Hosts as ecological traps for the vector of Lyme disease.

Vectors of infectious diseases are generally thought to be regulated by abiotic conditions such as climate or the availability of specific hosts or habitats. In this study we tested whether blacklegged ticks, the vectors of Lyme disease, granulocytic anaplasmosis and babesiosis can be regulated by the species of vertebrate hosts on which they obligately feed. By subjecting field-caught hosts to parasitism by larval blacklegged ticks, we found that some host species (e.g. opossums, squirrels) that are abundantly parasitized in nature kill 83-96% of the ticks that attempt to attach and feed, while other species are more permissive of tick feeding. Given natural tick burdens we document on these hosts, we show that some hosts can kill thousands of ticks per hectare. These results indicate that the abundance of tick vectors can be regulated by the identity of the hosts upon which these vectors feed. By simulating the removal of hosts from intact communities using empirical models, we show that the loss of biodiversity may exacerbate disease risk by increasing both vector numbers and vector infection rates with a zoonotic pathogen.

Interactions between mammals and trees: predation on mammal-dispersed seeds and the effect of ambient food.

The Janzen-Connell escape hypothesis predicts that the success of tree propagules increases with distance from the parent tree. Fleshy fruits that are transported in the guts of frugivores are believed to have evolved to facilitate the wide dispersal of seeds. However, some frugivores deposit seeds in latrines, thus creating aggregations of seeds that are large enough to attract seed predators and negate the advantages of dispersal. Raccoons (Procyon lotor) often produce large seed deposits since they habitually defecate in latrines. The survival of wild black cherry (Prunus serotina) seeds in simulated raccoon latrines was monitored in areas with natural levels of food availability and in areas to which supplemental food had been supplied to the primary seed predators. Dispersal of seeds by raccoons did not necessarily provide effective protection from post-dispersal seed predation at natural food levels. Once the resident seed predators had located the latrines, the majority of the seeds were quickly removed. However, seed removal from raccoon latrines was reduced significantly and dramatically by the addition of alternative food. This implies that raccoon latrines may represent safe sites for tree recruitment during periods of high food availability such as during masting events, thus providing conditional support for the escape hypothesis.