In general, turtle populations are in decline largely due to habitat fragmentation. In Wisconsin, the one exception is the painted turtle, Chrysemys picta, a turtle that seems to thrive in human-altered environments. We conducted a mark-recapture study of the painted turtle over five years in a 2.2 ha pond that was originally dug in 1995 in response to the creation of impermeable surfaces due to urbanization in Beloit, WI. The research was conceived by David Bowne as a project of the Ecological Research as Education Network (EREN, www.erenweb.org) to test the hypothesis that urbanization (as quantified using GIS) affects size and sex distribution. Analysis of the 2012 data from 16 schools showed a weak trend of increased proportion of females with increased development around the ponds and no trend between juveniles and urbanization (Bowne et al., 2013); these results were not predicted! Beloit, in particular, was an outlier with respect to the very high proportion (over 50%) of juveniles in such an urban area.
Results/Conclusions
Sampling in the same pond (i.e., no measurable change relative to urbanization) over the following four years yielded population structures that each differed significantly from other years suggesting a control other than urbanization. The varied proportion of juveniles (0% in the second year) may be attributed to timing of rainfall and freezing events (assuming that hatchlings are overwintering in the nests) or to drought. Cold winters seem to favor the males at the expense of larger females, another unpredicted result. In conclusion, in high latitude areas, sex and age structure of the painted turtle may be strongly affected by winter temperature and timing of freezing events.