functioning, yet our understanding of the empirical consequences of species loss for plant–pollinator interactions remains limited. It is hypothesized that the loss of abundant and generalized (well‐connected) species from a pollination network will have a large effect on the remaining species and their interactions. However, to date, relatively few studies have experimentally removed species from their natural setting to address this hypothesis. We investigated the consequences of losing an abundant, generalist native species from a series of plant–pollinator networks by experimentally removing the flowers of Helianthella quinquenervis (Asteraceae) from half of a series of 10 paired plots (15 m diameter) within a subalpine ecosystem. We then asked how the localized loss of this species influenced patterns of pollinator visitation, floral visitor composition, and interaction network structure. The experimental removal of Helianthella flowers led to an overall decline in plot‐level pollinator visitation rates and shifts in pollinator composition. Species‐level responses to floral removal differed between the two other abundant, co‐flowering plants in our experiment: Potentilla pulcherrima received higher visitation rates, whereas Erigeron speciosus visitation rates did not change. Experimental floral removal altered the structural properties of the localized plant–pollinator networks such that they were more specialized, less nested, and less robust to further species loss. Such changes to interaction network structure were consistently driven more by species turnover than by interaction rewiring. Our findings suggest that the local loss of an abundant, well‐linked, generalist plant can bring about diverse responses within intact pollination networks, including potential competitive and facilitative effects for individual species, changes to network structure that may render them more sensitive to future change, but also numerous changes to interactions that may also suggest flexibility in response to species loss.

CAPÍTULO II Salud ambiental: objetos de estudio, metodologías y métodos

Chapter

Full-text available

Dec 2021

La evolución del campo de la salud ambiental como un ámbito interdisciplinario del saber, se puede caracterizar a través del tiempo en etapas las cuales están marcadas principalmente por los objetos de estudio, los enfoques metodológicos y los métodos implementados. En este capítulo analizamos de forma histórica los grandes cambios que ha presentado la salud ambiental a partir de dos preguntas clave: ¿qué ha estudiado? y ¿cómo lo ha estudiado? Adicionalmente presentamos a manera de ejemplos tres casos de objetos de investigación correspondientes a la salud ambiental y describimos la metodología y los métodos de estudio que se aplican para su abordaje.

The stress gradient hypothesis explains plant-plant interaction networks in edapho climatic gradients

Article

Apr 2022
ACTA OECOL

The stress-gradient hypothesis (SGH) predicts a shift from facilitation to competition as the environment turns from severe to favorable. Different authors have reported conflicting results when testing the SGH, mainly concerning the role of facilitation in stressful environments. We aimed to infer the mechanisms best explaining the variation of interspecific interactions across gradients through the joint analysis of network metrics and abiotic variables. We analyzed six plant-plant interaction networks (size, number of links, connectance, average degree, nestedness, and modularity) in edapho-climatic gradients in northeastern Brazil. Nestedness occurs when many species connect both with each other and with a set of other species with few connections, indicating facilitation. Modularity occurs when the network is split into groups of species linking to each other only within the groups, indicating competition. We used correlation, multiple linear regressions, and a generalized linear model to understand how the abiotic variables could drive network alterations and if the abundance of a possible benefactor species (Fabaceae trees) could increase facilitation. All the climate, soil, and network variables varied widely across the sites. All the sites had aluminium-toxic, nutrient-poor and nitrogen-limited soils, and Holdridge's life zones varied from very dry to moist tropical forests. Climate, soil, and network variables were correlated to each other, but the soil was the main driver of variation in the network metrics. Nestedness and modularity were negatively correlated, and both were correlated with the number of Fabaceae trees in each community. Deciduous species in very dry and dry forests require more nitrogen than evergreen species in dry/moist and moist forests, so the soil was more limiting to the deciduous species, which associated with Fabaceae trees and increased network nestedness. Our data corroborated the SGH, which, in this case, was mediated by the soil nutrient status and had Fabaceae as the benefactor species.

Interacciones positivas entre plantas, en Pinares sobre arenas de cuarzo de Santa Teresa

Article

Full-text available

Aug 2020

Plant-Plant interactions on extreme environments

Endemic Mimosa species, forming resource islands or not, and rainfall seasonality jointly influence arbuscular mycorrhizal fungi communities in a semiarid ecosystem of Mexico

Article

Full-text available

Apr 2022
TREES-STRUCT FUNCT

Key message Woody Mimosa species, forming resource islands or not, affected the structure of mycorrhizal communities and increased soil fertility, being thus priority targets for conservation and reclamation of edaphic functions. Abstract In arid and semiarid ecosystems woody plants forming resource islands (RIs) contribute to improve soil fertility; however, its effect on arbuscular mycorrhizal fungi (AMF) communities is little known. The objectives of this study were to: (1) characterize the AMF communities and their mycorrhizal potential in soil associated to four woody species of Mimosa, three that are RIs-forming (M. lacerata, M. luisana and M. polyantha) and one that is not (M. purpusii-NRIs) compared to open areas (OAs) without plants; and (2) determine the relationship between AMF and soil properties in two seasons (rainy and dry) in the semiarid Tehuacán–Cuicatlán Valley (TCV), Puebla and Oaxaca, Mexico. All Mimosa species favoured AMF richness and spore abundance and altered AMF composition, but to varying degrees depending on the Mimosa species. The three Mimosa species forming RIs and M. purpusii-NRIs improved soil conditions and resources to a similar extent as compared to OAs changing thus AMF species composition; however, only the RIs of M. luisana and M. polyantha did promote AMF diversity under conditions of greater disturbance in the vegetation structure. In contrast, these Mimosa species did not increase mycorrhizal inoculum potential compared to OAs. In addition, the rainfall seasonality affected the fungal community mostly in M. luisana-RI and M. polyantha-RI than in M. lacerata-RI and M. purpusii-NRI. In conclusion, these four Mimosa species, RIs-forming or not, affected AMF communities and soil fertility, being thus priority targets for conservation and reclamation of edaphic functions that perform these fungi within semiarid TCV, so the biology of these woody plants and their symbionts must be better documented.

Sunbird pollination and the fate of strong contributors to a mutualistic network in a West African Montane Forest

Thesis

Full-text available

Jan 2014

Charles Nsor

The survival of most species depends on their network of mutualistic partnerships with other species. Network structure - the pattern and arrangement of species in a given interaction, can reveal predictable outcomes on the fate of species and network stability. Therefore understanding what makes networks stable is extremely important. However current investigations into network stability have mainly been through theoretical and simulation studies and often based on data from plant-insect visitation networks. Empirical testing is now imperative and networks other than just plant-insect ones need to be incorporated into such studies. Moreover, the use of visitation frequency as a proxy for pollination frequency in plant-pollination network studies needs to be evaluated. In this thesis, I tested theoretical views and models on network structure and species survival using empirical data from a sunbird-tree pollination network in a remote montane forest reserve in Nigeria. First I investigated how changing landscapes and habitats affected sunbird distribution in the reserve. Secondly I compared a sunbird-tree visitation with a sunbird-tree pollination network to determine how good a proxy bird visitation is for bird pollination. Two network properties which affect network stability and underpin this work are i) connectance/ interaction strength and ii) nestedness. I examined how species relative abundance influences their interaction strength in the network and whether a species contribution to nestedness determines its survival probability. This latter point was of special interest as theoretical studies on networks have suggested that species which contribute the most to nestedness are most prone to extinction, which seems counterintuitive. The visitation frequencies of sunbird species on flowers of as many tree species as was logistically possible were observed, and sunbird species were trapped to determine the amount of pollen they transported. Using these data, I developed the flower visitation (FVN) and pollen transport networks (PTN). To determine how FVN reflects PTN, I compared the two networks using null models that controlled for species’ degree (number of links) and network size. Differences in observed nestedness differed significantly from null model expectations. I worked out an extinction proneness based on IUCN criteria for determining species at risk of extinction using rarity as a measure of vulnerability. An assessment of species abundance and diversity in the reserve and nearby fragments provided the standard for risk categorisation and evaluation of species’ robustness to changing landscapes. FVN correlated significantly with PTN, despite 64 % dissimilarity in species composition. The PTN had fewer species than FVN, but was more nested and specialised than the FVN, indicating that analyses of FVN often overestimate pollination through the inclusion of interactions with variable effects such as nectar robbing and insectivory. Although some species were relatively stronger interactors in both networks, the strongest contributor for FVN was not the strongest for PTN. FVN is therefore an inadequate predictor of efficient pollinators and a poor reflection of PTN. Abundant species had a higher interaction strength overall. Strong contributors to nestedness were the rare species, which explains why they are more prone to extinction. In my empirical network, nestedness will decrease overall through the loss of rare species, but in accordance with network theory, this will not collapse the network, because it is the abundant species with the most links which maintain network stability. Although fragmentation is not yet a challenge to sunbird distribution, anthropogenic disturbance such as indiscriminate burning of grassland to stimulate re-growth, may alter crucial habitats for sunbird survival.

Predictions of primate–parasite coextinction

Article

Full-text available

Sep 2021

Future biodiversity loss threatens the integrity of complex ecological associations, including among hosts and parasites. Almost half of primate species are threatened with extinction, and the loss of threatened hosts could negatively impact parasite associations and ecosystem functions. If endangered hosts are highly connected in host–parasite networks, then future host extinctions will also drive parasite extinctions, destabilizing ecological networks. If threatened hosts are not highly connected, however, then network structure should not be greatly affected by the loss of threatened hosts. Networks with high connectance, modularity, nestedness and robustness are more resilient to perturbations such as the loss of interactions than sparse, nonmodular and non-nested networks. We analysed the interaction network involving 213 primates and 763 parasites and removed threatened primates (114 species) to simulate the effects of extinction. Our analyses revealed that connections to 23% of primate parasites (176 species) may be lost if threatened primates go extinct. In addition, measures of network structure were affected, but in varying ways because threatened hosts have fewer parasite interactions than non-threatened hosts. These results reveal that host extinctions will perturb the host–parasite network and potentially lead to secondary extinctions of parasites. The ecological consequences of these extinctions remain unclear. This article is part of the theme issue ‘Infectious disease macroecology: parasite diversity and dynamics across the globe’.

Plant-pollinator conservation from the perspective of systems-ecology

Article

Jul 2021

Ecosystems are interconnected and complex, but conservation has often focused on rehabilitating individual species. A systems-ecology approach aims to support overall ecosystem structure and maintain ecological functions, and may be especially pertinent for mutualistic plant-pollinator communities. This approach focuses on species interactions as the units to be conserved within the larger ecosystem. Analyzing species interactions is a more holistic approach because it incorporates a broader web of organisms, and considers the plethora of potential indirect influences from interacting partners. In this article, we suggest pollinator researchers focus on plant-pollinator networks to inform conservation programs and best support the coexistence of pollinators and plants within natural and agricultural systems. We propose that a system-ecology perspective is the most promising way to simultaneously improve pollinator conservation, agricultural sustainability, and human well-being.

Plant–plant co-occurrences under a complex land-use gradient in a temperate forest

Article

Full-text available

Jul 2021
OECOLOGIA

Land-use generates multiple stress factors, and we need to understand their effects on plant–plant interactions to predict the consequences of land-use intensification. The stress–gradient hypothesis predicts that the relative strength of positive and negative interactions changes inversely under increasing environmental stress. However, the outcome of interactions also depends on stress factor’s complexity, the scale of analysis, and the role of functional traits in structuring the community. We evaluated plant–plant co-occurrences in a temperate forest, aiming to identify changes in pairwise and network metrics under increasing silvopastoral use intensity. Proportionally, positive co-occurrences were more frequent under high than low use, while negative co-occurrences were more frequent under low than high. Networks of negative co-occurrences showed higher centralization under low use, while networks of positive co-occurrences showed lower modularity and higher centralization under high use. We found a partial relationship between co-occurrences and key functional traits expected to mediate facilitation and competition processes. Our results shows that the stress-gradient hypothesis predicts changes in spatial co-occurrences even when two stress factors interact in a complex way. Networks of negative co-occurrences showed a hierarchical effect of dominant species under low use intensity. But positive co-occurrence network structure partially presented the characteristics expected if the facilitation was an important mechanism characterizing the community under high disturbance intensity. The partial relationship between functional traits and co-occurrences may indicate that other factors besides biotic interactions may be structuring the observed negative spatial associations in temperate Patagonian forests.

Facilitation and plant phenotypic evolution

Article

Jun 2021
TRENDS PLANT SCI

While antagonistic interactions between plants have been a major topic of eco-evolutionary research, little evidence exists on the evolution of positive plant interactions (i.e., plant facilitation). Here, we first summarize the existing empirical evidence on the role of facilitation as a selection pressure on plants. Then, we develop a theoretical eco-evolutionary framework based on fitness-trait functions and interaction effectiveness that provides predictions for how facilitation-related traits may evolve. As evolution may act at levels beyond the individual (such as groups or species), we discuss the subject of the units of evolutionary selection through facilitation. Finally, we use the proposed formal evolutionary framework for facilitation to identify areas of future research based on the knowledge gaps detected.

Forbidden links, trait matching and modularity in plant-hummingbird networks: Are specialized modules characterized by higher phenotypic floral integration?

Article

Full-text available

Mar 2021

Background Plant-pollinator mutualistic networks show non-random structural properties that promote species coexistence. However, these networks show high variability in the interacting species and their connections. Mismatch between plant and pollinator attributes can prevent interactions, while trait matching can enable exclusive access, promoting pollinators’ niche partitioning and, ultimately, modularity. Thus, plants belonging to specialized modules should integrate their floral traits to optimize the pollination function. Herein, we aimed to analyze the biological processes involved in the structuring of plant-hummingbird networks by linking network morphological constraints, specialization, modularity and phenotypic floral integration. Methods We investigated the understory plant-hummingbird network of two adjacent habitats in the Lacandona rainforest of Mexico, one characterized by lowland rainforest and the other by savanna-like vegetation. We performed monthly censuses to record plant-hummingbird interactions for 2 years (2018–2020). We also took hummingbird bill measurements and floral and nectar measurements. We summarized the interactions in a bipartite matrix and estimated three network descriptors: connectance, complementary specialization (H 2 ’), and nestedness. We also analyzed the modularity and average phenotypic floral integration index of each module. Results Both habitats showed strong differences in the plant assemblage and network dynamics but were interconnected by the same four hummingbird species, two Hermits and two Emeralds, forming a single network of interaction. The whole network showed low levels of connectance (0.35) and high specialization (H 2 ’ = 0.87). Flower morphologies ranged from generalized to specialized, but trait matching was an important network structurer. Modularity was associated with morphological specialization. The Hermits Phaethornis longirostris and P. striigularis each formed a module by themselves, and a third module was formed by the less-specialized Emeralds: Chlorestes candida and Amazilia tzacatl . The floral integration values were higher in specialized modules but not significantly higher than that formed by generalist species. Conclusions Our findings suggest that biological processes derived from both trait matching and “forbidden” links, or nonmatched morphological attributes, might be important network drivers in tropical plant-hummingbird systems while morphological specialization plays a minor role in the phenotypic floral integration. The broad variety of corolla and bill shapes promoted niche partitioning, resulting in the modular organization of the assemblage according to morphological specialization. However, more research adding larger datasets of both the number of modules and pollination networks for a wider region is needed to conclude whether phenotypic floral integration increases with morphological specialization in plant-hummingbird systems.

Plant functional traits involved in the assembly of canopy–recruit interactions

Article

Feb 2021

Questions The assembly of plant communities depends strongly on mechanisms that determine the recruitment of different plant species. Studying recruitment using a trait‐based approach may help in the search for general or dominant mechanisms involved in this process. Here, we try to disentangle what traits of saplings and established (canopy) plants can be considered as functional for recruitment, and whether the complementarity of these functional traits may be a driver of the plant community assembly. Location Regional. Two pine–oak forest communities in Sierra Sur de Jaén and one in Sierra de Segura, southeast of the Iberian peninsula. Methods In each forest community, we established three 50 m × 50 m plots, where we identified the saplings of each species recruiting under the canopy of each species or in open interspaces. The study focuses on 37 woody species. Measures of 18 traits were conducted for 30 saplings and 10 adults of each species. Results Seed mass and the ratio height:basal diameter of saplings were positively associated with species abundance in the sapling bank under vegetation, while abundance in the sapling bank in open interspaces was only related to the type of mycorrhizal association. On the other hand, some traits of adult plants (leaf mass per unit area [LMA], seed dispersal mechanism, leaf habit and branch density) favour the recruitment of other species in their close proximity. However, we found only circumstantial evidence of canopy/recruit trait complementarity affecting recruitment. Conclusions Our results suggest that the assembly of canopy–recruit interactions is primarily driven by the filtering effect of canopy species on recruitment, through traits that affect both seed arrival and soil properties. Species abundance in the sapling bank was related to resource acquisition traits. We did not find any clear evidence supporting that trait complementarity is involved in the interaction between canopy and recruit species.

Facilitation between plants shapes pollination networks

Preprint

Full-text available

Jul 2017

Significance Although it is known that plant–plant and plant–pollinator interactions can strongly influence biodiversity and its effects on ecosystem functioning, the details of how competition and facili-tation among plants scale up to mutualistic interactions with pollinators and thus affect pollina-tion networks are poorly understood. We introduce a simple experimental system in which we control local plant interactions, measure pollinator responses and characterize plant–pollinator networks. We find that facilitation among plants produces synergistic and antagonistic effects on the pollinator community affecting the architecture and robustness of plant–pollinator net-works. Our results provide evidence for bottom-up non-additive effects of plant interactions on pollination networks and have implications for the way we study and manage ecosystems.

Scientists' warning on endangered food webs

Article

Full-text available

Apr 2020

All organisms are ultimately dependent on a large diversity of consumptive and non-consumptive interactions established with other organisms, forming an intricate web of interdependencies. In 1992, when 1700 concerned scientists issued the first “World Scientists' Warning to Humanity”, our understanding of such interaction networks was still in its infancy. By simultaneously considering the species (nodes) and the links that glue them together into functional communities, the study of modern food webs – or more generally ecological networks – has brought us closer to a predictive community ecology. Scientists have now observed, manipulated, and modelled the assembly and the collapse of food webs under various global change stressors and identified common patterns. Most stressors, such as increasing temperature, biological invasions, biodiversity loss, habitat fragmentation, over-exploitation, have been shown to simplify food webs by concentrating energy flow along fewer pathways, threatening long-term community persistence. More worryingly, it has been shown that communities can abruptly change from highly diverse to simplified stable states with little or no warning. Altogether, evidence shows that apart from the challenge of tackling climate change and hampering the extinction of threatened species, we need urgent action to tackle large-scale biological change and specifically to protect food webs, as we are under the risk of pushing entire ecosystems outside their safe zones. At the same time, we need to gain a better understanding of the global-scale synergies and trade-offs between climate change and biological change. Here we highlight the most pressing challenges for the conservation of natural food webs and recent advances that might help us addressing such challenges.

Measuring and Linking the Missing Part of Biodiversity and Ecosystem Function: The Diversity of Biotic Interactions

Article

Full-text available

Feb 2020
Diversity

Biotic interactions are part of all ecosystem attributes and play an important role in the structure and stability of biological communities. In this study, we give a brief account of how the threads of biotic interactions are linked and how we can measure such complexity by focusing on mutualistic interactions. We start by explaining that although biotic interactions are fundamental ecological processes, they are also a component of biodiversity with a clear α, β and γ diversity structure which can be measured and used to explain how biotic interactions vary over time and space. Specifically, we explain how to estimate the α-diversity by measuring the properties of species interaction networks. We also untangle the components of the β-diversity and how it can be used to make pairwise comparisons between networks. Moreover, we move forward to explain how local ecological networks are a subset of a regional pool of species and potential interactions, γ-diversity, and how this approach allows assessing the spatial and temporal dynamics of ecological networks. Finally, we propose a new framework for studying interactions and the biodiversity-ecosystem function relationship by identifying the unique and common interactions of local networks over space, time or both together.

Desert Rarity, Endemism and Uniqueness

Chapter

Jan 2019

Distribución especial, diversidad, respuesta ecofisiológica y morfo-anatómica de la macrófita Ranunculus limoselloides TURCZ en un gradient de elevación en páramos venezolanos

Thesis

Jul 2019

Plant networks are more connected by invasive brome and native shrub facilitation in Central California drylands

Article

Full-text available

Apr 2024

Dominant vegetation in many ecosystems is an integral component of structure and habitat. In many drylands, native shrubs function as foundation species that benefit other plants and animals. However, invasive exotic plant species can comprise a significant proportion of the vegetation. In Central California drylands, the facilitative shrub Ephedra californica and the invasive Bromus rubens are widely dispersed and common. Using comprehensive survey data structured by shrub and open gaps for the region, we compared network structure with and without this native shrub canopy and with and without the invasive brome. The presence of the invasive brome profoundly shifted the network measure of centrality in the microsites structured by a shrub canopy (centrality scores increased from 4.3 under shrubs without brome to 6.3, i.e. a relative increase of 42%). This strongly suggests that plant species such as brome can undermine the positive and stabilizing effects of native foundation plant species provided by shrubs in drylands by changing the frequency that the remaining species connect to one another. The net proportion of positive and negative associations was consistent across all microsites (approximately 50% with a total of 14% non-random co-occurrences on average) suggesting that these plant-plant networks are rewired but not more negative. Maintaining resilience in biodiversity thus needs to capitalize on protecting native shrubs whilst also controlling invasive grass species particularly when associated with shrubs.

Plant interaction networks reveal the limits of our understanding of diversity maintenance

Article

Full-text available

Feb 2024
ECOL LETT

Species interactions are key drivers of biodiversity and ecosystem stability. Current theoretical frameworks for understanding the role of interactions make many assumptions which unfortunately, do not always hold in natural, diverse communities. This mismatch extends to annual plants, a common model system for studying coexistence, where interactions are typically averaged across environmental conditions and transitive competitive hierarchies are assumed to dominate. We quantify interaction networks for a community of annual wildflowers in Western Australia across a natural shade gradient at local scales. Whilst competition dominated, intraspecific and interspecific facilitation were widespread in all shade categories. Interaction strengths and directions varied substantially despite close spatial proximity and similar levels of local species richness, with most species interacting in different ways under different environmental conditions. Contrary to expectations, all networks were predominantly intransitive. These findings encourage us to rethink how we conceive of and categorize the mechanisms driving biodiversity in plant systems.

Multitrophic Higher-Order Interactions Modulate Species Persistence

Article

Dec 2023

Ecologists increasingly recognize that interactions between two species can be affected by the density of a third species. How these higher-order interactions (HOIs) affect species persistence remains poorly understood. To explore the effect of HOIs stemming from multiple trophic layers on a plant community composition, we experimentally built a mesocosm with three plants and three pollinator species arranged in a fully nested and modified network structure. We estimated pairwise interactions among plants and between plants and pollinators, as well as HOIs initiated by a plant or a pollinator affecting plant species pairs. Using a structuralist approach, we evaluated the consequences of the statistically supported HOIs on the persistence probability of each of the three competing plant species and their combinations. HOIs substantially redistribute the strength and sign of pairwise interactions between plant species, promoting the opportunities for multispecies communities to persist compared with a non-HOI scenario. However, the physical elimination of a plant-pollinator link in the modified network structure promotes changes in per capita pairwise interactions and HOIs, resulting in a single-species community. Our study provides empirical evidence of the joint importance of HOIs and network structure in determining species persistence within diverse communities.

Economic complexity of cities and its role for resilience

Article

Full-text available

Aug 2022
PLOS ONE

The aim of the paper is to propose the construction of an index that captures the economic complexity of cities over the globe, as well as to explore whether it is a good predictor for a range of city-level economic outcomes. This index aspires to mitigate data scarcity for cities and to provide policy makers with the tools for monitoring the evolving role of cities in the global economy. Analytically, we implement the economic complexity methodology on data for the ownership, location and economic activities of the world’s 3,000 largest firms and their subsidiaries to propose a new indicator that quantifies the network of the largest cities worldwide and the economic activities of their globalized firms. We first show that complex cities are the highly diversified cities that host non-ubiquitous economic activities of firms with global presence. Then, in a sample of EU cities, we show that complex cities tend to be more prosperous, have higher population, and are associated with more jobs, human capital, innovation, technology and transport infrastructure. Last, using OLS methodology and accounting for several other confounders, we show that a higher ECI, at the city level, enhances the resilience of cities to negative economic shocks, i.e., their ability to bounce back after a shock. Specifically, we find that the expected increase of the ratio of employment in 2012 over 2006 is 0.01 (mean: 0.992; standard deviation: 0.081) when the ECI increases by 1 unit (mean: 0.371; standard deviation: 1.094), i.e., a satisfactory pace of recovery, in terms of employment. The ability to diversify in the presence of a shock, the reallocation of factors of production to other sectors and the ability to extract rents associated with those diversified activities, uncovers the mechanics of the ECI index.

Evidencias de facilitación entre plantas en las arenas cuarcíticas de San Ubaldo

Article

Full-text available

Mar 2017

Facilitation among plants

Tansley review, Facilitación y biodiversidad

Preprint

Full-text available

Jun 2021

La competencia y la beneficencia [facilitación] simultáneas pueden tener importantes repercusiones en la estructura de la comunidad vegetal". Hunter y Aarssen (1988) "... los mecanismos responsables del ensamblaje de una comunidad vegetal que son los que determinan la naturaleza y la magnitud de los efectos de la facilitación en la composición de las especies y la diversidad de una comunidad no están siendo entendidos en su totalidad". Schöb et al. (2012) Durante mucho tiempo se ha considerado que las interacciones entre los organismos son uno de los principales factores de la estructuración y organización de las comunidades naturales (Hairston et al., 1960; Tilman, 1982; Mittelbach, 2012). Específicamente, las interacciones dentro del mismo nivel trófico se han considerado en general como un elemento clave de estos factores debido a su efecto sobre la coexistencia y la biodiversidad (Chesson, 2000; Silvertown, 2004). Kropotkin (1902), Clements (1936), y Allee et al. (1949) demostraron que las comunidades son en realidad el resultado de una combinación de interacciones positivas y negativas entre las especies. Dado que el paradigma en el que se basa principalmente el campo de la ecología es la lucha por la existencia, se comprobó repetidamente que las interacciones negativas (e.g., competencia) eran más

Inoculation with Native Actinobacteria May Improve Desert Plant Growth and Survival with Potential Use for Restoration Practices

Article

Full-text available

Feb 2022
MICROB ECOL

Soil microorganisms, together with water, play a key role in arid ecosystems, being responsible for the nutrient cycle, facilitating nutrient incorporation into plants, influencing plant drought tolerance, and enhancing their establishment. Therefore, their use for restoration practices is promising. We tested the potential of native strains of Actinobacteria from Monte Desert as growth promoters of native vegetation, isolating them from two substrates from their habitat (bare soil and leaf-cutting ant refuse dumps). Strains were inoculated into the soil where seedlings of three native plant species (Atriplex lampa, Grindelia chiloensis, Gutierrezia solbrigii) were growing. Seedlings were grown following a full factorial design experiment under greenhouse and field conditions comparing native Actinobacteria effects with a known growth-promoting strain, Streptomyces sp. (BCRU-MM40 GenBank accession number: FJ771041), and control treatments. Seedlings survived greenhouse condition but species survival and growth were different among treatments at field conditions, varying over time. The highest survival was observed in a native soil strain (S20) while the lowest in MM40. The low survival in MM40 and in the other treatments may be explained by the higher herbivory observed in those seedlings compared to control ones, suggesting a higher nutritional status in inoculated plants. Strains from refuse dumps were the best at enhancing seedling growth, while strains from soil were the best at maintaining their survival. Native Actinobacteria studied may increase plant species survival and growth by improving their nutritional status, suggesting their potential to facilitate vegetation establishment and, therefore, being good candidates for restoration practices. Furthermore, plant species respond differently to different strains, highlighting the importance of microorganism diversity for ecosystem functioning.

Facilitative Role of Berberis mucrifolia in Maintaining Plant Species Diversity at High-altitude Langtang Valley of Central Nepal

Thesis

Full-text available

Mar 2012

Rabindra Parajuli

Facilitation is the phenomenon by which some plants benefit from closely associated neighbors. Although the facilitation or nurse effect has been a well-studied subject in plant ecology, the importance of nurse shrubs in maintaining community diversity and composition is not well evaluated. Therefore, this research aimed to assess the nurse effect of Berberis mucrifolia shrub in facilitating the maintenance of community richness and diversity in a high altitude Himalayan valley of Langtang National Park, Central Nepal. Likewise, the role of shrubs to enhance useful species richness was also evaluated, along with the exploration of B. mucrifolia shrubland dependent species. Field study was conducted twice, in July and October 2009, for pair-wise sampling in B. mucrifolia shrub (shrubland) and adjacent open-land (open areas) from Mundu village up to Kyangjing Gumpa, covering three altitudinal belts of 3600 m, 3725 m and 3850 m. Altogether 21 shrub patches and adjacent open areas were selected to sample 63 pairs of 1 m x 1 m plots in each season; thus totaling 252 plots combining both seasons. B. mucrifolia shrublands were found to be richer in terms of resources and less stressed by grazing as compared to open-lands. Mean species richness of all species and richness of useful species were significantly higher beneath shrubs. Likewise, cumulative numbers of species found in shrub patches was always higher than that of adjacent open-lands. Detrended Correspondence Analysis (DCA) and Multi Response Permutation Procedure (MRPP) showed that the shrub and open plots were different in terms of species composition. The Landscape Richness Enhancement (LRE) analysis showed that the presence of shrubs was crucial in adding 14 - 42% more species to the community. Similarly, shrubland enhanced useful species of the community by 16.07%. Nine different species were found as shrubland specialist species; five species were specific to open-land. Likewise, the number of species that preferred shrubland was higher than that of open-land. The findings of this study suggest that Berberis mucrifolia is a nurse shrub exhibiting strong facilitation, mainly through habitat amelioration for growth and survival of other species. Facilitation by nurse shrubs is an important phenomenon to consider while formulating management strategies for the effective conservation of biodiversity in high-altitude valleys of the Nepal Himalayas.

Grazing and the vanishing complexity of plant association networks in grasslands

Article

Jan 2021

Interactions are key drivers of the functioning and fate of plant communities. A traditional way to measure them is to use pairwise experiments, but such experiments do not scale up to species‐rich communities. For those, using association networks based on spatial patterns may provide a more realistic approach. While this method has been successful in abiotically‐stressed environments (alpine and arid ecosystems), it is unclear how well it generalizes to other types of environments. We help fill this knowledge gap by documenting how the structure of plant communities changes in a Mediterranean dry grassland grazed by sheep using plant spatial association networks. We investigated how the structure of these networks changed with grazing intensity to show the effect of biotic disturbance on community structure. We found that these grazed grassland communities were mostly dominated by negative associations, suggesting a dominance of interference over facilitation regardless of the disturbance level. The topology of the networks revealed that the number of associations were not evenly‐distributed across species, but rather that a small subset of species established most negative associations under low grazing conditions. All these aspects of spatial organization vanished under high level of grazing as association networks became more similar to null expectations. Our study shows that grazed herbaceous plant communities display a highly non‐random organization that responds strongly to disturbance and can be measured through association networks. This approach thus appears insightful to test general hypotheses about plant communities, and in particular understand how anthropogenic perturbations affect the organization of ecological communities.

Phenotypic structure of plant facilitation networks

Article

Full-text available

Dec 2020
ECOL LETT

Identifying the plant traits that determine the outcome of facilitation interactions is essential to understand how communities are assembled and can be restored. Plant facilitation networks are phylogenetically structured but which traits are behind such a pattern is unknown. We sampled plant interactions in stressful ecosystems from south‐eastern Spain to build seedling and adult facilitation networks. We collected 20 morphological and ecophysiological traits for 151 species involved in interactions between 879 nurse individuals benefiting 24 584 seedlings and adults. We detected a significant phenotypic signal in the seedling facilitation network that was maintained in the adult network, whereby functionally similar nurses tended to facilitate functionally similar species whose traits differ from those of their nurses. We provide empirical evidence to support a long‐lasting theoretical postulate stating that facilitation networks are phenotypically structured. Trait matching through which nurse and facilitated species avoid phenotypic overlap, and consequently competition, is the main linkage rule shaping plant facilitation networks.

Ecologia e Conservação da Caatinga - Curso de Campo 2015

Book

Full-text available

Dec 2020

Assim como os frutos de algumas plantas, o Curso de Campo Ecologia e Conservação da Caatinga - que gerou o livro Ecologia e Conservação da Caatinga - também veio de uma semente, uma concepção inicial. A tradição de realizar cursos de imersão em campo não é nova. Ela surge como uma necessidade de treinar/aperfeiçoar e repetir técnicas/etapas do método científico de forma eficiente, aplicando-o em diferentes subáreas da Ecologia e Conservação e sobre diferentes objetos de estudo. O primeiro curso de Ecologia de Campo foi criado pela Organization for Tropical Studies (OTS), na década de 1970, na Costa Rica. Ainda no final da década de 70, o ecólogo americano Woodruff Benson foi contratado pela Universidade Estadual de Campinas (Unicamp) e montou o primeiro curso de campo brasileiro, realizado na Amazônia. Esse primeiro curso foi uma colaboração entre a Unicamp, a OTS, o Instituto de Pesquisas da Amazônia (INPA) e o Smithsonian Tropical Research Institute (STRI). No final da década de 80, esse curso passou a ser realizado na floresta Atlântica, onde é realizado anualmente até hoje. Ao longo destes mais de 40 anos, as edições desse curso formaram inúmeros profissionais das áreas da Ecologia e Conservação, que naturalmente difundiram a proposta dos cursos de campo para outros ecossistemas do Brasil. Em 1993, o INPA e o STRI criaram o Curso de Campo Ecologia da Floresta Amazônia. Em 1998, foi a vez da Universidade Federal de Mato Grosso do Sul criar o Curso de Campo Ecologia do Pantanal. Por fim, a Universidade Federal de Minas Gerais criou o Curso de Ecologia de Campo do Programa de Pós-Graduação em Ecologia, Conservação e Manejo da Vida Silvestre em 2005, centrando esforços nos ecossistemas do Cerrado e floresta Atlântica. O Curso de Campo Ecologia e Conservação da Caatinga surgiu para aplicar e adaptar as ideias dos cursos de campo já existentes para a heterogeneidade e singularidade da Caatinga brasileira, contribuindo de forma essencial para a formação de recursos humanos, isto é, alunos internos e externos às instituições envolvidas. Sua primeira edição foi em 2008 e desde então é oferecido anualmente e seus resultados são publicados em livros como este. Este livro, resultado das atividades executadas durante o curso de 2015, sua oitava edição, é dividido em três partes. A primeira, contém os relatórios (na forma de artigos científicos) de projetos orientados por professores. Esses projetos foram elaborados e conduzidos (os dados foram analisados e reportados em conjunto entre alunos, monitores e professores (orientadores)) em um único dia. A segunda parte inclui os relatórios dos projetos individuais livres. Esses projetos foram idealizados pelos alunos, porém com eventual ajuda no desenho experimental ou em outras etapas da execução do trabalho de campo por parte dos monitores e professores participantes do curso. A terceira e mais densa parte corresponde aos estudos concebidos e executados pelos alunos na fase final do curso. Nos relatórios dos projetos individuais apresentamos os resultados dos projetos executados entre quatro e cinco dias. É interessante destacar que os capítulos deste livro são essencialmente fruto da capacitação e treinamento (contínuo) dos seus autores e participantes do curso, sendo necessário entender este material mais como produto educativo per se do que um compilado de estudos de referência para a Caatinga brasileira. Entretanto, toda a estrutura montada e alocada para a realização do curso também esteve voltada para garantir a qualidade dos produtos gerados e aqui presentados. Assim, estamos imensamente satisfeitos em publicarmos esse material que consolida o trabalho árduo de alunos, monitores e professores do Curso de Campo Ecologia e Conservação da Caatinga 2015.

The Structure of Ecological Networks Across Levels of Organization

Article

Aug 2020

Paulo Sérgio de Mello Guimarães Jr

Interactions connect the units of ecological systems, forming networks. Individual-based networks characterize variation in niches among individuals within populations. These individual-based networks merge with each other, forming species-based networks and food webs that describe the architecture of ecological communities. Networks at broader spatiotemporal scales portray the structure of ecological interactions across landscapes and over macroevolutionary time. Here, I review the patterns observed in ecological networks across multiple levels of biological organization. A fundamental challenge is to understand the amount of interdependence as we move from individual-based networks to species-based networks and beyond. Despite the uneven distribution of studies, regularities in network structure emerge across scales due to the fundamental architectural patterns shared by complex networks and the interplay between traits and numerical effects. I illustrate the integration of these organizational scales by exploring the consequences of the emergence of highly connected species for network structures across scales. Expected final online publication date for the Annual Review of Ecology, Evolution, and Systematics, Volume 51 is November 2, 2020. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Plant facilitation as a tool to restore diversity and ecosystem functions

Article

Full-text available

Aug 2019

Traditional restoration programmes have focused on conditioning plantation sites and reintroducing plant species. Nowadays, however, ecological restoration is conceived as the complete recovery of biodiversity and ecosystem performance. Here, we review the use of plantplant facilitation as a tool to restore both diversity and ecosystem functions. Facilitation is an ecological interaction between a nurse species, which is able to colonize a stressful habitat and modify the microenvironment beneath its canopy, and the beneficiary species that are not so stresstolerant and grow under the nurse. Differences in the establishment niche between the nurse and its beneficiaries imply that species sharing facilitative interactions have different functional traits, and can therefore coexist. This process increases, at the landscape scale, all taxonomic, functional and phylogenetic plant diversity. Plant diversity patterns further permeate into those of consumers and decomposers. Thus, restoration based on plantplant facilitation allows the recovery of multiple facets of diversity at several trophic levels and, eventually, the restoration of essential ecosystem functions (fertility, productivity, or decomposition). We illustrate these cascading effects in the text by means of observational surveys in natural ecosystems governed by facilitation, as well as manipulative experiments and restoration activities.

Perspectives for ecological networks in plant ecology

Article

Full-text available

Jun 2019

Background: Plant communities are usually characterised by species composition and abundance, but also underlie a multitude of complex interactions that we have only recently started unveiling. Yet, we are still far from understanding ecological and evolutionary processes shaping the network-level organisation of plant diversity, and to what extent these processes are specific to certain spatial scales or environments. Aims: Understanding the systemic mechanisms of plant–plant network assembly and their consequences for diversity patterns. Methods: We review recent methods and results of plant–plant networks. Results: We synthetize how plant–plant networks can help us to: (a) assess how competition and facilitation may balance each other through the network; (b) analyse the role of plant–plant interactions beyond pairwise competition in structuring plant communities, and (c) forecast the ecological implications of complex species dependencies. We discuss pros and cons, assumptions and limitations of different approaches used for inferring plant–plant networks. Conclusions: We propose novel opportunities for advancing plant ecology by using ecological networks that encompass different ecological levels and spatio-temporal scales, and incorporate more biological information. Embracing networks of interactions among plants can shed new light on mechanisms driving evolution and ecosystem functioning, helping us to mitigate diversity loss.

Using plant functional distances to select species for restoration of mining sites

Article

Full-text available

Jul 2019
J APPL ECOL

Plant facilitation, an ecological interaction that benefits at least one species without harming the other, is increasingly used as a restoration tool. To restore degraded habitats under a facilitation framework, practitioners must correctly select both the benefactor (nurse) and the beneficiary (facilitated) species. Based on community assembly and species coexistence theory, we propose selecting plant species that largely differ in a suite of functional traits so that competition is minimized and facilitation maximized due to functional complementarity. To apply this guideline in a pilot restoration experiment performed in metalliferous mine tailings in South‐Eastern Spain, we first built the plant–plant facilitative interaction network naturally occurring in a set of 12 tailings. After characterizing each species with 20 morphological and physiological traits, we verified that facilitative interactions were predominantly established between functionally distant species. Then, we designed a sowing experiment combining 50 nurse‐facilitated species pairs separated by a wide range of functional distances. The success of seedling establishment significantly increased with the functional distance between the nurse and the facilitated plant species. Synthesis and applications. We encourage the use of ecological facilitation together with trait‐based species selection to design restoration programmes based on the principle of increasing functional distance between target species. This method may not only promote the restoration of the plant cover but also impact paramount ecosystem functions, thus being an efficient low‐cost restoration practice in abiotically stressful ecosystems.

CAUSES OF LANDSCAPE-SCALE RARITY IN COBBLE BEACH PLANT COMMUNITIES

Article

Full-text available

Aug 2002

John F Bruno

Community-wide patterns of specialization in plant-pollinator interactions revealed by null models

Chapter

Full-text available

Feb 2005

The Network Structure of Food Webs

Chapter

Full-text available

Jan 2006

Jennifer A. Dunne

Descriptions of food-web relationships first appeared more than a century ago, and the quantitative analysis of the network structure of food webs dates back several decades. Recent improvements in food-web data collection and analysis methods, coupled with a resurgence of interdisciplinary research on the topology of many kinds of “real-world” networks, have resulted in renewed interest in food-web structure. This chapter reviews the history of the search for generalities in the structure of complex food webs, and discusses current and future research trends. Analysis of food-web structure has used empirical and modeling approaches, and has been inspired both by questions from ecology such as “What factors promote stability of complex ecosystems given internal dynamics and external perturbations? and questions from network research such as “Do food webs display universal structure similar to other types of networks?” Recent research has suggested that once variable diversity and connectance are taken into account, there are universal coarse-grained characteristics of how trophic links and species defined according to trophic function are distributed within food webs. In addition, aspects of food-web network structure have been shown to strongly influence the robust functioning and dynamical persistence of ecosystems.

Habitat modification and facilitation in benthic marine communities

Chapter

Full-text available

Jan 2001

Spatial vegetation patterns and imminent desertification in Mediterranean arid ecosystems

Article

Full-text available

Sep 2007

Humans and climate affect ecosystems and their services, which may involve continuous and discontinuous transitions from one stable state to another. Discontinuous transitions are abrupt, irreversible and among the most catastrophic changes of ecosystems identified. For terrestrial ecosystems, it has been hypothesized that vegetation patchiness could be used as a signature of imminent transitions. Here, we analyse how vegetation patchiness changes in arid ecosystems with different grazing pressures, using both field data and a modelling approach. In the modelling approach, we extrapolated our analysis to even higher grazing pressures to investigate the vegetation patchiness when desertification is imminent. In three arid Mediterranean ecosystems in Spain, Greece and Morocco, we found that the patch-size distribution of the vegetation follows a power law. Using a stochastic cellular automaton model, we show that local positive interactions among plants can explain such power-law distributions. Furthermore, with increasing grazing pressure, the field data revealed consistent deviations from power laws. Increased grazing pressure leads to similar deviations in the model. When grazing was further increased in the model, we found that these deviations always and only occurred close to transition to desert, independent of the type of transition, and regardless of the vegetation cover. Therefore, we propose that patch-size distributions may be a warning signal for the onset of desertification.

Causes of Landscape-Scale Rarity in Cobble Beach Plant Communities

Article

Full-text available

Aug 2002

John F Bruno

In most communities, a considerable number of the constituent species will only occupy a small percentage of sites or habitat patches. However, the factors that limit the distribution and abundance of rare species are seldom examined and are poorly un-derstood. I tested several explanations of landscape-scale rarity in the New England cobble beach plant community, an assemblage of halophytic forbs associated with fringing beds of the marine intertidal grass Spartina alterniflora. Spartina reduces flow velocity and stabilizes the cobble substrate, thereby reducing the burial of seeds and seedlings of other species. Frequencies of the presence of forb species behind 387 sampled Spartina beds distributed along 120 km of shoreline in Narragansett Bay, Rhode Island, USA, ranged from 0.005 to 0.382. Both the whole forb assemblage and individual species were strongly nested with respect to patch size and species richness. Species that were rare on a landscape scale were generally only found behind the longest beds, and bed length was positively related to species diversity. Experimental seed additions to 40 beds ranging in length from 8 to 688 m indicated that intermediate-sized beds often occupied by common species are not habitable by three rare forbs. When present behind the longest beds, these rare species are always associated with a microhabitat characterized by a relatively fine-grained and highly stable substrate. A series of substrate manipulations combined with experimental seed additions indicated that the rare annuals Spergularia marina, Salicornia biglovii, and Atriplex arenaria are restricted to the longest Spartina beds because smaller beds lack suitable substrate. These experiments also suggest that seed supply, competitors, and her-bivores are not the proximate causes of the absence of these species from smaller beds, although dispersal limitation may prevent the colonization of many larger habitable patches. The microhabitat required by the rare forbs appears to be generated by the deposition of fine-grained particles behind the center of the longest Spartina beds. Consequently, bed length is causally related to the distribution of populations at a landscape scale and to species richness and composition at the scale of a whole habitat patch.

Invariant properties in coevolutionary networks of plant–animal links

Article

Full-text available

Jan 2003
ECOL LETT

Plant–animal mutualistic networks are interaction webs consisting of two sets of entities, plant and animal species, whose evolutionary dynamics are deeply influenced by the outcomes of the interactions, yielding a diverse array of coevolutionary processes. These networks are two-mode networks sharing many common properties with others such as food webs, social, and abiotic networks. Here we describe generalized patterns in the topology of 29 plant–pollinator and 24 plant–frugivore networks in natural communities. Scale-free properties have been described for a number of biological, social, and abiotic networks; in contrast, most of the plant–animal mutualistic networks (65.6%) show species connectivity distributions (number of links per species) with a power-law regime but decaying as a marked cut-off, i.e. truncated power-law or broad-scale networks and few (22.2%) show scale-invariance. We hypothesize that plant–animal mutualistic networks follow a build-up process similar to complex abiotic nets, based on the preferential attachment of species. However, constraints in the addition of links such as morphological mismatching or phenological uncoupling between mutualistic partners, restrict the number of interactions established, causing deviations from scale-invariance. This reveals generalized topological patterns characteristic of self-organized complex systems. Relative to scale-invariant networks, such constraints may confer higher robustness to the loss of keystone species that are the backbone of these webs.

Woody vegetation spatial patterns in a semi-arid savanna of Burkina Faso, West Africa

Article

Full-text available

Jan 1997

Spatial patterns of woody individuals were studied in a semi-arid savanna of West Africa located in Burkina Faso at and around 14 12 N and 2 27 W. The study was based upon a 10.24 ha plot within which individuals were mapped. Spatial pattern analysis was carried out using second order characteristics of point processes as K functions and pair correlations. The overall density amounted to 298 individuals ha-1. The most abundant species were Combretum micranthum G. Don., Grewia bicolor Juss. and Pterocarpus lucens Lepr. Anogeissus leiocarpus (D.C.) G. et Perr. was also an important constituant of this vegetation type, owing to its taller stature. Clumped spatial distributions were identified for all species except for two, for which complete spatial randomness (CSR) was found (including P. lucens, a dominant woody plant). No regular pattern was found even when tall individuals were considered alone. Aggregation dominates interspecific relationships, resulting in multispecific clumps and patches. The overall aggregation pattern was constituted by two different structures. A coarse-grain pattern of ca. 30–40 m was based on edaphic features, and expresses the contrast between sparse stands on petroferric outcrops and denser patches on less shallow soils. A finer-grain pattern made of clumps ca. 5–10 m wide, with no obvious relation to pre-existing soil heterogeneity. There was no overall pattern for saplings (between 0.5 m and 1.5 m in height) irrespective of species, and thus no obvious common facilitation factor. For species with a high recruitment level there was no significant relationship between mature adult and saplings. The only case of clumped saplings with randomly distributed adults was found in P. lucens. However, this cannot be unequivocally interpreted as density dependent regulation since the existence of such a process was not consistent with the spatial distribution of dead P. lucens individuals (victims of the last drought). The mean density around dead P. lucens was lower than around surviving ones, indicating that the last drought tended to reinforce clumping rather than promote a regular pattern of trees. Spatial pattern analysis yielded no evidence supporting a hypothesis of stand density regulation through competition between individuals. Other processes, as surface sealing of bare soils or insufficient recruitment, may play a more important role in preventing a savanna-like vegetation from turning into denser woodlands or thickets.

The measure of order and disorder in the distribution of species in fragmented habitat

Article

Full-text available

Dec 1993

Species distribution patterns within naturally fragmented habitat have been found to often exhibit patterns of pronounced nestedness. Highly predictable extinction sequences are implied by these nested species distribution patterns, thus the patterns are important to both the philosophy and practice of conservation biology. A simple thermodynamic measure of the order and disorder apparent in the nested patterns is described. The metric offers (i) a measure of the uncertainty in species extinction order, (ii) a measure of relative populational stabilities, (iii) a means of identifying minimally sustainable population sizes, and (iv) an estimate of the historical coherence of the species assemblage. Four presumptions govern the development of the metric and its theory: (i) the fragmented habitat was once whole and originally populated by a single common source biota, (ii) the islands were initially uniform in their habitat heterogeneity and type mix, and have remained so throughout their post-fragmentation history, (iii) no significant clinal (latitudinal) gradation exists across the archipelago so as to promote species turnover across the archipelago, and (iv) all species of interest are equally isolated on all islands. The violation of these conditions promotes species distributions which are idiosyncratic to the general extinction order expected in fragmentation archipelagos. While some random variation in extinction order is to be expected, idiosyncratic distributional patterns differ from randomness and are readily segregatable from such noise. A method of identifying idiosyncratic species and sites is described.

Inclusion of Facilitation into Ecological Theory

Article

Full-text available

Mar 2003
TRENDS ECOL EVOL

Investigations of the role of competition, predation and abiotic stress in shaping natural communities were a staple for previous generations of ecologists and are still popular themes. However, more recent experimental research has uncovered the largely unanticipated, yet striking influence of facilitation (i.e. positive species interactions) on the organization of terrestrial and aquatic communities. Modern ecological concepts and theories were well established a decade before the current renaissance of interest in facilitation began, and thus do not consider the importance of a wide variety of facilitative interactions. It is time to bring ecological theory up to date by including facilitation. This process will not be painless because it will fundamentally change many basic predictions and will challenge some of our most cherished paradigms. But, ultimately, revising ecological theory will lead to a more accurate and inclusive understanding of natural communities.

Mutualism, Facilitation, and the Structure of Ecological Communities

Article

Full-text available

Mar 2001

John J. Stachowicz

Facilitative or positive, interactions are encounters between organisms that benefitat least one of the participants and cause harm to neither. Such interactions are considered "mutualisms" when both species derive benefit from the interaction. Positive interactions are ubiquitous: they may lie at the root of such divese evolutionary phenomena as the origin of eukaryotic cells, the radiation of flowering plants, and the flourishing of coral reefs. Although a few ecologists have long recognised the importance of positive interactions in stressful environments (e.g.Clements 1916; Addicott 1984), ecological research on positive interactions is still far less common than that on other forms of interactions among species (Bronstein 1994a, Bruno & Bertness 2000). Consequently, positive interactions are rarely factored into models or even into thinking about about factors impacting populations and communities. Recent empirical work and the conceptual models derived from this work (e.g. Bertness & Callaway 1994; Bruno & Bertness 2000) have helped to refocus attention on the role of positive interactions among species, however, and the scientists are beginning to better appreciate the importance of those interactions in the structuring of ecological communities.

The community structure of western atlantic patagonian rocky shores

Article

Full-text available

Dec 2005

We examined the structure of rocky intertidal communities on the central Patagonian coast of Argentina. Extensive beds of the mussel Perumytilus purpuratus cover wave-exposed headlands from the low to extreme high intertidal (.95%), and a diverse assemblage of diminutive mobile invertebrates including limpets, starfish, and crabs live exclusively in the mussel bed matrix to avoid physical stress. On nearby wave-protected rocky shores, the high intertidal habitat is dominated by bare space (.85%) with mussels restricted to tide pools and crevices. Mussel beds cover the middle intertidal, while the low intertidal habitat is dominated by the erect coralline alga Corallina officanalis. These patterns are driven overwhelmingly by variation in extreme physical conditions. Desiccation stress generated by the dry southern trade winds is harsher than in any previously studied rocky intertidal system, including the Gulf of Panama, by .30% and is more severe on wave-protected than wave-exposed shores. Transplant experiments suggest that on wave-protected shores desiccation stress limits the upper distribution of mussels in the high intertidal and Corallina in the midintertidal, but at low intertidal elevations Corallina outcompetes mussels, restricting mussel distribution to mid-intertidal elevations. Transplant experiments also demonstrated that the coralline alga is precluded from wave-exposed shores by wave stress. Recovery from disturbance is unusually slow, ostensibly due to extreme physical stress. Consumer pressure is weak, with no common predaceous crabs or snails, and grazing by limpets showed limited control of community development, mostly by regulating ephemeral algae. Patagonian rocky shore communities are exposed to unusually harsh physical conditions and consequently are more strongly organized by physical stress than previously studied rocky intertidal communities.

Plant-Animal Mutualistic Networks: The Architecture of Biodiversity

Article

Full-text available

Nov 2006

The mutually beneficial interactions between plants and their animal pollinators and seed dispersers have been paramount in the generation of Earth’s biodiversity. These mutualistic interactions often involve dozens or even hundreds of species that form complex networks of interdependences. Understanding how coevolution proceeds in these highly diversified mutualisms among free-living species presents a conceptual challenge. Recent work has led to the unambiguous conclusion that mutualistic networks are very heterogeneous (the bulk of the species have a few interactions, but a few species are much more connected than expected by chance), nested (specialists interact with subsets of the species with which generalists interact), and built on weak and asymmetric links among species. Both ecological variables (e.g., phenology, local abundance, and geographic range) and past evolutionary history may explain such network patterns. Network structure has important implications for the coexistence and stability of species as well as for the coevolutionary process. Mutualistic networks can thus be regarded as the architecture of biodiversity.

Endemic Mimosa species can serve as mycorrhizal "resource islands" within semiarid communities of the Tehuac?n-Cuicatl?n Valley, Mexico

Article

Full-text available

Jul 2003

This paper explores if Mimosa species (Fabaceae-Mimosoideae) can serve as arbuscular mycorrhizal (AM) and nutrient "resource islands" in six plant communities in the semiarid valley of Tehuacán-Cuicatlán, Mexico. Spatial heterogeneity related to the occurrence of Mimosa species results in temporal differences in AM-fungal spore numbers and soil nutrients. A higher number of AM-fungal spores were found in the soil below the canopies of six endemic Mimosa species than in the soil from non-vegetated areas. For four species, Mimosa adenantheroides, Mimosa calcicola, Mimosa luisana and Mimosa polyantha, the soil below their canopies had more AM-fungal spores than the soil in non-vegetated areas during the wet season than during the dry season. Two species, Mimosa lacerata and Mimosa texana var. filipes, however, had more spores under their canopies during the dry season than during the wet season. Although physical differences are present within and between sites, in general the soil below the canopies of Mimosa species had significantly higher nutrient levels than the soil from non-vegetated areas. Mimosa species thus form "resource islands" that are not only rich in nutrients but also in mycorrhizal propagules. Mimosa species can serve as mycorrhizal "resource islands" by directly affecting AM-fungal spore dynamics and/or by serving as spore-traps. A range of plants associated with Mimosa species may benefit from the higher number of AM propagules. We believe that the use of Mimosa resource islands as an option for biodiversity conservation and for land restoration ought to be considered in the Valley.

The nested assembly of plant-animal mutualistic networks

Article

Full-text available

Sep 2003

Most studies of plant-animal mutualisms involve a small number of species. There is almost no information on the structural organization of species-rich mutualistic networks despite its potential importance for the maintenance of diversity. Here we analyze 52 mutualistic networks and show that they are highly nested; that is, the more specialist species interact only with proper subsets of those species interacting with the more generalists. This assembly pattern generates highly asymmetrical interactions and organizes the community cohesively around a central core of interactions. Thus, mutualistic networks are neither randomly assembled nor organized in compartments arising from tight, parallel specialization. Furthermore, nestedness increases with the complexity (number of interactions) of the network: for a given number of species, communities with more interactions are significantly more nested. Our results indicate a nonrandom pattern of community organization that may be relevant for our understanding of the organization and persistence of biodiversity.

Tolerance of pollinator networks to species extinctions

Article

Full-text available

Jan 2005

Mutually beneficial interactions between flowering plants and animal pollinators represent a critical 'ecosystem service' under threat of anthropogenic extinction. We explored probable patterns of extinction in two large networks of plants and flower visitors by simulating the removal of pollinators and consequent loss of the plants that depend upon them for reproduction. For each network, we removed pollinators at random, systematically from least-linked (most specialized) to most-linked (most generalized), and systematically from most- to least-linked. Plant species diversity declined most rapidly with preferential removal of the most-linked pollinators, but declines were no worse than linear. This relative tolerance to extinction derives from redundancy in pollinators per plant and from nested topology of the networks. Tolerance in pollination networks contrasts with catastrophic declines reported from standard food webs. The discrepancy may be a result of the method used: previous studies removed species from multiple trophic levels based only on their linkage, whereas our preferential removal of pollinators reflects their greater risk of extinction relative to that of plants. In both pollination networks, the most-linked pollinators were bumble-bees and some solitary bees. These animals should receive special attention in efforts to conserve temperate pollination systems.

The smallest of all worlds: Pollination networks

Article

Full-text available

Jun 2006

A pollination network may be either 2-mode, describing trophic and reproductive interactions between communities of flowering plants and pollinator species within a well-defined habitat, or 1-mode, describing interactions between either plants or pollinators. In a 1-mode pollinator network, two pollinator species are linked to each other if they both visit the same plant species, and vice versa for plants. Properties of 2-mode networks and their derived 1-mode networks are highly correlated and so are properties of 1-mode pollinator and 1-mode plant networks. Most network properties are scale-dependent, i.e. they are dependent upon network size. Pollination networks have the strongest small-world properties of any networks yet studied, i.e. all species are close to each other (short average path length) and species are highly clustered. Species in pollination networks are much more densely linked than species in traditional food webs, i.e. they have a higher density of links, a shorter distance between species, and species are more clustered.

Invasive Plant Suppresses the Growth of Native Tree Seedlings by Disrupting Belowground Mutualisms

Article

Full-text available

Jun 2006
PLOS BIOL

The impact of exotic species on native organisms is widely acknowledged, but poorly understood. Very few studies have empirically investigated how invading plants may alter delicate ecological interactions among resident species in the invaded range. We present novel evidence that antifungal phytochemistry of the invasive plant, Alliaria petiolata, a European invader of North American forests, suppresses native plant growth by disrupting mutualistic associations between native canopy tree seedlings and belowground arbuscular mycorrhizal fungi. Our results elucidate an indirect mechanism by which invasive plants can impact native flora, and may help explain how this plant successfully invades relatively undisturbed forest habitat.

Asymmetries in specialization in ant-plant networks

Article

Full-text available

May 2006
Proc Biol Sci

Mutualistic networks involving plants and their pollinators or frugivores have been shown recently to exhibit a particular asymmetrical organization of interactions among species called nestedness: a core of reciprocal generalists accompanied by specialist species that interact almost exclusively with generalists. This structure contrasts with compartmentalized assemblage structures that have been verified in antagonistic food webs. Here we evaluated whether nestedness is a property of another type of mutualism-the interactions between ants and extrafloral nectary-bearing plants--and whether species richness may lead to differences in degree of nestedness among biological communities. We investigated network structure in four communities in Mexico. Nested patterns in ant-plant networks were very similar to those previously reported for pollination and frugivore systems, indicating that this form of asymmetry in specialization is a common feature of mutualisms between free-living species, but not always present in species-poor systems. Other ecological factors also appeared to contribute to the nested asymmetry in specialization, because some assemblages showed more extreme asymmetry than others even when species richness was held constant. Our results support a promising approach for the development of multispecies coevolutionary theory, leading to the idea that specialization may coevolve in different but simple ways in antagonistic and mutualistic assemblages.

Ecological networks and their fragility

Article

Full-text available

Aug 2006
NATURE

Darwin used the metaphor of a 'tangled bank' to describe the complex interactions between species. Those interactions are varied: they can be antagonistic ones involving predation, herbivory and parasitism, or mutualistic ones, such as those involving the pollination of flowers by insects. Moreover, the metaphor hints that the interactions may be complex to the point of being impossible to understand. All interactions can be visualized as ecological networks, in which species are linked together, either directly or indirectly through intermediate species. Ecological networks, although complex, have well defined patterns that both illuminate the ecological mechanisms underlying them and promise a better understanding of the relationship between complexity and ecological stability.

NULL MODEL ANALYSIS OF SPECIES CO-OCCURRENCE PATTERNS

Article

Sep 2000

Nicholas J. Gotelli

Mycorrhizae, nutrient trans‐location, and interactions between plants

Article

Jan 1992

The network structure of food webs. In: Ecological Networks: Linking Structure to Dynamics in Food Webs. Edited by M. P, Dunne JA

Article

Jan 2006

Jennifer A. Dunne

Improving the analyses of nestedness for large sets of matrices

Article

Oct 2006
ENVIRON MODELL SOFTW

Nestedness is a property of binary matrices of ecological data and quantified by the matrix's temperature, T. The program widely used to calculate T is Nestedness Temperature Calculator (NTC). NTC analyses matrices individually, turning the analysis of large sets time-consuming. We introduce ANINHADO, a program developed to perform rapid and automatic calculation of T over 10,000 matrices. ANINHADO can be useful to minimize the time spent in analysis and to compare real data against a variety of null models that typically generate a large number of replicates.

Shade as a Cause of the Association Between the Cactus Neobuxbaumia Tetetzo and the Nurse Plant Mimosa Luisana in the Tehuacan Valley, Mexico

Article

Dec 1991

The establishment phase of Neobuxbaumia tetetzo, a giant columnar cactus, occurs mostly beneath the canopies of trees and shrubs which act as nurse plants. This pattern cannot be attributed to preferential seed dispersion, as Neobuxbaumia fruits open while still on the plant, dropping c1000 seeds fruit-1 randomly around the parent plant. Mimosa luisana is the most abundant shrub in the community. Seed germination was lowest in open spaces. In all treatments, exclusion from predators significantly increased seedling survival. Only shaded treatments had live individuals at the end of the experiment, 2 yr later. Results suggest that the nurse-plant effect between N. tetetzo and M. luisana is chiefly the result of differential survival in shaded microsites with less direct solar radiation, and consequently with lower daytime temperatures and lower evaporative demand. Field samplings were conducted in two Mexican deserts located outside the tropical belt: the Vizcaino Desert in Baja California and the Gran Desierto de Altar in Sonora. In these deserts direct solar radiation has a southern azimuth all year round. Five of six succulent species analysed showed a significant pattern of greater establishment on the shaded north sides of nurse plants. -from Authors

The Dialectial Biologist

Article

Feb 1987

Spatial pattern analysis in Namaqualand desert plant communities

Article

Jun 1999

This paper investigates of the spatial arrangement of individual plants in mapped plots in two desert communities in the winter rainfall region of South Africa. In both communities there was a very strong tendency towards clumped patterns when all plants were considered together. There was also a predominance of clumped patterns when the most abundant species in both communities were considered individually. When the arrangement of the most abundant species was considered relative to the arrangement of all other individuals at the within-clump scale, there was a high frequency of positive associations in both communities (62% and 65%). We speculate that these patterns represent a combination of seed dispersal strategies that favour clumped patterns and a predominance of positive interactions between plants in both of the communities. When specific pairwise associations between the most abundant species were considered at the within-clump scale, differences were apparent between the two communities. In the short strandveld community neutral associations predominated, while in the medium strandveld, neutral and positive association accounted for equal proportions of the associations. This between-plot difference was also apparent when the volumes of plants were related to an index of neighbourhood competitiveness. In the short strandveld there were no significant relationships while in the medium strandveld there were some weak (but significant) relationships. These differences were not altogether unexpected. If we assume that plants in the medium strandveld are generally longer-lived, then interactions between plants are likely to develop over a longer time and, therefore, are likely to be stronger.

Temporal shifts from facilitation to competition occur between closely related taxa: Facilitation-competition balance

Article

May 2008

1. The relative contribution of positive and negative interactions to the organization of ecological communities is an important area, though poorly understood because of the complexity inherent to long-term interactions. For example, positive interactions like plant facilitation turn into negative interactions (competition) along the ontogeny of a plant or in response to temporal fluctuations in the environment. Furthermore, when many plants grow together indirect effects are usually positive and alleviate direct competitive effects. 2. The large number of direct and indirect interactions potentially occurring in natural communities and the temporal scale necessary to account for the ontogenetic shifts in the sign of the interaction makes a fully experimental approach prohibitive. Here, we propose that the phylogenetic distance among co-occurring species is a good proxy to detect competition as a long-term force assembling community composition. Our proposal is based on the observation that closely related species tend to be phenotypically similar and therefore compete for the same niche. 3. We test the relationship between phylogenetic relatedness and the persistence of pairwise (nurse-facilitated) interactions occurring between 102 woody species in three Mexican semi-arid communities in order to quantify the balance between competition and facilitation at the community level. 4. Our results indicate that facilitation turns into competition with increasing taxa relatedness. After validating the association between competition and phylogenetic relatedness, we estimate that 57% of the interactions remain with time while 43% become competitive. [Correction added after publication, 4 March 2008: in the preceding sentence, values corrected from 53% and 47%, respectively.] The preponderance of positive interactions may be explained if facilitation is considered as a mutualism in which both species benefit leading to vegetation clumps in communities. 5. Synthesis . We provide a new perspective on the balance between positive and negative interactions based on a phylogenetically structured network of interactions. This approach promises to contribute to our understanding of long standing issues in plant ecology and to reveal new areas of future research by testing the existence and the nature of the mutualisms as well as their complexity–stability properties on communities as a whole.

Vegetation of the Sonoran Desert

Article

Jan 1951

F Shreve

Community structure and positive interactions in constraining environments

Article

Nov 2005
OIKOS

Spatial patterns in plant communities are thought to be controlled by the interplay of species interactions and environmental constraints. To evaluate the role of plant–plant interactions in shaping these communities we quantified species co-occurrence and interaction in seven environmentally distinct communities. These included four different semiarid habitats in southeast Spain, one alpine system in the Sierra Nevada range (Spain), and two sites in Venezuela, a secondary savanna near Caracas (Altos de Pipe), and a sclerophyllous shrubland in the Gran Sabana plateau. We expected that facilitation would be stronger at sites with more spatial associations. The four semiarid sites in Spain and the shrubland in Gran Sabana showed a high degree of positive species associations. Of the other two communities, one showed both positive and negative associations while negative ones predominated in Altos de Pipe. The direct experimental measure of neighbors’ effect showed that positive interactions among species prevailed in communities where positive species associations dominated. The appearance of benefactor species in patches increased species richness compared with the surrounding inter-shrub spaces. Our results provide a link between spatial patterns and species interactions, where aggregation points to positive interactions and segregation to competitive or interference effects. Facilitation appears as a relevant process shaping communities under environmental constraints.

Degree distribution in plant-animal mutualistic networks: Forbidden links or random interactions?

Article

Dec 2004
OIKOS

Diego P. Vázquez

Recent studies show that ecological interaction networks depart from the “scale-free” topologies observed in many other real world networks. Such a departure has been hypothesized to result from non-matching biological attributes of species, such as phenology or morphology, that prevent the occurrence of certain interactions (“forbidden links”). Here I compare the topology of 17 plant–animal mutualistic networks with that predicted by a simple null model that assumes that a species’ degree (number of interspecific interactions) is a function of its frequency of interaction. The topology predicted by this null model is strikingly close to that observed in the real networks. Thus, this null model provides a simple alternative interpretation of patterns observed in ecological interaction networks that does not require the existence of non-matching species traits.

The Structure of Plant Communities

Chapter

Jul 2009

Michael J. Crawley

Vegetation, i.e., the plant life of a region, not only shapes terrestrial ecosystems but also serves several crucial functions in the biosphere. Due to the importance of vegetation for mankind, deterioration of plant communities under pollution impacts attracted considerable scientific and public attention more than a century ago (Holland 1888; Haselhoff & Lindau 1903; Stoklasa 1923). Historically, the majority of studies exploring pollution effects on plant communities were conducted in forested areas of Europe and North America. A large body of publications report decreases in forest vitality, often followed by forest decline, at different scales, from local, around point polluters (National Research Council of Canada 1939; Bunce 1979; Symeonides 1979; Sutherland & Martin 1990; Rigina & Kozlov 2000; Aznar et al. 2007), to regional (Pitelka & Raynal 1989; Kandler & Innes 1995; Bussotti & Ferretti 1998; Akselsson et al. 2004; Allen et al. 2007).

Null Model Analysis of Species Co-Occurrence Patterns

Article

Sep 2000

Nicholas J. Gotelli

The analysis of presence–absence matrices with ''null model'' randomization tests has been a major source of controversy in community ecology for over two decades. In this paper, I systematically compare the performance of nine null model algorithms and four co-occurrence indices with respect to Type I and Type II errors. The nine algorithms differ in whether rows and columns are treated as fixed sums, equiprobable, or proportional. The three models that maintain fixed row sums are invulnerable to Type I errors (false positives). One of these three is a modified version of the original algorithm of E. F. Connor and D. Simberloff. Of the four co-occurrence indices, the number of checkerboard com-binations and the number of species combinations may be prone to Type II errors (false negatives), and may not reveal significant patterns in noisy data sets. L. Stone and A. Robert's checkerboard score has good power for detecting species pairs that do not co-occur together frequently, whereas D. Schluter's V ratio reveals nonrandom patterns in the row and column totals of the matrix. Degenerate matrices (matrices with empty rows or columns) do not greatly alter the outcome of null model analyses. The choice of an ap-propriate null model and index may depend on whether the data represent classic ''island lists'' of species in an archipelago or standardized ''sample lists'' of species collected with equal sampling effort. Systematic examination of a set of related null models can pinpoint how violation of the assumptions of the model contributes to nonrandom patterns.

On nestedness analyses: Rethinking matrix temperature and anti-nestedness

Article

Nov 2007
OIKOS

The analysis of nested structures in sets of species assemblages across different sites or in networks of interspecific interactions has become common practice in ecological studies. Although new analyses and metrics have been proposed, few studies have scrutinized the concepts that subtend nestedness analysis. We note two important conceptual problems that can lead to terminological inconsistencies and flawed interpretations. First, the thermodynamic analogy that underlies the most common metric of nestedness, matrix temperature, is flawed and has led some authors to incorrect interpretations. Second, the term “anti-nestedness” is a potential source of confusion and inconsistencies. We review four concepts for anti-nestedness and examine how distinct they are. “Anti-nested” matrices, i.e. less nested than expected by chance, may result from different ecological processes and show distinct structural patterns. Thus, there is no single unequivocal opposite of nestedness to be represented as “anti-nestedness”. A more profitable approach is to designate and test each distinct non-nested pattern according to its specific assumptions and mechanistic hypotheses.

Resource-island soils and the survival of the giant cactus, cardon, of Baja California Sur

Article

Apr 2012

Early survival and growth of some plants in arid environments depends on facilitation by a nurse plant. Amelioration of soil temperature extremes through shading and accumulation of mineral nutrients near nurse-plants are mechanisms of facilitation. We investigated the effects of shading (soil temperature) and soil type on survival and growth of the giant columnar cactus, cardon (Pachycereus pringlei). Cardon was grown either in a sandy clay-loam soil obtained from resource islands formed under mature mesquite (Prosopis articulata) or in the loamy-sand soil from plant-free bare areas that surround the islands. Seedlings were potted in these soils and the pots were buried to ground level in the open. We also determined plant responses to fertilization with N, P, K or NPK in the bare-area soils. Enhancement of survival and growth in the resource-island soils compared to that in the bare-area soils was highly significant. Plants survived and grew better in resource-island soils than in bare-area soil, an effect that was enhanced by shading (one-half of full sun). Greater root/shoot ratios of plants grown in bare-area soil indicated increased resource allocation to roots under limiting conditions. Significant interactions (analysis of variance) indicated that the soil and sun factors of the experiment were not independent of one another. Plant growth in bare-area soil improved considerably (>200%) in response to N fertilization (screenhouse conditions), and approximated that of plants in resource-island soil without N amendment. The growth response to P was small (<50%), while K did not affect growth significantly. Responses to NPK were similar to those to N alone. The results suggested that shading and nutritional effects interact in determining early survival and growth of cardon in different soils.

Clump spacing in a desert dwarf shrub community

Article

Nov 1985

A Monte Carlo method based on Ripley's K function-a cumulative function related to the number of plants encountered at different distances from other plants-is used to test the null hypothesis of random distribution of shrub clumps in a desert dwarf shrub community in Namaqualand, South Africa, where Psilocaulon arenosum is the dominant shrub. The method takes into account the apparent regularity of pattern caused by the finite size (up to 2 m diameter) of the clumps. It is shown that the clump centres are significantly aggregated (compared to random expectation) at distances on the order of 1 m. Such aggregation is expected, as a simple result of regeneration near to seed sources, if the time between catastrophic droughts is short in relation to the time required for development of a non-aggregated or regular pattern determined by moisture competition. No significant regulatiry was detected at distances of 3 m or less. One subplot showed regularity above 3 m, but this pattern was not shown by the other subplot and may not be a competition effect. These results support a hypothesis of aggregation caused by regeneration pattern decaying slowly toward randomness as larger individuals compete.

Positive interactions among plants

Article

Jan 1995

Ragan M. Callaway

Experimental evidence for positive interactions, or facilitation, among plants has increased markedly during the last 10 years. Experiments documenting facilitation have been conducted in many diverse ecological systems, which suggests that positive interactions may be fundamental processes in plant communities. Here, I review the evidence for facilitation, the mechanisms by which facilitation operates, and the effects facilitation has on community structure. Facilitative mechanisms may act simultaneously with resource competition or allelopathy, and the overall effect of one species on another may be the product of multiple, complex interactions. Positive interactions may also determine community spatial patterns, permit coexistence, enhance diversity and productivity, and drive community dynamics. Once viewed as anecdotal and idiosyncratic, facilitation is now contributing to a more complete understanding of community structure and dynamics.

Hart MM, Reader RJ, Klironomos JN.. Plant coexistence mediated by arbuscular mycorrhizal fungi. Trends Ecol Evol 18: 418-423

Article

Aug 2003
TRENDS ECOL EVOL

Recent research has indicated the importance of arbuscular mycorrhizal fungi (AMF) in mediating plant coexistence. Coarse-scale studies compare the effects of the presence versus absence of AMF on plant coexistence, a phenomenon that is most relevant in early successional ecosystems where AMF are patchily distributed. By contrast, fine-scale studies investigate interactions that might occur once AMF have developed more fully within ecosystems, and most plants come into contact with AMF. Whereas coarse-scale effects are well understood, our understanding of fine-scale factors is just developing, as a result of investigations into AMF–plant specificity, AMF species richness, shared mycelial networks, and plant–AMF feedback effects. Further research into these areas will provide a better understanding of factors that mediate plant species co-existence and, ultimately, the maintenance of biodiversity within plant communities.

Species-specific effects on topsoil development affect Quercus ilex seedling performance

Article

Jun 2006
ACTA OECOL

We illustrate experimentally the importance of species-specificity in the soil-mediated interactions among plants inhabiting heterogeneous landscapes. Topsoils from nine microhabitats were used to experimentally grow Quercus ilex acorns in the laboratory. We recorded germination, emergence, acorn left and seedling performance (HGR, biomass and root allocation). Different topsoils had very contrasting physico-chemical properties, creating a heterogeneous arena. This heterogeneity translated to differences in seedling performance, since emergence and survival differed among topsoils. However, nutrient content in topsoils did not appear to benefit seedling performance. In addition, there were strong correlations among parameters of plant performance indicating a consistency of the effect of topsoil type on Q. ilex seedlings. This implies that it is crucial to consider the specificity of the interaction between plants to wholly understand the structure of plant communities. Species-specific interactions may play an important role in the organization and dynamic of plants spatial distribution.

Markovian Dynamics of Simple and Complex Desert Plant Communities

Article

Apr 1988

Joseph R. McAuliffe

Many simple plant communities in extremely arid regions of the Sonoran Desert consist essentially of 2 shrub species, Ambrosia dumosa and Larrea tridentata. The majority of space is devoid of perennial plant cover, and Ambrosia readily colonize this open space. Recruitment of Larrea occurs less frequently and is largely limited to areas beneath the canopies of large, older Ambrosia individuals. The dynamics of these systems can be modeled as Markov chains. The dynamics of species-rich plant communities in less xeric parts of the Sonoran Desert appear to be qualitatively similar. One shrub species in particular, A. deltoidea, is capable of colonizing open space, whereas for most other shrub, tree and succulent species, recruitment is largely limited to areas beneath canopies of other plants, especially canopies of A. deltoidea. Although seemingly more complex, a digraph model showing the transitions among states possesses the same fundamental characteristics as does a digraph of the simple two-species system. The mechanisms underlying these dynamics include factors that influence seed distributions, germination success and patterns of post-germination mortality. Even in the simple two-species systems, it is likely that no individual mechanism such as competition can be singled out as the predominant determinant of dynamics and, hence, of the patterns of community structure. -from Author

Direct and Indirect Species Interactions in an Early Old-Field Plant Community

Article

Jun 1994

Thomas Miller

The success of species in a community is determined not only by the direct interactions between species but also by indirect interactions. Indirect effects will occur if an associate species changes the abundance of intermediate species in a chain of interactions that ultimately affect the growth of some focal species. A model of species interactions in a community is presented here and used to quantify direct and indirect effects in a five-species weedy plant community. This method quantifies indirect effects by measuring changes in the abundance of the intermediate species and then estimating how such changes will affect the focal species. The experiments demonstrated that the direct effects in this community were generally negative (competitive) and could be quite large. Indirect effects were positive (facilitative) and negatively correlated with the direct effects, which thus acted to mitigate the usually larger competitive effects. The magnitudes of most species interactions in this community were primarily determined by large direct effects of Ambrosia artemisiifolia and, to a lesser extent, Agropyron repens. The species that exhibited the least competitive release following the removal of a competitor were those that were the most suppressed, because of the nonlinear nature of their response to increasing abundance of competitors.

On the Prevalence and Relative Importance of Interspecific Competition: Evidence from Field Experiments

Article

Nov 1983

Joseph H. Connell

In a strictly defined sample of competition studies using controlled field experiments, covering 215 species and 527 experiments, competition was found in most of the studies, in more than half of the species, and in c40% of the experiments. In most of these experiments interspecific competition was not distinguished from intraspecific competition. In the few studies in which the 2 were separated, interspecific competition was the stronger form in about a sixth of all experiments. When competition was demonstrated, intraspecific competition was as strong or stronger than interspecific in 3/4 of the experiments. Marine organisms showed consistently higher frequencies of competition than terrestrial ones as did large-sized organisms as compared to smaller ones. Plants, herbivores, and carnivores showed similar frequencies of competition in all habitats compared. The incidence of competition varied considerably from year to year and place to place. When both members of a pair were studied and some competition found, only one member was affected in well over half the experiments.-from AuthorDept of Biol Sci, Univ of California, Santa Barbara, CA 93106, USA. English

Are Positive Interactions Species-Specific?

Article

May 1998

Ragan M. Callaway

Positive interactions among plants, or facilitations, have been demostrated in a wide variety of communities around the world(see reviews by DeAngelis et.al.1986; Hunter & Aarssen 1988; Bertness & Callaway 1994; Callaway 1995, Callaway & Walker in press). Neighbouring plant species compete with one another for resources, but they may also provide benefits for each other such as shade, higher nutrient levels, soil oxygenation, protection from herbivores, more favourable soil microflora, transfer of resources and fixed carbon via mycorrhizae, and increased pollinator visits(Callaway 1995). The species-specificity of positive interactions among plants - whether or not benefactor species are highly interchangeable - is central to understanding the general role of positive interactions in plant communities. In other words, are the positive effects of plants simply due to general changes in the biophysical environment; that which can be imitated by inanimate objects like rocks, microtopography, or experimental shade cloth? Or can facilitation depend on the species, with some species eliciting strong positive effects and other morphologically similar species producing neutral or negative effects? The species-specificity of positive interactions is pertinent to our general concepts of plant communities(see Gleason 1926; Goodall 1963; Shipley & Keddy 1987; Austin 1990; Collins et.al.1993; Callaway 1997). If positive interactions are often speciec specific, then many plant communities may be more independent than currently thought. Here, I have explained the specificity of positive interactions among plants by examining the literature and asking the following questions 1) Are beneficiary species non-randomly associated with potential benefactors? 2) Are positive mechanisms produced by species specific plant traits? 3) Can potential benefactors have similar positive effects, but different negative ones?

Nested species subsets, gaps and discrepancy

Article

May 1999

The nested-subset hypothesis of Patterson and Atmar states that species composition on islands with less species richness is a proper subset of those on islands with greater species richness. The sum of species absences, referred to as gaps, was suggested as a metric for nestedness, and null models have been used to test whether or not island species exhibited nestedness. Simberloff and Martin stated that finding examples of non-nested faunas was difficult. We revisit previous analyses of nested faunas and introduce a new metric we call “discrepancy” which we recommend as a measure for nestedness. We also recommend that the sample spaces conserve both row sums (number of species per site) and column sums (number of sites per species) derived from the incidence matrix. We compare our results to previous analyses.

Mycorrhizal functioning : an integrative plant-fungal process / edited by Michael F. Allen

Article

Michael F Allen

Incluye bibliografía e índice

Plant-Animal Mutualistic Networks: The Architecture of Biodiversity

Article

Dec 2007

Jordi Bascompte

The mutualistic interactions between plants and the animals that pollinate them or disperse their fruits have molded the organization of Earths's biodiversity. These interactions create networks of interdependence often times involving dozens or hundreds of species. Recent research has used concepts from graph theory to characterize the architecture of these networks. Mutualistic networks are heterogeneous, nested and build upon weak and asymmetric links among species. This network architecture highly affects its robustness to perturbations such as the extinction of a species.

Invasive Plants Versus Their New and Old Neighbors: A Mechanism for Exotic Invasion

Article

Nov 2000

Invading exotic plants are thought to succeed primarily because they have escaped their natural enemies, not because of novel interactions with their new neighbors. However, we find that Centaurea diffusa, a noxious weed in North America, has much stronger negative effects on grass species from North America than on closely related grass species from communities to which Centaurea is native. Centaurea's advantage against North American species appears to be due to differences in the effects of its root exudates and how these root exudates affect competition for resources. Our results may help to explain why some exotic species so successfully invade natural plant communities.

Mycorrhizal perennials of the "matorral xerófilo" and the "selva baja caducifolia" communities in the semiarid Tehuacán-Cuicatlán Valley, Mexico

Article

May 2003

We investigated the mycorrhizal status of perennial xeric plant species occurring in the "matorral xerófilo" (arid tropical scrub) and the ecotone of the "selva baja caducifolia" (tropical deciduous forest) communities in the semiarid valley of Tehuacán-Cuicatlán, south-central Mexico. The perennial species examined are dominant/codominant elements within the "matorral xerófilo" and the "selva baja caducifolia", both endangered communities in the Biosphere Reserve Tehuacán-Cuicatlán Valley. Of the 50 sampled species, 45 were mycorrhizal. To our knowledge, we report arbuscular mycorrhizae (AM) for the first time in 37 species, of which 21 are endemic to Mexico and nine are endemic to the Valley. We also report AM for the first time in three genera, Buddleja, Hechtia and Zornia, and in one plant family, Buddlejaceae. Beaucarnea gracilis, a threatened species, and Mimosa purpusii, a potentially rare species, are both mycorrhizal. This is the first study of the mycorrhizal status of plant species within the Valley.

Application of network theory to potential mycorrhizal networks

Article

Dec 2005

The concept of a common mycorrhizal network implies that the arrangement of plants and mycorrhizal fungi in a community shares properties with other networks. A network is a system of nodes connected by links. Here we apply network theory to mycorrhizas to determine whether the architecture of a potential common mycorrhizal network is random or scale-free. We analyzed mycorrhizal data from an oak woodland from two perspectives: the phytocentric view using trees as nodes and fungi as links and the mycocentric view using fungi as nodes and trees as links. From the phytocentric perspective, the distribution of potential mycorrhizal links, as measured by the number of ectomycorrhizal morphotypes on trees of Quercus garryana, was random with a short tail, implying that all the individuals of this species are more or less equal in linking to fungi in a potential network. From the mycocentric perspective, however, the distribution of plant links to fungi was scale-free, suggesting that certain fungus species may act as hubs with frequent connections to the network. Parallels exist between social networks and mycorrhizas that suggest future lines of study on mycorrhizal networks.

The influence of biotic interactions on soil biodiversity

Article

Aug 2006
ECOL LETT

David Wardle

Belowground communities usually support a much greater diversity of organisms than do corresponding aboveground ones, and while the factors that regulate their diversity are far less well understood, a growing number of recent studies have presented data relevant to understanding how these factors operate. This review considers how biotic factors influence community diversity within major groups of soil organisms across a broad spectrum of spatial scales, and addresses the mechanisms involved. At the most local scale, soil biodiversity may potentially be affected by interactions within trophic levels or by direct trophic interactions. Within the soil, larger bodied invertebrates can also influence diversity of smaller sized organisms by promoting dispersal and through modification of the soil habitat. At larger scales, individual plant species effects, vegetation composition, plant species diversity, mixing of plant litter types, and aboveground trophic interactions, all impact on soil biodiversity. Further, at the landscape scale, soil diversity also responds to vegetation change and succession. This review also considers how a conceptual understanding of the biotic drivers of soil biodiversity may assist our knowledge of key topics in community and ecosystem ecology, such as aboveground-belowground interactions, and the relationship between biodiversity and ecosystem functioning. It is concluded that an improved understanding of what drives the diversity of life in the soil, incorporated within appropriate conceptual frameworks, should significantly aid our understanding of the structure and functioning of terrestrial communities.

The Nested Assembly of Plant Facilitation Networks Prevents Species Extinctions

Abstract

No full-text available

Recommended publications

Why dietary restriction substantially increases longevity in animal models but won't in humans

Re-Shuffling of Species with Climate Disruption: A No-Analog Future for California Birds?

Development of memory and the hippocampus: Comparison of food-storing and nonstoring birds on a one-...

Resurrecting the differential mortality model of sexual size dimorphism