Changes in Behavior due to Environmental Effects

Although variation in fitness is important for the evolution of sex-biased dispersal, whether or not an individual actually disperses in its lifetime depends on the environment (Bowler et al). The potential benefits and substantial risks associated with dispersal imply a species’ instinct to disperse is context-dependent, i.e. depends on actual environmental conditions, physical condition, or developmental stage of an individual (Gros et al). In addition, a plastic, conditional dispersal strategy such as one based on environmental needs has the advantage of being able to respond to the variation in costs and benefits of dispersal over the short term (Bowler et al).

A species’ environment affects its population density and sex ratio and thus, dispersal benefits and detriments. While extinction risk can be decreased through the colonization of empty habitats, high rates of movement within a system can in turn increase the extinction. Thus, it is evident that changes in special dynamics as a result of dispersal can affect the cost and benefits of dispersal as well as the evolution of dispersal itself (Bowler et al).

Context-specific dispersal is evident in West Indian and Amazonian manatees. Studies reveal seasonal and water level depending dispersal driven by changes in water temperature, food availability, and space. For example, T. manatus male manatees can only migrate through freshwater and are thus met with certain geographic barriers. As a result, they have learned to migrate between certain rivers because the area between the rivers contains seacoasts and wetland systems that provide the freshwater sources they need (Satizábal et al).

However, habitat differences between marine and riverine populations of manatees can inhibit male dispersal. Because of this environmental influence, marine males must learn to avoid osmoregulation stressors, strong currents, and the presence of seagrass beds to successfully migrate while riverine males are limited by stronger currents and water levels and must learn to rely on behavioral, acoustic, or chemical signals to migrate as opposed to visual (Satizábal et al).