Community structure and diversity of tropical forest mammals: data from a global camera trap network

Terrestrial mammals are a key component of tropical forest communities as indicators of ecosystem health and providers of important ecosystem services. However, there is little quantitative information about how they change with local, regional and global threats. In this paper, the first standardized pantropical forest terrestrial mammal community study, we examine several aspects of terrestrial mammal species and community diversity (species richness, species diversity, evenness, dominance, functional diversity and community structure) at seven sites around the globe using a single standardized camera trapping methodology approach. The sites-located in Uganda, Tanzania, Indonesia, Lao PDR, Suriname, Brazil and Costa Rica-are surrounded by different landscape configurations, from continuous forests to highly fragmented forests. We obtained more than 51 000 images and detected 105 species of mammals with a total sampling effort of 12 687 camera trap days. We find that mammal communities from highly fragmented sites have lower species richness, species diversity, functional diversity and higher dominance when compared with sites in partially fragmented and continuous forest. We emphasize the importance of standardized camera trapping approaches for obtaining baselines for monitoring forest mammal communities so as to adequately understand the effect of global, regional and local threats and appropriately inform conservation actions.     

Origination, extinction, and dispersal: integrative models for understanding present-day diversity gradients

Species diversity gradients seen today are, to a large degree, a product of history. Spatially nonrandom originations, extinctions, and changes in geographic distributions can create gradients in species and higher-taxon richness, but the relative roles of each of these processes remain poorly documented. Existing explanations of diversity gradients have tended to focus on either macroevolutionary or biogeographic processes; integrative models that include both are largely lacking. We used simple models that incorporate origination and extinction rates along with dispersal of taxa between regions to show that dispersal not only affects regional richness patterns but also has a strong influence on the average age of taxa present in a region. Failure to take into account the effects of dispersal can, in principle, lead to biased estimates of diversification rates and potentially wrong conclusions regarding processes driving latitudinal and other gradients in diversity. Thus, it is critical to include the effects of dispersal when formulating and testing hypotheses about the causes of large-scale gradients in diversity. Finally, the model results, in conjunction with the results of existing empirical studies, suggest that the nature of macroevolutionary and biogeographic processes may differ between terrestrial and marine diversity gradients.     

A critical analysis of the ubiquity of linear local–regional richness relationships

Synthesis Despite theoretical criticisms, the ubiquity of linear relationships between local and regional species richness has long been used to justify it as a valid framework to conclude that local communities are not saturated with species. However, we reanalyzed published studies with a new unbiased method and found no prevalence of linear relationships and more than 40% of misclassifications, including textbook examples. We thus conclude that the prevailing argument in favor of associating a valid ecological interpretation to local–regional species richness plots, its ubiquity, is not sustained, and that ecologists could use for instance metacommunity theory to make inference on the strength of local and regional processes. Identifying the relative importance of regional and local processes to local species diversity is a central issue to many questions in basic and applied ecology. One widely‐used method is to plot local species richness against its regional richness to infer whether regional or local processes determine local diversity. However, this method increases the tendency to find regional prevalence as suggested by a recent simulation. We reanalyzed studies in the literature with an unbiased method and found no prevalence of either regional or local processes. In addition, almost 40% of the studies and 50% of the ecology textbook examples using the traditional method were misclassified. Our findings reinforce the need of alternative, novel tools identified by for instance metacommunity theory to go beyond the studies of local–regional relationships in the ecological literature that focus on the interdependence of regional and local processes.     

Quantitative partitioning of regional and local processes shaping regional diversity patterns

Much recent research explaining plant community diversity has focused on comparing the relative impacts of regional and local processes. We employed a novel analysis to quantify the effects of multiple regional and local processes on species richness, and to make quantitative comparisons of those effects across two sites that differ in plot-level species richness, productivity and environmental conditions. While abiotic stress and competition limited richness within the communities at both sites, only differences in the overall pool of species at the site, likely resulting from long-distance dispersal and climate fluctuations, explained the differences in plot-level richness between sites. Patterns in local richness may be driven by a temporal storage effect, with greater richness in the site with greater climatic variability. By identifying both the factors that impact diversity within communities and those that vary systematically across communities, our integrated approach provides a better understanding of regional diversity patterns.     

Overdispersion of body size in Australian desert lizard communities at local scales only: no evidence for the Narcissus effect

Both local and regional processes may contribute to community diversity and structure at local scales. Although many studies have investigated patterns of local or regional community structure, few have addressed the extent to which local community structure influences patterns within regional species pools. Here we investigate the role of body size in community assembly at local and regional scales in Ctenotus lizards from arid Australia. Ctenotus has long been noted for its exceptional species diversity in the Australian arid-zone, and previous studies have attempted to elucidate the processes underlying species coexistence within communities of these lizards. However, no consensus has emerged on the role of interspecific competition in the assembly and maintenance of Ctenotus communities. We studied Ctenotus communities at several hundred sites in the arid interior of Australia to test the hypothesis that body sizes within local and regional Ctenotus assemblages should be overdispersed relative to null models of community assembly, and we explored the relationship between body size dispersion at local and regional scales. Results indicate a striking pattern of community-wide overdispersion of body size at local scales, as measured by the variance in size ratios among co-occurring species. However, we find no evidence for body size overdispersion within regional species pools, suggesting a lack of correspondence between processes influencing the distribution of species phenotypes at local and regional scales. We suggest that size ratio constancy in Ctenotus communities may have resulted from contemporary ecological interactions among species or ecological character displacement, and we discuss alternative explanations for the observed patterns. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Ecosystem consequences of the regional species pool

In this study we analyse with an experiment how the spatial area from which the species pool is sampled, i.e. local vs regional, can have functional consequences for ecosystem processes and structure. Particularly, we analysed how major stocks and processes respond to a change in basal productivity and how this depends on the source of the species pool. The experimental microcosms used in this experiment were developed by inoculating nutrient solution with samples of rockpool sediment containing resting stages. Here we show that communities developed from sediment samples of single origin (local communities) exhibit important differences in ecosystem structure and their response to a productivity gradient compared to systems developed from mixed samples of multiple and spatially dispersed origin (regional communities). The difference between local and regional communities was most pronounced for zooplankton which had much lower abundances in the local communities compared to the regional communities resulting in cascading effects on phytoplankton. We demonstrate that the spatial extend from which the species pool is sampled can affect ecosystem structure and functioning comparable in magnitude to changes in the basal productivity of the system. We discuss with a conceptual model how the regional species pool is important for sustaining diversity in functional groups, and how higher trophic levels are more sensitive to changes in the regional species pool.     

Species and individual replacements contribute more than nestedness to shape vertebrate scavenger metacommunities

Understanding the mechanisms that organize biodiversity is central in ecology and conservation. Beta diversity links local (alfa) and regional (gamma) diversity, giving insight into how communities organize spatially. Metacommunity ecology provides the framework to interpret regional and local processes interacting to shape communities. However, the lack of metacommunity studies for large vertebrates may limit the understanding and compromise the preservation of ecosystem functions and services. We aim to understand the mechanisms underlying differences in species composition among vertebrate scavenger communities ? which provide key ecosystem functions, e.g. carrion consumption ? within a metacommunity context. We obtained species richness and abundances at scavenger communities consuming ungulate carcasses monitored through motion‐triggered remote cameras in seven terrestrial ecosystems in Spain. We partitioned beta diversity to decompose incidence‐based (species presence/absence) and abundance‐based dissimilarities into their components (turnover/balanced variation and nestedness/abundance gradient, respectively). We identified the environmental factors explaining the observed patterns. The vertebrate scavenger metacommunity consisted of 3101 individuals from 30 species. Changes in composition among ecosystems were mostly (> 84%) due to species or individual replacement (i.e. turnover or balanced variation). Species or individual loss/gain (i.e. nestedness or abundance gradient) accounted for 13–16% of these changes. Mean carcass weight, elevation and habitat diversity were the main factors explaining species/individual replacement. Our findings suggest that local processes such as species‐sorting through habitat heterogeneity would dominate scavenger metacommunity dynamics together with stochastic forces (i.e. related to carrion unpredictability and scavenging being a widespread strategy among vertebrates). The presence of structured patterns (i.e. nestedness) in beta diversity could reflect a role of deterministic processes: mass‐effects through dispersal and defaunation. Vultures are long‐distance foragers and functionally dominant species, which would connect local assemblages within the metacommunity, supporting scavenger diversity and functions across space. These results highlight the importance of managing vertebrate scavenger assemblages within a metacommunity context.     

The influence of species pools and local processes on the community structure: a test case with woody plant communities in China's mountains

Understanding how patterns of biodiversity vary among taxonomic levels can provide insights into the mechanisms that regulate the assembly of ecological communities. In this study, we examined the scale and environmental dependence of the relationship between number of species and number of genera/families in woody plant communities to investigate the influences of species pool and local ecological processes on the taxonomic structures of local communities. The data we used are based on a large number of forest plots collected across the eastern part of China and the globe. The results showed that the ratio of the number of genera/families:species and the taxonomic exponents, i.e. the exponents of the genus/family–species relationship, were generally lower than null expectations based on the regional species pool, suggesting that abiotic filtering (e.g. environmental filtering and dispersal limitation) is more important than interspecific competition in shaping local communities. The extent of species pool and the area sampled for local communities both influenced our ability to infer whether local ecological processes were important. In particular, the deviation of the taxonomic ratios and exponents between empirical and null patterns increased as the extent of species pool increased, and the taxonomic exponents declined as area of the local community increased, due partly to the reduced effect of interspecific competition. We conclude that regional species pools and local processes both influenced the taxonomic structure of local woody plant communities, but their effects vary substantially among spatial scales.     

Local–regional richness relationship in fouling assemblages – Effects of succession

The number of species in a local habitat depends on local and regional processes. One common approach to explore ecological saturation of local richness has been to plot local versus regional richness. We expand this approach by incorporating two dimensions of diversity – taxonomic and functional – and different successional ages of marine fouling communities. In four different biogeographic regions (Mediterranean Sea, NE Atlantic, Western Baltic Sea and North Sea) 60 experimental units made from artificial substratum were deployed for colonization. Local richness was assessed as the average number of species and functional groups (FG) per unit area while regional richness was estimated as the estimated (Jack 2) asymptote of the accumulation curves for species or FG in local panel communities. Our findings indicate that the nature of the relationship between local and regional diversity is sensitive to successional stage and the dimension of diversity considered. However, as a general pattern, for taxonomic and functional richness, the slope of the local–regional relationship increased in the course of succession. We discuss how this pattern could have been produced by a combination of low number of recruiting species and incomplete competitive exclusion as is typical for early succession.     

The alpha–beta–regional relationship: providing new insights into local–regional patterns of species richness and scale dependence of diversity components

Ecologists frequently regress local species richness on regional species richness to draw inferences about the processes that structure local communities. A more promising approach is to quantify the contributions of alpha and beta diversity to regional diversity (the ABR approach) using additive partitioning. We applied this approach to four local–regional relationships based on data from 583 arboreal beetle species collected in a hierarchically nested sampling design. All four local–regional relationships exhibited proportional sampling, yet the ABR approach indicated that each was produced by a different combination of alpha and beta richness. Using the results of the ABR analysis, we also analysed the scale dependence of alpha and beta using a hierarchical linear model. Alpha diversity contributed less than expected to regional diversity at the finest spatial scale and more than expected at the broadest spatial scale. A switch in relative dominance from beta to alpha diversity with increasing spatial scale suggested scale transitions in ecological processes. Analysing the scale dependence of diversity components using the ABR approach furthers our understanding about the additivity of species diversity in biological communities.     

The relationship between local and regional diversity of indigenous forest fauna in KwaZulu-Natal Province, South Africa

The relationship between local and regional diversity was tested by regressing local community richness against regional species diversity for three taxa, birds, butterflies and mammals, in subtropical forest. The quadratic model best fits the relationship between local and regional diversity for birds. Local bird species richness is theoretically independent of the size of the regional pool of species and may represent saturated communities. A linear model best describes the relationship for mammals and butterflies. For mammals, the slope is shallow (0.264) and regional richness overestimates local species richness, suggesting communities are undersaturated. Extinction filtering may explain this pattern. Past climatic changes have filtered out many mammalian species, these changes have been too recent for autochthanous speciation, and the relatively low vagility of mammals has prevented extensive recolonisation. Differences in the nature of the diversity relationship between taxa are as much due to independent evolutionary histories as to differences in vagility and colonising potential. A pervasive role is suggested for regional biogeographic processes in the development of faunal assemblage structure. Large-scale processes are not considered in current conservation plans. We encourage the shift of conservation emphasis from local ecological processes and species interactions, to whole communities and consideration of regional processes.     

Community assembly along a successional gradient in sub‐alpine meadows of the Qinghai‐Tibetan Plateau,China

Community assembly is a dynamic progression that reflects the interaction of several processes functioning at multiple scales. Understanding how these processes work in communities at different successional stages is important for identifying when regional or local processes are more important for community assembly, and for developing effective preservation and restoration strategies. We examined community assembly using a chronosequence of sub‐alpine meadows in Qinghai‐Tibetan Plateau that range from ‘natural’ (never farmed), to those that have been protected from agricultural exploitation for 1 to 10 years. We tested for shifts in species and traits among meadows and also for changes in environmental and spatial correlates of species distributions within meadows. We found that species richness increased and species composition returned to natural conditions within ten years of protection. These changes coincided with shifts in species traits; abundant species had high seed mass and specific leaf area in late‐successional meadows, whereas the opposite occurred in early‐successional meadows. Despite these shifts among meadows of different ages, spatial distributions of species within meadows did not change – when associated with abiotic variables, these spatial patterns reflected changes in soil pH and nitrogen. There was also no consistent change in the relative importance of environmental and spatial correlates of species distributions within meadows. These trends indicate that local processes of community assembly are similar within meadows even when species in those meadows differ. We conclude that successional change is a large‐scale process that alters the species pool and resulting suite of traits that are present within meadows. As a result, regional planning that incorporates successional age should be the focus for the conservation of diversity in this area. In contrast, local processes work within the constraints of the species pool set by successional age, producing consistent patterns within meadows of different ages.     

Using functional diversity patterns to explore metacommunity dynamics: a framework for understanding local and regional influences on community structure

The metacommunity concept, describing how local and regional scale processes interact to structure communities, has been successfully applied to patterns of taxonomic diversity. Functional diversity has proved useful for understanding local scale processes, but has less often been applied to understanding regional scale processes. Here, we explore functional diversity patterns within a metacommunity context to help elucidate how local and regional scale processes influence community assembly. We detail how each of the four metacommunity perspectives (species sorting, mass effects, patch dynamics, neutral) predict different patterns of functional beta‐ and alpha‐diversity and spatial structure along two key gradients: dispersal limitation and environmental conditions. We then apply this conceptual model to a case study from alpine tundra plant communities. We sampled species composition in 17 ‘sky islands’ of alpine tundra in the Colorado Rocky Mountains, USA that differed in geographic isolation and area (key factors related to dispersal limitation) and temperature and elevation (key environmental factors). We quantified functional diversity in each site based on specific leaf area, leaf area, stomatal conductance, plant height and chlorophyll content. We found that colder high elevation sites were functionally more similar to each other (decreased functional beta‐diversity) and had lower functional alpha‐diversity. Geographic isolation and area did not influence functional beta‐ or alpha‐diversity. These results suggest a strong role for environmental conditions structuring alpine plant communities, patterns consistent with the species sorting metacommunity perspective. Incorporating functional diversity into metacommunity theory can help elucidate how local and regional factors structure communities and provide a framework for observationally examining the role of metacommunity dynamics in systems where experimental approaches are less tractable.     

Recruitment facilitation can promote coexistence and buffer population growth in metacommunities

Although positive species interactions are ubiquitous in nature, theory has generally focused on the role of negative interactions to explain patterns of species diversity. Here, we incorporate recruitment facilitation, a positive interaction prevalent in marine and terrestrial systems, into a metacommunity framework to assess how the interplay between colonisation, competition and facilitation mediates coexistence. We show that when subordinate species facilitate the recruitment of dominant species, multi-species metacommunities can persist stably even if the colonisation rate of the dominant species is greater than that of the subordinate species. In addition, recruitment facilitation can buffer population growth from changes in colonisation rates, and thus explain the paradoxical mismatch between patterns of abundance and recruitment in marine systems. Overall, our results demonstrate that recruitment facilitation can have profound effects on the assembly, dissolution and regulation of metacommunities by mediating the relative influence of local and regional processes on population abundance and species diversity.     

A macroecological perspective of diversity patterns in the freshwater realm

1. The aim of this paper is to review literature on species diversity patterns of freshwater organisms and underlying mechanisms at large spatial scales. 2. Some freshwater taxa (e.g. dragonflies, fish and frogs) follow the classical latitudinal decline in regional species richness (RSR), supporting the patterns found for major terrestrial and marine organism groups. However, the mechanisms causing this cline in most freshwater taxa are inadequately understood, although research on fish suggests that energy and history are major factors underlying the patterns in total species and endemic species richness. Recent research also suggests that not all freshwater taxa comply with the decline of species richness with latitude (e.g. stoneflies, caddisflies and salamanders), but many taxa show more complex geographical patterns in across‐regions analyses. These complexities are even more profound when studies of global, continental and regional extents are compared. For example, clear latitudinal gradients may be present in regional studies but absent in global studies (e.g. macrophytes). 3. Latitudinal gradients are often especially weak in the across‐ecosystems analyses, which may be attributed to local factors overriding the effects of large‐scale factors on local communities. Nevertheless, local species richness (LSR) is typically linearly related to RSR (suggesting regional effects on local diversity), although saturating relationships have also been found in some occasions (suggesting strong local effects on diversity). Nestedness has often been found to be significant in freshwater studies, yet this pattern is highly variable and generally weak, suggesting also a strong beta diversity component in freshwater systems. 4. Both geographical location and local environmental factors contribute to variation in alpha diversity, nestedness and beta diversity in the freshwater realm, although the relative importance of these two groups of explanatory variables may be contingent on the spatial extent of the study. The mechanisms associated with spatial and environmental control of community structure have also been inferred in a number of studies, and most support has been found for species sorting (possibly because many freshwater studies have species sorting as their starting point), although also dispersal limitation and mass effects may be contributing to the patterns found. 5. The lack of latitudinal gradients in some freshwater taxa begs for further explanations. Such explanations may not be gained for most freshwater taxa in the near future, however, because we lack species‐level information, floristic and faunistic knowledge, and standardised surveys along extensive latitudinal gradients. A challenge for macroecology is thus to use the best possible species‐level information on well‐understood groups (e.g. fish) or use surrogates for species‐level patterns (e.g. families) and then develop hypotheses for further testing in the freshwater realm. An additional research challenge concerns understanding patterns and mechanisms associated with the relationships between alpha, beta and gamma components of species diversity. 6. Understanding the mechanistic basis of species diversity patterns should preferably be based on a combination of large‐scale macroecological and landscape‐scale metacommunity research. Such a research approach will help in elucidating patterns of species diversity across regional and local scales in the freshwater realm.     

Dispersal ability links to cross‐scale species diversity patterns across the Eurasian Arctic tundra

Aim The role of dispersal in structuring biodiversity across spatial scales is controversial. If dispersal controls regional and local community assembly, it should also affect the degree of spatial species turnover as well as the extent to which regional communities are represented in local communities. Here we provide the first integrated assessment of relationships between dispersal ability and local‐to‐regional spatial aspects of species diversity across a large geographical area. Location Northern Eurasia. Methods Using a cross‐scale analysis covering local (0.64 m²) to continental (the Eurasian Arctic biome) scales, we compared slope parameters of the dissimilarity‐to‐distance relationship in species composition and the local‐to‐regional relationship in species richness among three plant‐like groups that differ in dispersal ability: lichens with the highest dispersal ability; mosses and moss allies with intermediate dispersal ability; and seed plants with the lowest dispersal ability. Results Diversity patterns generally differed between the three groups according to their dispersal ability, even after controlling for niche‐based processes. Increasing dispersal ability is linked to decreasing spatial species turnover and an increasing ratio of local to regional species richness. All comparisons supported our expectations, except for the slope of the local‐to‐regional relationship in species richness for mosses and moss allies which was not significantly steeper than that of seed plants. Main conclusions The negative link between dispersal ability and spatial species turnover and the corresponding positive link between dispersal ability and the ratio of local‐to‐regional species richness support the idea that dispersal affects community structure and diversity patterns across spatial scales.     

The roles of environment and space in shaping stream diatom communities

Diatoms are widely used in stream quality assessment due to their response to the local environment. Diatoms are also influenced by many large-scale processes and so the diatom communities of boreal streams incorporate a strong spatial component at a regional level. What is not properly known yet is whether the variation in diatom communities between regions is larger than the variation in measured environmental variables. We studied the roles of environment and space in accounting for variability in stream diatom communities across four regions in Finland. According to canonical correspondence analysis, geographical coordinates, nutrient concentrations (total N and P), and water conductivity were the most important factors affecting variation in diatom community composition. Of physical factors, depth and current velocity were also significant. According to Mantel tests, both environmental and geographical distances were related to dissimilarity in diatom community composition. Analysis of Similarities indicated that the regional differences in diatom community composition were larger than the regional differences in environmental variables. We also found many indicator species confined to certain regions. Our results suggest that the four study regions differ in their diatom species composition more than in their environmental features and that diatoms are structured not only by the local environment but also by large-scale processes, possibly related to history, climate and dispersal. These results imply that, while diatom species composition reflects well the environmental differences between regions, future bioassessments would benefit from regional stratification. Otherwise, relationships with environmental variables may be masked by trans-regional differences in species pools caused by the large-scale processes.     

The local introduction of strongly interacting species and the loss of geographic variation in species and species interactions

Species introductions into nearby communities may seem innocuous, however, these introductions, like long-distance introductions (e.g. trans- and intercontinental), can cause extinctions and alter the evolutionary trajectories of remaining community members. These 'local introductions' can also more cryptically homogenize formerly distinct populations within a species. We focus on several characteristics and the potential consequences of local introductions. First, local introductions are commonly successful because the species being introduced is compatible with existing abiotic and biotic conditions; many nearby communities differ because of historical factors and the absence of certain species is simply the result of barriers to dispersal. Moreover, the species with which they interact most strongly (e.g. prey) may have, for example, lost defences making the establishment even more likely. The loss or absence of defences is especially likely when the absent species is a strongly interacting species, which we argue often includes mammals in terrestrial communities. Second, the effects of the introduction may be difficult to detect because the community is likely to converge onto nearby communities that naturally have the introduced species (hence the perceived innocuousness). This homogenization of formerly distinct populations eliminates the geographic diversity of species interactions and the geographic potential for speciation, and reduces regional species diversity. We illustrate these ideas by focusing on the introduction of tree squirrels into formerly squirrel-less forest patches. Such introductions have eliminated incipient species of crossbills (Loxia spp.) co-evolving in arms races with conifers and will likely have considerable impacts on community structure and ecosystem processes.     

Disturbance,coral reef communities,and changing ecological paradigms

We examine changing ecological theory regarding the role of disturbance in natural communities and relate past and emerging paradigms to coral reefs. We explore the elements of this theory, including patterns (diversity, distribution, and abundance) and processes (competition, succession, and disturbance), using currently evolving notions concerning matters of scale (temporal and spatial), local versus regional species richness, and the equilibrium versus nonequilibrium controversy. We conclude that any attempt to categorize coral reef communities with respect to disturbance regimes will depend on the question being asked and the desired level of resolution: local assemblage versus regional species pool, successional versus geological time, and on the taxonomic and tropic affinities of species included in the study. As with many communities in nature, coral reefs will prove to be mosaics of species assemblages with equilibrial and nonequilibrial dynamics.     

Sources of diversity in a grassland metacommunity: quantifying the contribution of dispersal to species richness

Metacommunity theory suggests a potentially important role for dispersal in diversity maintenance at local, as well as regional, scales. In addition, propagule addition experiments have shown that dispersal often limits local diversity. However, actual dispersal rates into local communities and the contribution of immigrants to observed local diversity are poorly known. We present a new approach that partitions the diversity of a target community into dispersal-maintained and dispersal-independent components. Specifically, we quantify distances through space and time to the nearest potential seed source for naturally occurring recruits in target communities by using hierarchical data on species pools (local, site, region, and seed bank). Using this "recruit tag" approach, we found that dispersal contributed 29%-57% of the seedling diversity in perennial grasslands with different successional histories. However, both dispersal and seedling mortality remained remarkably constant, in absolute terms, over succession. The considerable loss of diversity over secondary succession (66%), therefore, could be understood only by considering how these processes interact with the decreasing disturbance rate (i.e., frequency of gaps) in later-successional sites. We conclude that a metacommunity perspective is relevant and necessary to understand the diversity and community assembly of this study system.