Movement ecology of juvenile pond-breeding salamanders: Implications for the management and conservation of amphibian populations.

摘要

Human-induced habitat change is widely regarded as a primary factor threatening the persistence of species. One major consequence of habitat alteration is its effect on the movement behavior of individuals. Animal movement is often strongly influenced by habitat type; knowledge of the strength, direction, and variation inherent in species' behavioral reactions to novel or altered habitat is crucial for identifying the mechanistic causes of population or metapopulation dynamics, and for maximizing the effectiveness of conservation and management practices. Natal dispersal is an important mechanism by which species mitigate the effects of unpredictable variation in the spatial distribution of resources and is critical to many species' spatial dynamics. Habitat alteration impacts the spatial patterning of resources and the risks associated with searching for resources. Spotted salamanders (Ambystoma maculatum ) are forest-dependent, pond-breeding amphibians with complex life cycles. Spotted salamanders metamorphose and move out of aquatic habitat with limited knowledge of the terrestrial habitat. I used a combination of empirical studies of juvenile spotted salamander movement and individual-based modeling to investigate the influence of habitat amount and arrangement on juvenile salamander survival.;I quantified the fine-scale movement behavior and search strategies of recently-metamorphosed spotted salamanders in three different habitat types (field, early successional forest, and forest) and at varying distances from both hard (field and forest) and soft (early successional forest and forest) edges using fluorescent powder tracking. I found that salamanders moved straighter and with fewer turns through field habitat compared to both forest and early successional habitat. I found that movement in forest was well approximated by a correlated random walk. I combined powder-tracking with drift fence mark-recapture to investigate both short and long-term movement decisions. Individuals were released in grassland habitat 5, 10, 20, and 35 meters from a forest edge lined with drift fences. I found significant initial orientation toward forest of individuals released 5 and 10 meters from the forest, and random orientation at 20 and 35 meters, indicating either a small perceptual range or decreasing motivation to move towards forest with distance. My empirical work found that juvenile pond-breeding salamanders exhibit considerable variation in natal dispersal behaviors such as speed of movement, path linearity, and settlement propensity. Habitat alteration and landscape change may alter the benefits associated with different movement strategies.;Using individual-based simulation techniques, I developed a movement model of initial natal dispersal in juvenile salamanders using empirical data to parameterize movement tendencies. I investigated the consequences of behavioral decisions in differing habitat modification scenarios, altering the amount and distribution of habitat within the landscape. I found that different movement strategies were optimal under different habitat modification scenarios. Increasing habitat clumping lowered the probability that dispersers would find habitat across all ranges of behaviors. The strength of movement bias toward habitat had a significant effect on the probability of individuals locating habitat. When density-dependent mortality was not included in the model, higher movement bias maximized the probability of locating habitat. When density-dependent mortality was included in the model, blind movement (no movement bias) was optimal. The configuration of habitat affected the movement strategy that generated the lowest probability of locating habitat under density-dependence. The degree to which movement bias affected the probability of locating habitat differed based on assumptions of habitat clumping. My results indicated that the amount and configuration of habitat surrounding wetlands affect optimal movement behavior, and habitat managers should consider the configuration of habitat surrounding wetlands when designing conservation measures.