Transmission patterns that reduce population size without increasing disease prevalence: masting and chronic wasting disease in white-tailed deer

Abstract How individuals use space and, thus, the rate and the nature of their interactions with others are shaped by their environment. Exogenous changes that alter aggregation patterns, such as resource pulses, can therefore have a significant impact on seemingly unrelated processes like disease spread. White-tailed deer ( Odocoileus virginianus ) aggregate in oak forests during mast events, and chronic wasting disease (CWD) transmission patterns vary with deer density, so we hypothesize a link between the masting cycle and CWD dynamics. We investigate various possible effects of masting on deer, including shifts to more frequency-dependent CWD transmission due to aggregation, as well as elevated fecundity and decreased mortality of deer in response to the resource pulse, using a simplified compartment model of CWD spread. When masting affects epidemiological parameters, including the strength of frequency dependence in CWD transmission, disease spread during masting events significantly reduces the size of deer populations but, paradoxically, without any change in the proportion of the population in the CWD-diseased state. In contrast, demographic parameters were found in principle to be capable of altering both population size and disease incidence, though the observed effects were very small. While our quantitative findings should be validated using more detailed models of CWD transmission before they are taken as specific predictions about this system, our fundamental qualitative result appears to be quite general. That is, our conclusion that epidemiological rates only influence population size, but demographic rates may affect both population size and disease incidence, can be derived not only from the model we studied but also from classical epidemiological models as well. Our work extends the understanding of the far-reaching impacts of resource pulses through ecological communities by highlighting the vastly different consequences of the same resource pulse acting in different ways.