Date of Award
Master of Science
Ecology, Evolution, and Organismal Biology
Ecology and Evolutionary Biology
Fredric J. Janzen
Species extinction is a major crisis facing the biological world today. Conservation biologists are striving to determine what factors contribute to species declines. Many of these factors are anthropogenic, with issues such as climate change, invasive species, pollution, and habitat alteration and destruction concurrently affecting populations. Turtles have proven to be particularly vulnerable; among the vertebrate taxa, turtles are the most endangered. These studies seek to determine the effects of anthropogenic habitat alteration on two sympatric species of turtles: the painted turtle (Chrysemys picta) and the ornate box turtle (Terrapene ornata) using fecundity, survival estimates, and/or capture-mark-recapture data from long-term research sites. The first study examines how fecundity and survival rates vary across age classes for a riverine, anthropogenically-affected population of C. picta compared to previously studied smaller, more remote systems. The second study examines how different amounts of human development affect survivorship of adult T. ornata.
According to the results of the first study, C. picta appear to be resilient across age classes to the effects of human presence. This was somewhat surprising, given observations of road mortality and injuries to adult turtles, as well as increased amount of disturbance while turtles were nesting. Juvenile survivorship was very low, though this could be due to methodological issues or biological causes. More research into juvenile survivorship is needed.
The second study found that the survivorship of adult female T. ornata decreased in a developed area compared to a refuge site. This implies that construction of cottages and the management of vegetation associated with development was a deleterious effect on survivorship. However, the same pattern was not seen with the construction of a bike path through the refuge site, although this could be due to a lack of time for effects to manifest in this long-lived population. Continued monitoring will be necessary to determine with confidence the long-term effects of bike path construction.
Overall, these studies present a mixed view on the effects of habitat alterations on turtles. One species, C. picta, appeared resilient to human presence; the other, T. ornata, did not appear to be resilient to human development. These results demonstrate that different types of human disturbance are likely to have different effects (e.g., human presence vs. human development), and that different species may demonstrate different levels of resilience.
Sarah M. Mitchell
Mitchell, Sarah M., "Differential demographic responses of two sympatric turtle species to anthropogenic disturbance" (2015). Graduate Theses and Dissertations. 14940.