Pathogen transmission is a complex process that scales from allocation of a host's energy to immune defense to contacts between individuals. I'm particularly interested in how heterogeneity in host resources (i.e., food availability) influences wildlife physiology and behavior and how these effects scale up to determine infection spread across landscapes. For many wildlife, interactions between consumers and their resources are being heavily modified by human activities that subsidize animals with novel and abundant food. Both intentional and unintentional forms of "resource provisioning" (e.g., bird feeders and fruit plantations) have been responsible for the emergence of virulent pathogens in wildlife and humans, encouraging a better understanding of how these resource shifts influence infection processes and when and where food supplementation may amplify pathogen transmission. My research combines simple theoretical models, phylogenetic meta-analyses, and field studies of wild bats and birds to better understand how resource provisioning affects pathogen transmission and spillover risks across scales. See below for brief summaries of projects and approaches.
linking consumer–resource and host–pathogen theory
Most epidemiological models ignore bottom-up relationships between hosts and their resource base, but integrating resource dependence into mechanistic frameworks of infection can have serious consequences for the local and spatial spread of pathogens. Past work has shown that resource-dependent host immune defense (i.e., resistance) can prevent pathogen invasion even in the face of resource-improved fecundity, survival, and contact rates. At larger scales, improving a moderate to large proportion of host habitat can allow virulent pathogens to invade a metapopulation and spread across all occupied patches, increasing spillover risk. Continued work in this area is now examining how variation in patch quality influences host colonization rates between habitat types and exploring the consequences for metapopulation persistence and infection dynamics. Future projects also principally aim to better link resource improvement effects on within- and between-patch host processes (e.g., stochastic and spatially explicit models).
resource supplementation and wildlife health
Much of my work on linking infectious disease dynamics and consumer–resource interactions is motivated by the applied example of how human activities accidentally and intentionally subsidize wildlife populations with food. I've used both systematic reviews and meta-analysis to show that substantial variation in decreased or increased infection outcomes from resource provisioning can be attributed to parasite taxonomy and the type of feeding used. More recent work shows that wide-ranging, dietary generalist wildlife species are most prone to experience elevated infection risks with bacteria and viruses when provisioned. I have also collaborated on a large-scale study of how food subsidies impact the health of urbanized white ibis in South Florida, both by assessing chronic stress and by using simple theory and sensitivity analyses to understand processes that allow Salmonella to persist in urbanized ibis flocks.
vampire bat ecology and epidemiology
The common vampire bat is the primary reservoir host of rabies virus throughout Latin America, with this pathogen being spread on a potentially nightly basis when blood-feeding bats feed. Livestock expansion into rainforest habitats could provide vampire bats with an abundant and stable food source, which could decrease stress from starvation and in turn improve antiviral defenses that help resist rabies infection. My PhD work used mark–recapture studies across 10 field sites in Peru and Belize that varied in local densities of livestock prey to explore the consequences of this diet shift for bat stress, immunity, and infection. More intensive laboratory work funded by a NSF DDIG has since used RNA-Seq to quantify differential immune gene expression between study sites that contrast markedly in livestock density and to develop better immunological tools for this important reservoir host species. We are also using population genetics to infer connectivity between bat colonies and to test if and how between-patch movement is influenced by livestock density and distribution. Relationships between resources availability, antiviral defense, and connectivity are being built into a spatially explicit model of vampire bat rabies dynamics using approaches from likelihood-based inference and parameter estimation.
persistence and network dynamics of bacteria in bats
Bats are notorious as important reservoirs for zoonotic viruses, yet we understand far less about their role in the spread of zoonotic bacteria and how such pathogens are maintained in wild populations. I have an emerging interest in understanding the dynamics of two bacterial (and potentially zoonotic) pathogens, Bartonella and hemoplasmas. Infection prevalence within our Belize and Peru vampire bat populations is quite high, ranging from 40% to nearly 100%. We are currently building some simple theory to explore the role that bat–bat contact plays in bacterial transmission (as opposed to vector–bat contact) and more generally building a time series of these infections within Belize to eventually confront models with data. Phylogenetic studies are also exploring the evolution of these bacteria across bat species and examining their zoonotic potential through tree building. I am also interested in testing for evidence of cross-species bacterial transmission in Neotropical bats through phylogenetic comparative approaches and network-based models of pathogen sharing to understand which types of bat species may be most central to transmission within bat communities.
distribution and impact of mercury exposure on bats
Mercury is a widespread contaminant that has neurotoxic effects on many wildlife taxa. Such impacts have been minimally studied in bats, which could be especially prone to negative fitness consequences of chronic mercury exposure owing to their slow life histories and ubiquitousness in contaminated anthropogenic environments. Long-term mercury exposure could also have distinct effects on bat immune defense, as bats may have components of their immune systems that are unique among mammals. Our work in the vampire bat system has shown that even concentrations of mercury considered sublethal correlate with distinct shifts in innate immunity. Ongoing work aims to assess mercury concentrations across a wide range of other Neotropical bat species and to test if this particular immune sensitivity of bat to chronic mercury exposure is a widespread phenomenon throughout the order Chiroptera.