Corridors affect spider trophic position

Background/Question/Methods

A key component of conservation biology is maintaining community structure and function in the face of anthropogenic threats, like habitat fragmentation. Wildlife corridors, which facilitate movement by increasing connectivity between isolated habitat patches, are the most popular land management solution to habitat fragmentation. However, most corridor studies have only addressed species movement and rarely consider impacts on the community driven by the movement of resources. Here, we use a large-scale landscape experiment (Savannah River Site) and stable isotopes (d¹⁵N) of a generalist predaceous spider (Peucetia viridans) to determine how corridors affect trophic structure. We test for effects of corridors in our experimental landscapes by controlling for size and manipulating edge-to-area ratios (high edge and low edge). We expect predators in connected habitats to have increased prey availability compared to isolated habitat patches. As the spiders' diet is constrained to insects, isotope enrichment (higher trophic position) is due to resource limitations (i.e. starvation or cannibalism). 

Results/Conclusions

We found that spiders in isolated, high-edge patches had significantly higher d¹⁵N values (F=4.213, p = 0.0464) than those in connected patches. We found no difference in d¹⁵N values between high and low edge patches (F_1,42 = 3.207; p = 0.0854). These results suggest that fragmentation can reduce the availability of high quality prey, while corridors may increase prey subsidies from connected patches. Our results suggest that corridors can maintain trophic relationships in fragmented landscapes. This is the first study to quantify the effects of corridors on predator-prey interactions, which are especially vulnerable from habitat fragmentation.