PARENT SESSION
Contributed Oral Session 144: Predator - Prey Ecology: Terrestrial Habitat and Food Webs
Thursday, August 11, 1:30 PM - 5:00 PM, Meeting Room 524 A, Level 5, Palais des congrès de Montréal

Differential effects of habitat connectivity on predators and prey: Implications for food web dynamics.

Martinson, Holly^*,1, Fagan, William¹, Denno, Robert¹, ¹ University of Maryland, College Park, MD, USA

ABSTRACT- In heterogeneous habitats, the area and isolation of patches are known to influence species occupancy patterns. However, it is less clear how these factors influence the interactions between suites of species. Specifically, if species respond individualistically to spatial factors, the communities on small, isolated patches will differ both in composition and in dynamics compared to larger, mainland patches. This may lead to differing competitive or trophic interactions depending on landscape context. Here, we present results from a field survey of three interacting arthropods on an array of naturally-occurring patches of salt marsh hay, Spartina patens, on an extensive mid-Atlantic marsh. We use the incidence function connectivity metric to predict occupancy and abundance of arthropods on patches; specifically, this metric accounts for distances between and areas of all potential source patches and is more informative than simple connectivity metrics such as nearest neighbor distances. The distribution of connectivity scores for 450 patches was strongly right-skewed, with most patches small and poorly connected. As many patch-inhabiting insects are wing-dimorphic and predominantly brachypterous (short-winged), dispersal limitation is likely strong for many species on this marsh. The abundances of both the herbivore Tumidagena minuta (Delphacidae) and its specialist egg predator, Tytthus alboornatus (Miridae), showed strong positive relationships to patch area; however herbivore abundance showed a two-fold stronger response to connectivity compared to that of its predator. This disparity may be due to differential dispersal abilities between the two insects and may have consequences for predator-prey interactions on patches of differing connectivities. Also, generalist spiders that were common both in S. patens and the matrix vegetation, Spartina alterniflora, showed no response to patch area or isolation. It is therefore likely that food web dynamics, such as the impacts of specialist vs. generalist predators, differ markedly between patches of different sizes and connectivities. This study highlights the importance of spatial influences on multi-species interactions in patchy habitats.

Key words: connectivity, dispersal, salt marsh invertebrates, food web dynamics