Influence of Fragmentation and Bottlenecks on Genetic Divergence of Wild Turkey Populations

Abstract: There are few empirical studies of the effects of human-induced fragmentation and bottlenecks on the genetic structure of field populations. Assessment of these effects is necessary to evaluate the relevance of predictions obtained from simulation and theoretical models to the management of wild populations. The genetic structure of populations of the Wild Turkey (Meleagris gallopavo), which have been heavily influenced by human activities, was examined using allozyme electrophoresis Allele frequencies at four polymorphic loci were estimated for 27 localities using 461 turkeys The estimated proportion of genetic variation resulting from differences among populations (F_st= 0.102) was one of the highest reported for any avian species and was also much higher than that observed between turkey populations that had not passed through known bottlenecks Almost all of the variation (89%) among populations was accounted for by differences between groups of populations with different histories of manipulation Fragmented distributions and population bottlenecks due to human activities appear to have increased genetic differentiation among populations of wild turkeys. This observation agrees with theoretical predictions concerning the effects of isolation and bottlenecks on the genetic structure of field populations.     

Judicious Use of Multiple Hypothesis Tests

Abstract:  When analyzing a table of statistical results, one must first decide whether adjustment of significance levels is appropriate. If the main goal is hypothesis generation or initial screening for potential conservation problems, then it may be appropriate to use the standard comparisonwise significance level to avoid Type II errors (not detecting real differences or trends). If the main goal is rigorous testing of a hypothesis, however, then an adjustment for multiple tests is needed. To control the familywise Type I error rate (the probability of rejecting at least one true null hypothesis), sequential modifications of the standard Bonferroni method, such as Holm's method, will provide more statistical power than the standard Bonferroni method. Additional power may be achieved through procedures that control the false discovery rate (FDR) (the expected proportion of false positives among tests found to be significant). Holm's sequential Bonferroni method and two FDR-controlling procedures were applied to the results of multiple-regression analyses of the relationship between habitat variables and the abundance of 25 species of forest birds in Japan, and the FDR-controlling procedures provided considerably greater statistical power.     

Individual- and Assemblage-Level Effects of Anthropogenic Sedimentation on Snails in Lake Tanganyika

Abstract:  Human impacts on aquatic biodiversity are often measured at the assemblage or community level, although it has been suggested that individual-level measures are more sensitive. We evaluated the effects of anthropogenic sedimentation on endemic snails in Lake Tanganyika, East Africa, by comparing assemblage-level (i.e., species richness, evenness, and abundance) and individual-level (i.e., frequencies of predation and parasitism, fecal organic content, life history) data between sediment-disturbed and reference sites. Previous studies have indicated that sedimentation kills snails and reduces mollusc diversity in this system, but we found little evidence of changes in species richness, evenness, or snail abundance at the levels of sedimentation recorded. In contrast, individual-level data revealed a variety of differences associated with sedimentation. Frequencies of shell scarring by predatory crabs and castration by parasitic trematodes were significantly lower at disturbed sites, indicating shifts in interspecific interactions. Snails ingested large amounts of inorganic sediments at disturbed sites, suggesting a reduction in food quality. In addition, sedimentation was associated with a large downward shift in size distribution within some species and reproduction at smaller size. These strong patterns in individual-level data contrast with the lack of effects at the assemblage level. We argue that incorporating individual-level measures will often enhance the sensitivity of impact surveys and may reveal effects of disturbance on important interspecific interactions.