Print PageMovement of individuals is a vital component of many ecological and evolutionary processes and is integral in the maintence of local populations, metapopulations, communities, and ecosystems. In the context of habitat loss and deterioration there is an even greater need to understand and predict causes, mechanisms, patterns, and consequences of animal movement. For juveniles the initial movement phase encompasses the first movements away from their natal site and is particularly crucial as they encounter novel habitats and are highly vulnerable. In many species, initial movement represents a bottleneck in which juveniles suffer high mortalities before establishing home ranges or dispersing to a new breeding population. Through manipulating factors predicted to affect movement, we can elucidate the basic determinants on movement patterns and fitness consequences. Pond-breeding amphibians are an ideal system for studying juvenile movements because they are often spatiotemporally concentrated at breeding ponds and can be studied at smaller scales than other vertebrates. The complex life cycle of pond-breeding amphibians necessitates larval development in aquatic habitats followed by metamorphosis and emergence into terrestrial habitats by juveniles. Juvenile are highly susceptible to desiccation and are thus dependent on their ability to located suitable moist, cool refuges within terrestrial habitats. Using replicated enclosures we examined how forest habitat alterations affected initial movement by juvenile spotted salamanders (Ambystoma maculatum). We tested for differences between closed forest canopy and open canopy habitats. We also tested the effects of specific habitat features known to affect habitat quality, including coarse woody debris, burrow density, and compacted soils, against unmanipulated controls.
Results/Conclusions
Canopy appeared to have the greatest effect on how far to move before settling. In open canopy habitats juvenile salamanders showed significantly less settling (23±4.7%) and more moving (77±4.7%) compared to forest habitats (42±5.1% and 58±5.1%, respectively). Mean settling distances were also significantly greater within open canopy habitats (14±1.1m) compared to forests (11±0.8m). Significantly more individuals settled in high coarse woody debris (48±7.3%) and high burrow density (41±7.8%) treatments than compacted soil treatments (20±5.7%). These findings indicate that decreases in habitat quality may result in increased initial movement distances and decreased settling by juvenile spotted salamanders. As a result, juvenile amphibians may experience increased risk of desiccation and mortality if they are unable to locate suitable refuges during the first movement night. Because juveniles represent the primary dispersal stage for most amphibians, any effects on this critical movement phase could greatly influence population dynamics and persistence.
