Abstract
Understanding the drivers of geographical variation in species distributions, and the resulting community structure, constitutes one of the grandest challenges in ecology. Geographical patterns of species richness and composition have been relatively well studied. Less is known about how the entire set of trophic and non-trophic ecological interactions, and the complex networks that they create by gluing species together in complex communities, change across geographical extents. Here, we compiled data of species composition and three types of ecological interactions occurring between species in rocky intertidal communities across a large spatial extent (~970km of shoreline) of central Chile, and analyzed the geographical variability in these multiplex networks (i.e., comprising several interaction types) of ecological interactions. We calculated nine network summary statistics common across interaction types, and additional network attributes specific to each of the different types of interactions. We then investigated potential environmental drivers of this multivariate network organization. These included variation in sea surface temperature and coastal upwelling, the main drivers of productivity in nearshore waters. Our results suggest that structural properties of multiplex ecological networks are affected by local species richness and modulated by factors influencing productivity and environmental predictability. Our results show that non-trophic negative interactions are more sensitive to spatially structured temporal environmental variation than feeding relationships, with non-trophic positive interactions being the least labile to it. We also show that environmental effects are partly mediated through changes in species richness and partly through direct influences on species interactions, probably associated to changes in environmental predictability and to bottom-up nutrient availability. Our findings highlight the need for a comprehensive picture of ecological interactions and their geographical variability if we are to predict potential effects of environmental changes on ecological communities.
Highlights
The geographic variation in environmental conditions is one of the key factors determining species distributions, contributing to community assembly and species composition (MacArthur 1972, Gaston 2000, Elith and Leathwick 2009)
Among the environmental variables analysed, the best predictors of food web structure were: (1) the long-term average of the sea surface temperature (LT SST), (2) the fraction of days of the upwelling season during which a community is exposed to temperatures below 14°C (Fr Days), (3) environmental unpredictability, measured as the fraction of variability in SST across the year that cannot be explained by the seasonal cycle (Fr Annual); (4) and the strength of the upwelling regime along the coast (Upwelling; Fig. 2a, Appendix S1: Table S3, and Appendix S1: Fig. S5)
Our results show that the structure of the multiplex network of biotic interactions in the marine rocky-shore intertidal of central Chile is systematically and differentially affected by environmental variation depending on the interaction type considered
Summary
The geographic variation in environmental conditions is one of the key factors determining species distributions, contributing to community assembly and species composition (MacArthur 1972, Gaston 2000, Elith and Leathwick 2009). Biotic interactions play an important role in determining which species constitute an ecological. Manuscript received 20 August 2019; revised 19 June 2020; accepted 29 June 2020. Vol 101, No 11 among all co-occurring species varies across geographical environmental gradients has scarcely been assessed
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