Competing theories for competitive metacommunities

Book · January 2005with 425 Reads
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  • Article
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    The concept of biological diversity, or biodiversity, is at the core of evolutionary and ecological studies. Many indices of biodiversity have been developed in the last four decades, with species being one of the central units of these indices. However, evolutionary and ecological studies need a precise description of species' characteristics to best quantify inter‐species diversity, as species are not equivalent and exchangeable. One of the first concepts characterizing species in biodiversity studies was abundance‐based rarity. Abundance‐based rarity was then complemented by trait‐ and phylo‐based rarity, called species' trait‐based and phylogenetic originalities, respectively. Originality, which is a property of an individual species, represents a species' contribution to the overall diversity of a reference set of species. Originality can also be defined as the rarity of a species' characteristics such as the state of a functional trait, which is often assumed to be represented by the position of the species on a phylogenetic tree. We review and compare various approaches for measuring originality, rarity and diversity and demonstrate that (i) even if attempts to bridge these concepts do exist, only a few ecological and evolutionary studies have tried to combine them all in the past two decades; (ii) phylo‐ and trait‐based diversity indices can be written as a function of species rarity and originality measures in several ways; and (iii) there is a need for the joint use of these three types of indices to understand community assembly processes and species' roles in ecosystem functioning in order to protect biodiversity efficiently.
  • Article
    Whether successional forests converge towards an equilibrium in species composition remains an elusive question, hampered by high idiosyncrasy in successional dynamics. Based on long-term tree monitoring in second-growth (SG) and old-growth (OG) forests in Costa Rica, we show that patterns of convergence between pairs of forest stands depend upon the relative abundance of species exhibiting distinct responses to the successional gradient. For instance, forest generalists contributed to convergence between SG and OG forests, whereas rare species and old-growth specialists were a source of divergence. Overall, opposing trends in taxonomic similarity among different subsets of species nullified each other, producing a net outcome of stasis over time. Our results offer an explanation for the limited convergence observed between pairwise communities and suggest that rare species and old-growth specialists may be prone to dispersal limitation, while the dynamics of generalists and second-growth specialists are more predictable, enhancing resilience in tropical secondary forests.
  • Article
    Understanding how common vs. rare species contribute to species richness patterns, and are differentially affected by landscape features, is essential for effective conservation monitoring and planning. Using common vs. rare dung beetles and ants, we test how species rarity shapes richness patterns across a timber plantation mosaic with remnant natural grassland conservation corridors as a mitigation measure. We then determine how environmental and spatial factors shape assemblage composition of common and rare grassland species, and how matrix-derived species influence these patterns. For each taxon, species were ranked from common-to-rare, and from rare-to-common. This ranking gave sequences of species richness patterns for increasing numbers of species. Along each stage of these two sequences, species richness of the sub-assemblage was correlated with that of the whole assemblage. This was repeated with matrix-derived species excluded. Deconstructing the species response matrices according to species traits, variation in composition of common vs. rare grassland specialists, as well as in matrix-derived species, were related to environmental (natural environmental heterogeneity and habitat quality) and spatial factors. For both taxa, common species reflected overall species richness patterns better than rare species. Matrix-derived species reduced the contribution of rare species to species richness patterns of dung beetles. Environmental variables were relatively more important for rare species than for common species composition, especially rare ants. We found that in a fragmented landscape: 1) common species reflect overall species richness patterns better than rare species, 2) overall species richness patterns do not reflect those of rare species, 3) the relative influence of regional-and local-scale factors are determined by an organ-ism's scale of life function, 4) rare species are especially affected by habitat quality, 5) knowledge of ecological processes governing communities in landscape mosaics are crucial for conserving grassland species diversity within these corridors.
  • Book
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    В книге изложены основные положения речной гидрологии, адаптированные для водных экологов, кратко представлены компоненты речных экосистем. Рассмотрено применение современного гидрологического и гидробиологического оборудования и приемов обработки данных. На конкретных примерах показаны широкие возможности привлечения гидрологических показателей для исследования структурно-функциональных характеристик речных сообществ и активного дрифта гидробионтов. Обозначены наиболее значимые характеристики речных экосистем как целостных природных комплексов. Предложена дренажно-транзитная концепция, определяющая функциональную значимость водосборных бассейнов при формировании речного континуума. Книга рассчитана на гидрологов, гидробиологов, специалистов водного хозяйства и охраны природы, преподавателей, аспирантов и студентов высших учебных заведений./This book offers the foundation of the river hydrology revised for aquatic ecologists, where the components of the river ecosystems are briefly described. The applications of modern hydrological and hydrobiological equipment and methods of data processing are considered. Specific examples show the wide possibilities of using hydrological parameters to study the structural-functional characteristics of river communities and their active drift. Demonstrated the most important characteristics of the river ecosystems as integrated natural systems. Proposed drainage-transit concept that determines the functional significance of the watersheds in the formation of the river continuum. The book is intended for hydrologists, hydrobiologists, specialists of water management and nature protection, teachers and graduate students of higher educational institutions.
  • Article
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    Metacommunity theory has advanced the understanding of the patterns and processes shaping community structure at multiple scales. Various models have been put forward to explain the relative effects of environmental filtering, dispersal, and species traits on community composition. Here, we focus on complex, three-dimensional webs of two social and two solitary spider species as habitat patches for associated communities of arthropods in a tropical rainforest in Ecuador. We used variance partitioning, constrained ordination, coherence analyses, and a colonization experiment to assess the role of environmental filtering and dispersal in this system. We found that the composition of communities associated with the four host species was mostly differentiated along two ordination axes, with the first axis roughly corresponding to level of sociality (solitary vs. social) and the other to web size. Associate abundance increased, but their density per unit volume decreased with host web size for all host species. Webs of social spider species had more variable communities and proportionally more aggressive (i.e., predatory) associates. After rarefaction to control for larger samples in larger webs, only one of the species showed a significant increase of species richness as a function of web size. The relatively quick colonization of experimentally established webs suggests high dispersal of more generalist species, but their lower proportion in older webs provides some evidence of a colonization–competition trade-off at longer temporal scales. The distinctness of the communities associated with the four host species, and the eventual change in proportion of associates in newly founded vs. old webs, despite high dispersal, is consistent with environmental filtering and species traits playing a major role in determining patterns of species distribution in this system.
  • Article
    Aim: In fresh waters, most biogeographical understanding of how extreme events such as drought modify biodiversity and ecosystem functioning derives from static, spatial comparisons of ecological communities, between intact and disturbed sites or along stress gradients. Impacts of drought on the development of ecological communities over time remain poorly resolved, with information on parallel trends in community structure and function particularly scarce. In theory, drought could progressively eliminate both species and functional traits, rendering communities increasingly taxonomically and functionally nested subsets of their pre-existing counterparts. Alternatively, drought could create new niche opportunities, producing a continuous turnover of species and traits, or simply constrain natural community succession. Location: Dorset, UK. Taxon: Aquatic invertebrates. Methods: We studied temporal changes in community structure and function in artificial streams over 2 years, comparing drought (frequent drying) with control (con-stant flow) conditions. Temporal beta diversity was partitioned into turnover and nestedness components, calculated using both presence-absence and abundance data, and analysed using time-lag and null modelling approaches. Results: Community development was comparable taxonomically under control and drought conditions, driven primarily by temporal turnover of species. Under control conditions, corresponding trends in functional composition were not apparent, and species turnover was characterized by the progressive replacement of some species by others of equivalent abundance. By contrast, species turnover in disturbed communities was accompanied by both functional turnover and greater loss of individuals , indicating that new colonists were not equivalent, either functionally or numerically, to those they replaced. Furthermore, functional dissimilarities between time points were greatest under drought, and more similar in magnitude to taxo-nomic dissimilarities, implying that drying reduced the stability and redundancy of functional attributes. Main conclusion: A shift to drier climate could disrupt the natural development of stream community structure, and undermine functional stability, at local and biogeographical scales, with potentially significant consequences for ecosystem services provisioning in fresh waters.
  • Article
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    We aimed to evaluate the structure of periphytic algae communities, the trait distribution and the patterns of functional diversity in the last non-dammed stretch of the Upper Paraná River floodplain. We hypothesize that there is an increase in the functional diversity and a change o f the traits and environmental variables structure along this floodplain. We expected an increase in the functional diversity due to the increase in tributaries propagule input leading to a functional divergence, provided by deterministic processes. The sampling was in channels, lakes and rivers in a floodplain area covering 230 km of extension of the main river. The periphyton was obtained from scraping petioles of the floating macrophyte Eichhornia azurea (Sw.) Kunth. The traits evaluated were life form and strength and form of adherence to the substrate. The functional diversity was calculated from a functional dendrogram and assembly rules. The hypotheses proposed in this study were partially accepted, since there was no increase in functional diversity along the sampled area, but we observed a change in the structure of the functional traits along the different stretches of the floodplain. The results showed diatoms as the dominant algae, and functional convergence as the assembly rule prevalent for this community. There was a large difference between local environmental factors along the floodplain. The protected areas housed the greatest functional diversity values, which was apparently influenced by the increase in functional diversity, which can be explained by the limnological factors and the input of propagules from the tributaries to the Paraná River. We noted the importance of the protected areas and local factors for assembly of this community.
  • Article
    Aims The community succession theory is much debated in ecology. We studied succession on Zokor rodent mounds on the Tibetan Plateau to address several fundamental questions, among them: (i) During secondary succession, does the community composition converge towards one community state or multiple states depending on the initial colonization? (ii) Do mound communities located in different background communities exhibit different assembly trajectories? Methods In a sub-alpine meadow, we investigated a total of 80 mound communities at several successional stages in three different background communities resulting from different management histories and compared their changes in species composition. The distribution of plant communities over time was analyzed with quantitative classification and ordination methods. The co-occurrence patterns of species were evaluated at each successional stage, and the degree of convergence/divergence among communities was obtained by calculating two beta-diversity indices. Important Findings During secondary succession, species richness of mound communities changed over time, and this change was dependent on the background community. Five life-form groups exhibited different dynamic patterns in species richness and plant cover. Community composition and the degree of species co-occurrence between communities increased over time since disturbance. There was much variation in species composition at earlier stages of succession, but communities on older mounds became more similar to each other and to their surrounding vegetation over the course of secondary succession. Post-disturbance succession of Zokor mound communities transitioned from 'multiple alternative states' to 'background-based deterministic community assembly' over time. Tradeoffs between competition and colonization, as well as the characteristics of different life-forms and mass effects within a limited species pool are the mechanisms responsible for convergence of mound communities.
  • Article
    Aims Species abundance distributions (SADs) are often used to verify mechanistic theories underlying community assembly. However, it is now accepted that SADs alone are not sufficient to reveal biological mechanisms. Recent attention focuses on the relative importance of stochastic dispersal processes versus deterministic processes such as interspecific competition and environmental filtering. Here, we combine a study of the commonness and rarity of species (i.e. the SAD) with mechanistic processes underlying community composition. By comparing the occurrence frequencies of each and every species with its abundance, we quantify the relative contributions of common and rare species to the maintenance of community structure. Essentially, we relate the continuum between commonness and rarity with that of niches and neutrality. Methods An individual-based, spatially explicit model was used to simulate local communities in niche spaces with the same parameters. We generated sets of assemblages from which species were eliminated in opposing sequences: from common to rare and from rare to common, and investigated the relationship between the abundance and frequency of species. We tested the predictions of our model with empirical data from a field experiment in the environmentally homogeneous alpine meadows of the Qinghai- Tibetan plateau. Important Findings Our simulations support the widespread notion that common species maintain community structure, while rare species maintain species diversity, in both local and regional communities. Our results, both from theoretical simulations and from empirical observations, revealed positive correlations between the abundance of a particular species and its occurrence frequency. SAD curves describe a continuum between commonness and rarity. Removing species from the 'rare' end of this continuum has little effect on the similarity of communities, but removing species from the 'common' end of the continuum causes significant increases in beta diversity, or species turnover, between communities. In local communities distributed in a homogenous habitat, species located at the 'common' end of the continuum should be selected by environmental filtering, with niche space partitioning governed by interspecific competition. Conversely, species located at the 'rare' end of the continuum are most likely subject to stochastic dispersal processes. Species situated at intermediate locations on this continuum are therefore determined by niche and neutral processes acting together. Our results suggest that, in homogeneous habitats, SAD curves describing the common-rare continuum may also be used to describe the continuum between niches and neutrality.
  • Article
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    We analysed the flora of 46 forest inventory plots (25 m x 100 m) in old growth forests from the Amazonian region to identify the role of environmental (topographic) and spatial variables (obtained using PCNM, Principal Coordinates of Neighbourhood Matrix analysis) for common and rare species. For the analyses, we used multiple partial regression to partition the specific effects of the topographic and spatial variables on the univariate data (standardised richness, total abundance and total biomass) and partial RDA (Redundancy Analysis) to partition these effects on composition (multivariate data) based on incidence, abundance and biomass. The different attributes (richness, abundance, biomass and composition based on incidence, abundance and biomass) used to study this metacommunity responded differently to environmental and spatial processes. Considering standardised richness, total abundance (univariate) and composition based on biomass, the results for common species differed from those obtained for all species. On the other hand, for total biomass (univariate) and for compositions based on incidence and abundance, there was a correspondence between the data obtained for the total community and for common species. Our data also show that in general, environmental and/or spatial components are important to explain the variability in tree communities for total and common species. However, with the exception of the total abundance, the environmental and spatial variables measured were insufficient to explain the attributes of the communities of rare species. These results indicate that predicting the attributes of rare tree species communities based on environmental and spatial variables is a substantial challenge. As the spatial component was relevant for several community attributes, our results demonstrate the importance of using a metacommunities approach when attempting to understand the main ecological processes underlying the diversity of tropical forest communities.
  • Article
    Local communities can be structured by both local interactions (competition, predation, environmental variables, etc.) and by regional interactions (dispersal of individ- uals between habitats). Using data from a three-year study on 34 neighboring ponds in an interconnected pond system, we tested whether zooplankton communities show a meta- community structure, how much variation in zooplankton community structure is related to local environmental factors vs. spatial configuration (taking into account the dispersal pathways), and what environmental variables are the locally structuring forces. In three different years, we found evidence for a metacommunity structure. We also found that spatial and environmental components act independently of each other due to the small geographic area and the high dispersal rates in this system. Despite these homogenizing forces, local environmental variables (associated with alternative equilibria in shallow lakes) were strongly related with zooplankton community structure in the studied years. This suggests that, even in this system of highly interconnected ponds, local environmental constraints can be strong enough to structure local communities.
  • Article
    Theory predicts that inter-patch dispersal rates and patterns of patch heterogeneity both have the potential to alter patterns of local and regional species diversity. To test this, we manipulated both rates of habitat connectivity and the geometric arrangement of habitat heterogeneity within regions of experimental zooplankton communities. We found no effects of habitat geometry on any metric of species diversity or composition. Additionally, we found no effect of habitat connectivity rate on local species diversity. We did, however, find that increasing connectivity led to a decrease in regional diversity, as well as an increase in the percent similarity of local communities within regions. Of all of the species in these communities, the relatively large cladoceran Ceriodaphnia reticulata significantly responded to the treatments, and had a higher probability of achieving high densities when connectance was high. As such, we suggest that this species played a large role in driving the increased local community similarity and decreased regional species richness as connectivity increased. These findings are in opposition to previous experimental studies of metacommunities, but support the notion that increased connectance among local patches may decrease regional diversity when patches are heterogeneous.
  • Article
    Understanding the processes that maintain diversity has been the focus of extensive study, yet there is much that has not been integrated into a cohesive framework. First, there is a separation of perspective. Ecological and evolutionary approaches to diversity have progressed in largely parallel directions. Second, there is a separation of emphasis. In both ecology and population genetics, classical theories favour local explanations with emphasis on population dynamics and selection within populations, while contemporary theories favour spatial explanations, with emphasis on population structure and interactions among populations. What is lacking is a comparative approach that evaluates the relative importance of local and spatial processes in maintaining genetic and ecological diversity. I present a framework for diversity maintenance that emphasizes the comparative approach. I use a well-known but little-used mathematical approach, the perturbation theorem for dynamical systems, to identify key points of contact between ecological and population genetic theories of coexistence. These connections provide for a synthesis of several important concepts: population structure (source–sink versus extinction–colonization), spatial heterogeneity (intrinsic versus extrinsic) in fitness and competitive ability, and temporal scales over which local and spatial processes influence diversity. This framework ties together a large and diverse body of theory and data from ecology and population genetics. It yields comparative predictions that can serve as guidelines in biodiversity management.
  • Article
    Ecologists have identified several kinds of pattern in the distribution of species among sites, including a) nested subsets, b) checkerboards, c) Clementsian gradients, d) Gleasonian gradients, and e) evenly spaced gradients. Most past efforts to diagnose such patterns have focused on only one at a time, often contrasted with a sixth type of pattern, f) “randomness”. While there are statistical tests to distinguish each of the first five patterns from randomness, there are currently no established methods for discriminating among these first five patterns in a given data set. Here we propose a method that will identify which of these possibilities is most prevalent in a site-by-species incidence matrix based on three basic aspects of meta-community structure. Our method is based on first ordinating the incidence matrix to identify the dominant axis of variation and identifying three aspects variation along this dominant axis. The first aspect, “coherence”, is the degree to which pattern can be collapsed into a single dimension. The second, “species turnover”, describes the number of species replacements along this dimension. The third aspect, “boundary clumping”, has to do with how the edges of species boundaries are distributed along this dimension. We present methods for analyzing these three aspects of meta-community structure, use them to identify the six different patterns, and illustrate them with a representative set of cases drawn from previously published data.
  • Article
    Studies that are unprecedented in scale, detail or approach show that niche partitioning contributes less, and chance events more, than expected to maintaining tree species richness via gap dynamics in tropical and temperate forests. Some tree species are differentially adapted for regeneration in different gap microenvironments. However, the stochastic availability of gaps, and limited recruitment of juveniles, mean that gaps are filled mostly by chance occupants rather than by best adapted species. This chance survival can slow competitive exclusion and maintain tree diversity. Gap dynamics do not explain the latitudinal gradient in tree richness.
  • Article
    Abstract I review the mathematical and biological aspects of Hubbell's (2001) neutral theory of species abundance for ecological communities, and clarify its historical connections with closely related approaches in population genetics. A selective overview of the empirical evidence for and against this theory is provided, with a special emphasis on tropical plant communities. The neutral theory predicts many of the basic patterns of biodiversity, confirming its heuristic power. The strict assumption of equivalence that defines neutrality, equivalence among individuals, finds little empirical support in general. However, a weaker assumption holds for stable communities, the equivalence of average fitness among species. One reason for the surprising success of the neutral theory is that all the theories of species coexistence satisfying the fitness equivalence assumption, including many theories of niche differentiation, generate exactly the same patterns as the neutral theory. Hubbell's neutral theory represents an important synthesis and a much needed demonstration of the pivotal role of intraspecific variability in ecology. Further improvements should lead to an explicit linking to niche-based processes. This research programme will depend crucially on forthcoming theoretical and empirical achievements.
  • Article
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    The metacommunity concept is an important way to think about linkages between different spatial scales in ecology. Here we review current understanding about this concept. We first investigate issues related to its definition as a set of local communities that are linked by dispersal of multiple potentially interacting species. We then identify four paradigms for metacommunities: the patch-dynamic view, the species-sorting view, the mass effects view and the neutral view, that each emphasizes different processes of potential importance in metacommunities. These have somewhat distinct intellectual histories and we discuss elements related to their potential future synthesis. We then use this framework to discuss why the concept is useful in modifying existing ecological thinking and illustrate this with a number of both theoretical and empirical examples. As ecologists strive to understand increasingly complex mechanisms and strive to work across multiple scales of spatio-temporal organization, concepts like the metacommunity can provide important insights that frequently contrast with those that would be obtained with more conventional approaches based on local communities alone.
  • Article
    Ecologists increasingly recognize that a consideration of spatial dynamics is essential for resolving many classical problems in community ecology. In the present paper, I argue that understanding how trophic interactions influence population stability can have important implications for the expression of spatial processes. I use two examples to illustrate this point. The first example has to do with spatial determinants of food chain length. Prior theoretical and empirical work has suggested that colonization–extinction dynamics can influence food chain length, at least for specialist consumers. I briefly review evidence and prior theory that food chain length is sensitive to area. A metacommunity scenario, in which each of various patches can have a food chain varying in length (but in which a consumer is not present on a patch unless its required resource is also present), shows that alternative landscape states are possible. This possibility arises if top predators moderate unstable interactions between intermediate predators and basal resources. The second example has to do with the impact of recurrent immigration on the stability of persistent populations. Immigration can either stabilize or destabilize local population dynamics. Moreover, an increase in immigration can decrease average population size for unstable populations with direct density-dependence, or in predator–prey systems with saturating functional responses. These theoretical models suggest that the interplay of temporal variation and spatial fluxes can lead to novel qualitative phenomena.
  • Article
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    Mechanisms proposed to explain the maintenance of species diversity within ecological communities of sessile organisms include niche differentiation mediated by competitive trade-offs, frequency dependence resulting from species-specific pests, recruitment limitation due to local dispersal, and a speciation-extinction dynamic equilibrium mediated by stochasticity (drift). While each of these processes, and more, have been shown to act in particular communities, much remains to be learned about their relative importance in shaping community-level patterns. We used a spatially-explicit, individual-based model to assess the effects of each of these processes on species richness, relative abundance, and spatial patterns such as the species-area curve. Our model communities had an order-of-magnitude more individuals than any previous such study, and we also developed a finite-size scaling analysis to infer the large-scale properties of these systems in order to establish the generality of our conclusions across system sizes. As expected, each mechanism can promote diversity. We found some qualitative differences in community patterns across communities in which different combinations of these mechanisms operate. Species-area curves follow a power law with short-range dispersal and a logarithmic law with global dispersal. Relative-abundance distributions are more even for systems with competitive differences and trade-offs than for those in which all species are competitively equivalent, and they are most even when frequency dependence (even if weak) is present. Overall, however, communities in which different processes operated showed surprisingly similar patterns, which suggests that the form of community-level patterns cannot in general be used to distinguish among mechanisms maintaining diversity there. Nevertheless, parameterization of models such as these from field data on the strengths of the different mechanisms could yield insight into their relative roles in diversity maintenance in any given community.
  • Article
    Patch occupancy theory predicts that a trade-off between competition and dispersal should lead to regional coexistence of competing species. Empirical investigations, however, find local coexistence of superior and inferior competitors, an outcome that cannot be explained within the patch occupancy framework because of the decoupling of local and spatial dynamics. We develop two-patch metapopulation models that explicitly consider the interaction between competition and dispersal. We show that a dispersal-competition trade-off can lead to local coexistence provided the inferior competitor is superior at colonizing empty patches as well as immigrating among occupied patches. Immigration from patches that the superior competitor cannot colonize rescues the inferior competitor from extinction in patches that both species colonize. Too much immigration, however, can be detrimental to coexistence. When competitive asymmetry between species is high, local coexistence is possible only if the dispersal rate of the inferior competitor occurs below a critical threshold. If competing species have comparable colonization abilities and the environment is otherwise spatially homogeneous, a superior ability to immigrate among occupied patches cannot prevent exclusion of the inferior competitor. If, however, biotic or abiotic factors create spatial heterogeneity in competitive rankings across the landscape, local coexistence can occur even in the absence of a dispersal-competition trade-off. In fact, coexistence requires that the dispersal rate of the overall inferior competitor not exceed a critical threshold. Explicit consideration of how dispersal modifies local competitive interactions shifts the focus from the patch occupancy approach with its emphasis on extinction-colonization dynamics to the realm of source-sink dynamics. The key to coexistence in this framework is spatial variance in fitness. Unlike in the patch occupancy framework, high rates of dispersal can undermine coexistence, and hence diversity, by reducing spatial variance in fitness.