| |
Presented at the NABS Annual meeting, Anchorage, Alaska, 2006
in Population Biology
No evidence for density dependent drift in western Colorado streams
B.L. Peckarsky1, A.C. Encalada2, B.W. Taylor3, and M. Álvarez4.1Department of Zoology, University of Wisconsin, Madison, Wisconsin, USA 53706, 2Departamento de Zoologia, Universidade de Coimbra, 3004-517Coimbra, PORTUGAL, 3Department of Biological Sciences, Dartmouth College, Lebanon, New Hampshire USA 03766, 4Departamento de Ecología y Biología Animal, Campus Lagoas-Marcosende, 36210 Vigo, Spain
The existence of density dependent drift is unresolved in stream ecology, in part because of its difficulty of measurement. Likewise, the relative influence of migration and demographic processes on stream insect population dynamics is poorly understood. We estimated benthic density and drift density of a highly mobile mayfly (Baetis bicaudatus) into and out of twelve 45m stream reaches in western Colorado. We also estimated benthic density upstream of each study reach as a potential source of immigrants. Results provided no evidence of density dependent drift. Furthermore, stream reaches with high benthic densities were “sticky”, accumulating individuals (immigration exceeded emigration), and those with low benthic densities were “leaky” (emigration exceeded immigration), but only if fish were present. In fishless stream reaches, there was no relationship between net migration and benthic density. However, differential migration did not explain why fish streams in this area have higher Baetis densities than fishless streams. Finally, net migration rates were negligible compared to the instantaneous loss rates of larvae from eggs to final instars estimated using a demographic model. These results suggest that natural loss rates of Baetis larvae can be attributed primarily to mortality and not to density dependent drift.
|
|
