écologie des virus influenza aviaires en Camargue - IRD

Annexe 2Ecology of ecosystems and parasites: a recent storyAlthough parasites were virtually ignored for decades by ecologists, considerableefforts have been made over the past 15 years to understand their functional importance inecosystems [1­5]. Although easy to overlook, parasites can sometimes account for asignificant portion of total biomass in natural ecosystems [6]. Most, if not all, ecologists andconservation biologists are now aware that the introduction or elimination of a parasite in anecosystem can strongly affect the interactions between a diverse range of species in thecommunity, and hence affect biodiversity [7]. Most studies concern apparent competitionphenomena – that is, how shared parasites impact on diversity by mediating competitionbetween different host species (Box 1) – and food webs [8,9].Very recently, interest in the relationship between ecosystem functioning andparasites has stimulated exploration in other directions, focusing in particular on the socalledcategory of ‘manipulative parasites’ (see Glossary). A wide range of protozoan andmetazoan parasites indeed manipulate the phenotype (e.g. behaviour, morphology and/orphysiology) of their hosts in a way that favours their own transmission (Figure 1). Thesealterations can vary greatly in their magnitude, from slight shifts in the percentage of timespent performing a given activity (e.g. biting rate in Leishmania­infected sandflies [10]) tothe production of complex and spectacular behaviours (e.g. Figure 1e) [11,12].While manipulative parasites have been traditionally approached from the viewpointof parasitology, they now constitute a common research area of interest to bothparasitologists and ecologists. Understanding their importance significantly contributes toexpanding our knowledge of the pivotal role of parasites in ecosystems. Manipulated hostscan be seen as complex organisms since they keep some of the properties and attributes ofuninfected individuals but they also display new characteristics, involving them in noveldirect and indirect interactions with other species and/or conspecifics. Because of thissingularity, manipulative parasites have unusual ecological effects compared with ‘regular’parasites (i.e. parasites that do not manipulate their host). Our primary purpose is to reviewevidence for these original consequences. We also outline future research needs to advanceour understanding of this emerging topic.194