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To purchase or authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.2007.0030-1299.14690.x Byline: Rachel S. Shulman, Jonathan M. Chase Abstract: The number of species that live in a habitat typically declines as that habitat becomes more isolated. However, the influence of habitat isolation on patterns of food web structure, in particular the ratio of predator to prey species richness, is less well understood. We placed aquatic mesocosms at varying distances from ponds that acted as sources of potential colonists; then we examined how isolation affected the ratio of predator:prey species richness in the communities that assembled. In the final sampling, a total of 21 species (12 prey and 9 predators) of insects, crustaceans, and amphibians had colonized the mesocosms. We found that total species richness, as well as the richness of predators and prey, declined with increasing isolation. However, predator richness declined more rapidly than prey richness with increasing isolation, which lead to decreasing predator:prey ratios. This result conflicts with prior demonstrations of invariant predator:prey ratios in freshwater communities. Article History: Manuscript Accepted 30 April 2007 Article note: R. S. Shulman (rshulman@lifesci.ucsb.edu) and J. M. Chase, Dept of Biology, Washington Univ. in St. Louis, St. Louis, MO 63130, USA. Present address for RSS: Dept of Ecology, Evolution & Marine Biology, Univ. of California, Santa Barbara, Santa Barbara, CA 93106, USA.

Current analyses of metacommunity data largely focus on global attributes across the entire metacommunity, such as mean alpha, beta, and gamma diversity, as well as the partitioning of compositional variation into single estimates of contributions of space and environmental effects and, more recently, possible contributions of species interactions. However, this view neglects the fact that different species and sites in the landscape can vary widely in how they contribute to these metacommunity‐wide attributes. We argue for a new conceptual framework with matched analytics with the goals of studying the complex and interactive relations between process and pattern in metacommunities that is focused on the variation among species and among sites which we call the 'internal structure' of the metacommunity. To demonstrate how the internal structure could be studied, we create synthetic data using a process‐based colonization–extinction metacommunity model. We then use joint species distribution models to estimate how the contributions of space, environment, and biotic interactions driving metacommunity assembly differ among species and sites. We find that this approach to the internal structure of metacommunities provides useful information about the distinct ways that different species and different sites contribute to metacommunity structure. Although it has limitations, our work points at a more general approach to understand how other possible complexities might affect internal structure and might thus be incorporated into a more cohesive metacommunity theory. [ABSTRACT FROM AUTHOR]

The island species–area relationship (ISAR) describes how the numbers of species increases with increasing size of an island (or island‐like habitat, such as lakes), and is one of the oldest laws in ecology. Despite its conceptual importance, there remains a great deal of ambiguity regarding the ISAR and its underlying processes. We compiled data from sampled zooplankton assemblages from several hundred lakes in North America and Europe to examine the influence of the three main hypothesized mechanisms leading to ISARs – passive sampling, disproportionate effects and habitat heterogeneity. We compiled data on lake zooplankton assemblages that reported sample‐level and lake level species richness estimates, as well as relative abundance data. In both North American and European lakes, we found a consistent and strong increase in total species richness with increasing lake area. However, when we compared the number of species standardized by number of individuals, there was no relationship between lake area and sample‐level species richness or an estimate of species relative abundances, calculated as the probability of interspecific encounter (PIE; a measure of evenness). This was true even when multiple samples were taken across lakes and combined, reducing the likelihood that habitat heterogeneity was driving the results. Overall, our results suggest that the ISAR of zooplankton in these lakes was most likely determined by sampling effects rather than disproportionate effects or habitat heterogeneity leading to more species in larger lakes. Understanding the mechanisms driving ISAR results such as ours can also help us develop predictions for biodiversity change when the area of these habitats changes. [ABSTRACT FROM AUTHOR]