The chapter focuses on animal populations of low genetic diversity, among which some have low population size and are, or have been, threatened by extinction. Genetic diversity is regarded as a must for a species to be able to adapt to environmental challenges, but despite this, several species, also among advanced animal groups like birds and mammals, seem to thrive well with low genetic diversity. Some species are assumed to have done so for thousands of years. Other species have low genetic diversity resulting from heavy bottleneck events, in some cases very close to extinction, caused by human activities. Although some species live with surprisingly low genetic diversity, being prone to further loss of genetic variation, this may be retarded due to sexual selection and fitness superiority of heterozygotes. Simulations with population size N = 25 showed that a homozygote fitness of 0.75 compared to fitness = 1.0 of the heterozygote resulted in exclusion of a p = 0.10 frequency allele in <10% of 50 simulation over 50 generations, whereas fitness 1.0 of all genotypes resulted in exclusion of the p = 0.10 allele in 78% of 50 simulations.
Part of the book: Genetic Diversity and Disease Susceptibility
Provided the predicted 2°C temperature increase during this century, lake ecology will go through dramatic changes, and this must be addressed in fish management in purpose of exploitation as well as in species preservation. In temperate lakes with fish communities dominated by cold-water and cool water fish, temperature increase will affect the species dominance. Extended growth season will benefit recruitment of less cool adapted species, total fish density may increase and growth will decrease of some species. Lakes dominated by salmonid fish may become dominated by cyprinids and percids. Primary production will increase due to extended growth season and increased precipitation. This can reduce the oxygen level in the deep layer of lakes when the organic matter decomposes, whereas the upper layer is too warm for cold-water species. In addition, increased density of small plankton feeding fish will reduce the algae feeding zooplankton. Lakes should be monitored by means of modern and sophisticated methods, monitoring lakes from satellites and in situ loggers, and pelagic fish may be counted by echosounding. To counteract increasing density of plankton feeding fish, fish biomass removal is a possible measure, though the effect is limited in time.
Part of the book: Biological Research in Aquatic Science