PARENT SESSION
Oral Session #78: Insect Population and Community Ecology. Presiding: R. Denno.
Friday, August 10, 2001. 8:00 AM to 11:45 AM. Hall of Ideas I.
Population dynamics during rapid response to climatic change.
Crozier, Lisa1, 1
ABSTRACT- As average temperature warmed in the US over the past century, many species shifted their geographic ranges northward. Although we expect this net movement, we have few case studies demonstrating the mechanistic link between range shift and climate change. Atalopedes campestris (Lepidoptera: Hesperiidae) is a native generalist skipper butterfly that has rapidly expanded its range northward into the Pacific Northwest over the past 40 years. Each step in the range expansion occurred during an unusually warm summer, suggesting that climate may influence the rate of expansion. I tested the hypothesis that population growth rate at the current range edge is greater in warmer summers by comparing population censuses in spring and fall over 3 years in two populations near the range edge in eastern Washington. I also tested the hypothesis that summer population growth declines across the range edge by measuring fecundity and transplant larval development time and survival. I found no significant difference in population growth rate between years or fecundity across the range boundary. Generation time was significantly slower outside the range, however, and lay near a threshold between 1 and 2 generations/year. An exceptionally warm summer could enable colonization by crossing that threshold. These results are consistent with the hypothesis that there is a mechanistic link between summer temperature and the rate of range expansion.
KEY WORDS: range change, climate change, insect population dynamics, butterflies