PARENT SESSION
Poster Session 39: Late Breaking and Newsworthy Posters
Friday, August 12, 8:30 AM - 10:30 AM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Independent effects of habitat amount and fragmentation on songbirds in a forest mosaic: an organism-based approach.

Betts, Matthew^*,1, Forbes, Graham^{1, 2}, Diamond, Anthony³, Taylor, Phil⁴, ¹ Greater Fundy Ecosystem Research Group, University of New Brunswick, Fredericton, New Brunswick, Canada² Faculty of Forestry and Environmental Management, University of New Brunswick, Fredericton, New Brunswick, Canada³ Atlantic Cooperative Wildlife Ecology Research Network, University of New Brunswick, Fredericton, New Brunswick⁴ Acadia University, Wolfeville, Nova Scotia, Canada

ABSTRACT- Habitat loss is considered to be one of the principal threats to global biodiversity. However, the influence of landscape fragmentation, the spatial patterning of remaining habitat, remains unclear. If landscape pattern affects population abundance, conservation biologists may be able to design landscapes that mitigate the negative impacts of habitat loss. We asked the following questions: (1) What are the relative influences of landscape composition and pattern on the abundance and persistence of forest songbirds? (2) Do thresholds exist in the response of forest songbirds to landscape composition and pattern? We used spatially explicit habitat suitability maps to define landscape composition and pattern according to the individual habitat associations of two species: Blackburnian Warbler (Dendrioca fusca) and Ovenbird (Seiurus aurocapillus). We used a stratified sampling design so that samples represented the range of variation in patch size and habitat amount at landscape extents. Fixed-radius point counts (N=363) were used to determine relative abundance of both species in two years. Generalized linear mixed models (GLMMs) were applied to determine habitat model parameter estimates. We used an information-theoretic (AIC) approach in model selection. Abundance and persistence of both species were strongly influenced by characteristics at scales greater than the individual territory. However, the type and spatial extent of landscape influence differed. Both abundance and persistence of Blackburnian Warbler were influenced by the amount of non-habitat matrix at a large (2000 m radius) spatial extent. The abundance and persistence of Ovenbird depended on a landscape pattern variable, patch size, but only in cases when low amounts of suitable habitat (<50%) existed at landscape extents. These results support the hypothesis that landscape pattern is important for some species only when the amount of suitable habitat is below a threshold.

Key words: fragmentation, thresholds, organism-based, information-theoretic