why do species co-occur a test of alternative hypotheses describing abiotic differences in sympatry versus allopatry using spadefoot toads为什么物种共现测试替代假设描述非生物同域分布的差异与异域性使用犁足蟾蜍.pdfVIP

Why Do Species Co-Occur? A Test of Alternative Hypotheses Describing Abiotic Differences in Sympatry versus Allopatry Using Spadefoot Toads 1 2 3 Amanda J. Chunco *, Todd Jobe , Karin S. Pfennig 1 Department of Geography, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America, 2 Signal Innovations Group, Inc., Durham, North Carolina, United States of America, 3 Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America Abstract Areas of co-occurrence between two species (sympatry) are often thought to arise in regions where abiotic conditions are conducive to both species and are therefore intermediate between regions where either species occurs alone (allopatry). Depending on historical factors or interactions between species, however, sympatry might not differ from allopatry, or, alternatively, sympatry might actually be more extreme in abiotic conditions relative to allopatry. Here, we evaluate these three hypothesized patterns for how sympatry compares to allopatry in abiotic conditions. We use two species of congeneric spadefoot toads, Spea multiplicata and S. bombifrons, as our study system. To test these hypotheses, we created ecological niche models (specifically using MAXENT) for both species to create a map of the joint probability of occurrence of both species. Using the results of these models, we identified three types of locations: two where either species was predicted to occur alone (i.e., allopatry for S. multiplicata and allopatry for S. bombifrons) and one where both species were predicted to co-occur (i.e., sympatry). We then compared the abiotic environment between these three location types and found