I’m posting this as further food for thought regarding my earlier post concerning rates of mtDNA diversification in humans with regard to the types of climate in which they live. In this linked paper, it’s elephant seals rather than humans who provide the focus of the research, with a look at how changing climate can cause marine mammal populations to move to and and away from habitats over long time-spans, in this case, 7,000 years. Here’s the abstract, whilst the entire paper is freely accessible at PLoS Genetics:
Environmental change drives demographic and evolutionary processes that determine diversity within and among species. Tracking these processes during periods of change reveals mechanisms for the establishment of populations and provides predictive data on response to potential future impacts, including those caused by anthropogenic climate change. Here we show how a highly mobile marine species responded to the gain and loss of new breeding habitat. Southern elephant seal, Mirounga leonina, remains were found along the Victoria Land Coast (VLC) in the Ross Sea, Antarctica, 2,500 km from the nearest extant breeding site on Macquarie Island (MQ). This habitat was released after retreat of the grounded ice sheet in the Ross Sea Embayment 7,500–8,000 cal YBP, and is within the range of modern foraging excursions from the MQ colony.
Using ancient mtDNA and coalescent models, we tracked the population dynamics of the now extinct VLC colony and the connectivity between this and extant breeding sites. We found a clear expansion signal in the VLC population ~8,000 YBP, followed by directional migration away from VLC and the loss of diversity at ~1,000 YBP, when sea ice is thought to have expanded. Our data suggest that VLC seals came initially from MQ and that some returned there once the VLC habitat was lost, ~7,000 years later. We track the founder-extinction dynamics of a population from inception to extinction in the context of Holocene climate change and present evidence that an unexpectedly diverse, differentiated breeding population was founded from a distant source population soon after habitat became available.
Although it’s not possible to make direct comparisons with ancient seal populations and hominids, I think this paper emphasizes how populations need not only to be able to move in response to pulses of climate change in order to avoid extinction due to loss of habitat, but also just how quickly a high degree of diversity can develop within a population of mammals relatively soon after occupying a new habitat. The idea of seals discovering new shoreline habitats – and returning to old ones – in the course of long distance foraging excursions is reminiscent of how early humans gradually found their way around the world, both by littoral and inland travel. Like the seals in Antarctica, there would have been times when humans too returned to previous habitats as they were pushed and pulled along with other fauna and flora into different refugia as cooling and warming phases waxed and waned. Moreover, I wonder from when, and to what extent human expansions and incursions were mediated by a curiosity to explore the unknown, rather than merely scouring the land for the next meal and somewhere to bed down for the night.
Reference: de Bruyn M, Hall BL, Chauke LF, Baroni C, Koch PL, et al. (2009) Rapid Response of a Marine Mammal Species to Holocene Climate and Habitat Change. PLoS Genet 5(7): e1000554. doi:10.1371/journal.pgen.1000554