Heterogeneity in the isolation of patches may be essential for the action of metacommunity mechanisms

The spatial isolation gradient of communities and the gradient in the species dispersal ability are recognized as determinants of biodiversity in metacommunities. In spite of this, mean field models, spatially explicit models, and experiments were mainly focused on idealized spatial arrangements of communities leaving aside the combining role of dispersal and isolation gradients in metacommunity processes. Consequently, we have an incipient understanding of the role of the real spatial arrangement of communities on biodiversity patterns. We focus on six metacommunities for which confident information about the spatial arrangement of water bodies is available. Using coalescent metacommunity models and null models that randomize the location of water bodies, we estimated the potential eect of the landscape on biodiversity and its dependence on species dispersal ability. At extremely lowor high dispersal abilities, the location of ponds does not influence diversity because dierent communities are equally aected by the low or high incoming dispersal. At intermediate dispersal abilities, peripheral communities present a much lower richness and higher beta diversity than central communities.Moreover,metacommunities from real landscapes host more biodiversity than randomized landscapes, a result that is determined by the heterogeneity in the geographic isolation of communities. In a dispersal gradient, mass eects systematically increase the local richness and decrease beta diversity. However, the spatial arrangement of patches only has a large importance in metacommunity processes at intermediate dispersal abilities, which ensures access to central locations but limits dispersal in isolated communities. The ongoing reduction in spatial extent and simplification of the landscape may consequently undermine the metacommunity processes that support biodiversity, something that should be explicitly considered in preserving and restoring strategies

Energetic constraints to food chain length in a metacommunity framework

As metabolism increases with body size, populations of large-sized species can become constrained to relatively low trophic positions within a local community due to their high energetic demands combined with the limited efficiency with which energy is transferred up the food chain from primary producers. In a metacommunity context, dispersal can become a major driver of population dynamics and persistence, having also the potential to ameliorate the aforementioned energetic constraints due to its effect on colonization and energy subsidies from connected patches. Here, we derive a size-dependent model for food chain length in communities subjected to migration, and show that populations with higher influx of migrants are able to persist at higher trophic positions. Simulations of random, dendritic, and real aquatic metacommunities corroborate this result, and further indicate that community location in the landscape (relative centrality-isolation) may determine local food web structure. More central patches contained larger populations and were less constrained in trophic position. This effect was particularly strong in dendritic metacommunities, which are representative of freshwater watersheds in general. Furthermore, the role of spatial processes is nonlinearly intensified with increases in body size, indicating that larger organisms have a much stronger dependence on landscape attributes.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author