PARENT SESSION
Oral Session # 69: Forest Ecology IV: Communities.
Presiding: D Gavin
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 200.

Assessment of habitat specialization of southeastern trees using large-extent co-occurrence data.

Vandermast, David^*,1, Fridley, Jason¹, Kuppinger, Dane¹, Peet, Robert¹, ¹ University of North Carolina - Chapel Hill, Chapel Hill, North Carolina

ABSTRACT- Much ecological theory is based on the characterization of ecological habits of species as generalist or specialist, but standard measures for placing species along a generalist-specialist gradient do not exist. We have developed a novel approach to quantifying degree of habitat specialization by using species co-occurrence data. Generalists should co-occur with many species across their range, while specialists should co-occur with relatively few species, given equal plot occurrences. We quantify this concept using a beta diversity statistic whereby a constant number of plots containing a given species are randomly selected, and mean plot richness is subtracted from the total number of species in the sample to obtain a species-centered beta diversity statistic. This calculation is repeated via permutation to obtain a mean beta value that places a species along a generalist-specialist gradient. Species that tend to occur in single habitats with the same species are specialists and have low beta values; a higher beta value indicates high species turnover among plots containing the focal species and thus that the species is a generalist. We introduce our approach with the large woody flora (> 10 cm dbh) of the Southeast using 2500 vegetation plots from the Carolina Vegetation Survey, and rank the generalist-specialist tendencies of 112 common species. Common understory forest species (American holly, ironwood) have among the highest beta values, and species associated with few habitat types (longleaf pine, bald cypress) are among the lowest. On average, generalist species are deciduous, shade-tolerant, and have short lifespans and bird-dispersed seed. Generalism is also correlated with the range of species along certain environmental gradients, including annual temperature, potential evapotranspiration, and soil pH and organic matter. We conclude that applying our co-occurrence-based approach to large-extent plot databases provides a robust means to rank species on a generalist-specialist gradient.

Key words: generalists, beta, co-occurrence, specialists