Varying responses of co-occurring endangered rodents to forest age, human disturbance, and invasive competitors in the Florida Keys

Abstract

Disturbances frequently modify habitat structure, leading to changes in resource availability and species interactions. The Key Largo woodrat (Neotoma floridana smalli) and Key Largo cotton mouse (Peromyscus gossypinus allapaticola) are two endangered subspecies, endemic to the tropical hardwood hammock found in Key Largo, Florida, USA. Both species face a high risk of extinction due to human-induced factors such as habitat loss and introduced invasive species. Following recent anthropogenic and natural disturbances, we sought to examine potential shifts in the interaction between the local abundance of woodrats and cotton mice and differences in habitat use. Using hierarchical N-mixture co-abundance models, we developed three competing models testing varying, constant, or no effects of woodrats on cotton mice while examining environmental drivers that may influence population variation, as well as the effect of invasive black rats (Rattus rattus). We found no interactive effect of woodrats on cotton mice with regression coefficients that had 95 % credible intervals spanning zero, suggesting coexistence with no competitive suppression. In contrast, invasive black rats had a significant negative effect on cotton mice but did not impact woodrats. Habitat associations differed between species as woodrats were positively associated with younger forests, while cotton mice responded positively to various forest age classes, indicating a broader habitat preference than previously suggested. Both cotton mice and woodrats exhibited a positive response with increasing distance from major development, likely reflecting the negative impact of habitat degradation and increasing pressure from invasive species near urban borders. Importantly, our N-mixture co-abundance models performed well with high correlations (r > 0.95) of estimates derived from unmarked data compared to minimum number known alive counts of marked individuals. Together, these results further our knowledge on the interactions and habitat use of woodrats and cotton mice that enable managers to assess both species’ current population status to inform future management strategies that promote species persistence as invasive species continue to shape Key Largo’s landscape.