From Genes to Communities: Effects of Habitat Change over Space and Time on Fish Diversity

Rapid habitat changes, caused by human activities within the last century, have resulted in biodiversity loss at all levels of biological organization. In light of these changes in the recent past, this thesis explores some of the effects of such changes on fish and wildlife populations, species, and communities using theoretical and empirical approaches. Using simulated genetic data, I first investigated the effects of recent population connectivity changes on the reliability of genetic inferences about connectivity. I found that, when connectivity has declined in the recent past, commonly-used genetic methods for estimating connectivity tend to overestimate current connectivity and underestimate historical connectivity. This could lead to incorrect inferences about gene flow and have negative consequences for conservation of populations and species at risk. Next, I conducted two empirical studies focusing on Canadian fishes that are threatened by habitat changes, making them excellent systems to investigate the effects of habitat change on their ecology and evolution. For Sockeye salmon populations in the Fraser River, I found that hydroelectric dams have fragmented habitats, changed connectivity among populations, and had significant effects on the ecology and evolution of some populations. Based on molecular data, I found evidence indicating very early differentiation between anadromous and resident forms of Sockeye salmon within one reservoir, where a dam has prevented the historically anadromous salmon from migrating to the ocean. In a second case study, on freshwater fish communities in northern Canadian lakes that were thought to be depauperate in biodiversity, I found higher species diversity and fish biomass than expected based on species-energy theory. My analyses indicate that fish diversity and biomass in northern lakes are not substantially lower than southern Canadian lakes. Thus, northern lakes could be important reserves of coldwater fish in light of climate change. In summary, I examined some effects of habitat change on populations, species and communities, and my thesis highlights: (i) areas for the improvement of methodologies and inferences used by conservation biologists; and (ii) specific northern communities of Canadian fishes that warrant attention to preserve Canadian fish diversity.Ph.D