The significance of small herbivores in structuring annual grassland

Abstract

Question: Herbivores can play a fundamental role in regulating the composition and structure of terrestrial plant communities. Relatively inconspicuous but nevertheless ubiquitous gastropods and small mammals are usually considered to influence grassland communities through distinct modes. 1. Do terrestrial gastropods and small mammals, either alone or in combination, influence plant community composition of an intact annual grassland? 2. Do these herbivores influence the plant size structure of the dominant grass Avena? Location: Jasper Ridge Biological Preserve (37°24’ N, 122° 13’ W, elevation 150 m) in northern California. Methods: Animal exclosures were used to examine the single and combined influences of these herbivores on annual grassland production, community composition, and plant size structure during the growing season of an intact annual grassland. Results: The removal and exclusion of the herbivores increased the prevalence of grasses relative to legumes and non‐legume forbs; increased total production of above‐ground plant biomass; and increased mean plant size and exacerbated size hierarchies in populations of Avena. The effect of both gastropods and small mammals, alone and in combination, was characterized by temporal oscillations in the relative dominance of grasses in plots with vs. without herbivores. Conclusions: Both groups of herbivores are important controllers of California annual grassland that exert similar influences on production and composition. While other factors appear to determine the absolute number of individuals in this plant community, selective consumption of grasses by gastropods and small mammals partially offsets the competitive advantages associated with their early germination.

Cryptic seedling herbivory by nocturnal introduced generalists impacts survival, performance of native and exotic plants

“…A priori, we might predict that introduced generalist herbivores will have greater impacts on evolutionarily naı¨ve native plant species than on introduced ones. However, a few recent studies have found no consistent relationship between introduced and native status and palatability to introduced mollusks (Buschmann et al 2005a, b, Holland et al 2007, Peters 2007.…”

“…1 E-mail: systrauss@ucdavis.edu and Kaufman 1975, Verling et al 2005). The impacts of these introduced generalists on populations of native and introduced plant species have only recently been studied (Keane and Crawley 2002, Holland et al 2007, Peters 2007. Introduced plant species that share an evolutionary history with particular generalists in their native habitat may possess traits that enable them to coexist with these herbivores.…”

Trade‐off between early emergence and herbivore susceptibility mediates exotic success in an experimental California plant community

“…Exclusion experiments have shown that herbivores, particularly small mammals, exert strong control over plant productivity in herbaceous communities in Mediterranean-climate regions (Peters, 2007). In these ecosystems, there is often little herbaceous vegetation suitable for consumption prior to the arrival of seasonal rains, meaning individuals that emerge first may initially represent the only herbaceous vegetation available to consumers and are also likely to be highly apparent and accessible in the landscape (Wainwright et al, 2012).…”

Herbivory of an invasive slug is affected by earthworms and the composition of plant communities

“…Gastropods (slugs and snails) influence the species composition and relative abundance of plant communities by selectively grazing certain plant species [32-38]. Slug grazing has been shown to shift plant competition in mixed swards and influencing the uptake and partitioning of nutrients among plants [39].…”