The effect of pond-level factors on the movement and persistence of pond-breeding amphibians in a theoretical landscape

Background/Question/Methods

Most amphibians have complex life histories that require aquatic habitats for development and reproduction and terrestrial habitats for growth and hibernation.  Despite these distinct life phases, detailed information about terrestrial movements of pond breeding amphibians has remained largely unknown.  Pond breeding amphibians are often highlighted as examples of metapopulations, which rely on vastly unstudied assumptions about terrestrial movement between populations.  Yet, with landscape modification, we may be unknowingly changing pond communities or the dispersal routes between populations.  Studies of juvenile movement have shown that individuals from ponds with higher predation rates also have higher movement rates that carry through to later life stages.  These variable rates of movement may have strong implications for the persistence of metapopulations in modified landscapes.  However, there is great difficultly associated with locating or tracking amphibians while not centralized in ponds.  Therefore, individually-based dispersal models may be a useful tool for understanding how movement of pond breeding amphibians and how pond-level factor affect their persistence.

Results/Conclusions

Simulated populations were modeled using the individual-based population model HexSim (www.HexSim.net).  Theoretical landscapes were designed to have multiple interacting metapopulations by having groups of ponds dispersed throughout the landscape, and parameterization is based on expert opinion.  Variance in movement behaviors were shaped by the range of observed behaviors in ponds with differing predation, hydro-period, and population density levels.  Observations from ponds in the Willamette Valley, Oregon have found that juveniles were notably more active in ponds with invasive warm water fish.  Factors that increase movement activity such as the presence of predatory fish and shorter hydro-periods increased dispersal from natal ponds.  These increased dispersal distances contributed to the persistence of the metapopulation.  The landscape features that are important to dispersal were structurally complex lands in between ponds and overwintering areas.  Understanding the how pond level factors change the movement behavior and population persistence is vital in knowing how to properly apply theoretical models and manage pond breeding amphibians.