Community composition can impact parasite transmission in host communities through mechanisms involving host species abundance, variation in species competency (the ability to acquire and transmit the parasite), and interspecific interactions. Larval amphibian communities represent discrete units to study how the competence of a community influences the transmission of a multi-host parasite. Moreover, declines of amphibians have been attributed to the spread of ranavirus, elevating the importance of understanding how community composition influences risk of transmission and associated host mortality. We characterized community structure in larval amphibian communities using observations from 20 wetlands over 6 months. By applying viral load data for 12 amphibian species positive for ranavirus, we then calculated community competence for each wetland-month combination and related this to dynamics of ranavirus prevalence, finding community competence to be associated with prevalence. Motivated by the ranavirus dataset, we developed a transmission model for ranavirus in a community of two host species with different competencies for ranavirus. We used the model to clarify how community competence promotes parasite invasion potential differently depending on the relative amount of contact vs environmental transmission (an open question in ranavirus disease ecology), and on potential associations between competency and other host life history traits (the ‘ecoimmunological pace-of-life hypothesis’) using a next-generation matrix method to calculate the community parasite basic reproductive number.
Results/Conclusions
Our analysis of the data showed that community competence is positively correlated with prevalence over time lagged by one month, representing a potential priming of a community due to its recent, prior community composition. Analysis of our model demonstrated how community competence plays a pivotal role in the ability for a parasite to invade, including separate effects of community abundance and average competence. Modeling also revealed that either contact or environmental transmission could compensate for transmission deficiencies in the other, and that the efficiency of this compensation was directly related to the half-life of free-infectious viral material in the environment. The model also demonstrated that with increasing environmental transmission, the importance of community composition was diminished. Further, model results suggested that potential ‘ecoimmunology’ tradeoffs are most important in competent species in terms of community susceptibility to parasite invasion.