Abstract
Parasites play pivotal roles in structuring communities, often via indirect interactions with non-host species. These effects can be density-mediated (through mortality) or trait-mediated (behavioural, physiological and developmental), and may be crucial to population interactions, including biological invasions. For instance, parasitism can alter intraguild predation (IGP) between native and invasive crustaceans, reversing invasion outcomes. Here, we use mathematical models to examine how parasite-induced trait changes influence the population dynamics of hosts that interact via IGP. We show that trait-mediated indirect interactions impart keystone effects, promoting or inhibiting host coexistence. Parasites can thus have strong ecological impacts, even if they have negligible virulence, underscoring the need to consider trait-mediated effects when predicting effects of parasites on community structure in general and biological invasions in particular.
Highlights
There is an increasing realization that parasitism can play as pivotal a role as predation in structuring biological communities, often via indirect interactions with non-host species [1,2]
Indirect interactions can be driven by trait changes, which may be as important for community structure and function [3,4,5]
Trait-mediated interactions may be relevant in parasite –host systems because parasites frequently modify host behaviour or physiology [6,7] and have been implicated as drivers behind a range of biological invasions, including wild oat (Avena fatua) in California, fire ants (Solenopsis invicta) in North America and amphipod crustaceans (Gammarus) in UK freshwaters [6,8]
Summary
There is an increasing realization that parasitism can play as pivotal a role as predation in structuring biological communities, often via indirect interactions with non-host species [1,2]. Indirect interactions can be driven by trait changes, which may be as important for community structure and function [3,4,5]. The invasive amphipod Gammarus pulex is a strong intraguild predator; parasitic infection alters both attack rates for intraguild predators and consumption of intraguild prey. Echinorhynchus truttae (Acanthocephala) infection increases maximal predation rates (functional responses) of G. pulex on native prey by 30% [10], but IGP on the native G. duebeni is nearly halved ( prey mortality data [8]). Pleistophora mulleri (Microspora) infection of native G. duebeni reduces predation on smaller invasive G. tigrinus two- to threefold but doubles their vulnerability to predation by G. pulex [11]
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