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Distribution of pollinator and plant species across distinct network roles (module hubs, network hubs, peripherals, and connectors) in grasslands with different times-since-fire in Southern Brazil. A Overall distribution of network roles. B Relative contribution of plant and pollinator groups in each role. For full species (or morphotype) names and roles, see Supplementary Material 3
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Fire is a frequent disturbance in most grasslands around the world, being key for the structure and dynamics of the biodiversity in such ecosystems. While grassland species may be resilient, little is known on how plant–pollinator networks reassemble after fire. Here, we investigate the structure and dynamics of plant–pollinator networks and the va...
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Ecological communities are maintained through species interactions, and the resilience of species interactions is critical to the persistence of natural communities. Keystone species play outsized roles in maintaining species interaction networks, and within plant-pollinator communities are high priorities for conservation. The loss of a keystone p...
Citations
... While the regenerative response of many key plant species has been well documented or inferred from their life-history traits, less research has been performed about fire effects on plant-animal interactions such as pollination (Brown et al., 2016;García et al., 2018;Teixido et al., 2022;Ballarin et al., 2023). However, interactions between plants and pollinators are of crucial importance in re-establishing community structure, community functioning and the services that fire-prone ecosystems provide to humankind da Silva Goldas et al., 2022a). ...
... Our findings are in accordance with previous evidence that have demonstrated an overall positive response to fire across various animal guilds that potentially act as pollinators (Winfree et al., 2009;Van Nuland et al., 2013;Carbone et al., 2019;Nicholson and Egan, 2020;Mason et al., 2021). Pollination in fire-prone ecosystems such as grasslands is highly resilient to fire effects (da Silva Goldas et al., 2022a). However, not all fires are beneficial nor do all groups of pollinators show positive responses. ...
Background and Aims
Fire may favour plant flowering by opening the vegetation and increasing abiotic resource availability. Increased floral display size can attract more pollinators and increase the absolute fruit and seed production immediately after the fire. However, anthropogenic increases in fire frequency may alter these responses. We aim to assess the effects of fire on pollination and reproductive success of plants at the global scale.
Methods
We performed a systematic literature review and meta-analyses to examine overall fire effects as well as different fire parameters on pollination and on plant reproduction. We also explored to what extent the responses vary among pollinators, pollination vectors, plant regeneration strategies, compatibility systems, vegetation types and biomes.
Key Results
Most studies were conducted in fire-prone ecosystems. Overall, single fires increased pollination and plant reproduction but this effect was overridden by recurrent fires. Floral visitation rates of pollinators were enhanced immediately following a wildfire, and especially in bee-pollinated plants. Fire increased the absolute production of fruits or seeds but not the fruit or seed set. The reproductive benefits were mostly observed in wind-pollinated (graminoids), herbaceous and resprouter species. Finally, fire effects on pollination were positively correlated with fire effects on plant reproductive success.
Conclusions
Fire has a central role in pollination and plant sexual reproduction in fire-prone ecosystems. The increase in the absolute production of fruits and seeds suggests that fire benefits on plant reproduction are likely driven by increased abiotic resources and the consequent floral display size. However, reproduction efficiency, as measured by fruit or seed set, does not increase with fire. In contrast, when assessed on the same plant simultaneously, fire effects on pollination are translated into reproduction. Increased fire frequency due to anthropogenic changes can alter the nature of the response to fire.
... We therefore expected a higher connectivity between the trophic levels and a greater number of modules in the intact than in the invaded network. In addition, we expected species to change their structural role between the intact and invaded networks, as has been recorded for other disturbances [32]. We tested this hypothesis by measuring connectivity between trophic levels, modularity, and the structural role of species. ...
... These shifts fragmented the network by reducing the "bridges" among modules [13]. Previous studies also demonstrated the structural role of species change in response to disturbances, such as fire and habitat loss [32,46]. ...
Species interactions are the backbone of the structure and dynamics of communities. The extensive research into the link between structure and stability has been primarily theoretical and focused on monotrophic networks. Therefore, how the disruption of multitrophic interactions alters communities' response to perturbations in nature remains an open question. Here, we explored how non-native ungulates affect pollination-seed dispersal multilayer networks in Patagonia, Argentina. Ungulates disrupt a hummingbird-mistletoe-marsupial keystone interaction, which alters community composition. We calculated interlayer connectivity, modularity, and species' roles in connecting modules for intact vs. invaded networks. To link structural changes to stability, we quantified network tolerance to a single random species removal (disturbance propagation) and sequential species removal (robustness) using a stochastic coextinction model. Non-native ungulates reduced the connectivity between pollination and seed dispersal and produced fewer modules with a skewed size distribution. Moreover, species shifted their structural role, primarily from connectors to peripherals, thereby fragmenting the network by reducing the "bridges" among modules. These structural changes altered the dynamics of cascading effects in the community, increasing disturbance propagation and reducing network robustness. Our results highlight the importance of understanding the mechanisms that alter the structure and subsequent stability of multitrophic communities in nature.
... A recent study that examined ten bipartite network metrics included a separate biological justification for each (Valido et al., 2019). H 2 ′ is typically the only bipartite network metric used to evaluate specialization (Bucharova et al., 2022;da Silva Goldas et al., 2022;Vinagre-Izquierdo et al., 2022;Virgo et al., 2022). Whereas it is indeed the case that most bipartite network metrics are related to the concept of specialization (Fründ et al., 2016), the decision in the original study to calculate a plethora of metrics for the sake of quantifying the very same phenomenon (specialization) is far from accepted practice in ecology. ...
Paleobotany is at a crossroads. Long-term trends in the fossil record of plants, encompassing their interactions with herbivores and with the environment, are of the utmost relevance for predicting global change as pCO2 continues to rise. Large data compilations with the potential to elucidate those trends are increasingly easy to assemble and access. However, in contrast to modern ecology and unlike various other paleontological disciplines, paleobotany has a limited history of “big data” meta-analyses. Debates about how much data are needed to address particular questions, and about how to control for potential confounding variables, have not examined paleobotanical data. Here I demonstrate the importance of analytical best practices by applying them to a recent meta-analysis of fossil angiosperms. Two notable analytical methods discussed here are propensity score matching and specification curve analysis. The former has been used in the biomedical and behavioral sciences for decades; the latter is a more recent method of examining relationships between, and inherent biases among, models. Propensity score matching allows one to account for potential confounding variables in observational studies, and more fundamentally, provides a way to quantify whether it is possible to account for them. Specification curve analysis provides the opportunity to examine patterns across a variety of schemes for partitioning data—for example, whether fossil assemblages are binned temporally by stage, epoch, or period. To my knowledge, neither of these methods has been used previously in paleontology, however, their use permits more robust analysis of paleoecological datasets. In the example provided here, propensity score matching is used to separate latitudinal trends from differences in age, climate, and plant community composition. Specification curve analysis is used to examine the robustness of apparent latitudinal trends to the schema used for assigning fossil assemblages to latitudinal bins. These analytical methods have the potential to further unlock the promise of the plant fossil record for elucidating long-term ecological and evolutionary change.
Background
Anthropogenic activities significantly impact natural ecosystems, leading to alterations in plant and pollinator diversity and abundance. These changes often result in shifts within interacting communities, potentially reshaping the structure of plant-pollinator interaction networks. Given the escalating human footprint on habitats, evaluating the response of these networks to anthropization is critical for devising effective conservation and management strategies.
Methods
We conducted a comprehensive review of the plant-pollinator network literature to assess the impact of anthropization on network structure. We assessed network metrics such as nestedness measure based on overlap and decreasing fills (NODF), network specialization (H 2 ’), connectance (C), and modularity (Q) to understand structural changes. Employing a meta-analytical approach, we examined how anthropization activities, such as deforestation, urbanization, habitat fragmentation, agriculture, intentional fires and livestock farming, affect both plant and pollinator richness.
Results
We generated a dataset for various metrics of network structure and 36 effect sizes for the meta-analysis, from 38 articles published between 2010 and 2023. Studies assessing the impact of agriculture and fragmentation were well-represented, comprising 68.4% of all studies, with networks involving interacting insects being the most studied taxa. Agriculture and fragmentation reduce nestedness and increase specialization in plant-pollinator networks, while modularity and connectance are mostly not affected. Although our meta-analysis suggests that anthropization decreases richness for both plants and pollinators, there was substantial heterogeneity in this regard among the evaluated studies. The meta-regression analyses helped us determine that the habitat fragment size where the studies were conducted was the primary variable contributing to such heterogeneity.
Conclusions
The analysis of human impacts on plant-pollinator networks showed varied effects worldwide. Responses differed among network metrics, signaling nuanced impacts on structure. Activities like agriculture and fragmentation significantly changed ecosystems, reducing species richness in both pollinators and plants, highlighting network vulnerability. Regional differences stressed the need for tailored conservation. Despite insights, more research is crucial for a complete understanding of these ecological relationships.
The study of ecological stability continues to fill the pages of scientific journals almost seven decades after the first ecologists initiated this line of research. The many advances in this field have focused on understanding the stability of populations, communities or functions within single guilds or trophic levels, with less research conducted across multiple trophic levels and considering the different interactions that relate species to each other. Here, we review the recent literature on the multiple dimensions of ecological stability specifically within plant-pollinator communities. We then focus on one of stability´s dimensions, temporal invariability, and adapt an existing partitioning framework that bridges invariability and synchrony measures across spatial scales and organizational levels to accommodate interactions between plants and their pollinators. Finally, we use this framework to analyze temporal invariability in plant reproductive success, partitioning it on invariability and synchrony components across plant and pollinator populations and communities, as well as their interactions, using a well-resolved dataset that encompasses data for two years. Our review of the literature points to several significant gaps in our current knowledge, with simulation studies clearly overrepresented in the literature as opposed to experimental or empirical approaches. Our quantitative approach to partitioning invariability shows similar patterns of decreasing temporal invariability across increasing organizational levels driven by asynchronous dynamics amongst populations and communities, which overall stabilize ecosystem functioning (plant reproductive success). This study represents a first step towards a better comprehension of temporal invariability in ecosystem functions defined by interactions between species and provides a blueprint for the type of spatially replicated multi-year data that needs to be collected in the future to further our understanding of ecological stability within multi-trophic communities.
Species interactions are critical for maintaining community structure and dynamics, but the effects of invasive species on multitrophic networks remain poorly understood. We leveraged an ongoing invasion scenario in Patagonia, Argentina, to explore how non-native ungulates affect multi-trophic networks. Ungulates disrupt a hummingbird-mistletoe-marsupial keystone interaction, which alters community composition. We sampled pollination and seed dispersal interactions in intact and invaded sites. We constructed pollination and seed dispersal networks for each site, which we connected via shared plants. We calculated pollination-seed dispersal connectivity, identified clusters of highly connected species, and quantified species' roles in connecting species clusters. To link structural variation to stability, we quantified network tolerance to single random species removal (disturbance propagation) and sequential species removal (robustness) using a stochastic coextinction model. Ungulates reduced the connectivity between pollination and seed dispersal and produced fewer clusters with a skewed size distribution. Moreover, species shifted their structural role, fragmenting the network by reducing the 'bridges' among species clusters. These structural changes altered the dynamics of cascading effects, increasing disturbance propagation and reducing network robustness. Our results highlight invasive species' role in altering community structure and subsequent stability in multitrophic communities.
Despite the dynamic nature of communities, most research typically treated interaction networks as static entities, and only a few analysed the spatial and the temporal scales simultaneously. Here, we used spatial and temporal multilayer networks to explore the persistence of species and interactions in space and time, as well as the variation of species role (centrality) according to biotic factors. We further investigated, for the first time, the spatio-temporal variation in multilayer network structure. Species exhibited substantial turnover across time mainly due to differences in species phenology. In contrast, interaction turnover was more pronounced across habitats, which seems to be a common strategy of pollinators to adjust interactions spatially to different ecological scenarios. Plant species were comparatively more important to the cohesiveness of spatial than temporal networks whereas the centrality of pollinators correlated between scales. The importance of plant species fluctuated temporally due mainly to changes in flower density, whereas that of pollinators fluctuated in space and time according to their relative abundance. Module composition was highly unstable in time. Species were highly capable of changing partners and module affiliation across both scales. We conclude that plant-pollinator interactions are highly dynamic in space and time and that there are differences between plants and pollinators in their use of resources across habitats and subseasons with implications for the understanding of functional connectivity and multilayer structure.
Flower-butterfly networks on three grassland types in the National Park Neusiedler See-Seewinkel were analysed, viz. (1) a fenced pasture grazed mainly by Przewalski's horses at low densities, (2) pastures grazed by non-stationary cattle and (3) meadows maintained by mowing. Sampling took place in June and July 2021 during a drought period. We observed 4,160 flower-butterfly interactions involving 27 butterfly and 59 plant species, including 147 interaction pairs not previously recorded. Species diversity and composition of interacting communities varied across the three grassland types and two survey months, with highest diversities on mown meadows. Nectar flower abundance did not differ between grassland types, but decreased from early to high summer. Network specialization H2' and modularity Q did not vary systematically between grassland types, but decreased in response to drought. All observed flower-visiting butterfly species visit multiple nectar plant species, but average species-level specialization d' was higher on meadows than on pastures and further decreased with summer drought. This suggests that partitioning of nectar sources among butterflies is more effective at times of high supply, while overlap in resource use increases during drought. These results suggest that grassland butterflies in the study area respond opportunistically to shortages in nectar flower abundance caused by summer drought, whereas extensive management by grazing vs. mowing left a rather minor signature on these ecological networks. Due to their higher nectar flower abundance mown meadows are important for maintaining butterfly diversity in this large conservation area.
