COS 35-3
Trophically transmitted parasites in size-structured predator-prey systems
Food web science has recently advanced by considering: (1) the importance of size structure for predator-prey interactions and (2) the importance of parasites for food web structure. However, these aspects have not been previously combined in community dynamical settings. Here we formulate and analyze models that simultaneously address the importance of size structure and parasitism for community dynamics. We include the structural aspect of host energetics in free-living populations in the context of predator-prey and competitor interactions, as well as the structural aspect of parasite infection. The ecological role of parasites in food web composition has become particularly clear from estuarine systems with trematode parasites, where parasite biomass can dominate top-predator biomass and trematodes exhibit complex life cycles, energetically linking different trophic levels and independent system components. The importance of parasites at the food web level comes from food web topologies and standing stock biomass data, i.e., static information. Less is known about the dynamic impact of such parasites on community structure and trophic interactions. This study seeks to address this knowledge gap by generating dynamical models that capture important aspects of the parasite life cycles and their interactions with hosts, additionally incorporating host population size and energetic structure.
Results/Conclusions
The models presented here reflect two components of the ecological community and describe 1) a snail host with a castrating trematode parasite and a crab predator; and 2) a killifish host with a behavior modifying trematode parasite and predation by birds, which is essential for the completion of the parasite life cycle. These modules together comprise a generalized representation of the core of a well-described estuarine food web. We present the conditions for host persistence, in particular when competing with non-host consumers. The impact of host-predation markedly affects the prevalence of parasitic infection in the snail host population, while at the same time parasite infection impacts the availability of prey for the predator. Explicitly accounting for host size-/ stage-structure results in the occurrence of alternative stable system states, including and excluding top predators. Overall, we explicitly compare four system settings: 1) including parasites and their energetic impact on their hosts; 2) including within host population size-structure; 3) including both parasites and host population structure; and 4) excluding all complexity. This combination of the integrated effects of population structure and parasitism is generalizable and can inform our understanding of food web dynamics in other systems.