Scale-dependent effects of nonnative plant invasion on host-seeking tick abundance.

Solny A Adalsteinsson,Vincent D'Amico,Dustin Brisson,Jeffrey J Buler,W Gregory Shriver,D P C Peters

doi:10.1002/ecs2.1317

Abstract

Nonnative, invasive shrubs can affect human disease risk through direct and indirect effects on vector populations. Multiflora rose (Rosa multiflora) is a common invader within eastern deciduous forests where tick-borne disease (e.g. Lyme disease) rates are high. We tested whether R. multiflora invasion affects blacklegged tick (Ixodes scapularis) abundance, and at what scale. We sampled host-seeking ticks at two spatial scales: fine-scale, within R. multiflora-invaded forest fragments; and patch scale, among R. multiflora-invaded and R. multiflora-free forest fragments. At a fine scale, we trapped 2.3 times more ticks under R. multiflora compared to paired traps 25 m away from R. multiflora. At the patch scale, we trapped 3.2 times as many ticks in R. multiflora-free forests compared to R. multiflora-invaded forests. Thus, ticks are concentrated beneath R. multiflora within invaded forests, but uninvaded forests support significantly more ticks. Among all covariates tested, leaf litter volume was the best predictor of tick abundance; at the patch scale, R. multiflora-invaded forests had less leaf litter than uninvaded forests. We suggest that leaf litter availability at the patch-scale plays a greater role in constraining tick abundance than the fine-scale, positive effect of invasive shrubs.

Highlights

We tested the following: 1) whether I. scapularis abundance differs under R. multiflora compared with other shrub species or open understory within the same forest patch; and 2) whether I. scapularis abundance differs between R. multiflora-invaded forest fragments and forest fragments without R. multiflora invasion
The lack of leaf litter in R. multiflora-invaded forest fragments creates an inhospitable environment for ticks, from which they are rescued by invasive shrubs with dense growth forms (e.g., Williams et al 2009)
We found more than four times the volume of leaf litter in uninvaded forest fragments compared with R. multiflora-invaded forest fragments (P < 0.01), and there was no difference in leaf litter volume between paired points within invaded forests

Summary

Introduction

Dense understory structure is used preferentially by host animals (e.g., white-tailed deer, Odocoileus virginianus) that are important to tick reproduction and survival (Allan et al 2010) Both of these mechanisms (improved microclimate and increased host use) support a potential positive association between I. scapularis abundance and the presence of nonnative, invasive shrubs. There is a critical need to determine whether fine-scale habitat associations between invasive shrubs and ticks create larger vector populations at broad enough scales to increase human disease risk (Allan et al 2010). Nonnative plant invasion may increase tick abundance at a fine scale within a given forest patch, but it is unclear whether this would produce a larger vector population at a landscape scale relevant to human disease risk. We tested the following: 1) whether I. scapularis abundance differs under R. multiflora compared with other shrub species or open understory within the same forest patch; and 2) whether I. scapularis abundance differs between R. multiflora-invaded forest fragments and forest fragments without R. multiflora invasion

Methods

Results

Discussion

Findings

Conclusions and Future Directions

Literature Cited