PARENT SESSION
Oral Session # 91: Biogeography III: Aquatic Communities.
Presiding: B Taylor
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 103.
Separating historical and contemporary factors that determine distribution and co-occurrence patterns in freshwater copepods.
Thum, Ryan*,1, Stemberger, Richard1, 1 Dartmouth College, Hanover, NH, USA
ABSTRACT- Patterns of species occurrence are influenced by historical (e.g., phylogenetic and biogeographic) and proximal (e.g., species interactions, habitat selection) factors. For example, two closely related species may not co-occur at local sites because of historical/contemporary dispersal barriers or because they mutually exclude one another via reciprocal competitive interactions. Finally, the degree to which the two species are reproductively isolated may also influence their patterns of co-occurrence via Allee effects and/or incompatibilities of hybrid genotypes. Separating historical and contemporary factors is particularly difficult when direct estimation of dispersal capacity is impossible. If dispersal is not limiting to species′ distributions, mutually exclusive distribution patterns should result from fitness differences at local sites. However, if dispersal is limiting, mutually exclusive distributions can be maintained in the absence of ecological and/or reproductive differentiation. I addressed these issues to consider the potential mechanisms maintaining the parapatric distributions of sister species of Skistodiaptomus (Copepoda: Calanoida). Mating experiments showed these species to be almost completely reproductively isolated despite a very high degree of morphological similarity. Discriminant function analysis had great difficulty separating these species according to the range of habitat variables among northeastern US lakes (e.g., water chemistry, physical characteristics of lakes, and surrogate variables for potential competitors and predators). Moreover, the functions discriminating lakes inhabited by each species may be confounded by large-scale landscape patterns. These results, in combination, suggest that allopatric speciation and range expansion of these species to distributional limits set by dispersal barriers, and not competition or ecological differentiation, determine the distribution patterns of these closely related diaptomid copepods.
Key words: co-ocurrence, copepods, distribution limits, parapatry