Thursday, August 5, 2010

PS 78-107: Effects of urbanization on life history traits in two anurans

Matthew A. Jennette, Towson University and Joel. W Snodgrass, Towson University.


Habitat loss and degredation are significant threats to the persistence of amphibian populations, and urbanized areas represent some of the most impacted landscapes used by these organisms. Amphibians may be particularly susceptible to fragmentation and urban development because of their complex life cycles that require aquatic resources for breeding and larval development, in addition to adjacent terrestrial habitat for foraging and overwintering. Although urbanization leads to a loss of some species, others still persist in these areas and little information is available on how these organisms adapt to urban environments. We are currently studying growth rates, age structure, and reproductive investment in two species of anurans – wood frogs (Lithobates sylvaticus) and American toads (Anaxyrus americanus). Our study populations are associated with artificial ponds in Baltimore County, Maryland, and classified as urban, suburban, and rural based on the amount of remaining forest cover in the landscape. Amphibians were collected in or near breeding ponds, sexed, measured, weighed, and toe-clipped for age determination via skeletochronology prior to being released at their original point of capture. Additionally, to quantify reproductive investment we collected a subset of the females to measure egg size and fecundity.   


American toads and wood frogs from rural populations were significantly larger (mass and snout-urostyle length) than those breeding in urban and suburban populations. Skeletochronology revealed that ages of breeding individuals range from 2-4 years in wood frogs, 2-7 years in male American toads and 3-6 years in female American toads, though population age structure did not differ between sexes or among sites for either species. We found that mean egg size, clutch dry mass, and the number of eggs produced were greater in females from rural landscapes as a result of their larger body sizes. Our preliminary results suggest that energy allocation patterns are altered in urban landscapes in response to higher maintenance costs in these stressful habitats.