Disrupting evolutionary processes: The effect of habitat fragmentation on collared lizards in the Missouri Ozarks

Humans affect biodiversity at the genetic, species, community, and ecosyste m levels. This impact on genetic diversity is critical, because genetic div ersity is the raw material of evolutionary change, including adaptation and speciation. Two forces affecting genetic variation are genetic drift (whic h decreases genetic variation within but increases genetic differentiation among local populations) and gene flow (which increases variation within bu t decreases differentiation among local populations). Humans activities oft en augment drift and diminish gene flow for many species, which reduces gen etic Variation in local populations and prevents the spread of adaptive com plexes outside their population of origin, thereby disrupting adaptive proc esses both locally and globally within a species. These impacts are illustr ated with collared lizards (Crotaphytus collaris) in the Missouri Ozarks. F orest fire suppression has reduced habitat and disrupted gene flow in this lizard, thereby altering the balance toward drift and away from gene flow. This balance can be restored by managed landscape burns. Some have argued t hat, although human-induced fragmentation disrupts adaptation, it will also ultimately produce new species through founder effects. However, populatio n genetic theory and experiments predict that most fragmentation events cau sed by human activities will facilitate not speciation. but local extinctio n. Founder events have played an important role in the macroevolution of ce rtain groups, but only when ecological opportunities are expanding rather t han contracting. The general impact of human activities on genetic diversit y disrupts or diminishes the capacity for adaptation, speciation, and macro evolutionary change. This impact will ultimately diminish biodiversity at a ll levels.