Habitat-based constraints on food web structure and parasite life cycles

Abstract

Habitat is frequently implicated as a powerful determinant of community structure and species distributions, but few studies explicitly evaluate the relationship between habitat-based patterns of species' distributions and the presence or absence of trophic interactions. The complex (multi-host) life cycles of parasites are directly affected by these factors, but almost no data exist on the role of habitat in constraining parasite-host interactions at the community level. In this study the relationship(s) between species abundances, distributions and trophic interactions (including parasitism) were evaluated in the context of habitat structure (classic geomorphic designations of pools, riffles and runs) in a riverine community (Raritan River, Hunterdon County, NJ, USA). We report 121 taxa collected over a 2-year period, and compare the observed food web patterns to null model expectations. The results show that top predators are constrained to particular habitat types, and that species' distributions are biased towards pool habitats. However, our null model (which incorporates cascade model assumptions) accurately predicts the observed patterns of trophic interactions. Thus, habitat strongly dictates species distributions, and patterns of trophic interactions arise as a consequence of these distributions. Additionally, we find that hosts utilized in parasite life cycles are more overlapping in their distributions, and this pattern is more pronounced among those involved in trophic transmission. We conclude that habitat structure may be a strong predictor of parasite transmission routes, particularly within communities that occupy heterogeneous habitats.

Where are the parasites in food webs?

“…Some specific examples include the blackwater streams of New Jersey where the food web has 62 free-living species and 11 parasitic helminths [8,19,20]. At other locations in New Jersey, food webs in the Raritan River have 116 free living species and 21 parasites; and food webs in the Tuckerton salt marshes contain 92 free-living species and 16 parasites [21,22]. Some studies report greater proportions of parasites in food webs, e.g., in foodwebs from Carpinteria marsh (US) [23], tidal marshes in the Meadowlands (US) [24] or the Ythan estuary (Europe) [9].…”

“…Total biomass for each species was measured for 8 consecutive seasons to determine biomass fluctuations used to calculate unreliability scores. Rossiter 2012 [22] found that parasitized hosts were among those hosts with the lowest unreliability scores. The parasitized host with the highest unreliability score (arrow) is a seasonal frog species.…”

Niche construction: evolutionary implications for parasites and hosts

“…indirect life cycles, environmental heterogeneity may lead to spatial associations of definitive and intermediate hosts [29].…”

The Intestinal Parasites of an Assemblage of Stream Fishes in Central Utah

“…Parasites with complex life cycles (like the 2 species we found) use trophic webs as a route of transmission between fish hosts (Timi et al 2011, Rossiter andSukhdeo 2014). By exploiting predator interactions in an aquatic system, parasites can evolve transmission tactics and promote host range expansion (Strona 2015).…”