**Abstract**

Climate change and habitat loss alter the landscape for wildlife, resulting in shifts in geographic ranges, occupation of smaller, remnant habitat patches, or use of novel environments. These processes often lead to sympatry between species that historically were non-sympatric. Such interactions increase competition for resources and expose species to novel parasites that reduce a species' fitness leading to wildlife declines. We explore these interactions in species of endangered North American rodents—Northern flying squirrels (*Glaucomys sabrinus*) and Allegheny woodrats (*Neotoma magister*). Northern flying squirrels are declining in the United States due to competition with its congener, southern flying squirrels (*Glaucomys volans*). Evidence indicates that competition is mediated by a shared nematode, *Strongyloides robustus*. Transmission of this nematode to northern flying squirrels is increasing due to forest fragmentation and climate change. We also note the recent discovery of *S. robustus* as a novel parasite and a factor in the decline of the European red squirrel (*Sciurus vulgaris*). Likewise, in Allegheny woodrats, shrinking landscape changes have resulted in increased range overlap with raccoons (*Procyon lotor*) that harbor a nematode fatal to woodrats. The subsequent transmission of this nematode, *Baylisascaris procyonis*, to woodrats is a contributing factor to woodrat decline throughout the Appalachians.

**Keywords:** Allegheny woodrat, flying squirrels, Eastern gray squirrels, *Baylisascaris*, *Strongyloides*

### **1. Introduction**

Global climate change and human-induced habitat loss alter the landscape for native wildlife, resulting in shifts in geographic ranges, occupation of smaller, remnant habitat patches, or use of novel or new environments. These processes often lead to sympatry between species that historically occupied non-overlapping ranges and habitats. Such interactions may result in increased competition for resources and expose species to novel parasites that adversely affect a species' fitness leading to wildlife declines. For example, if the distribution of a host species shifts, so too will the distribution of its parasites. Therefore, in some ecosystems, invasive and endemic hosts may experience new parasites which may be pathogenic to naïve hosts [1, 2].

Species may shift their distribution as a response to changing climate but some species also may be introduced incidentally or purposefully by human activities – resulting in similar novel host-parasite interactions [3]. For instance, global trade, transport, and the introduction of exotic species likely facilitates parasite-mediated competition between species. These trends may worsen under climate change because new species assemblages may occur, thus creating opportunities for parasite exchange. When previously allopatric host species come into sympatry, novel host–parasite interactions may emerge if parasites are able to successfully infect newly exposed hosts [4]. These parasitic 'co-invaders' may mediate the impacts of biological introductions by potentially amplifying transmission to native species [3]. However, evaluating threats from introduced parasites to native wildlife is difficult due to limited information associated with distribution shifts or introductions [5]. Complicating these interactions, climate change may alter parasite survival, development rates, and periods of transmission between intermediary hosts [2]. We explore these interactions and concurrent species declines in several species of wild rodents demonstrating conservation challenges in a globalizing planet experiencing climate change.
