Species Distribution Modeling of Telescopefishes (Actinopterygii: Giganturidae)

Abstract

Speciation is the cornerstone of all biodiversity on Earth. It is the foundation of evolutionary biology that new species are derived from ancestral species. The world’s oceans cover over 70% of the Earth’s surface and account for more than ten times the area than that of terrestrial habitats. However, little is known of the conditions promoting speciation in this realm. The absence of visible barriers in this zone make the mechanisms shaping oceanic diversity a particularly fascinating topic of research. For my research project, I investigated the ecological divergence of two closely related midwater fishes, Gigantura chuni and Gigantura indica. I built two species distribution models (SDMs)-one for each of the sister-species pair of telescopefishes. SDMs are conceptually based on ecological niche theory and these principles are used to produce distributional models. Using occurrence records together with environmental data, I used the machine-learning program Maxent to calibrate models optimized for predictive performance. I tested the validity of the models via cross-validation, area under the curve (AUC) of the receiver operating characteristic (ROC), and omission test rate values. The models performed well and successfully identified the three top contributing environmental variables relative to habitat suitability for each species. I also examined how reliably each model predicted its sister-species’ occurrence by projecting presence data on to the other species' model and vice-versa. The G. chuni model predicted the occurrence of G. indica 73.40% of the time, while the G. indica model predicted the presence of G. chuni at a rate of 69.32%. These results illustrate the sister-species pair of G. chuni and G. indica are using similar environmental variables. Ecological niche similarity relative to environmental requirements is a line of evidence for niche conservatism. Without visible barriers to promote physical and reproductive isolation, we might hypothesize new conditions by which populations diverge from ancestral lines.