Parasite Facilitates Plant Species Coexistence in a Coastal Wetland

Abstract

Outbreaks of infectious agents in natural ecosystems are on the rise. Understanding host-pathogen interactions and their impact on community composition may be central to the conservation of biological diversity. Infectious agents can convey both exploitive and facilitative effects that regulate host populations and community structure. Parasitic angiosperms are highly conspicuous in many plant communities, and they provide a tractable model for understanding parasite effects in multispecies communities. I examined host identity and variation in host infectivity of a holoparasitic vine (Cuscuta salina) within a California salt marsh. In a two-year parasite removal experiment, I measured the effect of C. salina on its most frequent host, a rare hemiparasite, and the plant community. C. salina clearly suppressed the dominant host, but rare plant fitness and plant species diversity were enhanced through indirect effects. Priority effects played a role in the strength of the outcome due to the timing of life history characteristics. The differential influence of parasites on the fecundity of multiple hosts can change population dynamics, benefit rare species, and alter community structure. The continuum of negative to positive consequences of parasitic interactions deserves more attention if we are to understand community dynamics and successfully restore tidal wetlands.

Parasitism by Cuscuta chilensis and gender affect how the nurse cushion Laretia acaulis increases diversity in Andean alpine communities

“…Thus, our results suggest that C. chilensis , by strongly preferentially infecting Laretia , may suppress the competitive effects of Laretia , which in turn indirectly enhances the facilitative effects of this cushion plant. Our results add to a growing body of work showing that parasitic plants such as Cuscuta can structure plant communities (Pennings & Callaway ; Callaway & Pennings ; Marvier ; Grewell ) and in some cases function as ‘ecological keystone species’ (Watson , , ).…”

Ecology of neotropical mistletoes: an important canopy-dwelling component of Brazilian ecosystems

“…Th is eff ect on host growth and architecture may reduce host photosynthetic effi ciency and alter the respiration rates of the plants (Watling & Press 2001;Cameron et al 2008). In spite of the direct negative eff ect on their hosts through the uptake of resources, parasitic plants have an important role in controlling plant populations (Pennings & Callaway 1996;Marvier 1998;Grewell 2008;Watson 2001;. Th e impact of parasitic plants on a community may be widespread, especially if the most parasitized plant species are dominant, which allows inferior competitors to persist via reduced competition (Press & Phoenix 2005;Grewell 2008).…”

“…In spite of the direct negative eff ect on their hosts through the uptake of resources, parasitic plants have an important role in controlling plant populations (Pennings & Callaway 1996;Marvier 1998;Grewell 2008;Watson 2001;. Th e impact of parasitic plants on a community may be widespread, especially if the most parasitized plant species are dominant, which allows inferior competitors to persist via reduced competition (Press & Phoenix 2005;Grewell 2008). Th ese changes in the host population at the community level occur when the parasitized individuals either die or suff er fi tness reduction ).…”

A holoparasitic plant severely reduces the vegetative and reproductive performance of its host plant in the Caatinga, a Brazilian seasonally dry forest

“…Once parasitic plants have severely reduced host performance, parasitism may lead to changes in competitive interactions between host and non-host plants and impact the community structure, diversity, vegetation cycling and zonation (Pennings & Callaway 2002;Aukema 2003;Grewell 2008;Graffis & Kneitel 2015;Mourão et al 2016). These effects on community structure are often dynamic and may change depending on the performance of the parasite itself or due to environmental conditions (Pennings & Callaway 2002;Press & Phoenix 2005;Grewell 2008;Irving & Cameron 2009;Graffis & Kneitel 2015).…”

“…These effects on community structure are often dynamic and may change depending on the performance of the parasite itself or due to environmental conditions (Pennings & Callaway 2002;Press & Phoenix 2005;Grewell 2008;Irving & Cameron 2009;Graffis & Kneitel 2015). An aggressive parasite can drive a preferred host to local extinction, which may, in turn, result in the local extinction of the parasite (e.g.…”