Process-based approach reveals directional effects of environmental factors on movement between habitats (original) (raw)

Habitat variation influences movement rates and population structure of an intertidal fish

Oecologia, 2008

Understanding how variation in habitat characteristics influences the demography and behavior of organisms is of primary interest in ecological research. I studied how patterns of distribution, abundance, mortality and movement of the fluffy sculpin, Oligocottus snyderi, are related to variation in habitat characteristics within and between sites. The recruitment levels of O. snyderi are very similar at two different intertidal sites, yet post-recruitment processes modify the original recruitment signal at only one of the two sites. The two sites differ significantly in only one measured aspect of their tidepool habitat—the amount of cover provided by surfgrass or algae. Both recruits and adults of O. snyderi exhibit positive associations with the amount of tidepool cover, particularly the presence of surfgrass. A mark-recapture study determined that these differences in the habitat characteristics between the two sites are associated with differences in post-recruitment movement rates. In fact, the absence of a correlation at one site between O. snyderi recruit and adult abundances, which would typically be considered evidence for significant post-recruitment mortality, appears to be driven by strong within-site post-recruitment movement. Furthermore, although post-recruitment mortality rates do not vary significantly across the two sites, variation in post-recruitment mortality is weakly related to within-site variation in tidepool characteristics at one site. The results of this study suggest that post-settlement intertidal fishes continue to sample their surrounding environment as they mature and will redistribute themselves according to within-site spatial variation in habitat characteristics—a behavioral process that may obscure estimates of post-settlement mortality.

Ecosystem-level consequences of movement: seasonal variation in the trophic impact of a top predator

Spatio-temporal patterns of species abundance influence the strength of trophic interactions, while movement of individuals helps determine those patterns of abundance. Thus, understanding movement is a basis for quantifying interactions within a food web. In Puget Sound, Washington, USA, the North Pacific spiny dogfish Squalus suckleyi is an abundant top predator with a diverse, generalist diet. Coastal dogfish populations make seasonal north−south migrations, but populations in inland waters are thought to be more resident. In this study, we combined acoustic telemetry and bioenergetics modeling to determine patterns of movement and to quantify seasonal variation in the predatory impact of dogfish in Puget Sound. All tagged dogfish migrated out of Puget Sound in the winter and were absent until the following summer. Individuals that returned to Puget Sound in subsequent years showed consistent timing and duration of residence across years, but these metrics varied across individuals. Incorporating movement data into the bioenergetics model resulted in a 70% decrease in the predatory impact of dogfish in the winter and a 30% decrease in the summer, compared to a year-round resident Puget Sound population. Incorporating metrics of movement into food web or ecosystem models will increase our understanding of species interactions and will improve our ability to predict changes in food web dynamics under various environmental and management scenarios.