In the past five years, Iowa has experienced weather extremes with records or near-records set for spring flooding in 2008, summer rainfall in 2010 and drought in 2012. To determine whether these weather events affected growth or body condition in ornate box turtles (Terrapene ornate ornata), we analyzed the changes in shell morphology and mass/volume ratio during their active season of May to August of 2005-2006 and 2008-2012.
For turtles we captured more than once, we assessed growth rate as a function of precipitation. We used residuals of regressions of change in size (or mass) vs. initial size (or mass) as our measures of size-specific growth. These were then regressed on annual precipitation to see if growth is positively related to precipitation as we expected.
We also assessed variation in mass/volume ratio as an index of body condition for all turtles and compared this index across years with different weather. If turtles are in poor condition in drought years, we would expect the residuals of the regression of mass on shell volume to be more negative in those years and positive in wet years.
We suggest that if the growth or mass/volume ratio increased when precipitation increased, it would indicate that male and female turtles were in better condition when the previous year received greater rainfall. For females, greater shell volume provides room to produce more or larger eggs and greater mass enables them to fulfill this potential as they have more resources to commit to their eggs.
Angela Dugan, ’13
Lake Forest, IL
Majors: Environmental Studies, Classical Studies
Brittani Yost, ’13
Major: Environmental Studies
Sponsor: S. Andrew McCollum