Influence of local social-structure on inter-deme dispersal and landscape genetic patterns in a metapopulation of collared lizards

Background/Question/Methods

Understanding the forces that contribute to dispersal dynamics is essential for conservation, particularly for species that exist in a metapopulation.  Because demes in a metapopulation often have small population sizes, the potential exists for local habitat variation to have a significant effect on larger patterns of dispersal and gene flow; however many models of dispersal assume patch quality to be homogenous.  The metapopulation of collared lizards on Stegall Mountain in the Missouri Ozarks presents a unique opportunity to examine the impact of local forces on dispersal and gene flow in a natural population.

We hypothesized the distribution of high-quality bedrock habitat to be a local factor with high potential to influence dispersal in this territorial species; greater clustering of high quality habitat would facilitate monopolization of those territories by a few males, and resulting high levels of competition would drive male dispersal from those glades at greater rates than on glades with evenly distributed resources and less mate competition. 

To quantify degree of resource clustering, aerial photographs of Stegall Mountain were classified to identify areas of exposed bedrock.  The resulting distribution of bedrock in each glade was classified according to correlation length; glades with smaller correlation lengths had more clustered resources, populations with larger correlation lengths had more evenly distributed resources.  Dispersal events between all glades between 2000 and 2006 were extracted from a long-term mark-recapture study of Stegall Mountain.  To examine predicted patterns of dispersal with and without the impact of local habitat variation, we produced current maps in Circuitscape; which models the dispersal of individuals across a landscape as current flowing through a circuit.

Results/Conclusions

Glades with longer correlation lengths produced more male dispersers than glades with shorter correlation lengths (R²=0.29, F_(1,52)=22.16,p=1.9E-05), but no significant relationship observed for females(R²=0.02, F_(1,37)=1.60,p=0.21),.  The influence of resource distribution solely on dispersal patterns of males supports our hypothesis that local social structure is a significant force contributing to dispersal patterns.   

To model dispersal patterns, each glade was a current source; under the null model, current was proportional to glade area, under the local habitat model, glade area was weighted by its correlation length. We compared the resulting maps to networks of observed dispersal events from a long-term mark recapture study.  Models that incorporated local habitat variation produced patterns of predicted dispersal that were more congruent with observed patterns of dispersal than models that assumed no influence of local habitat variation.