PARENT SESSION
Oral Session #47: Animal Population Ecology: Amphibians, reptiles, others. Presiding: K. Hatch.
Wednesday, August 8, 2001. 8:00 AM to 11:45 AM. Hall of Ideas J.
Tests of habitat fragmentation and resource distribution effects on the population performance of Microtus pennsylvanicus.
Dooley, James1, Bowers, Michael2, 1 2
ABSTRACT- We examined population responses of Microtus pennsylvanicus to manipulations in habitat continuity and quality within 48 40 x 40-m patches grouped onto 12 "micro-landscapes" of four patches each. Manipulations included: (1) the creation of "fragmented" or "continuous" landscapes by mowing (or not) 20-m areas between patches within a landscape; and (2) adding (or not) supplemental food to individual patches to alter local patch quality. We predicted that alterations in patterns of food availability and habitat continuity would be associated with imbalances in patterns of movement in and out of habitat patches as well as shifts in basic demographic responses. Over a 39 month period we captured more than 23,000 individuals. We observed higher emigration/immigration rates in unfragmented relative to fragmented landscapes, and higher immigration rates, female biased sex ratios and other differences for +food compared to no-food patches. Population-level differences included slightly higher and less variable abundance in no-food than +food patches except during population peaks when abundance in +food patches significantly exceeded that of no-food patches. Mean abundance was positively correlated with high proportions of residents while peak abundance was correlated with high proportions of emigrants. Adding food appeared to alter dominance hierarchies and social organization which then appeared to affect local densities. Understanding responses of organisms to habitat heterogeneity will require a consideration of individual movement trajectories and how these effect or are affected by social structure.
KEY WORDS: habitat fragmentation, resource availability, population demography, Microtus pennsylvanicus