The responses of individual species to patch size and other spatial variables (edges, connectivity, landscape-level factors) have received much attention in the recent literature. Far fewer studies, however, have identified how the occurrence of pairwise species interactions might depend on these factors. In this study, I investigated how various aspects of landscape change impact the spatial occurrence of consumer-resource pairs and other community subunits. Via a literature review and analysis, I identified the types of food web modules (or sets of interacting species within a larger community) that have been studied in the context of habitat patch size and other fragmentation-related variables. On Web of Science, I used combinations of the following keywords: habitat, interaction, fragment, patch, connectivity, and isolation, and I supplemented this list with citations from recent reviews and knowledge of the literature.
Results/Conclusions
Of the 1526 papers discovered by this method, I identified 539 studies that treated species interactions, multi-species assemblages, or metacommunities in fragmented habitats, or were reviews or concept papers. I identified a subset of these papers that explicitly examined the presence or strength of an interaction, or the co-occurrence of interacting species (potential interaction) as functions of patch size. An overwhelming majority of the interactions involved two species, largely parasitoid-prey and herbivore-plant modules. Few studies investigated interactions between 3 or more species, such as three-species food chains, apparent competition, omnivory, or intraguild predation. Whether a module was more or less likely to occur as a function of patch size or isolation was largely a function of the ecological traits of the component species, such that modules involving the most specialized species exhibited the strongest relationships with patch size. Overall, understanding how local species interactions and food web structure vary spatially may be a key to predicting what consequences habitat loss will have at higher levels of biological organization.
