Abstract
Comparing cases of parasitism and predation that lead to victim death,
parasites need more time to complete victim exploitation. This longer
“interaction durability” delays energy transfer from host to parasite.
During exploitation, parasite virulence differentiates the infected from
the susceptible host dynamics. However, how this parasite characteristic
influences the dynamics of their host and nonhost (insusceptible)
species in the same community is largely unknown. Here, we use
mathematical modelling to investigate the influence, exemplifying an
experimental plankton community. In this community, nonhost zooplankton
feeds on edible nonhost phytoplankton (resource competitor of the host)
and parasite propagules released from infected inedible phytoplankton
(“mycoloop” pathway). To assess the effects of parasite-host
durability, we contrast parasite-host implementations as Lotka-Volterra
predator-prey interaction (immediate energy transfer) with
susceptible-infected (SI) host-parasite interactions. For the latter,
parasite energy intake depends on infected host density but not
susceptible hosts directly (delayed transfer). We further consider the
difference between susceptible and infected host dynamics modulated by
parasite virulence via its effect on host nutrient uptake. To assess the
within-community effects, subcommunities are also investigated,
excluding/including the parasite without/with the mycoloop. Our results
show that, besides host elimination, longer interaction durability of
the host-parasite interaction delays parasite attacks on susceptible
hosts, allowing them to increase further (a hydra effect), independent
of parasite virulence level. This effect observed in the isolated
host-parasite systems is preserved in larger communities with negative
consequences for the nonhost species, independent of the mycoloop. These
theoretical results are supported by empirical observations within and
beyond plankton realms. Our study reveals distinctive influences of
parasites on community shot-term dynamics, which stem from the longer
interaction durability.