Biodiversity–productivity relationship in ponds: Community and metacommunity patterns along time and environmental gradients

Primary production correlates with diversity in various ways. These patterns may result from the interaction of various mechanisms related to the environmental context and the spatial and temporal scale of analysis. However, empirical evidence on diversity‐productivity patterns typically considers single temporal and spatial scales, and does not include the effect of environmental variables. In a metacommunity of macrophytes in ephemeral ponds, we analysed the diversity‐productivity relationship patterns in the field, the importance of the environmental variables of pond size and heterogeneity on such relationship, and the variation of these patterns at local (community level) and landscape scales (metacommunity level) across 52 ponds on twelve occasions, over five years (2005–2009). Combining all sampling dates, there were 377 ponds and 1954 sample‐unit observations. Vegetation biomass was used as a proxy for productivity, and biodiversity was represented by species richness, evenness, and their interaction. Environmental variables comprised pond area, depth and internal heterogeneity. Productivity and species richness were not directly related at the metacommunity level, and were positively related at the community level. Taking environmental variables into account revealed positive species richness‐productivity relationships at the metacommunity level and positive quadratic relationships at the community level. Productivity showed both positive and negative linear and nonlinear relationships with the size and heterogeneity of ponds. We found a weak relationship between productivity and evenness. The identity of variables associated with productivity changed between spatial scales and through time. The pattern of relationships between productivity and diversity depends on spatial scale and environmental context, and changes idiosyncratically through time within the same ecosystem. Thus, the diversity‐productivity relationship is not only a property of the study system, but also a consequence of environmental variations and the temporal and spatial scale of analysis.     

Does biodiversity increase spatial stability in plant community biomass?

We tested the hypothesis that biodiversity decreases the spatial variability of biomass production between subplots taken within experimental grassland plots. Our findings supported this hypothesis if functional diversity (weighted Rao's Q ) was considered. Further analyses revealed that diversity in rooting depth and clonal growth form were the most important components of functional diversity stabilizing productivity. Using species or functional group richness as diversity measures there was no significant effect on spatial variability of biomass production, demonstrating the importance of the biodiversity component considered. Moreover, we found a significant increase in spatial variability of productivity with decreasing size of harvested area, suggesting small-scale heterogeneity as an important driver. The ability of diverse communities to stabilize biomass production across spatial heterogeneity may be due to complementary use of spatial niches. Nevertheless, the positive effect of functional diversity on spatial stability appears to be less pronounced than previously reported effects on temporal stability.     

Phylogenetic diversity stabilizes community biomass

Aims The relationship between biodiversity and ecological stability is a long-standing issue in ecology. Current diversity–stability studies, which have largely focused on species diversity, often report an increase in the stability of aggregate community properties with increasing species diversity. Few studies have examined the linkage between phylogenetic diversity, another important dimension of biodiversity, and stability. By taking species evolutionary history into account, phylogenetic diversity may better capture the diversity of traits and niches of species in a community than species diversity and better relate to temporal stability. In this study, we investigated whether phylogenetic diversity could affect temporal stability of community biomass independent of species diversity.Methods We performed an experiment in laboratory microcosms with a pool of 12 bacterivorous ciliated protist species. To eliminate the possibility of species diversity effects confounding with phylogenetic diversity effects, we assembled communities that had the same number of species but varied in the level of phylogenetic diversity. Weekly disturbance, in the form of short-term temperature shock, was imposed on each microcosm and species abundances were monitored over time. We examined the relationship between temporal stability of community biomass and phylogenetic diversity and evaluated the role of several stabilizing mechanisms for explaining the influence of phylogenetic diversity on temporal stability.Important findings Our results showed that increasing phylogenetic diversity promoted temporal stability of community biomass. Both total community biomass and summed variances showed a U-shaped relationship with phylogenetic diversity, driven by the presence of large, competitively superior species that attained large biomass and high temporal variation in their biomass in both low and high phylogenetic diversity communities. Communities without these species showed patterns consistent with the reduced strength of competition and increasingly asynchronous species responses to environmental changes under higher phylogenetic diversity, two mechanisms that can drive positive diversity–stability relationships. These results support the utility of species phylogenetic knowledge for predicting ecosystem functions and their stability.     

Is the relationship between algal diversity and biomass in North American lakes consistent with biodiversity experiments?

Over the past few decades, a large body of research has examined how biodiversity loss influences the functioning of ecosystems, as well as the cascading impacts on the goods and services ecosystems provide to humanity. The relationship between biodiversity and ecosystem functions quantified in prior experiments suggests that initial losses of biodiversity have relatively small impacts on properties like community biomass production; however, beyond some threshold, increasing losses lead to accelerating declines in function. Some have questioned whether a saturating relationship between diversity and community biomass production is an artifact of overly simplified experiments that manipulate diversity in homogeneous conditions over short time‐scales in which niche differences may not be realized. Others have questioned whether even the modest effects of biodiversity observed in experiments would be discernible in natural systems where they could be over‐ridden by the stronger influence of abiotic factors. Here, we used a biogeographic dataset to assess how the taxonomic richness of aquatic primary producers relates to community biomass in unmanipulated lake ecosystems in the US, and then compared these findings to prior experiments. We used structural equation modeling to evaluate hypotheses about the effects of algal richness on community biomass while accounting for covariance with environmental parameters measured in the USEPA's National Lakes Assessment (NLA), which sampled 1157 freshwater lakes. These analyses converged on a single best‐fit model (χ²= 0.31, p = 0.58) wherein community algal biomass was a function of three explanatory variables – nitrogen, phosphorus, and algal richness. The quantitative magnitude of the algal diversity (x) – biomass (y) relationship in the NLA dataset is statistically greater than that documented in the average biodiversity experiment. It did, however, lie at approximately the 75th percentile of experimental relationships, indicating the diversity–biomass relationship in unmanipulated lakes is within the range that has been characterized experimentally.     

Effects of land-use change on productivity depend on small-scale plant species diversity

Understanding the interplay between land-use change, species diversity and ecosystem function is critical for the prediction of global change impacts on ecosystem services. Biodiversity experiments with artificial species assemblages have shown that community-scale species richness may affect ecosystem productivity and spatial stability. However, the use of synthetic communities with controlled levels of species density for biodiversity experiments has been criticised and their relevance for natural communities has been questioned. Here, we use a land-use change experiment to investigate the biodiversity effects on production within managed, upland grasslands. We examine species diversity and productivity at both the small plant-neighbourhood scale (14×14 cm) and the field scale (15 m×25 m) for two land-use trajectories under field conditions: intensification through fertilisation, and extensification through the cessation of mowing. Both intensification and extensification were associated with a decrease in species number, but the magnitude of this decrease was greater at the small scale. Extensification was associated with a decrease in small-scale productivity whereas intensification had no significant effect on small-scale productivity. Effects of land-use treatments on biomass production were mediated by variation in small-scale species number; species number showed a significant positive relationship with small-scale productivity within each land-use treatment. Furthermore, species number was associated with a decrease in the variance of small-scale green biomass. In contrast, no species diversity effects were found on productivity at the field scale. Instead, field-scale species diversity decreased with increase in the total above-ground biomass (green biomass+litter). This study demonstrates that biodiversity effects can be observed under field conditions at the small scale and may play an important role for ecosystem functioning and stability even in low-diversity plant communities.     

The reliability of a composite biodiversity indicator in predicting bird species richness at different spatial scales

Several biodiversity features can be linked to landscape heterogeneity, that, in turn, can be informative for management and conservation purposes. Usually, the more the landscape is complex the more the biodiversity increases. Biodiversity indicators can be a useful tool to assess biodiversity status, in function of landscape heterogeneity. In this study, we developed a biodiversity indicator, based on Shannon diversity index and built from distribution maps of protected species. With such an approach, we seek to evaluate the feasibility of using a combination of target species as a surrogate for assessing the status of the whole bird community. Our approach was spread over multiple spatial scales, to determine which was the most informative. We selected four species protected by European regulation and generated a presence-absence map from species distribution modelling. We, therefore, used the FRAGSTATS biodiversity metric to calculate Shannon index for the overlapped presence-absence maps, at two spatial scales (500 m and 1000 m). Then, the relationships with the whole community was assessed through generalised least square models, at the spatial scale of 4 ha, 9 ha and 25 ha. Results showed that the higher rate of variability of community was explained by the biodiversity indicator at 1000 m scale. Indeed, the more informative spatial scale for the whole bird community was 9 ha. In addition, a pattern emerged about the relationships between biodiversity indicator and community richness, that is worth of further research. Our study demonstrates that the usefulness of surrogate species for biodiversity and community assessment can become clear only at a certain spatial scales. Indeed, they can be highly predictive of the whole community, and highly informative for conservation planning. Moreover, their use can optimize biodiversity monitoring and conservation, focusing on a small number of noteworthy species.     

Spatial and temporal homogenisation of freshwater macrofaunal communities in ditches

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Urbanization promotes the loss of seasonal dynamics in the semi-natural grasslands of an East Asian megacity

The biodiversity of agricultural landscapes has been noticeably affected by rapid urbanization. Although many studies have examined species diversity per unit area (alpha diversity), knowledge about the patterns of species turnover (beta diversity) in urban areas remains limited. Furthermore, most beta diversity studies have focused on spatial heterogeneity; however, losses of temporal heterogeneity resulting from urbanization remain limited. In this study, we examined how urbanization is associated with decreases in the seasonal heterogeneity of species composition, which could be used as an indicator of the loss of seasonality by ecologists and policy makers aiming to conserve biodiversity. We investigated (1) changes in species richness based on seasonal averages (alpha diversity) and (2) the seasonal turnover of species composition (beta diversity) for flowering plants and butterflies along a rural-urban gradient in semi-natural grasslands. The response variables were alpha and beta diversity for flowering plants and butterflies, and the explanatory variables were urban areas within a 1-km radius of the center of each site. Increasing urban area caused both the seasonal alpha and beta diversity of flowering plants and butterflies to decline. These results supported the homogenization hypothesis for the seasonality of plants and butterflies in semi-natural grasslands of dominant urban areas in East Asia. Future studies should focus on investigating how urbanization is causing both declines in seasonality and changes in the spatial heterogeneity of species composition and associated biodiversity loss. Ecologists and policy makers should focus on developing strategies to halt the loss of temporal biological heterogeneity to maintain biodiversity.     

Understanding the Spatio-Temporal Response of Coral Reef Fish Communities to Natural Disturbances: Insights from Beta-Diversity Decomposition

Understanding how communities respond to natural disturbances is fundamental to assess the mechanisms of ecosystem resistance and resilience. However, ecosystem responses to natural disturbances are rarely monitored both through space and time, while the factors promoting ecosystem stability act at various temporal and spatial scales. Hence, assessing both the spatial and temporal variations in species composition is important to comprehensively explore the effects of natural disturbances. Here, we suggest a framework to better scrutinize the mechanisms underlying community responses to disturbances through both time and space. Our analytical approach is based on beta diversity decomposition into two components, replacement and biomass difference. We illustrate this approach using a 9-year monitoring of coral reef fish communities off Moorea Island (French Polynesia), which encompassed two severe natural disturbances: a crown-of-thorns starfish outbreak and a hurricane. These disturbances triggered a fast logistic decline in coral cover, which suffered a 90% decrease on all reefs. However, we found that the coral reef fish composition remained largely stable through time and space whereas compensatory changes in biomass among species were responsible for most of the temporal fluctuations, as outlined by the overall high contribution of the replacement component to total beta diversity. This suggests that, despite the severity of the two disturbances, fish communities exhibited high resistance and the ability to reorganize their compositions to maintain the same level of total community biomass as before the disturbances. We further investigated the spatial congruence of this pattern and showed that temporal dynamics involved different species across sites; yet, herbivores controlling the proliferation of algae that compete with coral communities were consistently favored. These results suggest that compensatory changes in biomass among species and spatial heterogeneity in species responses can provide further insurance against natural disturbances in coral reef ecosystems by promoting high levels of key species (herbivores). They can also allow the ecosystem to recover more quickly.     

Spatial diversity patterns of Pristimantis frogs in the Tropical Andes

Although biodiversity gradients have been widely documented, the factors governing broad‐scale patterns in species richness are still a source of intense debate and interest in ecology, evolution, and conservation biology. Here, we tested whether spatial hypotheses (species–area effect, topographic heterogeneity, mid‐domain null model, and latitudinal effect) explain the pattern of diversity observed along the altitudinal gradient of Andean rain frogs of the genus Pristimantis. We compiled a gamma‐diversity database of 378 species of Pristimantis from the tropical Andes, specifically from Colombia to Bolivia, using records collected above 500 m.a.s.l. Analyses were performed at three spatial levels: Tropical Andes as a whole, split in its two main domains (Northern and Central Andes), and split in its 11 main mountain ranges. Species richness, area, and topographic heterogeneity were calculated for each 500‐m‐width elevational band. Spatial hypotheses were tested using linear regression models. We examined the fit of the observed diversity to the mid‐domain hypothesis using randomizations. The species richness of Pristimantis showed a hump‐shaped pattern across most of the altitudinal gradients of the Tropical Andes. There was high variability in the relationship between area and species richness along the Tropical Andes. Correcting for area effects had little impact in the shape of the empirical pattern of biodiversity curves. Mid‐domain models produced similar gradients in species richness relative to empirical gradients, but the fit varied among mountain ranges. The effect of topographic heterogeneity on species richness varied among mountain ranges. There was a significant negative relationship between latitude and species richness. Our findings suggest that spatial processes partially explain the richness patterns of Pristimantis frogs along the Tropical Andes. Explaining the current patterns of biodiversity in this hot spot may require further studies on other possible underlying mechanisms (e.g., historical, biotic, or climatic hypotheses) to elucidate the factors that limit the ranges of species along this elevational gradient.     

Biodiversity effects on productivity and stability of marine macroalgal communities: the role of environmental context

The influence of biodiversity on ecosystem functioning has been the focus of much recent research, but the role of environmental context and the mechanisms by which it may influence diversity effects on production and stability remain poorly understood. We assembled marine macroalgal communities in two mesocosm experiments that varied nutrient supply, and at four field sites that differed naturally in environmental conditions. Concordant with theory, nutrient addition promoted positive species richness effects on algal growth in the first mesocosm experiment; however, it tended to weaken the positive diversity relationship found under ambient conditions in a second experiment the next year. In the field experiments, species richness increased algal biomass production at two of four sites. Together, these experiments indicate that diversity effects on algal biomass production are strongly influenced by environmental conditions that vary over space and time. In decomposing the net biodiversity effect into its component mechanisms, seven of the eight experimental settings showed positive complementarity effects (suggesting facilitation or complementary resource use) countered by negative selection effects (i.e. enhanced growth in mixture of otherwise slow growing species) to varying degrees. Under no conditions, including nutrient enrichment, did we find evidence of positive selection effects commonly thought to drive positive diversity effects. Species richness enhanced stability of algal community biomass across a range of environmental settings in our field experiments. Hence, while species richness can increase production, enhanced stability is also an important functional outcome of maintaining diverse marine macroalgal communities.     

Multifractal spatial patterns and diversity in an ecological succession

We analyzed the relationship between biodiversity and spatial biomass heterogeneity along an ecological succession developed in the laboratory. Periphyton (attached microalgae) biomass spatial patterns at several successional stages were obtained using digital image analysis and at the same time we estimated the species composition and abundance. We show that the spatial pattern was self-similar and as the community developed in an homogeneous environment the pattern is self-organized. To characterize it we estimated the multifractal spectrum of generalized dimensions D(q). Using D(q) we analyze the existence of cycles of heterogeneity during succession and the use of the information dimension D(1) as an index of successional stage. We did not find cycles but the values of D(1) showed an increasing trend as the succession developed and the biomass was higher. D(1) was also negatively correlated with Shannon's diversity. Several studies have found this relationship in different ecosystems but here we prove that the community self-organizes and generates its own spatial heterogeneity influencing diversity. If this is confirmed with more experimental and theoretical evidence D(1) could be used as an index, easily calculated from remote sensing data, to detect high or low diversity areas.     

Herbivores control effects of algal species richness on community biomass and stability in a laboratory microcosm experiment

Hundreds of studies that have explored how biodiversity affects the productivity and stability of ecosystems have produced a consensus that communities composed of more species tend to have higher biomass that is more stable through time. However, the majority of this work stems from studies performed using highly simplified food webs, often composed of just primary producers competing for inorganic resources in the absence of trophic interactions. When studies have incorporated trophic interactions, diversity‐function relationships have been more variable, leaving open the question of how biodiversity affects the functioning of ecosystems with more trophic levels. Here we report the results of a laboratory experiment that used freshwater microcosms to test for effects of algal diversity (one or four species) on community biomass and temporal variability in the presence and absence of two different herbivore species (cladocerans Ceriodaphnia dubia and Daphnia pulex). When no herbivores were present, we found the classic pattern observed in hundreds of other studies – as species richness of algae increased, algal biomass increased, and the temporal variation in biomass decreased. This pattern was retained when one of the herbivores (C. dubia) was present. Ceriodaphnia dubia exhibited weak and non‐selective grazing on the focal algae, leaving the effect of diversity on biomass and variability essentially intact. In contrast, D. pulex exhibited strong and selective grazing in algal polycultures that qualitatively altered both diversity–function relationships. As algal richness increased, total algal biomass decreased and variation through time increased. These changes were coupled with larger and less variable populations of D. pulex. Our results show that herbivory leads to a richer array of diversity–function relationships than often observed in studies focused on just one trophic level, and suggests trophic interactions should be given more attention in work that seeks to determine how biodiversity impacts the functioning of ecosystems.     

Annual variation of community biomass is lower in more diverse stream fish communities

Anthropogenic influences have disproportionally affected freshwater ecosystems, and a loss of biodiversity is forecasted to greatly reduce ecosystem function and services. Loss of species may destabilize communities by limiting the stabilizing forces of compensatory dynamics and/or statistical averaging, both of which are effects that can buffer variation in aggregate community properties. Currently, support for positive diversity‐stability relationships stems from experiments with simple communities at small spatial and temporal scales, and application to natural communities is limited. Using a long‐term dataset of 35 stream fish communities matched with hydrologic data, we show that community stability (annual variation of standing biomass of fishes) was less variable in more species‐rich communities and was not associated with stream hydrology. Only the statistical averaging model of community stability was consistent with observed patterns of lower biomass variation in more species‐rich communities. Our findings suggest anthropogenically induced extirpation of vertebrate consumers may lower community biomass stability in complex ecosystems.     

The shift from plant–plant facilitation to competition under severe water deficit is spatially explicit

The stress‐gradient hypothesis predicts a higher frequency of facilitative interactions as resource limitation increases. Under severe resource limitation, it has been suggested that facilitation may revert to competition, and identifying the presence as well as determining the magnitude of this shift is important for predicting the effect of climate change on biodiversity and plant community dynamics. In this study, we perform a meta‐analysis to compare temporal differences of species diversity and productivity under a nurse plant (Retama sphaerocarpa) with varying annual rainfall quantity to test the effect of water limitation on facilitation. Furthermore, we assess spatial differences in the herbaceous community under nurse plants in situ during a year with below‐average rainfall. We found evidence that severe rainfall deficit reduced species diversity and plant productivity under nurse plants relative to open areas. Our results indicate that the switch from facilitation to competition in response to rainfall quantity is nonlinear. The magnitude of this switch depended on the aspect around the nurse plant. Hotter south aspects under nurse plants resulted in negative effects on beneficiary species, while the north aspect still showed facilitation. Combined, these results emphasize the importance of spatial heterogeneity under nurse plants for mediating species loss under reduced precipitation, as predicted by future climate change scenarios. However, the decreased water availability expected under climate change will likely reduce overall facilitation and limit the role of nurse plants as refugia, amplifying biodiversity loss.     

Effects of algal diversity on the production of biomass in homogeneous and heterogeneous nutrient environments: a microcosm experiment

Background

One of the most common questions addressed by ecologists over the past decade has been-how does species richness impact the production of community biomass? Recent summaries of experiments have shown that species richness tends to enhance the production of biomass across a wide range of trophic groups and ecosystems; however, the biomass of diverse polycultures only rarely exceeds that of the single most productive species in a community (a phenomenon called ‘transgressive overyielding’). Some have hypothesized that the lack of transgressive overyielding is because experiments have generally been performed in overly-simplified, homogeneous environments where species have little opportunity to express the niche differences that lead to ‘complementary’ use of resources that can enhance biomass production. We tested this hypothesis in a laboratory experiment where we manipulated the richness of freshwater algae in homogeneous and heterogeneous nutrient environments.

Methodology/Principal Findings

Experimental units were comprised of patches containing either homogeneous nutrient ratios (16∶1 nitrogen to phosphorus (N∶P) in all patches) or heterogeneous nutrient ratios (ranging from 4∶1 to 64∶1 N∶P across patches). After allowing 6–10 generations of algal growth, we found that algal species richness had similar impacts on biomass production in both homo- and heterogeneous environments. Although four of the five algal species showed a strong response to nutrient heterogeneity, a single species dominated algal communities in both types of environments. As a result, a ‘selection effect’–where diversity maximizes the chance that a competitively superior species will be included in, and dominate the biomass of a community–was the primary mechanism by which richness influenced biomass in both homo- and heterogeneous environments.

Conclusions/Significance

Our study suggests that spatial heterogeneity, by itself, is not sufficient to generate strong effects of biodiversity on productivity. Rather, heterogeneity must be coupled with variation in the relative fitness of species across patches in order for spatial niche differentiation to generate complementary resource use.     

江西柘林水库鱼类群落结构及功能多样性分析

为了解江西柘林水库鱼类群落结构和多样性的时空变化特征,研究鱼类物种多样性和功能多样性的关系,于2020年9月至2021年4月在该水库调查分析了鱼类物种组成、优势度及群落物种多样性和功能多样性。结果表明,共采集鱼类53种,分属于5目12科36属。其中,鲤形目(38种)种类最多,占调查物种数的71.69%,柘林水库上、中、下游库区分别采集到鱼类36、40和32种,各库区均以鲤形目鱼类为主,分别占采集物种数的72.97%、85.00%和75.00%。优势物种主要是■(Hemiculter leucisculus)、鳙(Aristichthys nobilis)和黄尾鲴(Xenocypris davidi),重要种主要是草鱼(Ctenopharyngodon idella)、鲢(Hypophthalmichthys molitrix)、鳊(Parabramis pekinensis)、鲫(Carassius auratus)、蒙古红鲌(Erythroculter mongolicus)等。鱼类群落结构季节性差异大于空间格局差异,主要表现为秋季和冬季之间;生物多样性指数Margalef和功能丰富...     

Biotic homogenisation and differentiation as directional change in beta diversity: synthesising driver–response relationships to develop conceptual models across ecosystems

Biotic homogenisation is defined as decreasing dissimilarity among ecological assemblages sampled within a given spatial area over time. Biotic differentiation, in turn, is defined as increasing dissimilarity over time. Overall, changes in the spatial dissimilarities among assemblages (termed ‘beta diversity’) is an increasingly recognised feature of broader biodiversity change in the Anthropocene. Empirical evidence of biotic homogenisation and biotic differentiation remains scattered across different ecosystems. Most meta-analyses quantify the prevalence and direction of change in beta diversity, rather than attempting to identify underlying ecological drivers of such changes. By conceptualising the mechanisms that contribute to decreasing or increasing dissimilarity in the composition of ecological assemblages across space, environmental managers and conservation practitioners can make informed decisions about what interventions may be required to sustain biodiversity and can predict potential biodiversity outcomes of future disturbances. We systematically reviewed and synthesised published empirical evidence for ecological drivers of biotic homogenisation and differentiation across terrestrial, marine, and freshwater realms to derive conceptual models that explain changes in spatial beta diversity. We pursued five key themes in our review: (i) temporal environmental change; (ii) disturbance regime; (iii) connectivity alteration and species redistribution; (iv) habitat change; and (v) biotic and trophic interactions. Our first conceptual model highlights how biotic homogenisation and differentiation can occur as a function of changes in local (alpha) diversity or regional (gamma) diversity, independently of species invasions and losses due to changes in species occurrence among assemblages. Second, the direction and magnitude of change in beta diversity depends on the interaction between spatial variation (patchiness) and temporal variation (synchronicity) of disturbance events. Third, in the context of connectivity and species redistribution, divergent beta diversity outcomes occur as different species have different dispersal characteristics, and the magnitude of beta diversity change associated with species invasions also depends strongly on alpha and gamma diversity prior to species invasion. Fourth, beta diversity is positively linked with spatial environmental variability, such that biotic homogenisation and differentiation occur when environmental heterogeneity decreases or increases, respectively. Fifth, species interactions can influence beta diversity via habitat modification, disease, consumption (trophic dynamics), competition, and by altering ecosystem productivity. Our synthesis highlights the multitude of mechanisms that cause assemblages to be more or less spatially similar in composition (taxonomically, functionally, phylogenetically) through time. We consider that future studies should aim to enhance our collective understanding of ecological systems by clarifying the underlying mechanisms driving homogenisation or differentiation, rather than focusing only on reporting the prevalence and direction of change in beta diversity, per se.     

Top predators determine how biodiversity is partitioned across time and space

Natural ecosystems are shaped along two fundamental axes, space and time, but how biodiversity is partitioned along both axes is not well understood. Here, we show that the relationship between temporal and spatial biodiversity patterns can vary predictably according to habitat characteristics. By quantifying seasonal and annual changes in larval dragonfly communities across a natural predation gradient we demonstrate that variation in the identity of top predator species is associated with systematic differences in spatio‐temporal β‐diversity patterns, leading to consistent differences in relative partitioning of biodiversity between time and space across habitats. As the size of top predators increased (from invertebrates to fish) habitats showed lower species turnover across sites and years, but relatively larger seasonal turnover within a site, which ultimately shifted the relative partitioning of biodiversity across time and space. These results extend community assembly theory by identifying common mechanisms that link spatial and temporal patterns of β‐diversity.     

Spatiotemporal dynamics of α‐ and β‐diversity across topographic gradients in the herbaceous layer of an old‐growth deciduous forest

Understanding the factors that regulate biodiversity over spatial and temporal gradients is an important scientific objective with ramifications for theory and conservation. Species composition is known to vary across spatial gradients, but how this spatial variation is linked to temporal dynamics is less well studied. Our objective was to understand how Shannon (α) diversity, spatial species turnover (Bray–Curtis dissimilarity), and temporal species turnover (Bray–Curtis dissimilarity) varied with regard to three topographic gradients (aspect, slope and elevation) over one growing season. In April, June and August of 2011, the herbaceous layer was sampled in 320 1‐m² plots within Big Everidge Hollow, an old‐growth forest in southeastern Kentucky. Multiple regression models revealed that Shannon diversity was linearly related to aspect (negative) and slope (positive), but unimodally related to elevation, indicating steep, mid‐elevation, and south‐facing plots were most diverse. Distance decay analysis showed that significant spatial species turnover occurred across all three topographic gradients, but aspect and elevation had a greater influence on compositional dissimilarity than slope. Mean temporal species turnover was significantly greater (p < 0.001) between April and June (0.39 ± 0.02 SE) than between June and August (0.20 ± 0.01). April‐to‐June turnover was related to aspect (linear) and elevation (quadratic; r²= 0.23, p < 0.0001), suggesting greater temporal species turnover occurred on north‐facing and mid‐elevation plots during this period; however, June‐to‐August turnover was weakly related to slope only (positive linear; r²= 0.08, p = 0.006). Environmental heterogeneity generated by topography is one of many factors that may constrain or promote biodiversity through space and across time, and a solid understanding of these spatiotemporal patterns of diversity can benefit both conservation and ecological theory.