Biodiversity is the variety of genes, species and ecosystems. Shaped by billions of years of evolutionary history of life forms interactions with each other and their environment. Altered by human activity with lasting impacts at large scales that are difficult to predict. Evolution evolves in change of proportions of variants in population. Freshwater bivalves develop in 3 ways: by producing veligers larvae (dreissena polymorphall, by releasing ully developed young mussels (rare, by passing early development as a parasitic stage on a host (unionids) Glochidia can"t swim or crawl attach to host fish grills. Strategies for infecting fish hosts: conglutinates glochidia enclosed in membranous capsules that mimic host prey, lures modified mantle tissue, mimics fish or invertebrate prey item to attract fish host. Mussel may physically grip host and pump glochidia over the gills. A well sampled population = a normal distribution. Change in allele frequencies as individuals join a population and reproduce.