Ecological niches and geographic distributions of lanternfishes
Lanternfishes (Myctophidae) dominate fish diversity and biomass within the mesopelagic ocean between 200-1000m deep. In the face of exploitation and climate change there is a need to predict their current and future biogeography as well as the ecological and evolutionary mechanisms responsible for these patterns. This thesis aimed to fill this gap by using Ecological Niche Models (ENMs) to estimate species’ fundamental niches and associated distributions. With a focus on Southern Ocean species, uncertainties were investigated regarding (i) the application of ENMs to a 3-dimensional environment by comparing ‘3D’ and ‘2D’ approaches, and (ii) the use of climate data when projecting ecological responses to climate change by undertaking a literature review and using Electrona antarctica to reveal the variability in projections that can result from multiple levels of climate uncertainty. These results were then used to predict the current and future distribution of ten lanternfish species using a ‘2D’ ENM and an ensemble of climate change simulations. Species showed high affiliation to water masses and contrasting future responses. Antarctic species with restricted thermal niches and available habitat in which to disperse were most vulnerable to climate change which has implications for the size structure of the myctophid community and wider consequences for predators and prey. The global phylogeography of lanternfishes was investigated to elucidate the mode and mechanisms of speciation. Species grouped in to broad biogeographic clusters with recently diverged species displaying highest spatial overlap. The niche, depth, and photophore patterns analysed gave no clear indication of the mechanisms facilitating speciation, but there is strong evidence that sympatric or parapatric speciation is a dominant mode of divergence. Overall, these findings demonstrate that the unique physical and environmental setting of the vast pelagic ocean has played, and will continue to play, an important role in the biogeography and diversification of lanternfishes.