Species' Responses to Climatic Change

Persisting in refugia is just one of the theories that have been put forward to explain species’ responses to changing climatic conditions. As there has been a bit of a debate over whether species in Northern latitudes persisted in and then recolonised from local refugia or, in fact, responded to climate change in a slightly different way and recolonised from further away, I thought it would be useful to look at the other possibilities before jumping into the literature on cryptic Northern refugia.

The plant and animal species that exist today have managed to survive long periods of variable climate, withstanding changes in temperature, precipitation, atmospheric carbon dioxide concentration as well as glacial and interglacial cycles (Davis and Shaw 2001). However, the majority of species can only survive within a certain range of environmental conditions so a response to climate change on this scale is inevitable.

Palaeoecologists (people who carry out research to try and infer past ecological and environmental conditions from studying fossil records) have predicted that when species are faced with a significant change in climate they will respond in one of the following ways (Davis et al 2005):

1. Migration/shift in range – Altering their distributions in order to remain within suitable climatic conditions
2. Persistence in refugia
3. Adaption
4. Extinction – If a species is not able to respond to significant changes in climate in any of the above ways then it will no longer be able to survive

If all these different responses to climatic change have been identified, why are many scientists so certain that particular species in the Northern latitudes responded by sticking out the extreme cold of the last glaciation in refugia rather than responding in a different way? Well, the evidence they have put forward for the existence and locations of these refugia is based on variation at supposedly ‘neutral genetic marker loci’ (Davis et al 2005). A genetic marker is a ‘gene or DNA sequence with a known location on a chromosome that can be used to identify individuals or species’.

Scientists use this information, typically collected from mitochondrial DNA samples from fossils, to determine the location of refugia and the migration routes taken from the time of recolonisation from the refugia. So, if the evidence is there then these refugia must have existed, right? Well, before I make my mind up completely, I think I need to look at some of this evidence in detail so my next few blog posts will summarise some recent literature in this area, focusing on specific species, so that I can hopefully outline the case for the existence of these cryptic Northern refugia.