PHYSIOLOGICAL-RESPONSES BY LAGOMORPHS TO RESOURCE LIMITATIONS IMPOSEDBY HABITAT FRAGMENTATION - IMPLICATIONS FOR CONDITION-SENSITIVE PREDATION

Human land uses have resulted in landscape mosaics with habitat patche s that vary in quality. Patch quality (including the abundance of food and the risk of predation) can affect the survival of animals that ar e sequestered in remnant patches of habitat. Recent investigations of the demography of New England cottontails (Sylvilagus transitionalis) have shown that cottontails on small (resource poor) patches were in p oor physical condition (based on body mass) and often foraged at sites with limited cover. This resulted in a higher mortality rate than amo ng rabbits occupying large (resource rich) patches. To gain additional insight into the consequences of habitat fragmentation, we tracked th e physiological condition of rabbits occupying small and large patches during winter. The physiological condition of rabbits was determined using the urinary urea nitrogen:creatinine ratio, and the results were compared with similar indices obtained from captive rabbits. Consiste nt with our expectations, the nitrogen:creatinine ratios indicated tha t rabbits on small patches were nutrient limited for a longer period t han rabbits on large patches. Transmitter-equipped rabbits on small pa tches had a lower survival rate and died earlier than rabbits on large patches. All mortalities were predator related. Using these data, we developed a simple model that supports the role of ''condition-sensiti ve predation'' as a major factor limiting populations of New England c ottontails. Our results also demonstrate the utility of sampling physi ological condition to provide an index of quality of lagomorph habitat in human-dominated landscapes.