Comparing functional similarity between a native and an alien slug in temperate rain forests of British Columbia

Mariano A Rodriguez-Cabal,M Noelia Barrios-Garcia,Taylor C Gibbons,Gregory M Crutsinger,Patricia M Schulte

doi:10.3897/neobiota.25.8316

Abstract

The impacts of invasive alien species are greatest when they become dominant members of a community, introduce novel traits, and displace native species. Invasions by alien mollusks represent a novel context by which to compare trait differences between generalist native and introduced herbivores in terrestrial ecosystems. Here, we determined the abundance, habitat, feeding preferences, as well as the metabolic rate of the native Pacific banana slug (Ariolimax columbianus) and the alien black slug (Arion rufus) in the coastal forests of British Columbia, Canada. Through a series of observational and experimental studies, we found that alien slugs are more abundant, differ in their habitat preferences, and consumed more fungi (mushrooms) than native banana slugs. Conversely, in an enclosures experiment we found that herbivory damage by native slugs was higher compared to enclosures with alien only and control enclosures. Finally, metabolic rates were similar for both slug species. These results suggest that alien black slugs possess a suite of traits that make them functionally different from native banana slugs.

Highlights

The rampant loss of biodiversity and the spread of alien invasive species are pervasive components of global change (Vitousek et al 1997, Chapin et al 2000, Simberloff et al 2012), and a major priority in ecology is to understand the effects of biological invasions on native communities and ecosystems (Wardle et al 2011, Simberloff et al 2012)
We found that black slugs were ~9× more abundant than banana slugs (GLM on Poisson distribution; χ2 = 263.99, P < 0.0001), and there was a significant interaction between slug type and forest type (Table 1 and Fig. 1)
We found no difference between slug species in the amount of fruit consumed by the slugs in our cafeteria experiment (GLM on binomial proportions; χ2 = 0.01, P = 0.9260)

Summary

Introduction

The rampant loss of biodiversity and the spread of alien invasive species are pervasive components of global change (Vitousek et al 1997, Chapin et al 2000, Simberloff et al 2012), and a major priority in ecology is to understand the effects of biological invasions on native communities and ecosystems (Wardle et al 2011, Simberloff et al 2012). Alien herbivores can modify plant communities by directly affecting plant survival, growth and fitness through browsing, grazing and trampling (Crawley 1986, BarriosGarcia et al 2012) or through indirect effects by altering nutrient cycles, primary productivity, disturbance regimens, and disrupting mutualisms (Williamson 1996, Mack and D’Antonio 1998, Rodriguez-Cabal et al 2013). It remains unclear whether alien herbivores are introducing novel traits and are, functionally different than native herbivores or whether alien herbivores are performing to native herbivores, but have higher abundances. Such functional comparisons are increasingly important given that native terrestrial mollusks have the highest number of documented extinctions of any major taxonomic group, most of which can be directly linked to introduced mollusk species (Lydeard et al 2004, Nash 2004)

Methods

Results

Conclusion