Since introduction into California, plague has spread eastward through the Rocky Mountains. The enzootic cycle is one of near maintenance, where infection does not lead to widespread mortality, while epizootic cycles lead to local extirpations of hosts. We hypothesize that the ecological niche of Yersinia pestis is independent of the ecological niches of host reservoirs, and that enzootic cycles are maintained by mammal species where their ranges overlap with the range of plague. To test this hypothesis, we use Ecological Niche Models (ENMs) and randomization tests to assess niche identity (NI) and niche similarity (NS). NI tests randomly assign point localities from two different taxa to null taxa, and generate associated ENMs to derive a null distribution if niches were identical. NS tests use random localities drawn from a designated background area, and compare similarities of these models to those from the observed geographic space. Point locality data were derived from extensive records of plague infections maintained by the CDC, as well as general mammal occurrence records from natural history museums, and were related to 7 climate layers to generate ENMs using Maxent, with NI and NS measured using ENM Tools.

Results/Conclusions
Initial findings show that NI tests reject identity (P < 0.001) between plague-infected and overall range for Taxidea taxus, Spermophilus spp., and Cynomys spp. NS tests were less conclusive: plague occurrences of T. taxus and Cynomys were not statistically similar to museum data (P < 0.05), but Spermophilus comparisons failed to reject the null hypothesis. Only one test comparing plague-infected ecology with overall occurrences suggested non-similarity, whereas the remaining comparisons failed to reject the null hypothesis of non-similarity. We tentatively conclude that plague niches are independent of the ecology of reservoir species, and that the distribution of plague in North America is not shaped by mammalian host ecology.