The Role of Microhabitats in the Desiccation and Survival of Anurans in Recently Harvested Oak–Hickory Forest

Juvenile survival is an important life history feature, because recent modeling efforts suggest that modest changes in juvenile survival rates due to habitat change may greatly affect population growth rates. We compared water loss and survival rates of recently metamorphosed American Toad (Anaxyrus americanus), Green Frog (Lithobates clamitans), and Wood Frog (Lithobates sylvaticus) juveniles contained within four microhabitats, two of which occur in uncut control forest (i.e., forest ridgetop, forest drainage) and two within recently harvested forest (i.e., clearcut open, clearcut brushpile). Survival was higher in forest drainage than forest ridgetop, indicating that microhabitats within continuous forest are not equally suitable. Brushpiles of coarse woody debris reduced desiccation risks in clearcuts as indicated by survival differences between clearcut open and clearcut brushpile and survival in clearcut open was very low for all species in both years. We found species differences in survival as well as a species by microhabitat interaction in water loss rates. These results are best explained by observed behavioral differences as opposed to physiological differences among species. We conclude that desiccation can be a major source of mortality for juveniles entering terrestrial habitats, especially habitat altered by anthropogenic land-use. Desiccation risks are greatest in areas with low soil moisture conditions, which for our study included microhabitats within clearcuts without coarse woody debris, forested ridgetops, and years with below average rainfall.

Fig. 1

Water loss among species differed among microhabitats. This result also differed between year 1 (A) and year 2 (B). Water loss was measured as proportion of initial mass. Dead individuals were weighed during the time interval when initially found and then removed from the experiment. Error bars represent standard error.

Fig. 2

Mean proportion water loss over time differed among microhabitats. Water loss was measured as proportion of initial mass. Dead individuals were weighed during the time interval when initially found and then removed from the experiment, thus sample size decreased over time. Water loss increased at 06:00 for all species, but the increase was greatest in clearcut open where many individuals were dead. Clearcut microhabitats are indicated with dashed lines and open symbols. Forest microhabitats are indicated by solid lines and closed symbols. Error bars represent standard error.

Fig. 3

Survival curves for A. americanus (A, B), L. clamitans (C, D), and L. sylvaticus (E, F) held within enclosures in four microhabitats in year 1 (A, C, E) and year 2 (B, D, F). Clearcut microhabitats are indicated with dashed lines and open symbols. Forest microhabitats are indicated by solid lines and closed symbols. Error bars represent 95% confidence intervals.

Fig. 4

Soil temperature over time differed among microhabitats. Soil temperature decreased during the night and increased during the day in all microhabitats, but the magnitude of the change within a year was much greater in clearcut open compared to the other microhabitats. Soil temperature was hotter in year 1 (open symbols) compared to year 2 (closed symbols). Clearcut microhabitats are represented by dashed lines, and forest microhabitats are represented by solid lines. Error bars represent standard error.

Contributor Notes

Associate Editor: M. J. Lannoo.

¹ Division of Biological Sciences, 105 Tucker Hall, University of Missouri, Columbia, Missouri 65211-7400, e-mail: (RDS) semlitschr@missouri.edu.

² Department of Botany, 312 Birge Hall, University of Wisconsin, Madison, Wisconsin 53706-1381, e-mail: trittenhouse@wisc.edu. Send reprint requests to this address.

³ Department of Environmental and Forest Biology, 226 Illick Hall, State University of New York, Syracuse, New York 13210-2724, e-mail: eharper@esf.edu.

Received: 13 Aug 2007

Accepted: 12 Mar 2008