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Due to the ongoing expansion of Ixodes scapularis (blacklegged tick) throughout the northeastern and midwestern United States, there is need to identify the role wildlife hosts play in the establishment and maintenance of tick populations. To quantify and synthesize the patterns of I. scapularis and Borrelia burgdorferi sensu stricto and sensu lato prevalence relative to wildlife hosts, we reviewed the findings of independent studies conducted throughout the United States. We performed a comprehensive literature search from 1970 to 2017 using the ISS Web of Science Core Collection and the keywords "Ixodes scapularis," "Ixodes dammini" and "Borrelia burgdorferi." We identified 116 studies for inclusion in our meta-analysis, with 187,414 individual wildlife hosts captured and examined for I. scapularis and either the host or ticks collected subsequently tested for B. burgdorferi. We found that only 13% of the wildlife mammals sampled comprised species other than Odocoileus virginianus (white-tailed deer) and Peromyscus leucopus (white-footed mouse). To examine whether there were regional differences between the Northeast, Midwest and the Southeast U.S. in I. scapularis infestation rates on wildlife hosts, we used general linear models (glm), with post hoc pairwise comparisons. In most cases, detection of I. scapularis and B. burgdorferi was significantly higher in the Northeast than the Midwest. Using data on host-specific I. scapularis infestation prevalence, B. burgdorferi prevalence in feeding larvae, and host permissiveness, we developed an epizootiological model to determine the relative contributions of individual hosts to B. burgdorferi-infected nymphs. Our model provides additional evidence that wildlife hosts other than P. leucopus may contribute more to Lyme disease risk than commonly thought. To aid in understanding the ecology of Lyme disease, we propose that additional studies sample non-Peromyscus spp. hosts to obtain more detailed tick and pathogen infestation and infection estimates, respectively, for these less frequently sampled wildlife hosts.

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Metapopulation viability depends upon a balance of extinction and colonization of local habitats by a species. Mechanisms that can affect this balance include physical characteristics related to natural processes (e.g. succession) as well as anthropogenic actions. Plant restorations can help to produce favorable metapopulation dynamics and consequently increase viability; however, to date no studies confirm this is true. Population viability analysis (PVA) allows for the use of empirical data to generate theoretical future projections in the form of median time to extinction and probability of extinction. In turn, PVAs can inform and aid the development of conservation, recovery, and management plans. Pitcher's thistle (Cirsium pitcheri) is a dune endemic that exhibited metapopulation dynamics. We projected viability of three natural and two restored populations with demographic data spanning 15-23 years to determine the degree the addition of reintroduced population affects metapopulation viability. The models were validated by comparing observed and projected abundances and adjusting parameters associated with demographic and environmental stochasticity to improve model performance. Our chosen model correctly predicted yearly population abundance for 60% of the population-years. Using that model, 50-year projections showed that the addition of reintroductions increases metapopulation viability. The reintroduction that simulated population performance in early-successional habitats had the maximum benefit. In situ enhancements of existing populations proved to be equally effective. This study shows that restorations can facilitate and improve metapopulation viability of species dependent on metapopulation dynamics for survival with long-term persistence of C. pitcheri in Indiana likely to depend on continued active management.

A better understanding of the mechanisms through which host diversity can influence reservoir pathogen infection is needed to mitigate disease risk. Efforts may involve computational modeling, especially since it is infeasible to perform large‐scale experimental studies of different host composition scenarios in natural settings. We used individual‐based models to examine how changes in host diversity characterized by differences in host reservoir competency for both Ixodes scapularis and Borrelia burgdorferi can influence the maintenance of the pathogen and subsequent human Lyme disease risk. We simulated 1440 different host communities, with 10 repetitions each, consisting of varying densities of Peromyscus leucopus (white‐footed mouse, 0–50), Tamias striatus (eastern chipmunk, 0–30), Blarina brevicauda (short‐tailed shrew, 0–30), Sciurus carolinensis (eastern gray squirrel, 0–15), and Didelphis virginiana (Virginia opossum, 0–2). We then quantified support for three mechanisms (i.e., vector regulation, encounter reduction, and transmission reduction) through which biodiversity–disease relationships occurred using species richness, Shannon H diversity, and host abundance. For each of the dilution effect mechanisms, host abundance was consistently the best‐supported predictor of disease risk. In our model, a dilution effect occurred via vector regulation and transmission reduction, where increasing both species richness and host abundance reduced both density of nymphs (DON) and density of infected nymphs (DIN). However, if disease risk is measured solely by calculating nymphal infection prevalence (NIP), it may seem that host diversity amplifies disease risk. Understanding the mechanisms through which the wildlife host community influences pathogen transmission cycles in nature will help foster effective control and reduction of disease risk in humans.

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