Nicolas Mouquet

Community Patterns in Source‐Sink Metacommunities

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 (α) diversity is maximal at an intermediate level of dispersal, whereas between‐community (β) and regional (γ) 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.

Biodiversity as spatial insurance in heterogeneous landscapes

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.

Spatial mismatch and congruence between taxonomic, phylogenetic and functional diversity: the need for integrative conservation strategies in a changing world

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.

Empirical approaches to metacommunities: a review and comparison with theory

Metacommunity theory has advanced understanding of how spatial dynamics and local interactions shape community structure and biodiversity. Here, we review empirical approaches to metacommunities, both observational and experimental, pertaining to how well they relate to and test theoretical metacommunity paradigms and how well they capture the realities of natural ecosystems. First, we show that the species-sorting and mass-effects paradigms are the most commonly tested and supported paradigms. Second, the dynamics observed can often be ascribed to two or more of the four non-exclusive paradigms. Third, empirical approaches relate only weakly to the concise assumptions and predictions made by the paradigms. Consequently, we suggest major avenues of improvement for empirical metacommunity approaches, including the integration across theoretical approaches and the incorporation of evolutionary and meta-ecosystem dynamics. We hope for metacommunity ecology to thereby bridge existing gaps between empirical and theoretical work, thus becoming a more powerful framework to understand dynamics across ecosystems.

Coexistence in Metacommunities: The Regional Similarity Hypothesis

Species richness has historically been studied with a separation between smalland large-scale processes. Species diversity has been approached, on the one hand, from a local perspective, based on niche theory (Pianka 1966; MacArthur and Levins 1967; Schoener 1974), and on the other hand, from a regional perspective, through island biogeography (MacArthur and Wilson 1967), with no strong interactions between these two levels. At the local scale, interactions between competing species constrain diversity, and coexistence is a function of niche dimensions and resource heterogeneity (MacArthur and Levins 1967) or differences in species life-history traits as in colonization-competition trade-off models (Hastings 1980; Tilman 1994). At the regional scale, the theory of island biogeography (MacArthur and Wilson 1967) ignores local dynamics and considers local diversity as the result of regional processes such as chance events of immigration and extinction. There are no limits to diversity except those arising from the size of the regional species pool (continent size) and the constraints on immigration events (continent-island distance). This apparent contradiction has been named “MacArthur’s paradox” (Schoener 1983; Loreau and Mouquet 1999) because MacArthur’s contribution has been central in both niche theory (Mac-

Rare species support vulnerable functions in high-diversity ecosystems

The most unusual, and thus irreplaceable, functions performed by species in three different species-rich ecosystems are fulfilled by only the rare species in these ecosystems.

Immigration and the Maintenance of Local Species Diversity.

Explaining the maintenance of high local species diversity in communities governed by competition for space has been a long‐standing problem in ecology. We present a simple theoretical model to explore the influence of immigration from an external source on local coexistence, species abundance patterns, and ecosystem processes in plant communities. The model is built after classical metapopulation models but is applied to competition for space between individuals and includes immigration by a propagule rain and an extinction threshold for rare species. Our model shows that immigration can have a huge effect on local species diversity in competitive communities where competition for space would lead to the exclusion of all but one species if the community were closed. Local species richness is expected to increase strongly when immigration intensity increases beyond the threshold required for the successful establishment of one or a few individuals. Community structure and species relative abundances are also expected to change markedly with immigration intensity. Increasing immigration causes total space occupation by the community to increase but primary productivity on average to either decrease or stay constant with increasing diversity, depending on the relation between immigration and local reproduction rates. These results stress the need for a regional perspective to understand the processes that determine species diversity, species abundance patterns, and ecosystem functioning in local communities.

Ecophylogenetics: advances and perspectives

Ecophylogenetics can be viewed as an emerging fusion of ecology, biogeography and macroevolution. This new and fast‐growing field is promoting the incorporation of evolution and historical contingencies into the ecological research agenda through the widespread use of phylogenetic data. Including phylogeny into ecological thinking represents an opportunity for biologists from different fields to collaborate and has provided promising avenues of research in both theoretical and empirical ecology, towards a better understanding of the assembly of communities, the functioning of ecosystems and their responses to environmental changes. The time is ripe to assess critically the extent to which the integration of phylogeny into these different fields of ecology has delivered on its promise. Here we review how phylogenetic information has been used to identify better the key components of species interactions with their biotic and abiotic environments, to determine the relationships between diversity and ecosystem functioning and ultimately to establish good management practices to protect overall biodiversity in the face of global change. We evaluate the relevance of information provided by phylogenies to ecologists, highlighting current potential weaknesses and needs for future developments. We suggest that despite the strong progress that has been made, a consistent unified framework is still missing to link local ecological dynamics to macroevolution. This is a necessary step in order to interpret observed phylogenetic patterns in a wider ecological context. Beyond the fundamental question of how evolutionary history contributes to shape communities, ecophylogenetics will help ecology to become a better integrative and predictive science.

A Critical Review of Twenty Years’ Use of the Resource‐Ratio Theory

A model of species interactions based on their use of shared resources was proposed in 1972 by Robert MacArthur and later expanded in an article (1980) and a book (1982) by David Tilman. This “resource‐ratio theory” has been used to make a number of testable predictions about competition and community patterns. We reviewed 1,333 papers that cite Tilman’s two publications to determine whether predictions of the resource‐ratio theory have been adequately tested and to summarize their general conclusions. Most of the citations do not directly test the theory: only 26 studies provide well‐designed tests of one or more predictions, resulting in 42 individual tests of predictions. Most of these tests were conducted in the laboratory or experimental microcosms and used primary producers in freshwater systems. Overall, the predictions of the resource‐ratio theory were supported 75% of the time. One of the primary predictions of the model, that species dominance varies with the ratio of resource availabilities, was supported by 13 of 16 tests, but most other predictions have been insufficiently tested. We suggest that more experimental work in a variety of natural systems is seriously needed, especially studies designed to test predictions related to resource supply and consumption rates.

Diversity and productivity peak at intermediate dispersal rate in evolving metacommunities

Positive relationships between species diversity and productivity have been reported for a number of ecosystems. Theoretical and experimental studies have attempted to determine the mechanisms that generate this pattern over short timescales, but little attention has been given to the problem of understanding how diversity and productivity are linked over evolutionary timescales. Here, we investigate the role of dispersal in determining both diversity and productivity over evolutionary timescales, using experimental metacommunities of the bacterium Pseudomonas fluorescens assembled by divergent natural selection. We show that both regional diversity and productivity peak at an intermediate dispersal rate. Moreover, we demonstrate that these two patterns are linked: selection at intermediate rates of dispersal leads to high niche differentiation between genotypes, allowing greater coverage of the heterogeneous environment and a higher regional productivity. We argue that processes that operate over both ecological and evolutionary timescales should be jointly considered when attempting to understand the emergence of ecosystem-level properties such as diversity–function relationships.