Parasites alter community structure

Abstract

Parasites often play an important role in modifying the physiology and behavior of their hosts and may, consequently, mediate the influence hosts have on other components of an ecological community. Along the northern Atlantic coast of North America, the dominant herbivorous snail Littorina littorea structures rocky intertidal communities through strong grazing pressure and is frequently parasitized by the digenean trematode Cryptocotyle lingua. We hypothesized that the effects of parasitism on host physiology would induce behavioral changes in L. littorea, which in turn would modulate L. littorea's influence on intertidal community composition. Specifically, we hypothesized that C. lingua infection would alter the grazing rate of L. littorea and, consequently, macroalgal communities would develop differently in the presence of infected versus uninfected snails. Our results show that uninfected snails consumed 40% more ephemeral macroalgal biomass than infected snails in the laboratory, probably because the digestive system of infected snails is compromised by C. lingua infection. In the field, this weaker grazing by infected snails resulted in significantly greater expansion of ephemeral macroalgal cover relative to grazing by uninfected snails. By decreasing the per-capita grazing rate of the dominant herbivore, C. lingua indirectly affects the composition of the macroalgal community and may in turn affect other species that depend on macroalgae for resources or habitat structure. In light of the abundance of parasites across systems, we suggest that, through trait-mediated indirect effects, parasites may be a common determinant of structure in ecological communities.behavior modification ͉ ecosystem functioning ͉ herbivory ͉ intertidal zone ͉ trait-mediated indirect interactions

Parasitism may enhance rather than reduce the predatory impact of an invader

“…For G. pulex with another acanthocephalan, Pomphorynchus laevis, elevated levels of glycogen (Plaistow et al 2001) and respiratory pigment suggest higher oxygen consumption (Bentley & Hurd 1993). Parasite-driven changes in host trophic interaction strengths have the potential to alter the wider community structure (Hatcher et al 2006;Wood et al 2007). Here, we find that the predatory impact of the invasive G. pulex is enhanced by parasitism.…”

Ants mediate the structure of phytotelm communities in an ant‐garden bromeliad

“…Although such an assumption cannot be verified from our data, further experimental studies addressing this type of hypothesis might help to disentangle the processes underlying the relationships between biological interactions, biodiversity patterns, and ecosystem functioning. Lastly, it is clear that either mutualistic or antagonistic interactions often play an important role in modifying some of the biological traits of the partners (e.g., physiology, morphology, behavior) and may, consequently, mediate the influence hosts have on other components of an ecological community (Wood et al 2007). Although two-species mutualisms (and not only those between plants and insects) are widespread and are found in all ecosystem types, the study of their ecological influences on other community members has mostly been limited to third species (Schmitt andHolbrook 2003, Savage andPeterson 2007), while their influence on the diversity of entire communities (this study) remains largely unexplored.…”

Trematode parasites of Otago Harbour (New Zealand) soft‐sediment intertidal ecosystems: Life cycles, ecological roles and DNA barcodes

“…1). Because trematodes occur at relatively high abundance in intertidal zones, and because of their well-documented impacts on the growth, survival, reproduction and behaviour of their hosts (e.g., Curtis 1987;Huxham et al 1993;Lafferty 1993;Probst & Kube 1999;Ferreira et al 2005;Thieltges 2006), they can be important drivers of host population dynamics, community structure, and foodweb stability (Sousa 1991;Mouritsen & Poulin 2002; Thompson et al 2005;Lafferty et al 2006;Wood et al 2007). …”