Abstract
Species interactions are well known to affect species diversity in communities, but the effects of parasites have been less studied. Previous studies on parasitic plants have found both positive and negative effects on plant community diversity. Cuscuta howelliana is an abundant endemic parasitic plant that inhabits California vernal pools. We tested the hypothesis that C. howelliana acts as a keystone species to increase plant species richness in vernal pools through a C. howelliana removal experiment at Beale Air Force Base in north-central California. Vernal pool endemic plants were parasitized more frequently, and Eryngium castrense and Navarretia leucocephala were the most frequently parasitized host plant species of C. howelliana. Cuscuta howelliana caused higher plant species richness, both natives and exotics, compared with removal plots. However, there was no single plant species that significantly increased with C. howelliana removal. Decreases in Eryngium castrense percent cover plots with C. howelliana is a plausible explanation for differences in species richness. In conclusion, C. howelliana led to changes in species composition and increases in plant species richness, consistent with what is expected from the effects of a keystone species. This research provides support for a shift in management strategies that focus on species-specific targets to strategies that target maintenance of complex species interactions and therefore maximize biodiversity and resilience of ecosystems.
Highlights
A host of species interactions within and among trophic levels affects ecological community structure
Of the 1365 parasitized plants, E. castrense and N. leucocephala together made up 84.3 %, of all the individual plants parasitized by C. howelliana
The goal of this study was to evaluate the role of a parasitic plant C. howelliana on the plant species composition of California vernal pools
Summary
A host of species interactions within and among trophic levels affects ecological community structure. Keystone predation increases species diversity by the preferential consumption of dominant competitors and thereby prevents the extinction of inferior competitors (Paine 1966; Mills et al 1993). These effects are documented with various predators (Estes and Palmisano 1974; Mills et al 1993), herbivores (Naiman et al 1986; Bowers et al 1987; Sarnelle 2005) and parasites (Pennings and Callaway 1996; Grewell 2008; Watson 2009; Hatcher et al 2012). Rhinanthus minor, a hemiparasitic plant, decreased diversity of sand
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