Abstract
Conservation biologists are facing a huge challenge. Ongoing, human-induced global change is leading to accelerating biodiversity loss, particularly in freshwater ecosystems where many highly mobile and migratory species live. To halt this decline, effective conservation strategies for threatened species are required. Such conservation strategies should take ecological and evolutionary processes into account, and ultimately aim to maintain genetic diversity and gene flow within a species. One little studied, highly mobile and threatened species is the black-fronted tern/tarapirohe (Chlidonias albostriatus). It is endemic to New Zealand and specialises in breeding on shingle bars in the braided river beds of the South Island, while migrating to the coast of all three main islands during winter. It is currently in decline, primarily due to habitat loss and predation by introduced predators. Effective conservation actions are urgently needed, but critical information has been lacking.
My thesis aim was to illustrate how genetic and ecological research can inform holistic conservation planning by investigating diversity, connectivity, demographic processes, and management actions in black-fronted terns. To be able to incorporate genetic considerations into management requires the development of appropriate molecular markers first. I developed 18 species-specific polymorphic microsatellite markers and mitochondrial control region primers as well as using universal primers to amplify the mitochondrial cytochrome b gene. I then evaluated the level of genetic diversity present and assessed geographic patterns of genetic and phenotypic divergence throughout the species’ breeding range based on microsatellite markers, mitochondrial DNA, and phenotypic data (weight, head-bill length, bill depth, wing length) with the aim of delineating conservation units within the species. Analyses showed that black-fronted terns have 1) relatively high levels of genetic diversity; 2) low genetic differentiation between breeding colonies; and 3) no genetic signature of isolation-by-distance; but, 4) a phenotypic signature of isolation-by-distance consisting of increasing body size with increasing latitude. Furthermore, I assessed the demographic history and the current status of the species using the genetic data set. My analyses provided evidence for an expansion during the last glaciation period and a recent human-induced decline, emphasising the effect of poor recruitment on the population. Lastly, I evaluated the effectiveness of creating clear (i.e. free of introduced vegetation) islands to create ‘safe’ nesting refugia to increase nesting success of black-fronted terns. Unexpectedly, I identified native southern black-backed gulls/karoro (Larus dominicanus) as primary predators of black-fronted tern nests, and nesting success was low, independent of island vegetation cover.
My results highlighted that it is critical to confirm the impact of current threats for species of conservation interest throughout their range. Based on my findings, I recommend that black-fronted terns are managed as a single metapopulation in one conservation unit to maintain gene flow throughout their range and conserve phenotypic variation and genetic diversity. To achieve the primary goal of increasing recruitment, catchments throughout the whole South Island should be protected and the specific impacts of different predator guilds evaluated to ensure that conservation interventions are achieving the desired outcomes.
This work demonstrates how genetic data can provide the basis to inform many conservation issues and decisions and how the gap between science and implementation can be bridged, so that genetic management can be included in long-term conservation strategies in highly mobile and migratory species.