The effect of forest fragmentation on genetic diversity and structure: A landscape ecology perspective.

摘要

In many parts of the world, the fragmentation of large expanses of forests into small stands has isolated local populations of organisms. Sugar maple (Acer saccharum Marsh) was used as a model species to address two specific questions: (1) are there significant genetic differences among cohorts in a relatively large, old-growth forest and (2) does the degree of forest fragment isolation affect genetic diversity and structure of local populations?; Genetic data were collected for five developmentally-based cohorts in a large nature preserve and analyzed to determine whether there were significant differences. Genotypes were inferred from phenotypic enzyme patterns of seven enzymes representing eight loci extracted from cambium and resolved with starch gel electrophoresis. Data indicated little genetic differentiation among cohorts, as only seedlings had allele and genotype frequencies significantly different from other cohorts. Therefore, there was little temporal differentiation within the forest.; I also collected genetic data from canopy (pre-fragmentation) and juvenile (post-fragmentation) individuals in 15 woodlots and analyzed them to determine the effect of forest isolation on genetic diversity and structure. Genetic diversity was not significantly different between juvenile or canopy subdivisions, or between woodlots with a low or high degree of isolation. There was a significant difference in genetic structure, with a lower degree of genetic differentiation among juveniles compared to canopy trees. In addition, juveniles in some woodlots had alleles not present in the canopy. These findings suggest that there is gene flow into the woodlots and that post-fragmentation gene flow rates are higher than pre-fragmentation rates. Apparently, sugar maple's high potential for long distance gene flow is enhanced by altered flux of wind across a fragmented landscape.; My results provide the beginning of the body of data necessary to develop and evaluate models of genetic dynamics of species in fragmented landscapes, information essential to conservation biology. The results also show that forest fragmentation does not always result in greater isolation of local populations. Indeed, the effects of fragmentation may depend on life-history characteristics of individual species.