Biotic interactions vary across species' ranges and are likely conserved through geological time

Abstract

AimThe evolutionary interactions between western spadefoot toads (genus Spea) represent a textbook example of character displacement, facilitated by dietary specialization of one Spea species on fairy shrimp (Anostraca) when all three co‐occur. The aim of this study is to understand the covariation between predator (Spea) and prey (Anostraca) range shifts in response to climate change oscillations, and whether biotic interactions can be used to project species distribution models on different time scales when studying species with dietary specialization. Taxon: Amphibia: Spea spp. and Crustacea: Anostraca.LocationNorth America.MethodsUsing multiple modelling techniques, we first estimated the potential distribution of central and western North American fairy shrimp species (Crustacea: Anostraca) and two western spadefoot toad species (Spea bombifrons and Spea multiplicata). We then created a shrimp species richness map by aggregating individual species estimates. Third, we studied the relationship between the probability of spadefoot toad presence and fairy shrimp species richness during the present and Last Glacial Maximum conditions. Finally, we estimated the strength and direction of the co‐occurrence between spadefoot toads and fairy shrimp sampled at the level of entire predicted range and at the regional level (allopatric and sympatric).ResultsFirst, the same abiotic environmental variables shape spadefoot toad and fairy shrimp species' distributions in central and western North America across time. Second, areas of sympatry of Spea bombifrons and Spea multiplicata correspond with dry conditions and higher shrimp richness. Finally, the spatial patterns of predator–prey co‐occurrence are highly variable across geography, forming a spatial mosaic over the species' ranges.Main ConclusionPredator–prey relationships form a spatial mosaic across geography and species ranges. Including biotic interactions into species distribution estimates for organisms with dietary specialization is highly recommended. Biotic interactions can be projected across different time frames for organisms with dietary specialization as they are likely conserved.