Stable Isotopes of C and N Reveal Habitat Dependent Dietary Overlap between Native and Introduced Turtles Pseudemys rubriventris and Trachemys scripta

Steven H Pearson,Harold W Avery,James R Spotila,David J Velinsky,Susan S Kilham,David L Roberts

doi:10.1371/journal.pone.0062891

Abstract

Habitat degradation and species introductions are two of the leading causes of species declines on a global scale. Invasive species negatively impact native species through predation and competition for limited resources. The impacts of invasive species may be increased in habitats where habitat degradation is higher due to reductions of prey abundance and distribution. Using stable isotope analyses and extensive measurements of resource availability we determined how resource availability impacts the long term carbon and nitrogen assimilation of the invasive red-eared slider turtle (Trachemys scripta elegans) and a native, threatened species, the red-bellied turtle (Pseudemys rubriventris) at two different freshwater wetland complexes in Pennsylvania, USA. At a larger wetland complex with greater vegetative species richness and diversity, our stable isotope analyses showed dietary niche partitioning between species, whereas analyses from a smaller wetland complex with lower vegetative species richness and diversity showed significant dietary niche overlap. Determining the potential for competition between these two turtle species is important to understanding the ecological impacts of red-eared slider turtles in wetland habitats. In smaller wetlands with increased potential for competition between native turtles and invasive red-eared slider turtles we expect that when shared resources become limited, red-eared slider turtles will negatively impact native turtle species leading to long term population declines. Protection of intact wetland complexes and the reduction of introduced species populations are paramount to preserving populations of native species.

Highlights

Habitat degradation is the leading cause of extinction and population declines worldwide [1]
After four monthly surveys the cumulative number of species surveyed at Fort Mifflin (FM) had leveled off while at Silver Lake Nature Center (SLNC) the number of species was still increasing (Figure 1)
At FM no significant differences in d13C and d15N values existed for turtle tissue that represented short term diets (Plasma/RBC) (Table 2)

Summary

Introduction

Habitat degradation is the leading cause of extinction and population declines worldwide [1]. Species richness and species diversity generally decrease as habitat availability is reduced and rates of disturbance increase [2,3]. Disturbed habitats are susceptible to the establishment of introduced species due to alteration of community structure with open niches that can be filled by non-native species [8,9]. Naturally evolved and established ecological communities are being disrupted at unprecedented rates through habitat degradation and species introductions [1], leading to alterations in resource availability and changes in community structure [2]. Introduced competitors cause decline of native species by increasing rates of exploitative and interference competition [7,13]. Co-existence between competing species can occur if inferior competitors disperse more rapidly or utilize resources that shift in space and time [16]. Competition between species may result when dietary resources are not partitioned and will cause reduced fitness levels of one or all competing species [7]

Methods

Results

Conclusion