Theory of island biogeography applied to tree stump communities in a lake

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Eric R. Daugherty and Christopher W. Habeck, Environmental Science/Biology, Kutztown University, Kutztown, PA

Background/Question/Methods
The theory of island biogeography is widely acknowledged as a robust model to explain biodiversity patterns at landscape scales, however the number of studies relating this theory on smaller scales is lacking. To test this theory on a small scale, lichens, bryophytes, and vascular plant communities were surveyed on partially submerged tree stumps in Promised Land Lake, Greentown, PA. For each stump we measured the surface area and the distance from the lake shoreline. We used multiple linear regression to describe the potential effects of area and distance on species richness at the whole community level and separately for vascular plants, bryophytes, and lichens.
Results/Conclusions
We sampled a total of 20 stumps whose distance from shoreline ranged from 0.85 m to 69.25 m, and surface area from 7.32 m² to 148.7 m². We found 55 species, of which 21, 26, and 8 were vascular plants, bryophytes, and lichens, respectively. Stump area, but not distance from the lakeshore, influenced richness of the total community (β = 16.2, R2 = 0.47, p = 0.03), bryophytes (β = 6.1, R2 = 0.38, p = 0.03) and lichens (β = 5.1, R2 = 0.68, p = 0.02). Vascular plant richness was not related to stump area, distance from shoreline, or their interaction. One hypothesis for the lack of distance effect among taxa could be time since the initial dispersal event and consequently shifting community dynamics related to competition on the stumps. We observed the bryophyte species Brachythecium rutabulum dominated most stumps. This and other dominant species may have reduced the distance signal since original establishment.