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Hydrologically Defined Niches Reveal a Basis for Species Richness in Plant Communities
Abstract
Species-rich plant communities are prized repositories of biodiversity and a dwindling resource, but how the large numbers of species that characterize such communities are able to coexist is poorly understood. Resource-based competition theory predicts that stable coexistence between species depends on each being a superior competitor in its own niche. The theoretical problem is that plants all require the same resources and acquire them in a very limited variety of ways, so observed niche overlaps are high, and exclusion of all but the best competitor is the predicted result. This problem, central to community ecology, has elicited a variety of theoretical solutions,,,, several of which invoke some degree of niche separation in time or space,. The signature of niche separation in the field is to be found in community structure, which should indicate (i) smaller than expected niche overlaps on relevant niche axes and (ii) a trade-off between species' resource use on orthogonal axes. Here we provide evidence for the existence of both these conditions in a species-rich plant community.
... Other studies characterize them at very large spatial scales (Ervin et al. 2006), but this does not fully account for the spatial variability of water conditions occurring in particular along elevation gradients (Alexander et al. 2016;García-Baquero et al. 2016;Stein et al. 2014). Moreover, although a diversity of water regime descriptors is expected to influence plant communities (notably through flooding, soil aeration deficit and dryness (Araya et al. 2011;Gowing et al. 1997;Large et al. 2007;Silvertown et al. 1999), these metrics have rarely been explored together (Webb et al. 2012). The effect of soil dryness has been rarely investigated, even though it can be severe and an important driver of plant communities: out of approximately 80 papers consulted for the present study, soil dryness is mainly considered by Gowing and collaborators through the hydrological niche of grassland plants (Araya et al. 2011;Gowing et al. 1997;Silvertown et al. 1999) and in a few other studies (Brotherton and Joyce 2015;Brotherton et al. 2019;Jung et al. 2009), and by Dwire et al. (2006) through ground topography. ...
... Moreover, although a diversity of water regime descriptors is expected to influence plant communities (notably through flooding, soil aeration deficit and dryness (Araya et al. 2011;Gowing et al. 1997;Large et al. 2007;Silvertown et al. 1999), these metrics have rarely been explored together (Webb et al. 2012). The effect of soil dryness has been rarely investigated, even though it can be severe and an important driver of plant communities: out of approximately 80 papers consulted for the present study, soil dryness is mainly considered by Gowing and collaborators through the hydrological niche of grassland plants (Araya et al. 2011;Gowing et al. 1997;Silvertown et al. 1999) and in a few other studies (Brotherton and Joyce 2015;Brotherton et al. 2019;Jung et al. 2009), and by Dwire et al. (2006) through ground topography. ...
... The absence of a relationship between flooding frequency -or soil moisture -and species richness in wet grasslands has even been reported (Baattrup-Pedersen et al. 2013;Lafage et al. 2015). The limited responsiveness of community diversity to water regime probably relies on the turnover of species with different hydrological niches (Silvertown et al. 1999), along with water conditions. In our study, flooding-tolerant species such as Glyceria fluitans, Oenanthe fistulosa or Eleocharis spp. ...
We studied the levels of importance of water regime components for plant community composition, hygrophilous character and species diversity in semi-natural wet grasslands. We also investigated to what extent the water level in adjacent canals drives the water regime in grasslands in two marshes of the Marais poitevin region (Atlantic coast of France). The species composition of homogenous plant communities, hygrophilous character and diversity were described from frequency data. The water regime was characterized by flooding duration, soil aeration deficit and soil dryness, and soil conductivity measured in the sub-halophilous marsh.
Plant species composition and hygrophilous character were well predicted by the combined effects of all water regime components; flooding duration and dryness were most important, while soil water conductivity had a significant but limited impact. Diversity was poorly predicted by the environment, with a weak negative pattern related to flooding duration. The elevation contrasts within grasslands greatly contributed to species beta diversity.
Different water regime components act as complementary drivers of plant communities in wet grasslands and need to be monitored, among other local environmental conditions. The importance of dryness stress is underlined, despite the dryness tolerance of many wet grassland species in relation to natural alternating wet/dry periods. Water level management in canals was found insufficient on its own to restore or maintain long flooding conditions in grasslands, probably because of its limited relationship with water regime in wet grasslands.
... However, when the WT is too shallow, fluctuating within the root zone, the stress of waterlogging and anoxia stresses plants and limits rooting depth (6,7). The "hydrologic niche theory" argues that species segregate according to trade-offs from drought adaptations in one end to waterlogging adaptations in the other (8)(9)(10). In between lies the physiological challenge of tolerating double stresses alternating between the wet (waterlogging) and the dry (drought) seasons. ...
... Waterlogging restricts roots to shallow depths, while deeper roots are often needed to escape drought, and seasonal switching between shallow and deep roots would require fast root turnover, imposing high metabolic costs at the expense of biomass production (13), thus favoring species that can complete full aboveground life cycles in a short season, replacing aerial organs following the waterlogging and drought cycles (14). This framework of vegetation tolerance to multiple abiotic stresses (11) has been useful for understanding species distribution at the local level based on their ability to cope with these stresses (8)(9)(10)15). However, the tradeoff in the context of double stresses, central to the niche hypothesis, has mostly been demonstrated for herbaceous species, in the strict sense of ref. 8. Here, we test this hypothesis at the ecosystem level to explain forest-savanna coexistence across tropical South America. ...
... This framework of vegetation tolerance to multiple abiotic stresses (11) has been useful for understanding species distribution at the local level based on their ability to cope with these stresses (8)(9)(10)15). However, the tradeoff in the context of double stresses, central to the niche hypothesis, has mostly been demonstrated for herbaceous species, in the strict sense of ref. 8. Here, we test this hypothesis at the ecosystem level to explain forest-savanna coexistence across tropical South America. ...
Forest–savanna boundaries are ecotones that support complex ecosystem functions and are sensitive to biotic/abiotic perturbations. What drives their distribution today and how it may shift in the future are open questions. Feedbacks among climate, fire, herbivory, and land use are known drivers. Here, we show that alternating seasonal drought and waterlogging stress favors the dominance of savanna-like ecosystems over forests. We track the seasonal water-table depth as an indicator of water stress when too deep and oxygen stress when too shallow and map forest/savanna occurrence within this double-stress space in the neotropics. We find that under a given annual precipitation, savannas are favored in landscape positions experiencing double stress, which is more common as the dry season strengthens (climate driver) but only found in waterlogged lowlands (terrain driver). We further show that hydrological changes at the end of the century may expose some flooded forests to savanna expansion, affecting biodiversity and soil carbon storage. Our results highlight the importance of land hydrology in understanding/predicting forest–savanna transitions in a changing world.
... In the valleys, the WT is shallow year-round, and can become too shallow in the wet season, creating waterlogging. This different exposure to hydrologic stress (drought under the hills, waterlogging in the valleys) is hypothesized to select for plant species according to their adaptations to hydrologic stress [34]. evidence from the tropics [13][14][15][16][17] and temperate areas [9,18,19]. ...
... On the hills, the WT is deep and out of reach for most trees, which rely either on adaptations to withstand drought or mechanisms to avoid it, such as deep rooting, accessing moisture stored in the deep soil [29][30][31][32][33]. The resulting gradient in water access from hills to valleys creates hydrologic niches, which species occupy according to their adaptations to drought and waterlogging [34,35]. At the regional scale, mean annual precipitation (MAP) and rainfall seasonality influence the distribution of floristic composition and physiological traits related to drought tolerance [40][41][42][43][44][45], with lower rainfall and higher seasonality being associated with higher drought resistance [43][44][45][46]. ...
Droughts are predicted to increase in both frequency and intensity by the end of the 21st century, but ecosystem response is not expected to be uniform across landscapes. Here we assess the importance of the hill-to-valley hydrologic gradient in shaping vegetation drought resistance under different rainfall regimes using hydraulic functional traits. We demonstrate that rainfall and hydrology modulate together the drought resistance of species in different sites and topographic postions. Valleys are more vulnerable to drought due to stable groundwater access, regardless of rainfall. In all study sites, the variability in drought resistance is higher on hills than on valleys, suggesting that the diversity of strategies to cope with drought is more important for tree communities on hills. When comparing our results with previously published data across the tropics, we show greater variability at the local scale than previously reported. Our results reinforce the urgent need to extend sampling efforts across rainfall regimes and topographic positions to improve the characterization of ecosystem resistance to drought.
... Toogood et al. 2008;Wheeler et al. 2009). Root zone aeration stress, which is strongly influenced by the depth to the water table, has been identified as an important determinant of plant species distribution (Silvertown et al. 1999;Gowing et al. 2002aGowing et al. , 2002bDwire et al. 2006;Clilverd et al. 2022). Similarly, the hydrological regime of floodplains and associated wetlands influences habitat suitability for animals. ...
... It employs water table position as a proxy for aeration stress under shallow water table conditions -i.e. where the water table is less than 1 m below the soil surface (Gowing et al. 1998a;Silvertown et al. 1999). Aeration stress is calculated as the integral of the difference between modelled and a reference water table depth: ...
The hydro-ecological impacts of 40 UK Climate Projections 2018 scenarios on a restored lowland England river floodplain are assessed using a MIKE SHE / MIKE 11 model. Annual precipitation declines for 60% of scenarios (range: -26%–21%, with small, <5%, declines for the central probability level). Potential evapotranspiration increases for all probability levels except the most extreme, very unlikely, 10% level (range: -4%–43%, central probability 9%–20%) Mean, peak and low river discharges are reduced for all but the extreme 90% probability level. Reduced frequency of bankfull discharge dominates (at least halved for the central probability level). Floodplain inundation declines for over 97% of 320 scenario-events. Winter water table levels still intercept the surface, while mean and summer low levels are reduced. Declines in mean summer floodplain water table levels for the central probability level (0.22 m and 0.28 m for the 2050s and 2080s, respectively) are twice as large as those in the more dynamic riparian area. Declines reach 0.39 m for some 10% probability level scenarios. Simulated hydrological changes differ subtly from a previous assessment using earlier UK climate projections. A soil aeration stress index demonstrates that, under baseline conditions, prolonged high winter floodplain water tables drive long periods of low root-zone oxygen, in turn favouring vegetation communities adapted to waterlogged conditions. Climate change reduces aeration stress and the extent of appropriate conditions for these plant communities in favour of communities less tolerant of wet conditions.
... Plant species have individual tolerance ranges to aeration stress with species separation along fine-scale hydrological gradients. These have been investigated using both qualitative (Ellenberg, 1974) and quantitative (Gowing et al., 1998;Silvertown et al., 1999) methods. Gowing et al. (1997) used a cumulative stress index based on water table position to predict root zone aeration stress and to account for spatial patterns in UK wet-meadow plant communities. ...
... Applied Vegetation Science CLILVERD Et aL. communities characterised by stress-tolerant, competitive perennials (Joyce, 1998 Silvertown et al., 1999;Dwire et al., 2006). The degree of waterlogging, and resultant root zone aeration stresses, control plant functioning, productivity and survival (Visser et al., 2003). ...
Aims
Channelization and artificial embankments have altered the natural flood regime of many rivers, impacting the hydrological characteristics of floodplain ecosystems and their biological communities. This study was undertaken on a floodplain meadow to assess spatial patterns of plant communities in relation to soil physical and chemical conditions, and the impacts of floodplain restoration that involved embankment‐removal.
Location
River Glaven, Hunworth, Norfolk, UK.
Methods
Fine‐scale plant and soil chemistry sampling was conducted prior to embankment removal, and hydrological and climatological conditions were monitored prior to and after embankment removal. Hydrological/hydraulic modelling simulated groundwater levels for a 10‐year period to assess changes in soil aeration stresses and plant community composition following embankment‐removal.
Results
Hydrology was identified as the primary driver of plant community composition. Soil fertility was also important. Unique continuous measurements of vadose dissolved oxygen concentrations using oxygen optodes indicated strong coupling between water table depth and root zone dissolved oxygen concentrations. Reinstatement of overbank flows did not substantially affect aeration stress across most of the meadow because of pre‐existing wet conditions. However, along the river‐floodplain ecotone, aeration stress increased substantially from conditions normally associated with dry grassland to those characteristic of fen communities ( p < 0.05).
Conclusions
This restored water table regime may be suitable for more diverse plant assemblages. Benefits of flooding for increased species richness and transport of propagules may, however, be over‐ridden without accompanying water level management during the growing season, or hay removal to balance additional supply of nutrients from river floodwater and sediment. Our results show that hydrological/hydraulic modelling combined with quantitative measures of plant water‐requirements can provide practical and adaptive management tools to estimate the response of floodplain communities to changing water regimes.
... The hydrological niche is a spatial environmental niche that has been postulated to stabilize species coexistence in English floodplain meadows (Silvertown et al. 1999), South African fynbos (Araya et al. 2011) and Iberian grasslands (García-Baquero et al. 2016). In studies of these habitats, within-site hydrological heterogeneity along topographic gradient was understood as a physical feature that creates, at a fine scale, patchy conditions of varying water deficit stress (due to soil drying) and oxygen deficit stress (due to waterlogging). ...
... Since appropriate sampling methods and data from 15 field sites have been used, it seems reasonable to consider these results as widely representative of English species-rich floodplain meadows. Consistent with the previously reported segregation patterns (Silvertown et al. 1999), monotonic responses (63% of the fitted models) were either increasing or decreasing with increasing mWTD (i.e. with increased soil drying), thereby contributing to species segregation over hydrological heterogeneity. The hump-shaped responses (37% of the fitted models) often, but not always, contribute to segregation. ...
The hydrological niche is one of the few below ground spatial environmental niches, which has been shown to structure English floodplain meadows and other European and African herbaceous ecosystems. However, both the relative contribution of hydrological heterogeneity to the structure of English floodplain meadows across spatial scales and the forms of the individual species’ responses to hydrological heterogeneity remain largely unknown. Here, we use a survey database of 2440 evaluation units sampled in 15 English floodplain meadows to dissect the spatial architecture of this metacommunity and describe the relationship between the abundance of individual species and hydrological heterogeneity. Of the tested species, 65% responded to spatial hydrological heterogeneity, with both monotonic and hump-shaped responses. We found that between-site beta-diversity is much stronger than within-site beta-diversity, with between-site scale hydrological variation explaining twice as much variation in community structure as within-site scale. This leads to the conclusion that a conservation strategy of rare plant communities should include not only the preservation of the diversity of local hydrological regimes, but also, specially, the inclusion in the conservation system of as many and environmentally varied local plant communities as possible.
... OTUs were identified as high-impact indicators, suggesting that the (Sigwart et al., 2021). When highly diverse groups are analysed, evenness among shorter branches of closely related species and genera can be overshadowed by clustering at deeper levels (Silvertown et al., 1999(Silvertown et al., , 2001Webb et al., 2002Webb et al., , 2006. Data on the diversity and distribution of Strombidae, a large group of Indo-Pacific gastropods, indicated that species richness was a poor predictor of the morphological diversity within a site (Roy et al., 2001). ...
Both human populations and marine biodiversity are concentrated along coastlines, with growing conservation interest in how these ecosystems can survive intense anthropogenic impacts. Tropical urban centres provide valuable research opportunities because these megacities are often adjacent to mega-diverse coral reef systems. The Pearl River Delta is a prime exemplar, as it encompasses one of the most densely populated and impacted regions in the world and is located just northwest of the Coral
Triangle. However, the spatial and taxonomic complexity of this biodiversity, most of which is small, cryptic in habitat and poorly known, make comparative analyses challenging. We deployed standardized settlement structures at seven sites differing in the intensity of human impacts and used COI metabarcoding to characterize benthic biodiversity, with a focus on metazoans. We found a total of 7184 OTUs, with an average of 665 OTUs per sampling unit; these numbers exceed those observed in many previous studies using comparable methods, despite the location of our study in an urbanized environment. Beta diversity was also high, with 52% of the OTUs found at just one site. As expected, we found that the sites close to point sources of pollution had substantially lower diversity (44% less) relative to sites bathed in less polluted
oceanic waters. However, the polluted sites contributed substantially to the total animal diversity of the region, with 25% of all OTUs occurring only within polluted sites. Further analysis of Arthropoda, Annelida and Mollusca showed that phylogenetic clustering within a site was common, suggesting that environmental filtering reduced
biodiversity to a subset of lineages present within the region, a pattern that was most pronounced in polluted sites and for the Arthropoda. The water quality gradients surrounding the PRD highlight the unique role of in situ studies for understanding the impacts of complex urbanization pressures on biodiversity.
... Therefore, offspring may experience much less or much more drought than their mother did in the previous year, when seeds were produced. Moreover, pollen is dispersed by bumble bees (He et al., 2019), which easily can travel between drier and wetter microenvironments (Silvertown et al., 1999). Thus, the paternal moisture environment often will be different from that of the maternal moisture environment. ...
While there is long‐standing interest in the role of inter‐ and transgenerational plasticity via the maternal line, it rarely has been studied via the paternal line. Thus, consequences of the paternal environment for parental fitness and for performance of offspring in the environments experienced by either fathers or mothers are not known. We studied the intergenerational plasticity (IGP) of the plant species Paeonia ostii (Paeoniaceae) and tested the hypothesis that exposure of fathers to environmental stress (i) reduces parental fitness and performance of offspring grown under non‐stressful conditions, but (ii) mitigates the negative effects of environmental stress on fitness of parents and performance of offspring.
Crosses were made in a greenhouse within six families of P. ostii between parents grown under drought and in a mesic environment, and the offspring of each cross were grown under both dry and mesic conditions. Production and germination of seeds and morphological and physiological traits of offspring were measured as indicators of parental fitness and offspring performance, respectively.
Paternal drought decreased seed number per fruit, except when maternal plants also were grown in drought conditions. Offspring drought decreased seedling performance. However, when fathers experienced drought this negative effect on the offspring was partly mitigated, in particular when mothers also had experienced drought. In contrast, offspring grown in mesic conditions had improved seedling performance, especially when either parent (or both) also were grown in mesic conditions. Such statistical differences remained when seed mass was included as a covariate.
Overall, paternal pollen of P. ostii mediated IGP to drought almost as well as it did for maternal ovules. IGP was adaptive if environments remained constantly dry across generations but maladaptive if environments changed. Hence, under future climate changes, paternal IGP might be both a blessing and a curse, with the blessing occurring when the focal habitat becomes drier and pollen comes from already‐dry places, while the curse may dominate in predictably moist habitats surrounded by drier habitats.
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... In many plant communities, environmental variability is the main factor determining species composition (Silvertown et al. 1999). Recently, it has become recognised that differences in colonising ability may also play an important role. ...
Plant species of ancient forests tend to be poor dispersers, but recent field studies suggest that dispersal may be strongly accelerated in streams. To further test this idea, we addressed the following two questions: (1) which traits facilitate transport and deposition of seeds by streams? (2) do ancient forest species differ from other forest species with respect to these traits?. In the Boven Slinge, a forested lowland stream in the Netherlands, we measured seed transport and deposition and analysed which traits best explained this. We subsequently compared ancient forest species with other forest species with respect to these key traits. Our field measurements indicated that stream dispersal is determined by both source- and path-related processes. Significance of upstream population size, seed production and seed release period mirrored source effects, whereas significance of buoyancy and seed mass indicated that the path, i.e. stream transport and deposition, further constrains the number of species that can be dispersed by streams. Compared to other forest species, ancient forest species do not differ with respect to seed release period, buoyancy and seed mass, but at a given plant height, ancient forest species produce less seeds than other forest species. This may reflect an adaptation to their relatively stable habitat which comes at the expense of (stream) dispersal capacity. In conclusion, ancient forest plants are just as well equipped for stream dispersal as other forest species, but success will critically depend on upstream population size, given their low per plant seed production.
... K E Y W O R D S belowground niche partitioning, climate change, extreme drought, grasslands, hydrological niche segregation, oxygen stable isotopes, rainout shelter, water-uptake depth INTRODUCTION How competing plant species coexist is a major unresolved question in ecology. Niche partitioning, and in particular belowground niche partitioning, has long been hypothesized as the key mechanism promoting species coexistence and diversity by effective resource exploitation and diminishing interference of roots during nutrient and water uptake (Guderle et al., 2018;Herberich et al., 2017;Silvertown, 2004;Silvertown et al., 1999Silvertown et al., , 2015. Although the importance of this mechanism is largely accepted, experimental tests examining the extent of belowground niche partitioning in natural communities and the magnitude of its change as a response to stress are still scarce. ...
Belowground niche partitioning presents a key mechanism for maintaining species coexistence and diversity. Its importance is currently reinforced by climate change that alters soil hydrological conditions. However, experimental tests examining the magnitude of its change under climate change are scarce. We combined measurements of oxygen stable isotopes to infer plant water‐uptake depths and extreme drought manipulation in grasslands. Belowground niche partitioning was evidenced by different water‐uptake depths of co‐occurring species under ambient and extreme drought conditions despite an increased overlap among species due to a shift to shallower soil layers under drought. A co‐occurrence of contrasting strategies related to the change of species water‐uptake depth distribution was likely to be key for species to maintain some extent of belowground niche partitioning and could contribute to stabilizing coexistence under drought. Our results suggest that belowground niche partitioning could mitigate negative effects on diversity imposed by extreme drought under future climate.
... Flooding is considered to be the major driver affecting floodplain vegetation (Blom and Voesenek, 1996). Over the last decades basic surface water properties, such as surface water depths or inundation duration (Keddy, 1984;Ferreira and Stohlgren, 1999;Capon, 2005;Murray-Hudson et al., 2014), groundwater properties, such as depth of the groundwater table, or soil moisture content (Silvertown et al., 1999;Dwire et al., 2006;Jabłońska et al., 2011), and water chemistry indicators such, as electrical conductivity (EC) and pH (Ellery et al., 1993;Llampazo et al., 2022) were identified as relevant for floodplain vegetation development. Gradients in these chemical and physical properties can originate from water from different sources that can be present undiluted or be mixed with other water types. ...
... A terrestrial ecosystem characterized by bare soil is very favorable for uncompetitive plant species that rapidly colonize this ecosystem, either from the seed bank (Silvertown et al., 1999) or by the vegetative extension of clonal species (Bonis et al., 2005). ...
Recently, pastoral ecosystem has been strongly studied by naturalists. However, phytoecological research must focus on species richness and enhance these ecosystems. The main objective of this research is to prove that the Moroccan pastoral ecosystem is very rich in terms of soil biodiversity and plant formations. In such areas, some pastoral plants maintain the physicochemical characteristics of soil. The field experiment was based on BraunBlanquet sampling method with 90 surveys. The vegetation surveys carried out during the spring of the 2014–2018 period showed that there were 30 families, 23 orders, and 99 plant species (47 perennial species and 52 annual or biennial species). Of the 99 species inventoried, 14 species are very rare (RR) (14% of the total flora), six are rare (R), five are suspected rare (R?), three species are extinct or of doubtful presence (??), two are vulnerable (or seem to be), in decline, and could become rare in the short term (V), and one is a suspected very rare taxon (RR?). Investigation of life forms based on Raunkiaer method showed that there were various plants in different life forms. Among them, terophytes (47%) and 2% phanerophytes had the highest and the lowest plant species, respectively. This work led us to discover six species (Atractylis cancellata, Carduus pycnocephalus, Scorzonera angustifolia, Telephium sphaerospermum, Teucrium luteum, and Androsace maxima) and five types of rangeland in eastern Morocco. Chorology results showed a high proportion of Mediterranean biogeographic species in the study area, with a percentage of 35%. North African species followed the Mediterranean, with 14%. Euro-Mediterranean species constituted the major flora in the arid regions and played a significant role in the Mediterranean rangelands with 8%. The percentage of North African and Eurasian species was 6%, followed by North African and Asian species forming 4% of the total species. Eurasian, Paleo temperate, and Mediterranean Asian species had the same percentage (3%). The remains represented a low percentage, but contributed to the diversity and the richness of phytogeographic potential in the rangelands of eastern Morocco.
... Since the effect of the abiotic engine on the ecosystem is stream-order dependent, we propose that the target scale for the biodiversity and ecosystem function model is defined by stream order. Stream order defines the hydrological niches (sensu Silvertown et al., 1999) available at a given watershed, which in turn determine plant community structure in terms of species composition, functional diversity, and vegetation pattern, that is, the biotic patch mosaic of the dry riverbed. Ephemeral streams sustain a range of functional plant patches, such as annual and perennial herbaceous plants, shrubs, and trees (Breslau et al., 2019;Fossati et al., 1999;Tooth & Nanson, 2000). ...
Abstract The forecasted increased frequency and intensity of extreme climatic events may strongly affect ecosystem structure and function in the future. It is unclear how ecosystems will function in the long run over a large spatial scale under a new extreme water cycle. This open question calls for a conceptual framework as a fundamental basis for theoretical and experimental exploration of ecosystem function on a large scale driven by an extreme climate envelope. To assess the problem on a large scale, we investigated hyper‐arid ecosystems (HAEs) as natural tangible models that already function under an extreme climatic envelope. Our new assertion is that if extreme climate change drives arid lands to function under alternate extreme conditions, then arid land ecosystems will function like an HAE as an alternative state, rather than progress to desertification. To support our assertion, we developed a conceptual framework of HAEs that includes a geo‐hydrological “abiotic engine” that drives HAE function by soil moisture diversity and plant functional groups. Based on this conceptual framework, we suggest incorporating two new hypotheses in climate change studies to advance our understanding of responses of large‐scale, water‐limited ecosystems: (1) Hydro‐climatic extremes in water‐limited ecosystems will reduce the degree of resource conservation by slope ecosystems due to reduction in plant cover and soil. The decreased ecosystem function on the slope will be compensated for by increasing the effect of the abiotic engine on the ephemeral stream, thus enhancing meta‐ecosystem functioning in the ephemeral stream. (2) In water‐limited ecosystems, climate change toward hydro‐climatic extremes will rescale the dominant hydro‐ecological processes of pulse–reserve, source–sink, and connectivity along the semiarid, arid, and HA gradients in two ways: (i) shrinking of both spatial and temporal dimensions; and (ii) shrinking in the temporal dimension and expanding in the spatial dimensions. The first rescaling trajectory is related to biodiversity–ecosystem function and the second to the abiotic engine processes.
... In many plant communities environmental variability is the main factor determining species composition (Silvertown et al. 1999). Recently it has become recognised that differences in colonising ability may also play an important role. ...
Plant species of ancient forests tend to be poor dispersers, although field studies suggest that dispersal may be strongly accelerated in streams. To further test this idea we addressed the following two questions: 1) which traits facilitate transport and deposition of seeds by streams? 2) do ancient forest species differ from other forest species with respect to these traits?
In the BovenSlinge, a forested lowland stream in the Netherlands we measured water transport and deposition and analysed which traits best explained this. We subsequently compared ancient forest species with other forest species with respect to these key traits.
Our field measurements indicated that stream dispersal is strongly determined by both source related traits, i.e. upstream population size, seed production and seed release period and the path related variables buoyancy and seed weight. These traits seemed to affect transport and deposition similarly, but seed mass had a much stronger, negative impact on deposition.
Ancient forest species do not differ with respect to seed release period, buoyancy and seed mass, but at a given plant height, ancient forest species produce less seeds than other forest species. This may reflect an adaptation to their relatively stable habitat which comes at the expense of (stream) dispersal capacity. In conclusion, ancient forest plants are just as well equipped for stream dispersal as other forest species, but success will critically depend on upstream population size, given their low per plant seed production.
... However, the exact mechanisms that underlie such complementarity have proven very difficult to identify. An early idea was that abiotic resources such as soil nutrients are partitioned, but to date there is little direct empirical evidence for this (Silvertown et al. 1999;McKane et al. 2002; A c c e p t e d M a n u s c r i p t von Felten et al. 2012), despite decades of research, except for simple and relatively obvious cases (e.g. symbiotic nitrogen fixation in legumes, see (Spehn et al. 2002)). ...
Crop variety mixtures can provide many benefits, including pathogen suppression and increased yield and yield stability. However, these benefits do not necessarily occur in all mixtures, and the benefits of diversity may be compromised by disadvantages due to increased crop heterogeneity. In-field development of mixtures by assembling many combinations of crop genotypes without prior expectation about which genotypes need to be combined to produce well-performing mixtures results in prohibitively large designs. Therefore, effective tools are required to narrow down the number of promising variety mixtures, and to then identify in experiments which of these deliver the highest benefits. Here, we first review current knowledge about the mechanisms underlying effects in ecological diversity experiments and in current agricultural applications. We then discuss some of the principal difficulties arising in the application of this knowledge to develop good variety mixtures. We also discuss non-conventional approaches to solve some of these issues. In particular, we highlight the potential and limitations of trait-based methods to determine good variety mixing partners, and argue that non-traditional traits and trait-derived metrics may be needed for the trait-based approach to deliver its full potential. Specifically, we argue that good mixing partners can be identified using modern genetic and genomic approaches. Alternatively, good mixtures may be obtained by combining varieties that respond differently to environmental variation; such varieties could easily be identified in standard variety testing trials. Preliminary analyses show that niche differences underlying the different environmental responses can indicate functional complementarity and promote mixture yield and yield stability.
... Niche width mainly reflects the degree to which species utilize available resources. The wider the niche, the higher the utilization degree of resources [42][43][44]. In this study, we found that T. sutchuenensis and B. juliae have the largest niche width in the arbor layer and shrub layer, which indicates that these plant species experience a greater amount of adaption to their environment and demonstrate superior resource utilization compared to other species in the community. ...
The protection of endangered species is a hot topic for scholars worldwide, and interspecific association and community stability analysis are important methods with which to explore the structure and function of the endangered species community. Thuja sutchuenensis Franch. is an endangered species; however, studies on the T. sutchuenensis community remain insufficient. Here, based on the data of the plot survey of the T. sutchuenensis community in the Ta-pa Mountains and Xuebao Mountains, we analyzed the interspecific associations, niche width, and niche overlap of major species in the arborous and shrub layers, as well as community stability. The results showed that the overall interspecies association between the species of the arbor layer was non-significantly negatively associated, while the shrub layer was non-significantly positively associated. The Chi-square test results showed that the species pairs without interspecific association in the arbor layer and the shrub layer were much higher than those with significant interspecific association; in other words, the interspecific association of species in the T. sutchuenensis community was loose. The results of interspecific association coefficient analysis showed that the number of negatively associated species pairs was significantly higher than that of positive association species pairs, but Pearson’s correlation coefficient and Morisita’s niche overlap index analysis showed that the degree of competition between species in the community was small. In the arbor layer, the niche width of T. sutchuenensis was the widest, while in the shrub layer, the niche width of T. sutchuenensis was relatively high, indicating that T. sutchuenensis had a strong ability to adapt to the environment and use available resources. In addition, the intersection point of community stability (32.11, 67.89) in the vegetative community of T. sutchuenensis suggested that the community displayed a better stability. The survival strategy of T. sutchuenensis is based on its strong adaptability to the harsh environment to escape the competition among species, and this knowledge can provide a reference for the protection and restoration of endangered species.
... Local hydrology is an important ecological force driving community assembly (Silvertown et al., 1999(Silvertown et al., , 2015 and is related with palm floristic variation (Costa et al., 2009;Schietti et al., 2014). Although local hydrological gradients may drive species selection, many species are generalists , or at least have wide niche breadths, raising the question of how they adjust to the varying soil moisture conditions. ...
With more than 2,600 species and 181 genera, palms (Arecaceae) are one of the
most diverse and widely distributed plant families in tropical environments (Baker and Dransfield, 2016). Although they make up a modest portion of the above-ground biomass in most neotropical forests (DeWalt and Chave, 2004), their contribution increases in places where palms are dominant (Muscarella et al., 2020). In the Amazon forests, palms are hyperdominant elements(ter Steege et al., 2013). Their sheer abundance secures them a key role in forest function and forest structure (Boukili and Chazdon, 2017). Palms provide food for a wide variety of animal species (Onstein et al., 2017), including key resources for frugivores, which in turn disperse canopy trees that store most of the carbon in mature forests (Bello et al., 2015). Many human groups value palms and use them as raw material for building, food, drink, clothing, fuel, and medicine (Sylvester et al., 2012).
Palms tissues stretch the limits of plant cells to reach tree-like heights while
preserving mechanical stability and long-term function using only apical meristems
(Tomlinson, 2006). Little is known about the functional mechanisms governing
palms’ adaptation to environmental gradients, despite their ecological significance
and distinctive morphological and physiological structure. Here, we summarize the
functional role of palms from a variety of perspectives, which concentrate on the
analysis of functional traits and their influence on adaptation to environmental gradients. Contributions are grouped into the analysis of functional traits and conservation issues.
... When the environment varies from place to place, differences in how species respond to local conditions can facilitate their coexistence at the landscape scale, even when local coexistence is impossible (Chesson 2000;Amarasekare 2003). This connection between environmental heterogeneity and the mainte-nance of species diversity has deep roots in ecology (Andrewartha and Birch 1954;MacArthur et al. 1966;Whittaker 1967) and has been well studied both theoretically (Horn and MacArthur 1972;Chesson 1985Chesson , 2000Iwasa and Roughgarden 1986) and empirically (Schoener 1974;Silvertown et al. 1999;Codeco and Grover 2001;Oliver et al. 2010). ...
Classic ecological theory explains species coexistence in variable environments. While spatial variation is often treated as an intrinsic feature of a landscape, it may be shaped and even generated by the resident community. All species modify their local environment to some extent, driving changes that can feed back to affect the composition and coexistence of the community, potentially over timescales very different from population dynamics. We introduce a simple nested modeling framework for community dynamics in heterogeneous environments, including the possible evolution of heterogeneity over time due to community-environment feedbacks. We use this model to derive analytical conditions for species coexistence in environments where heterogeneity is either fixed or shaped by feedbacks. Among other results, our approach reveals how dispersal and environmental specialization interact to shape realized patterns of habitat association and demonstrates that environmental feedbacks can tune landscape conditions to allow the stable coexistence of any number of species. Our flexible modeling framework helps explain feedback dynamics that arise in a wide range of ecosystems and offers a generic platform for exploring the interplay between species and landscape diversity.
... The ecological range of Alopecurus pratensis and Sanguisorba officinalis is getting even wider in the floodplains of non-regulated rivers in Eastern Europe and Siberia (Kucherov et al., 2020). A detailed study of the hydrological requirements of floodplain meadow species using floristic data and hydrological models (Silvertown et al., 1999;Gowing et al., 2002b;Garcia-Baquero Moneo et al., 2022) demonstrated that the dominant factor in determining community distribution and composition in Britain was soil moisture; with communities clearly segregated by their tolerance to both soil aeration (waterlogging) and soil-drying stress using the sum exceedence values approach (SEV; Sieben, 1965). Data for this study were restricted to 18 sites with relevés systematically arranged across the hydrological gradient at the site. ...
Nature conservation requires classification of vegetation types for site assessment and assignment. Species-rich floodplain meadows are a declining habitat in Britain and Europe yet their classification in Britain has been based on just a few samples and fails to describe community response to environmental change adequately. European classification, in opposite, has been based on samples from the wide geographical range with no environmental data/analysis supporting the choices. We propose a revised classification of the lowland meadow Alopecurus pratensis-Sanguisorba officinalis community of the British National Vegetation Classification (NVC) linked to variation in local water-table depth. Data have been collated from 58 British floodplain meadows. Based on botanical and hydrological data, four subcommunities within the Alopecurus-Sanguisorba community have been defined. Assessment of conservation sites at the subcommunity level allows temporal and spatial evaluation of the trends and suggests hydrological management towards desirable vegetation. This approach, developed on data from the British meadows, has much wider geographical applications if compared with European plant communities. Seventy-two British and European plant associations were compared via Canonical Correspondence Analysis (CCA). Species ordinations were used to study the coherence of floodplain syntaxonomic alliances across Europe from Ireland to Bulgaria. CCA confirmed the spread of the British subcommunities of the Alopecurus-Sanguisorba community along a strong hydrological gradient and highlighted their lower fertility compared to their Dutch counterparts. The hydrological gradient separating the British subcommunities should help inform site management for the conservation of the species-rich communities, especially where hydrological control is possible.
... Topographical effects cannot explain the effects of fungal hyphae on the maintenance of diversity In addition to increasing the dispersal and expansion range of bacterial individuals, the complex topography of the hyphal network could also have positive effects on the maintenance of diversity via increased spatial heterogeneity. 51,52 Spaces between the hyphae could spatially segregate distinct bacterial populations and allow their simultaneous occurrence. We tested for this effect by quantifying the degree of spatial intermixing between pairs of P. aeruginosa PAO1 strains that are unable to produce a functional flagellum (strains PAO1-DfliC-rfp and PAO1-DfliC-gfp). ...
... These spatiotemporal controls of groundwater on transpiration suggest that groundwater can explain patterns in plant diversity where precipitation cannot (Fan & Miguez-Macho, 2011, 2013Fan, 2015). Species segregate along fine-scale soil moisture gradients (Silvertown et al., 1999(Silvertown et al., , 2015 and valley-to-ridge hillslope position (e.g., Schietti et al., 2014), suggesting the species have strong affiliations for particular positions along gradients of groundwater depth (and its temporal variability). Similarly, plant traits vary intraspecifically along gradients in soil moisture (Alder et al., 1996) and groundwater depth (Zolfaghar et al., 2015). ...
Hydrogeologists are trained to think about belowground processes, and their importance is apparent to them. Other scientific disciplines have traditionally emphasized processes that occur on or above Earth’s surface, and thus groundwater’s roles sometimes go unnoticed in studies of weather, climate, and plant diversity and traits, among others. Over her career, Ying Fan has persistently highlighted the critical importance of groundwater processes on global climate, surface hydrology, and vegetation as well as the need to improve the representation of these processes in Earth system models. Here, we review Fan’s scientific contributions and frame them within some of the simple yet profound questions that she asks: How deep is groundwater? Where, when, and how does groundwater affect weather and climate? Where and when is groundwater a dominant driver of vegetation’s spatial patterns across the landscape? How deep do roots grow? We examine these questions through the valuable insights gained from the work by Fan, her colleagues and mentees, and other works that preceded them, highlighting impacts of Fan’s work on the scientific community.
... Topographical effects cannot explain the effects of fungal hyphae on the maintenance of diversity In addition to increasing the dispersal and expansion range of bacterial individuals, the complex topography of the hyphal network could also have positive effects on the maintenance of diversity via increased spatial heterogeneity. 51,52 Spaces between the hyphae could spatially segregate distinct bacterial populations and allow their simultaneous occurrence. We tested for this effect by quantifying the degree of spatial intermixing between pairs of P. aeruginosa PAO1 strains that are unable to produce a functional flagellum (strains PAO1-DfliC-rfp and PAO1-DfliC-gfp). ...
The amount of bacterial diversity present on many surfaces is enormous; however, how these levels of diversity persist in the face of the purifying processes that occur as bacterial communities expand across space (referred to here as range expansion) remains enigmatic. We shed light on this apparent paradox by providing mechanistic evidence for a strong role of fungal hyphae-mediated dispersal on regulating bacterial diversity during range expansion. Using pairs of fluorescently labeled bacterial strains and a hyphae-forming fungal strain that expand together across a nutrient-amended surface, we show that a hyphal network increases the spatial intermixing and extent of range expansion of the bacterial strains. This is true regardless of the type of interaction (competition or resource cross-feeding) imposed between the bacterial strains. We further show that the underlying cause is that flagellar motility drives bacterial dispersal along the hyphal network, which counteracts the purifying effects of ecological drift at the expansion frontier. We finally demonstrate that hyphae-mediated spatial intermixing increases the conjugation-mediated spread of plasmid-encoded antibiotic resistance. In conclusion, fungal hyphae are important regulators of bacterial diversity and promote plasmid-mediated functional novelty during range expansion in an interaction-independent manner.
... Besides, Silvertown et al. (1999) revealed that fine-scale variation in soil moisture allows for niche differentiation and co-existence in meadow plant communities. This could hold for weed communities, but studies considering fine-scale environmental heterogeneity are lacking. ...
Bocage landscapes are characterized by a network of hedgerows that delimits arable fields. Such landscapes provide many ecosystem services, including biodiversity conservation, but their effects on weed communities remain largely unknown. Bocage landscapes could affect weed communities through two main processes: plant spillover from hedgerows and increased environmental heterogeneity in arable fields. These bocage effects are also likely to vary between farming systems (conventional vs. organic) due to differences in management practices.
We sampled weed communities more than 20 m from field margins in 74 arable fields (37 per farming system). Fields were located along two independent landscape gradients of total length of hedgerows (with or without a shrub layer) and organic farming cover, in Brittany (France). We analysed the effect of ‘bocage’ (i.e. the density and complexity of hedgerow networks) and farming systems at field and landscape scales on species and functional diversity of weed communities. Further, we used fidelity to non‐crop habitats and Ellenberg indicator values to assess the ‘plant spillover’ and ‘environmental heterogeneity’ hypotheses, respectively.
Weed communities were more diverse and more abundant in organic farming systems. In addition, weed communities were more diverse, but not more abundant, in denser and more complex bocage landscapes. ‘Bocage’ increased species diversity of weeds, but also community‐weighted variance of specific leaf area, plant height and seed mass. Positive effects of ‘bocage’ on weed diversity were driven by increased environmental heterogeneity rather than spillover of transient species from hedgerows. ‘Bocage’ effects were independent of farming systems at field and landscape scales.
Synthesis and applications. Maintaining diverse weed communities is key to agroecological weed management and biodiversity conservation in agricultural landscapes. Farmers are often concerned that hedgerows harbour competitive plants spreading into field edges, thereby increasing weed pressure. However, our study shows that dense and complex bocage landscapes promote weed diversity in field cores, most likely by increasing environmental heterogeneity. Thus, bocage landscapes could actually enhance ecosystem services provided by weed communities and reduce weed‐crop competition.
... Under climate change, drought and waterlogging stresses will become more frequent and intense in many parts of the world (IPCC et al., 2021). Plants evolved different strategies to cope with such stress (Silvertown et al., 1999(Silvertown et al., , 2015. Drought and waterlogging stress lead to diverse morphological (plant growth), physiological (reduced net photosynthetic activity, pigment content, membrane integrity), biochemical (changes in metabolism), and molecular (expression of stress-related genes) changes (Farooq et al., 2012;Fahad et al., 2017). ...
Transgenerational stress memory transferred from parents to offspring may enable plants to respond to changing environments rapidly. Yet transgenerational adaptive effects and underlying mechanisms in response to waterlogging and drought are still unclear. Furthermore, transgenerational cross-stress tolerance, pre-adapting offspring to any stress when maternal plants experienced stress, is currently understudied. We conducted a full-factorial pot experiment over two generations, using four perennial plant species and subjecting maternal and offspring plants to waterlogging and drought. We hypothesized that offspring experiencing stress performed better when mothers had experienced stress before, irrespective of the type of stress. We found increased biomass and reproductive output in offspring experiencing the same stress conditions as their mothers (transgenerational adaptive effects). However, a maternal stress experience per se did not pre-condition offspring to other types of stress. Transgenerational adaptive effects were linked to changes in the antioxidative system of one species, reducing oxidative damage through upregulation of protective enzymes in offspring experiencing the same conditions as their mothers. Our research provides evidence for transgenerational waterlogging and drought memory and links this to underlying photosynthetic and redox-related mechanisms. Transgenerational adaptive effects acting on the antioxidative system might therefore contribute to the rapid responses of plants to environmental change.
... These results reveal the response patterns and change trends of wetland plants in Poyang Lake in response to hydrological processes from different perspectives and scales. In contrast, relatively few studies have analyzed and quantified wetland vegetation's water demand from the perspective of ecological niche [44][45][46]. Moreover, traditional studies of vegetative hydrological niches focus more on the mechanistic and microscopic levels [47]. ...
Hydrological processes are known as major driving forces in structuring wetland plant communities, but the specific relationships are not always well understood. The recent dry conditions of Poyang Lake (i.e., the largest freshwater lake in China) are having a profound impact on its wetland vegetation, leading to the degradation of the entire wetland ecosystem. We developed an integrated framework to quantitatively investigate the relationship between the spatial distribution of major wetland herbaceous communities and the hydrological regimes of Poyang Lake. First, the wetland herbaceous community classification was built using a support-vector machine and simultaneous parameter optimization, achieving an overall accuracy of over 98%. Secondly, based on the inundation conditions since 2000, four hydrological drivers of the spatial distribution of these communities were evaluated by canonical correspondence analysis. Finally, the hydrological niches of the communities were quantified by Gaussian regression and quantile methods. The results show that there were significant interspecific differences in terms of the hydrological niche. For example, Carex cinerascens Ass was the most adaptable to inundation, while Triarrhena lutarioriparia + Phragmites australis Ass was the least. Our integrated analytical framework can contribute to hydrological management to better maintain the wetland plant community structure in the Poyang Lake area.
... This systematic variation in drainage is the foundation of the topo-sequence or soil catena notion (see Section 1.4). Along the catena, systematic changes in species distribution have been documented, encapsulated in the hydrologic niche concept (Silvertown et al. 1999(Silvertown et al. , 2014. Terborgh et al. (1992) notes that the slight undulations in topography, imperceptible on the ground, can dramatically influence vegetation structures, owing to selective vegetation response to water stress (excessively drained sand hills) and waterlogging (shallow water table in valleys), forming elevation zones from igapó to terra firme forests along a drainage gradient. ...
This Report provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development.
... In Central Amazonia, the vertical distance to the nearest drainage, a proxy for the water-table depth, is a robust hydrological predictor of plant species composition, explaining the variation of plant assemblages across the landscape (Schietti et al. 2014). In this way, the hydrological gradient may provide a major habitat axis of plant species differing in water use requirements (Silvertown et al. 1999;Balvanera et al. 2011). If true, we expect this gradient to be strongly correlated with the variation in liana taxonomic and functional composition, followed by secondary ecological axes such as edaphic and forest disturbance gradients. ...
Soil hydrology, nutrient availability, and forest disturbance determine the variation of tropical tree species composition locally. However, most habitat filtering is explained by tree species' hydraulic traits along the hydrological gradient. We asked whether these patterns apply to lianas. At the community level, we investigated whether hydrological gradient, soil fertility, and forest disturbance explain liana species composition and whether liana species-environment relationships are mediated by leaf and stem wood functional traits. We sampled liana species composition in 18 1-ha plots across a 64 km² landscape in Central Amazonia and measured eleven leaf and stem wood traits across 115 liana species in 2000 individuals. We correlated liana species composition, summarized using PCoA with the functional composition summarized using principal coordinate analysis (PCA), employing species mean values of traits at the plot level. We tested the relationship between ordination axes and environmental gradients. Liana species composition was highly correlated with functional composition. Taxonomic (PCoA) and functional (PCA) compositions were strongly associated with the hydrological gradient, with a slight influence from forest disturbance on functional composition. Species in valley areas had larger stomata size and higher proportions of self-supporting xylem than in plateaus. Liana species on plateaus invest more in fast-growing leaves (higher SLA), although they show a higher wood density. Our study reveals that lianas use different functional solutions in dealing with each end of the hydrological gradient and that the relationships among habitat preferences and traits explain lianas species distributions less directly than previously found in trees.
... An important goal in plant ecology is to predict the occurrence and abundance of species inhabiting natural communities and examine the mechanisms behind their distribution [1]. Gradients of vital growth resources such as light, water and nutrients generate distinct distribution patterns of terrestrial species [2,3]. Topographically related soil wetness is the most important determinant of terrestrial habitat types on large scales such as across the entire 43,000 km 2 in Denmark [4]. ...
Plant species often separate strongly along steep environmental gradients. Our objective was to study how coupling between plant physiology and environmental conditions shapes vegetation characteristics along a distinct hydrological gradient. We therefore investigated species photosynthesis in air and under water within a limited area from dry-as-dust to complete submergence in a nutrient-poor limestone habitat on Öland's Alvar, Sweden. We found structural and physiological adaptations of species to endure water limitation at the dry end (e.g., moss cushions and CAM-metabolism) and diffusive carbon limitation (e.g., bicarbonate use) at the submerged end of the gradient. As anticipated, mean photosynthesis in air increased 18-fold from the species-poor assembly of cushion-mosses and Sedum CAM-species on mm-thin limestone pavements to the species-rich assembly of C-3 terrestrial plants in deeper and wetter soils. A GLM-model indicated that 90% of the variation in species richness could be explained by a positive effect of soil depth, a negative effect of the duration of water cover and their interaction. In water, mean photosynthesis was highest among aquatic species, low among Sedum species and cushion mosses, and negligible among C-3 terrestrial plants. While aquatic species dried out in air, drought-resistant small species were probably competitively excluded from the more suitable terrestrial habitats on deeper soils with moderate flooding by taller species of high photosynthetic capability. In conclusion, the clear distribution of species along the steep hydrological gradient reflects distinct structural and physiological adaptations, environmental filtering and interspecific competition.
... Under climate change, drought and waterlogging stresses will become more frequent and intense in many parts of the world (IPCC et al., 2021). Plants evolved different strategies to cope with such stress (Silvertown et al., 1999(Silvertown et al., , 2015. Drought and waterlogging stress lead to diverse morphological (plant growth), physiological (reduced net photosynthetic activity, pigment content, membrane integrity), biochemical (changes in metabolism), and molecular (expression of stress-related genes) changes (Farooq et al., 2012;Fahad et al., 2017). ...
... Typically increased water levels resulted in an increase in wetland grasses and sedges. Micro-topographical scale variations in elevation and drainage, and therefore the likelihood of plants experiencing either drought or aeration stress, were high and resulted in large floral variation (high species richness) (Silvertown et al. 1999). ...
... Despite many morphological similarities, SLA, LDMC and L th varied over 7-fold among species (Table 2). Variation in leaf functional traits related to resource use and productivity is connected to niche differences that may serve to reduce interspecific competition via resource partitioning (Goud et al., 2021;Kraft et al., 2015;Silvertown et al., 1999). For instance, the thicker, dense leaves with smaller SLA observed in M. gale may reflect a resource-conservative ecological strategy that allows individuals to succeed in more resource-poor microhabitats or time periods (Pierce et al., 2016). ...
Leaf anatomical and physiological traits influence rates of individual plant and ecosystem function. Although leaf trait variation among different species can be largely attributed to broad climatic gradients, variation at finer spatial scales and within species is less known for many habitats and taxa. Pine barrens are particularly understudied despite regional and ecological significance in northeastern North America. We assessed variation in specific leaf area (SLA), leaf dry matter content (LDMC) and leaf thickness (Lth) for three dominant understory shrub species in the New Jersey Pine Barrens. We hypothesized that traits would vary among and within species along an environmental gradient from upland forest to lowland bog. We further hypothesized that SLA would be larger and LDMC and Lth would be smaller in the upland forest than in the wetter, more nutrient-poor bog, reflective of stress tolerant plant strategies. Unexpectedly, all three species had smaller SLA and larger Lth in the forest than in the bog. LDMC was larger in the forest for Black Huckleberry (Gaylussacia baccata) and Sweetgale (Myrica gale) but smaller in the forest for Lowbush Blueberry (Vaccinium angustifolium). A trade-off between SLA and Lth appears constrained and potentially adaptive in multiple ecological contexts. However, trait-trait correlations involving LDMC were inconsistent across scales. These shrub species may be responding in similar ways to dominant environmental variables in the bog, while multiple environmental variables in the forest may promote species-specific responses and divergent trait correlations. Differences in light and water availability may be influencing leaf trait variation more than soil nutrient availability, while soil pH may be an additional driver of variation in leaf functional traits for these understory temperate shrubs.
... F I G U R E 3 Boxplots of native perennial forb cover and richness stratified by vegetation group and sampling period mesic grassland (Silvertown et al., 1999). Similarly, vegetation composition is strongly influenced by length of inundation time during the growing season in semi-arid and arid grass and shrublands (Clausnitzer & Huddleston, 2002;Dippenaar, 2014;Gibson et al., 2005;Keeley & Zedler, 1998). ...
Grasslands are among the most threatened and least protected terrestrial biome. Grassland forbs: (1) account for most of the floral diversity; (2) are not well studied because they have been overshadowed by grass-centered research; and (3) have been a major source for biodiversity loss. The Pacific Northwest Bunchgrass Prairie (PNB) of North America is one of the most endangered grasslands on earth. Knowledge of vegetation community dynamics in the PNB is based primarily on bunchgrasses. There is a paucity of information related to the PNB's diverse native perennial forbs (hereafter “forbs”). Consequently, PNB forb community patterns and dynamics are largely unknown. We describe forb community structure and its relationship to environmental factors and phenology. We sampled 29 plots in the Starkey Experimental Forest and Range, northeastern Oregon, at three different times during 2016 (April; May; July). Nonmetric multidimensional scaling (NMS) indicated that the dominant gradient in forb composition was related (R2 = 0.66) to slope and soil P and K, contrasting flat, poorly drained soils (scabflats) at one end with steep, well-drained soils at the other end. The secondary gradient (R2 = 0.16) contrasted deeper, finer textured soils at one end with shallow, rocky soils at the other. Forb richness decreased by ~40% from April to July. NMS and Indicator Species Analysis (ISA) showed that most forbs had affinities toward spring. Ubiquitous forbs (e.g., Triteleia grandiflora, Camassia quamash) were sparse to absent by July. Contradictory to general descriptions of the PNB, forb cover and richness in drought-prone sites were comparable to mesic sites when spring data were considered. Our findings suggest that PNB grasslands contain diverse forb communities that are structured primarily by water drainage and soil depth. Conventional sampling concomitant with peak grass biomass is insufficient to characterize PNB forb communities, particularly for scabflats and the most drought-prone soils.
... It has been proposed that complementary resource use results from spatial, temporal, or other forms of resource partitioning among species, and that this then translates into a more efficient or more complete resource use in more diverse plant communities, and therefore into a higher productivity (Loreau et al., 2001;Turnbull et al., 2016). However, surprisingly little evidence exists to date about which resources are partitioned and through which actual biological mechanisms this occurs (Barry et al., 2019;Silvertown et al., 1999;von Felten et al., 2012). An important (but also long-known) exception are ecosystems that contain species associated with symbiotic nitrogen fixers such as rhizobia. ...
Interspecific niche complementarity is a key mechanism posited to explain positive species richness–productivity relationships in plant communities. However, the exact nature of the niche dimensions that plant species partition remains poorly known.
Species may partition abiotic resources that limit their growth, but species may also be specialized with respect to their set of biotic interactions with other trophic levels, in particular with enemies including pathogens and consumers. The lower host densities present in more species‐diverse plant communities may therefore result in smaller populations of specialized enemies, and in a smaller associated negative feedback these enemies exert on plant productivity.
To test whether such host density‐dependent effects of enemies drive diversity–productivity relationships in young forest stands, we experimentally manipulated leaf fungal pathogens and insect herbivores in a large subtropical forest biodiversity–ecosystem functioning experiment in China (BEF‐China).
We found that fungicide spraying of tree canopies removed the positive tree‐species richness–productivity relationship present in untreated control plots. The tree species that contributed the most to this effect were the ones with the highest fungicide‐induced growth increase in monoculture. Insecticide application did not cause comparable effects.
Synthesis. Our findings suggest that tree species diversity may not only promote productivity by interspecific resource‐niche partitioning but also by trophic niche partitioning. Most likely, partitioning occurred with respect to enemies such as pathogenic fungi. Alternatively, similar effects on tree growth would have occurred if fungicide had eliminated positive effects of a higher diversity of beneficial fungi (e.g. mycorrhizal symbionts) that may have occurred in mixed tree species communities.
... All plants require a certain range of water availability to germinate, survive, grow and reproduce. Below or above this range of water availability (plant fundamental niche for water), plants underperform or even die due either to dehydration or inundationinduced physiochemical stresses such as anoxia (Silvertown et al., 1999;Silvestri et al., 2005;Osakabe et al., 2014). Although mechanisms of vegetation responses to hydrological changes can be multifaceted, one common distinction is between linear continuum responses and discontinuous non-linear threshold responses (Suding and Hobbs, 2009). ...
Hydrological processes are a fundamental driver of vegetation across Earth’s ecosystems and have been increasingly altered and managed by humanity. Whether vegetation exhibits threshold responses to gradual changes in hydrology is an important but unresolved question. Here, we examined this question by providing the first remote sensing-based investigation of decadal-scale vegetation changes along hydrological gradients over early-period wetland development. We focused on wetlands on three estuarine fluvial islands, where sedimentation was driving wetlands to transition from an initially mudflat state to a vegetated marsh state (dominated by Suaeda salsa). Our results showed that Suaeda marshes decreased in a nonlinear, threshold manner with increasing flooding frequency, a pattern consistently observed in periods when plants were still acquiring their hydrological niches. Further, although the breadth of Suaeda’s hydrological niche (i.e., the range of flooding frequencies with Suaeda presence) expanded linearly or nonlinearly on all three islands, changes in niche position (i.e., lower and upper limits) differed. Both lower and upper limits of their hydrological niche expanded on sheltered islands in the inner part of the estuary, while their upper limits expanded and lower limits retreated on more exposed, outer islands. Our findings provide unique evidence that nonlinear, threshold hydrological controls of vegetation may be pervasive even in early stages of wetland development, although the underlying mechanisms may be specific and depend on other factors (e.g., wave exposure). Incorporating these threshold behaviors are key to predicting and managing transitions between vegetated and unvegetated states of ecosystems in an anthropogenic hydrosphere.
... This systematic variation in drainage is the foundation of the topo-sequence or soil catena notion (see Section 4). Along the catena, systematic changes in species distribution have been documented, encapsulated in the hydrologic niche concept (Silvertown et al. 1999(Silvertown et al. , 2014. Science Panel for the Amazon Terborgh et al. (1992) notes that the slight undulations in topography, imperceptible on the ground, can dramatically influence vegetation structures, owing to selective vegetation response to water stress (excessively drained sand hills) and waterlogging (shallow water table in valleys), forming elevation zones from igapó to terra firme forests along a drainage gradient. ...
This Report provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development.
... This systematic variation in drainage is the foundation of the topo-sequence or soil catena notion (see Section 4). Along the catena, systematic changes in species distribution have been documented, encapsulated in the hydrologic niche concept (Silvertown et al. 1999(Silvertown et al. , 2014. Science Panel for the Amazon Terborgh et al. (1992) notes that the slight undulations in topography, imperceptible on the ground, can dramatically influence vegetation structures, owing to selective vegetation response to water stress (excessively drained sand hills) and waterlogging (shallow water table in valleys), forming elevation zones from igapó to terra firme forests along a drainage gradient. ...
This report on geology and geo diversity of the Amazon belongs to the: Science Panel for the Amazon/Amazon Assessment Report 2021
The Science Panel for the Amazon is an unprecedented initiative convened under the auspices of the United Nations Sustainable Development Solutions Network (SDSN). The SPA is composed of over 200 preeminent scientists and researchers from the eight Amazonian countries, French Guiana, and global partners. These experts came together to debate, analyze, and assemble the accumulated knowledge of the scientific community, Indigenous peoples, and other stakeholders that live and work in the Amazon.
The Panel is inspired by the Leticia Pact for the Amazon. This is a first-of-its-kind Report which provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development.
... K. Kirkman et al., 2001;Mitchell et al., 1999). Although it is well known that soil moisture availability can vary on the microhabitat scale and is strongly linked to soil texture and topography (Abrahamson et al., 1984;Moeslund et al., 2013;Silvertown et al., 1999), there is also a positive correlation between precipitation and soil moisture (Sehler et al., 2019); therefore, in this study, we used precipitation as a proxy for site-level differences in soil moisture. Although precipitation is a strong driver of productivity and richness across grasslands globally and in LLP savannas (Adler & Levine, 2007;Del Grosso et al., 2008;Knapp & Smith, 2001;Mitchell et al., 1999;O. ...
Questions
Restoration of ecosystems is complex, with multiple targets that can work in concert or conflict with each other, such as biodiversity, species dominance and biomass. When properly managed, longleaf pine (LLP) savannas are among the most biologically diverse habitats in the world. However, anthropogenic influences, such as fire suppression, have decimated this ecosystem and its biodiversity, making restoration a priority. Here, we describe the biodiversity and community dynamics seen in the understory layer across xeric LLP savannas in North Carolina and then answer the following questions: What are the predictors of (1) biodiversity, (2) dominance and (3) biomass at multiple spatial scales?
Location
Fifteen observational study sites in North Carolina spanning from the Sandhills to the Coastal Plain.
Methods
At each of the 15 sites, 25 sampling plots were established where above‐ground herbaceous biomass, species presence and abundance, soil characteristics and light availability were measured along with numerous other environmental variables.
Results
Considerable variation exists across study plots within and across sites, with plant species richness ranging from 1 to 17 per m ² . The relative cover of the dominant grass species, Aristida stricta (wiregrass), also varied greatly within and across sites, with a median of ca. 30% relative cover per plot. Wiregrass was a significant predictor of biomass and biodiversity at small scales. With increasing wiregrass abundance, richness decreases, with 25% relative wiregrass cover leading to the highest levels of biodiversity. Likewise, because wiregrass abundance is one of the stronger predictors of above‐ground biomass, we also found a unimodal richness–biomass relationship.
Conclusions
Our results indicate that at lower ends of the productivity and richness gradients, land managers can increase all three restoration targets in the understory at the same time; however, at more diverse and productive sites, restoration practitioners may need to prioritize one target or find a balance between all three.
... • Direct gradients, such as flood frequency, stream power and depth to ground water (Shipley and Keddy 1987;Hughes 1988;Bendix 1999;Hughes et al. 2000;Boucher 2002;Lite et al. 2005;Thayer et al. 2005;Dwire et al. 2006;Baker and Wiley 2009;Reinecke et al. 2015). • Resource gradients, such as water availability, soil moisture and nutrient status (Birkhead et al. 1997;Silvertown 1998;Silvertown et al. 1999;Botha 2001;Silvertown 2004;Araya et al. 2011). Studies along northern hemisphere temperate floodplain rivers, for example, described links between life-history requirements of specialist floodplain species and the timing and magnitude of annual floods (Mahoney and Rood 1998). ...
Riparian zones can be characterised botanically into two main areas, a wet bank and a dry bank. These areas have been linked to the duration of inundation by river flow, the boundary between the two being the 1:2 year floodline. Therefore the wet bank is inundated regularly by small floods and the dry bank by larger, less frequent floods, and each may support one to a few distinct plant communities laterally up the bank. Understanding these plant distributions helps rehabilitation projects and Environmental Flow (EFlows) studies as it can inform re-vegetation strategies in the former and help understanding of the links between plants and the river’s flow regime in the latter. Systematic sampling and data analysis methods were developed for single channel rivers with relatively undisturbed natural vegetation to identify and locate the different plant communities in the riparian zone. Generic rules using distance and height from the water’s edge, rather than the presence or absence of plant species, were calculated to locate the communities. While these statistics were derived from the riparian vegetation along perennial Western Cape rivers, South Africa, the methods could be applied to other perennial single channel river anywhere.
... • Direct gradients, such as flood frequency, stream power and depth to ground water (Shipley and Keddy 1987;Hughes 1988;Bendix 1999;Hughes et al. 2000;Boucher 2002;Lite et al. 2005;Thayer et al. 2005;Dwire et al. 2006;Baker and Wiley 2009;Reinecke et al. 2015). • Resource gradients, such as water availability, soil moisture and nutrient status (Birkhead et al. 1997;Silvertown 1998;Silvertown et al. 1999;Botha 2001;Silvertown 2004;Araya et al. 2011). Studies along northern hemisphere temperate floodplain rivers, for example, described links between life-history requirements of specialist floodplain species and the timing and magnitude of annual floods (Mahoney and Rood 1998). ...
... Obvious spatial-temporal differences in water uptake have been observed among co-occurring trees in the semiarid grassland of Nebraska (Eggemeyer et al., 2009), in the tropical dry forest of Panama (Meinzer et al., 1999), and in the subtropical karst forest of China (Nie et al., 2011). Moreover, the formation of hydrological niches among co-occurring plant species is an important mechanism that affects the structure of plant communities and maintains plant coexistence in ecosystems with limited water resources (Silvertown et al., 1999;Araya et al., 2011;Moreno-Gutiérrez et al., 2012). Significant intraspecific and interspecific competitions for water resources have also been reported among plants with similar water uptake depth and root distribution in a West African humid savanna (Roux et al., 1995), in a subtropical coniferous plantation (Yang et al., 2015), and in different agroforestry systems (Yang et al., 2020(Yang et al., , 2021. ...
Southern China houses the largest subtropical broadleaf forest in the world, with abundant rainfall brought by the Pacific and Indian monsoons. As the intensity and frequency of drought are increasing, understanding the water use patterns of co-occurring trees is a key issue for predicting the response of these subtropical forests. The water uptake depths and water use-related leaf traits of three dominant canopy tree species at different ages (DBH) were investigated in a subtropical forest (2018–2019). We found that the δ²H and δ¹⁸O of various water pools, such as fog, soil, stream, lake, and groundwater, plotted almost entirely on the local meteoric water lines (2018: y = 8.2x +11.5; 2019: y = 8.1x +10.4). This result suggested that water bodies within the forest experienced minor evaporation. An interspecific partitioning of water acquisition was detected among tree species of similar ages in 2018 (a regular year), but they tapped soil water from similar depths after experiencing drought event in 2019. Most large (DBH > 50 cm) and middle-sized (15 cm < DBH < 30 cm) trees switched their major water sources from shallow (2018) to deep (2019) soil layers, whereas the seedlings (DBH < 2 cm) relied on shallow soil water during the study periods. The water use patterns of different trees were related to the leaf-level intrinsic water use efficiency (WUEi) and specific leaf area (SLA). The spatial-temporal differentiation of water use in regular years can facilitate plant co-existence among the canopy trees, but the interspecific competition for similar water sources in drought years may increase the risk of tree dieback in the subtropical forests. These fingdings provide a mechanistic explanation for the high diversity of subtropical forests in China from the perspective of differentiation in plant water use.
The African Restionaceae (Poales), the dominant graminoid layer in the megadiverse Cape Floristic Region of South Africa, are distributed across a wide range of moisture availability, yet currently there is very little known about the underlying hydraulics of this group.
We tested two methods for measuring culm vulnerability to embolism, the optical and pneumatic methods, in three species of Cannomois ranging in habitat from semi‐riparian ( Cannomois virgata ) to dryland ( Cannomois parviflora and C. congesta ). Estimates of culm xylem vulnerability were coupled with measures of turgor loss point (Ψ TLP ) and minimum field water potential (Ψ MD ) to assess hydraulic safety margins.
The optical and pneumatic methods produced similar estimates of P 50 , but differed for P 12 and P 88 . All three species were quite vulnerable to embolism, with P 50 of –1.9 MPa ( C. virgata ), −2.3 MPa ( C. congesta ), and −2.4 MPa ( C. parviflora ). Estimates of P 50 , Ψ TLP and Ψ MD aligned with habitat moisture stress, with highest values found in the semi‐riparian C. virgata . Consistent differences in P 50 , Ψ MD and Ψ TLP between species resulted in consistent hydraulic safety margins across species of 0.96 ± 0.1 MPa between Ψ MD and P 50 , with onset of embolism occurring 0.43 ± 0.04 MPa after Ψ TLP for all three species.
Our study demonstrates that restio occupancy of dry environments involves more than the evolution of highly resistant xylem, suggesting that other aspects of water relations are key to understanding trait–environment relationships in this group.
Climate change has remarkable effects on the hydrological regime in floodplain wetlands. However, the hydrodynamic simulation under climate change conditions suffers from the uncertainty of the downstream water level boundary. In this study, an effective approach was developed by integrating an advanced machine learning algorithm and a process-based watershed hydrological model to predict the lake level under climate change. The developed approach was validated in a vital conservation wetland in the Ramsar Convention, the Poyang Lake floodplain wetland in China and utilized to simulate the hydrological regime in climate change. We found that the Long Short–term Memory (LSTM) performed relatively well in the simulation of water level, with coefficients of determination (R2) of 0.94 and 0.83 in the training and testing periods, respectively. The mean cumulative flooding time in the future period was slightly less than that in the baseline period, with a decreased range of 1.01 ~ 12.05 days/year. The highest and mean water levels rose significantly in the wet season, with a risen range of 1.01 ~ 3.3 and 1.56 ~ 2.44 m, respectively, and the appearance of extreme flood events became more frequent. The maximum, minimum, and mean inflows for Poyang Lake in the dry season exhibited a remarkable reduction trend, especially for the minimum inflow, with a reduced range of 59.37%~79.22%, indicating that more serious extreme drought events would appear in Poyang Lake. The developed approach has good performance for water level simulation and extreme runoff prediction, thus providing a viable way for future water resources management in floodplain wetlands.
Plant-specific NAC proteins constitute a major transcription factor family that is well-known for its roles in plant growth, development, and responses to abiotic and biotic stresses. In recent years, there has been significant progress in understanding the functions of NAC proteins. NAC proteins have a highly conserved DNA-binding domain; however, their functions are diverse. Previous understanding of the structure of NAC transcription factors can be used as the basis for their functional diversity. NAC transcription factors consist of a target-binding domain at the N-terminus and a highly versatile C-terminal domain that interacts with other proteins. A growing body of research on NAC transcription factors helps us comprehend the intricate signalling network and transcriptional reprogramming facilitated by NAC-mediated complexes. However, most studies of NAC proteins have been limited to a single function. Here, we discuss the upstream regulators, regulatory components and targets of NAC in the context of their prospective roles in plant improvement strategies via biotechnology intervention, highlighting the importance of the NAC transcription factor family in plants and the need for further research.
There is increasing evidence that the structure and functioning of ecological communities and ecosystems are strongly influenced by flexible traits of individuals within species. A deep understanding of how trait flexibility alters direct and indirect species interactions is crucial for addressing key issues in basic and applied ecology. This book provides an integrated perspective on the ecological and evolutionary consequences of interactions mediated by flexible species traits across a wide range of systems. It is the first volume synthesizing the rapidly expanding research field of trait-mediated indirect effects and highlights how the conceptual framework of these effects can aid the understanding of evolutionary processes, population dynamics, community structure and stability, and ecosystem function. It not only brings out the importance of this emerging field for basic ecological questions, but also explores the implications of trait-mediated interactions for the conservation of biodiversity and the response of ecosystems to anthropogenic environmental changes.
There is increasing evidence that the structure and functioning of ecological communities and ecosystems are strongly influenced by flexible traits of individuals within species. A deep understanding of how trait flexibility alters direct and indirect species interactions is crucial for addressing key issues in basic and applied ecology. This book provides an integrated perspective on the ecological and evolutionary consequences of interactions mediated by flexible species traits across a wide range of systems. It is the first volume synthesizing the rapidly expanding research field of trait-mediated indirect effects and highlights how the conceptual framework of these effects can aid the understanding of evolutionary processes, population dynamics, community structure and stability, and ecosystem function. It not only brings out the importance of this emerging field for basic ecological questions, but also explores the implications of trait-mediated interactions for the conservation of biodiversity and the response of ecosystems to anthropogenic environmental changes.
There is increasing evidence that the structure and functioning of ecological communities and ecosystems are strongly influenced by flexible traits of individuals within species. A deep understanding of how trait flexibility alters direct and indirect species interactions is crucial for addressing key issues in basic and applied ecology. This book provides an integrated perspective on the ecological and evolutionary consequences of interactions mediated by flexible species traits across a wide range of systems. It is the first volume synthesizing the rapidly expanding research field of trait-mediated indirect effects and highlights how the conceptual framework of these effects can aid the understanding of evolutionary processes, population dynamics, community structure and stability, and ecosystem function. It not only brings out the importance of this emerging field for basic ecological questions, but also explores the implications of trait-mediated interactions for the conservation of biodiversity and the response of ecosystems to anthropogenic environmental changes.
Seafood security is essential in modern society. In 2013, Bush and colleagues stated, ‘Aquaculture, farming aquatic organisms, provides close to 50% of the world’s supply of seafood, with a value of United States $125 billion. It makes up 13% of the world’s animal-source protein (excluding eggs and dairy) and employs an estimated 24 million people’. With the increase in the human population and reducing fishing resources, humans increasingly rely on aquacultural products as the primary protein sources for many countries. Aquacultural productivity has been improving in recent years, and in certain countries, the aquaculture output is more than the fishing output. For example, Chinese aquaculture production is more than fishing output, which provides one-third of animal protein. Thus, intensive aquaculture has become the main supply with global aquatic products (FAO). In recent years, it is estimated that each person consumption of aquaculture products is 130 kg in some countries (Iceland). Here, we illustrate the road blocker in farmed shrimp production and provide our resolution. The global pandemic of white spot syndrome (WSS), caused by the white spot syndrome virus (WSSV), bears a devastating economic loss in farmed shrimp production, thereby jeopardizing seafood security. Currently, there is no effective control for WSS. Conventional single-species intensive farming removes the spatiotemporal interaction between different species. We hypothesize that establishing the spatiotemporal interface of a predator–prey may control WSS outbreak. We search for the pathways for the mechanisms by which predator–prey species interact and compete across spatial scales to characterize WSSV dispersal at regional scales for the local spatiotemporal structure of viral transmission. Thus, we create a generalizable and turnable engineered ecosystem that provides a clear route to prosperity and well-being to harness the world’s aquatic “blue” food systems to help end hunger.
Striving for an integrated semi-natural stream-floodplain system as restoration target would optimally serve biodiversity and the provisioning of ecosystem services. This pursuit is currently limited by multiple pressures and constraints that come with, amongst others, a high human population density and intensive land-use. To be able to weigh the ecological and societal needs in lowland-stream watersheds, we analysed the developments in lowland-stream restoration in relation to the actual and potential state of ecosystems services these systems provide. To reach an ecological-societal balance in stream restoration, we pose five steps: (i) Choose a clear and realistic restoration target, (ii) Map and quantify environmental stressors at local to watershed scale, (iii) Map and quantify biological indicators at local to regional scale, (iv) List potential restoration measures to remove or mitigate stressors, and (v) Build scenarios, composed of combinations of measures fitting the societal context of the watershed. The most promising scenarios make use of watershed processes and involve establishing a transverse landscape zonation, from the streams’ riparian zone to the uplands. Such landscape transition poses a challenge for policy makers and implies a strong societal change. Therefore, a framework is provided with building blocks that help to find a suitable balance in practice.
Large water resource projects may severely alter hydrological regimes and thus the habitat conditions for biota in wetlands. Plenty of habitat models for fish, vegetation, and invertebrates have been developed and widely used; however, there is a lack of effective models to assess the effects of water resource projects on waterbird habitat in wetlands. This study developed a habitat model by integrating two-dimensional hydrodynamic, multicriteria evaluation Cellular Automata–Markov and habitat suitability modules (HMH) to evaluate the effects of hydraulic structures on the habitat of waterbirds in wetlands. The developed HMH model was applied to the Duchang Provincial Nature Reserve (DPNR) of Poyang Lake in China, which is an important conservation wetland in the Ramsar Convention. For demonstration, the HMH model analyzed the habitat suitability for Grus leucogeranus, a rare species in the region, with a scheduled sluice under two different regulating rules (named Rule 1 and Rule 2), and compared it to the habitat suitability without the sluice. Results showed that the sluice operations would increase the water body during dry seasons, and thus increase the area of shallow water, a preferential habitat to Grus leucogeranus. The sluice operation in Rule 1 would either change the location or remarkably reduced the area of suitable habitat in the northern DPNR. The sluice operation in Rule 2 would either slightly increase the area or change the location of suitable habitats in the northern DPNR. The study demonstrated that the developed method for habitat suitability assessment could provide a viable approach for eco-hydrological management of wetlands.
The effects of a progressive increase in soil water deficit on the leaf conductance and gas exchange of lupin (Lupinus cosentinii) and wheat (Triticum aestivum) were investigated in pot experiments in a temperature-regulated glasshouse, using a coarse, sandy soil characteristic of the Western Australian wheatbelt.
Transpiration rates decreased rapidly in both species after water was withheld, mainly as a result of stomatal closure. Photosynthesis declined also, but to a lesser extent than conductance. Leaf extension in lupin was equally as sensitive to a decrease in leaf water potential and soil water potential as stomatal conductance. Stomatal closure served to maintain the water potential of lupin leaves to within 0.1 MPa of that of control (watered) plants as the soil water content decreased from 0.14 to 0.06 m3 m-3 and as the leaf conductance and the relative transpiration rate fell to less than 50% of control values. Maintenance of leaf water potential with decreasing soil water content and stomatal conductance was less evident in wheat. In both lupin and wheat, leaf conductance decreased linearly with soil water content and curvilinearly with bulk soil matric potential, indicating that water uptake was restricted at similar water contents and matric potentials in both species. Diurnal measurements on lupin indicated a substantial reduction in stomatal conductance after water was withheld, even when the leaf water potential at midday was reduced by only 0.1 MPa and no change could be detected in the bulk leaf turgor pressure. Conductance in lupin was reduced even though the soil matric potential decreased in only part of the rooting zone. This, together with the absence of any significant change in the leaf water potential, turgor pressure, or relative water content in lupin during the initial stages of stomatal closure, suggests that a soil or root factor initiates the reduction in leaf conductance - and hence regulates the shoot water status - in response to soil drying.
CAIC is an application for the Apple Macintosh which allows the valid analysis of comparative (multi-species) data sets that include continuous variables. Comparison among species is the most common technique for testing hypotheses of how organisms are adapted to their environments, but standard statistical tests like regression should not be used with species data. Such tests assume independence of data points, but related species often share traits by common descent rather than through independent adaptation. CAIC uses a phylogeny of the species in the data set to partition the variance among species into independent comparisons (technically, linear contrasts), each comparison being made at a d node in the phylogeny. There are two partitioning procedures—one used when all variables are continuous, the other when one variable is discrete. The resulting comparisons can be analysed validly in standard statistical packages to lest hypotheses about correlated evolution among trails, to estimate parameters such as allometric exponents, and to compare rates of evolution. Previous versions of the package have already been used widely; this version is simpler to use and works on a wider range of machines. The package and manual are freely available by anonymous ftp or from the authors.
Fertilization experiments in an 8-yr-old field demonstrated that N was the major limiting nutrient of N, P, K, Ca, and Mg, and suggested that Mg became limiting when N was added. After the fertilization experiments, this field was disturbed via thorough disking and divided into 36 plots for a Latin square design experiment on the effect of N:Mg fertilization ratios on vegetation patterns. By the second year, the major species had separated along the imposed N:Mg gradient, with Agrostis scabra dominant at the low Mg but high N end, followed by Agropyron repens, Berteroa incana, Oenothera biennis, and Aristida basiramea, which was dominant at the high Mg but low N end of the gradient. An unmanipulated resource, light availability at the soil surface, was significantly affected by the treatments. The results demonstrate that spatial heterogeneity in the relative availability of soil nutrient may be one cause of spatial heterogeneity in early successional vegetation.
Data are given on the niches of 8 perennial plant species which occurred commonly in a species-rich limestone grassland. The niche axes were: phenology of above-ground growth and flowering over a 5 month growing season, together with soil depth, pH and levels of available N, P and K, in samples taken at the end of the season. There was little separation of the species on any single niche axis, nor could the species be separated in 6-dimensional niche space. An attempt to separate the species on a resource-ratio gradient of N/P was also unsuccessful. Separation in niche space is unlikely to make a major contribution to coexistence in this community. Investigation of models which permit coexistence in the absence of niche differentiation could prove more fruitful. -from Authors
The unsteady water-table movement caused by intermittent rainfall and varying evaporation in flat lands intersected by a network of ditches is modelled using land-drainage theory. The unsteady water tables are assumed to behave as a continuous succession of steady states with the flux through the water table given by the sum of components due to rainfall and evaporation through the soil surface and due to water released or taken up by the unsaturated soil above the water table. A simple steady-state drainage equation is used for the relationship between water-table height and flux, and the specific yield is assumed to have a constant value. The simulated seasonal water table using estimated hydraulic soil properties and meteorological records for a field site agreed with available dip-well observations. The water table was much lower than the ditch-water level during the summer months. The sensitivity of simulated results to model parameters is demonstrated.
Plant competition for space is studied using analytical and simulation models. Here, the interaction is viewed as a local competition between juveniles of different species for environmentally variable sites vacated by the random deaths of adults. Because plants are sedentary and have finite fecundity, often only a subset of species will compete for an available site. When a dominant species is recruitment limited, inferior competitors will win some sites by forfeit. It is shown that recruitment limitation allows “winning-by-forfeit” which lessens the effect of competitive asymmetries and slows population and community dynamics. Moreover, since recruitment limitation is likely to be most pronounced in highly diverse communities because of the rarity of many species, it is suggested that there is no conflict between the hypothesis that species-rich plant communities are more influenced by chance and history than regulated by competition, and observations of strong interspecific differences among plants.
A stochastic model is developed for competition among organisms living in a patchy and varying environment. The model is designed to be suitable for species with sedentary adults and widely dispersing larvae or propagules, and applies best to marine systems but may also be adequate for some terrestrial systems. Three kinds of environmental variation are incorporated simultaneously in the model. These are pure spatial variation, pure temporal variation, and the space × time interaction. All three kinds of variation can promote coexistence, and when variation is restricted to immigration rates, all three kinds act very similarly. Moreover, for long-lived organisms their action is nearly identical, and their effects, when present together, combine equivalently. For short-lived organisms, however, pure temporal variation is a less effective promoter of coexistence. Variation in death rates acts quite differently from variation in birth rates for it may demote coexistence in some circumstances, while promoting coexistence in other circumstances. Furthermore, pure spatial variation in death rates has quite different effects than other kinds of death-rate variation. In addition to conditions for coexistence, information is given on population fluctuations, convergence to stationary distributions, and asymptotic distributions for long-lived organisms. While the model is presented as an ecological model, a genetical interpretation is also possible. This leads to new suggested mechanisms for the maintenance of polymorphisms in populations.
In the context of a simple mathematical model, we derive several mechanisms whereby plant species can coexist in a community without differing in their trophic niches (their relations with habitats, resources and exploiters). The model is based on the dynamics of species turnover in microsites, and incorporates localized competition, non-uniform seed dispersal and aspects of spatiotemporal environmental heterogeneity. These factors, which are not included in most standard competition models, allow stable coexistence of trophically equivalent species due to:
(a)
Differences in life-history ‘strategy’.
(b)
Input of seeds from neaby habitats (spatial Mass Effect).
(c)
Differences in demographic responses to environmental fluctuations (temporal Mass Effect).
(d)
Turnover in species composition between different habitat patches.
Quantitative descriptive studies are presented, demonstrating the occurrence of vegetation patterns predicted on the basis of the hypothesized mechanisms. We also review previously proposed mechanisms that would allow trophically equivalent species to coexist, and explore the theoretical and methodological implications of recognizing coexistence mechanisms independent of trophic niche differentiation. In particular, we propose that these mechanisms contribute to the dissimilarity of within-community replicate samples and the maintenance of many rare species in plant communities.
From Darwin onward, it has been second nature for evolutionary biologists to think comparatively because comparisons establish the generality of evolutionary phenomena. Do large genomes slow down development? What lifestyles select for large brains? Are extinction rates related to body size? These are all questions for the comparative method, and this book is about how such questions can be answered.
The first chapter elaborates on suitable questions for the comparative approach and shows how it complements other approaches to problem-solving in evolution. The second chapter identifies the biological causes of similarity among closely related species for almost any observed character. The third chapter discusses methods for reconstructing phylogenetic trees and ancestral character states. The fourth chapter sets out to develop statistical tests that will determine whether different characters that exist in discrete states show evidence for correlated evolution. Chapter 5 turns to comparative analyses of continuously varying characters. Chapter 6 looks at allometry to exemplify the themes and methods discussed earlier, while the last chapter looks to future development of the comparative approach in both molecular and organismic biology.
Japanese translation (1997) The Comparative Method in Evolutionary Biology. Hokkaido University Press in cooperation with Oxford University Press.
Vanadium metabolism was studied in a wild type and respiratory-deficient strain of S. cerevisiae. Inhibition of growth by vanadate [V(+5)], vanadate accumulation, and conversion of medium vanadate [V(+5)] to both cell-associated and medium vanadyl [V(+4)] and vanadate [V(+5)] were compared. The growth of both the parental and respiratory-deficient strains was inhibited by vanadate at concentrations greater than or equal to 1 mM. Both parental and respiratory-deficient strains accumulated vanadate and converted medium vanadate to cellular vanadyl as detected using electron spin resonance (ESR). The accumulation of cell-associated vanadyl was correlated with the loss of medium vanadate in both strains using a chemical assay. In contrast, the respiratory-deficient strain showed a greater amount of a cell-associated vanadate compound, as detected with vanadium-51 nuclear magnetic resonance (51V-NMR), than the wild type strain or a representative respiratory-competent vanadate-resistant mutant. These data imply that mitochondrial function may be directly involved in vanadium metabolism.
Het verband tussen outwatering en obrengst bij de jonge zavelgranden in de Noordoostpolder
- W H Sieben
- WH Sieben
Sieben, W. H. Het verband tussen outwatering en obrengst bij de jonge zavelgranden in de Noordoostpolder. Van Zee Land 40, 1±117 (1965).
The Effect of the Hydrology of a Thames Flood Meadow on its Vegetation 68±80
- D J G Gowing
- E G Youngs
Gowing, D. J. G. & Youngs, E. G. The Effect of the Hydrology of a Thames Flood Meadow on its Vegetation 68±80 (British Hydrological Society, Occ. Pap. 8, London, 1997).
The Effect of the Hydrology of a Thames Flood Meadow on its Vegetation
- D J G Gowing
- E G Youngs
- DJG Gowing