Abstract
The nine currently recognized species of moa (Order – Dinornithiformes; Bonaparte 1853) suffered extinction soon after New Zealand was settled by humans. They were the result of an evolutionary radiation that produced a unique guild of birds – giant, and totally wingless species that evolved in the absence of non-volant mammals. Recent advances in dating and paleoclimatology, and compilations of data on distributions of the nine species of moa, along with information on the geographic, topographic, climatic and edaphic characteristics of sites from which moa remains have been recovered, enabled us to test whether their evolutionary radiation truly was ‘adaptive’, producing ecologically distinct species. Randomization, resampling analyses of moa distributions across North and South Islands revealed highly significant geographic and ecological segregation, with different species tending to occupy different islands, regions within islands, or elevations within regions. Quadratic Discriminant Analyses demonstrated niche segregation at even finer scales, including that based on vegetation-defined habitats and on local climatic, topographic and edaphic conditions. Moa distributions also appear to have been dynamic over time, shifting in their upper elevational limits as climatic conditions changed and vegetative zones shifted upward during the Holocene Epoch. Our ongoing studies are building on the results presented here to explore the temporal dynamics of moa distributions, assess differential responses of moa species to natural and anthropogenic drivers, and determine how these forces may have combined to cause the extinction of moa just a few centuries ago.
Highlights
Adaptive radiations describe the ecological and evolutionary diversification of monophyletic lineages, largely driven by divergent selection from competition among closely related species (Lomolino et al 2017)
Evolution of moa represents one of the most compelling examples of ‘reversals in natural selection’ yet described for insular birds – they became flightless in the absence of non-volant mammals, and occupied the niches filled by large, herbivorous mammals on continents
More limited in terminal diversity than other, classic cases of evolutionary divergence of insular linages, the diversification of moa may have been the largest avian radiation in New Zealand and clearly was adaptive
Summary
Adaptive radiations describe the ecological and evolutionary diversification of monophyletic lineages, largely driven by divergent selection from competition among closely related species (Lomolino et al 2017). Evolutionary diversification of New Zealand’s extinct moa (Fig. 1) was not nearly as extensive in numbers as some of the more spectacular cases (e.g., Hawaiian honeycreepers and lobeliads (Callicrate et al 2014, Givnish et al 2009); Madagascar’s lemurs and other Malagasy animals and plants (Wirta et al 2008, Reddy et al 2012, Herrera 2017) or the cichlids of East Africa’s Rift Valley Lakes (Salzburger et al 2014, McGee et al 2016)) It produced one of the most anomalous assemblages of native vertebrates known to science – giant wingless birds that converged on the large herbivore niches typically filled on continents by ungulates. The current diversity of moa, appears to have arisen relatively recently, being closely associated with uplift of the Southern Alps (5 – 8.5 Ma; Fig. 1), which simultaneously created intra-island dispersal barriers and increased diversity of habitats and potential niches (Bunce et al 2009)
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