Do dense layers of invasive plants elevate the foraging intensity of small mammals in temperate deciduous forests? A case study from Pennsylvania, USA

Ryan M Utz,Alysha Slater,Walter P Carson,Hannah R Rosche

doi:10.3897/neobiota.56.49581

Abstract

Monospecific stands of invasive plants can dramatically restructure habitat for fauna, thereby elevating population densities or promoting foraging of consumer species who benefit in the altered habitat. For example, dense stands of invasive plants may protect small mammals from predators, which in turn could increase foraging pressure on seeds that small mammals feed upon. We used a before-after, control-impact experimental design to test whether small mammal capture rates were higher and giving-up densities (GUDs) lower beneath dense stands of Berberis thunbergii, an invasive shrub with a rapidly expanding range throughout eastern North America. Our experimental design included three plot categories: 1) plots heavily invaded by B. thunbergii, 2) control plots lacking invasive shrub cover, and 3) invaded plots where we eradicated B. thunbergii midway through the study. Although our overall small mammal capture rate was low, small mammal captures were 65% higher in B. thunbergii invaded habitat relative to control plots and eradication lowered capture rates by 77%. GUDs were also 26% higher within B. thunbergii relative to control plots and eradication decreased GUDs by 65%. Our findings suggest that small mammals perceive dense stands of B. thunbergii as relatively safe foraging habitat. Prior surveys within our study locations revealed dramatically depressed tree seedling densities under B. thunbergii, thus invasive plants may promote intensive foraging by small mammals and reduce recruitment for species with foraged seeds or seedlings.

Highlights

Nonnative plant species that become invasive frequently form dense, nearly monospecific layers that can cause substantial declines in native plant species abundance and diversity
We cannot rule out the possibility that the activity of removing barberry itself altered the behavior activity of small mammals after the event, dependent variables in control plots lacking barberry were nearly identical to barberryremoved plots during the second half of the field season
Our findings highlight the potential for elevated foraging intensity in a key faunal assemblage resulting from invasive plants that form recalcitrant understories

Summary

Introduction

Nonnative plant species that become invasive frequently form dense, nearly monospecific layers that can cause substantial declines in native plant species abundance and diversity. Any reduction in the diversity and abundance of native plant species could be caused by habitat-mediated predation rather than interspecific resource competition between exotics and natives (e.g., Royo and Carson 2005, 2008; Durra et al 2011). Both experimental (Dutra et al 2011) and observational (Mattos et al 2010) studies have demonstrated that dense layers of the invasive Amur honeysuckle (Lonicera maackii) protected small mammals from predators, thereby resulting in elevated foraging event frequencies. We focus on one of the most widespread and pernicious invaders, Japanese barberry, and evaluate whether barberry creates privileged foraging grounds across three different urban forests using a rigorous BACI experimental design (see below)

Methods

Results

Discussion

Conclusion