Combined effects of intraspecific competition and parasitoid attacks on the dynamics of a host population: a stage‐structured model

Spataro, Thierry; Bernstein, Carlos

doi:10.1111/j.0030-1299.2004.13104.x

Cited by 14 publications

(12 citation statements)

References 45 publications

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“…This theory agrees with Spataro and Bernstein (2004), in that strong parasitised-larval competition enhances stability, despite the major differences between the two models and the experiments from which they were derived (directly competing, mixed populations of parasitised and unparasitised hosts in our model versus unmixed populations). For the Spataro and Bernstein (2004) model the authors claim two important facts. Firstly, that if parasitised hosts are more susceptible to competition than healthy ones, then the Table 2 with c LL 01 )10 (6 and x0c01.…”

Section: Discussionsupporting

confidence: 89%

Population dynamic consequences of parasitised-larval competition in stage-structured host?parasitoid systems

White¹,

Sait²,

Rohani³

2007

Oikos

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Parasitism can influence many aspects of the host's behaviour and physiology, which in turn can have a profound impact on their population and evolutionary ecology. In many host Áparasite interactions there is often a time lag between infection and the death of the host, yet little is known, experimentally or theoretically, about the effects that intra-class competition between parasitised and unparasitised hosts have on the host Á parasite population dynamics.In this article we address this gap in our understanding using a stage-structured mathematical model for a host Áparasitoid interaction, which has been parameterised for the Plodia ÁVenturia experimental system.In the case where parasitised larvae do not compete and do not cannibalise unparasitised larvae, our model predicts a wide range of host Áparasitoid dynamics, ranging from host Áparasitoid generation cycles, to host generation cycles with parasitoid half-generation cycles, to host Áparasitoid equilibria, to host generation cycles with parasitoid extinction.However, when parasitised larvae can compete with their unparasitised larvae counterparts, the host Á parasitoid population dynamics can dramatically change. In particular, we show that high levels of competition exerted by unparasitised larvae upon parasitised larvae is more likely to lead to parasitoid extinction.In addition, we demonstrate that unparasitised host larvae that are sufficiently susceptible to intra-class competition, or parasitised host larvae that are sufficiently strong competitors, can have a stabilising effect on the host Áparasitoid population dynamics.The implications of these theoretical results are discussed in light of our understanding of host Áparasitoid interactions and host Áparasite systems in general.

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Section: Discussionsupporting

confidence: 89%

Population dynamic consequences of parasitised-larval competition in stage-structured host?parasitoid systems

White¹,

Sait²,

Rohani³

2007

Oikos

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“…If host populations are experiencing high levels of resource competition aVecting both individual survival and quality then the parasitoid too will suVer and its population growth rate may fall below zero so that it is unable to invade. This eVect will be exacerbated if parasitised hosts are particularly susceptible to density-dependent mortality, as has been observed in some aphid parasitoid systems (Ives and Settle 1995), though examples exist of interactions where parasitised hosts are at a competitive advantage (Spataro and Bernstein 2004;Cameron et al 2007;White et al 2007). By the time we released parasitoids into our microcosms, aphid densities were already high and intraspeciWc competition severe, and this may have hindered their ability to invade and persist.…”

Section: Discussionmentioning

confidence: 99%

Resource competition and shared natural enemies in experimental insect communities

2008

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Much theory has been developed to explore how competition for shared resources (exploitation competition) or the presence of shared natural enemies (apparent competition) might structure insect and other communities. It is harder to predict what happens when both processes operate simultaneously. We describe an experiment that attempted to explore how shared natural enemies and resource competition structured a simple experimental insect community. Replicated communities were assembled in population cages consisting of the aphid species Acyrthosiphon pisum and Megoura viciae either alone or competing for a resource, their shared host plant Vicia faba. Each combination was set up with and without the parasitoid Praon dorsale which attacked both species of aphid. Population dynamic data show that interspecific resource competition was the dominant process structuring the community. Though juvenile parasitoids could develop successfully inside hosts of both species, they failed to suppress either aphid below their carrying capacities and were unable to persist on one species. We suggest that intense resource competition may reduce the value of individual aphids as hosts for parasitoids such that their population growth rate is less than zero and discuss whether this phenomenon occurs in natural and agricultural communities.

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“…Other experimental studies have shown that parasitoidism may considerably modify the effects of intraspecific competition among hosts [10–15], and theoretical studies have suggested that it can be an important factor in their population dynamics [16–18]. However, the consequences of a modification in the intensity of intraspecific competition by parasitism on parasite virulence and its evolutionary consequences were not explored.…”

Section: Discussionmentioning

confidence: 99%

“…Modifications of the competitive ability of hosts by parasites have been shown to affect the population dynamics of hosts and parasites [17,18]. For example, in our system, in low-prevalence conditions, the strength of intraspecific competition against infected hosts is intense and leads to a large increase in developmental time.…”

Section: Discussionmentioning

confidence: 99%

Prevalence-Dependent Costs of Parasite Virulence

et al. 2005

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Costs of parasitism are commonly measured by comparing the performance of infected groups of individuals to that of uninfected control groups. This measure potentially underestimates the cost of parasitism because it ignores indirect costs, which may result from the modification of the competitiveness of the hosts by the parasite. In this context, we used the host-parasite system consisting of the yellow fever mosquito Aedes aegypti and the microsporidian parasite Vavraia culicis to address this question: Do infected individuals exert a more or less intense intraspecific competition than uninfected individuals? Our experimental results show that, indeed, infected hosts incur a direct cost of parasitism: It takes them longer to become adults than uninfected individuals. They also incur an indirect cost, however, which is actually larger than the direct cost: When grown in competition with uninfected individuals they develop even slower. The consequence of this modification of competitiveness is that, in our system, the cost of parasitism is underestimated by the traditional measure. Moreover, because the indirect cost depends on the frequency of interactions between infected and uninfected individuals, our results suggest that the real cost of parasitism, i.e., virulence, is negatively correlated with the prevalence of the parasite. This link between prevalence and virulence may have dynamical consequences, such as reducing the invasion threshold of the parasite, and evolutionary consequences, such as creating a selection pressure maintaining the host's constitutive resistance to the parasite.

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Combined effects of intraspecific competition and parasitoid attacks on the dynamics of a host population: a stage‐structured model

Cited by 14 publications

References 45 publications

Population dynamic consequences of parasitised-larval competition in stage-structured host?parasitoid systems

Population dynamic consequences of parasitised-larval competition in stage-structured host?parasitoid systems

Resource competition and shared natural enemies in experimental insect communities

Prevalence-Dependent Costs of Parasite Virulence

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