Plant diversity, herbivory and resistance of a plant community to invasion in Mediterranean annual communities

Abstract

Several components of the diversity of plant communities, such as species richness, species composition, number of functional groups and functional composition, have been shown to directly affect the performance of exotic species. Exotics can also be affected by herbivores of the native plant community. However, these two possible mechanisms limiting invasion have never been investigated together. The aim of this study was to investigate the relationships between plant diversity, herbivory and performance of two annual exotics, Conyza bonariensis and C. canadensis, in Mediterranean annual communities. We wanted to test whether herbivory of these exotics was influenced either by species richness, functional-group richness or functional-group composition. We also studied the relationship between herbivory on the exotic species and their performance. Herbivory increased with increasing species and functional-group richness for both Conyza species. These patterns are interpreted as reflecting a greater number of available herbivore niches in a richer, more complex, plant community. The identities of functional groups also affected Conyza herbivory, which decreased in the presence of Asteraceae or Fabaceae and increased in the presence of Poaceae. Increasing herbivory had consequences for vegetative and demographic parameters of both invasive species: survival, final biomass and net fecundity decreased with increasing herbivory, leading to a loss of reproductive capacity. We conclude that communities characterised by a high number of grass species instead of Asteraceae or Fabaceae may be more resistant to invasion by the two Conyza species, in part due to predation by native herbivores.

Impacts of the invasive exotic Prosopis juliflora (Sw.) D.C. on the native flora and soils of the UAE

“…Several studies have shown that the ecological impacts of invasive plants include displacement of indigenous species and declines in species richness and diversity (e.g., Lonsdale 1999;Brooks and Pyke 2001;Kedzie-Webb et al 2001;Lesica and Miles 2001;Prieur-Richard et al 2002;Badano and Pugnaire 2004;Hoffmann et al 2004). The present study showed a great depressive effect of the invasive P. juliflora on the number, richness, evenness, density and frequency of the associated native species.…”

“…For example, in Florida, about 39-64% of the invasive exotic species has potentially altered ecosystem properties including geomorphology, hydrology and biogeochemistry (Gordon 1998). In addition, several recent investigations have shown that invasive plants have changed several community attributes including species diversity, richness, species composition and abundance (Prieur-Richard et al 2002;Collier et al 2002;Badano and Pugnaire 2004;Hoffmann et al 2004). For example, Lockhart et al (1999) showed that the invasive Cupaniopsis anacaudioides significantly reduced species richness in Florida.…”

Restoration of Themeda australis swards suppresses soil nitrate and enhances ecological resistance to invasion by exotic annuals

“…This can involve mechanisms that directly suppress the invader, such as the secretion of growthlimiting chemicals (allelopathy; e.g. Hobbs and Atkins 1991), or selective herbivory (Maron and Vila 2001;Prieur-Richard et al 2002). More commonlystudied mechanisms involve the pre-emption of resources such as moisture, nutrients and/or light (Dukes 2001; Thomsen and D'Antonio 2007), such that a potential invader has insufficient resources for establishment or persistence (competitive resistance, D'Antonio and Thomsen 2004;D'Antonio and Chambers 2006).…”

Phylogenetic diversity of plants alters the effect of species richness on invertebrate herbivory

“…Attempts to include more of the natural complexity of plant communities to understand community herbivory include using functional diversity in addition to plant species richness (Siemann et al, 1998; Koricheva et al, 2000; Prieur-Richard, Lavorel & Linhart, 2002; Scherber et al, 2006; Scherber et al, 2010b) reducing species composition to low dimensional quantitative measures using ordination (Koricheva et al, 2000; Pfisterer, Diemer & Schmid, 2003; Schaffers et al, 2008), and incorporating information about plant species’ evolutionary history, using community phylogenetics. Here, I explore the use of community phylogenetics to understand insect herbivory at the plant community level.…”