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.

We present a model of a source-sink competitive metacommunity, defined as a regional set of communities in which local diversity is maintained by dispersal. Although the conditions of local and regional coexistence have been well defined in such systems, no study has attempted to provide clear predictions of classical community-wide patterns. Here we provide predictions for species richness, species relative abundances, and community-level functional properties (productivity and space occupation) at the local and regional scales as functions of the proportion of dispersal between communities. Local (alpha) diversity is maximal at an intermediate level of dispersal, whereas between-community (beta) and regional (gamma) diversity decline as dispersal increases because of increased homogenization of the metacommunity. The relationships between local and regional species richness and the species rank abundance distributions are strongly affected by the level of dispersal. Local productivity and space occupation tend to decline as dispersal increases, resulting in either a hump-shaped or a positive relationship between species richness and productivity, depending on the scale considered (local or regional). These effects of dispersal are buffered by decreasing species dispersal success. Our results provide a niche-based alternative to the recent neutral-metacommunity model and have important implications for conservation biology and landscape management.

The potential consequences of biodiversity loss for ecosystem functioning and services at local scales have received considerable attention during the last decade, but little is known about how biodiversity affects ecosystem processes and stability at larger spatial scales. We propose that biodiversity provides spatial insurance for ecosystem functioning by virtue of spatial exchanges among local systems in heterogeneous landscapes. We explore this hypothesis by using a simple theoretical metacommunity model with explicit local consumer-resource dynamics and dispersal among systems. Our model shows that variation in dispersal rate affects the temporal mean and variability of ecosystem productivity strongly and nonmonotonically through two mechanisms: spatial averaging by the intermediate-type species that tends to dominate the landscape at high dispersal rates, and functional compensations between species that are made possible by the maintenance of species diversity. The spatial insurance effects of species diversity are highest at the intermediate dispersal rates that maximize local diversity. These results have profound implications for conservation and management. Knowledge of spatial processes across ecosystems is critical to predict the effects of landscape changes on both biodiversity and ecosystem functioning and services.T he potential consequences of biodiversity loss for ecosystem functioning and services have received considerable attention during the last decade (1-3). Several controlled experiments have now established that species diversity influences ecosystemlevel processes such as primary production in grasslands (4-7) and heterotrophic consumption of suspended resources in streams (8). These experiments, however, have typically been performed over small spatial and temporal scales relative to the size and generation time of the organisms involved. At these small scales, uncontroversial effects of biodiversity due to functional complementarity among species with different traits have been shown only at low to moderate levels of diversity (1).It is possible that the functional significance of biodiversity will fully appear only at larger spatial and temporal scales. The insurance hypothesis (9) proposes that species or phenotypes that are functionally redundant for an ecosystem process at a given time may show temporal complementarity because of asynchronous responses to environmental fluctuations. In this case, biodiversity acts as insurance for ecosystem functioning against temporal environmental change because functional compensations among types provide enhanced and more predictable aggregate ecosystem properties. A number of theoretical studies have provided support for this hypothesis (9-15) although experimental evidence remains scanty and controversial (reviewed in ref. 16). Similarly, species or phenotypes may complement each other in space, such that a more diverse species pool allows better occupation of spatial gradients (17).This theoretical work has usually not considered explicitl...

Functional and phylogenetic diversity are increasingly quantified in various fields of ecology and conservation biology. The need to maintain diversity turnover among sites, so-called beta-diversity, has also been raised in theoretical and applied ecology. In this study, we propose the first comprehensive framework for the large-scale mapping of taxonomic, phylogenetic and functional diversity and of their respective turnover. Using high-resolution data on the spatial distribution and abundance of birds at a country scale, we disentangled areas of mismatches and congruencies between biodiversity components. We further revealed unequal representation of each component in protected areas: functional diversity was significantly under-represented whereas taxonomic diversity was significantly over-represented in protected areas. Our results challenge the use of any one diversity component as a surrogate for other components and stress the need to adopt an integrative approach to biodiversity conservation.