The Concept of Refugia

I thought it might be useful to look into the concept of refugia in population biology and see how this has been used and applied to the study of past global environmental change. 

Source: Haffer (1969)

The concept of refugia was first put forward by Haffer (1969) as a historical explanation for the range in genetic diversity found among bird populations in the Amazon. He proposed that a shift to more arid climatic conditions in the late Pleistocene led to changes in vegetation (significant decrease in the number of trees), leaving the birds confined to small ‘habitable reservoirs’ of forest (shown in Fig. 1) that were sufficiently humid enough to sustain the bird populations until the end of the Pleistocene. However, this time spent in refugia was long enough for allopatric speciation to occur among the isolated bird populations. As the climate became more humid the development of tropical rainforest vegetation re-connected the refugia, eventually resulting in an ‘immense variety’ of bird populations throughout the Amazon River basin.

Since the concept of refugia is used in such a wide range of academic fields from conservation biology to palaeocology, a definition of the term is often disputed. In a more recent paper, (Stewart et al 2010) define ‘Quaternary refugia’ as the ‘geographical region or regions that a species inhabits during the period of a glacial/interglacial cycle that represents the species' maximum contraction in geographical range’. They point out that this definition is flexible enough to ‘accommodate species that are adapted to different climatic conditions’, whilst also ‘highlighting the idea that species in general respond to climatic changes independently of each other’. They also distinguish between various categories of refugium in their discussion, based on geographical location and the adaptations of the species that they are inhabited by (whether the plants and animals are adapted to cold climatic conditions or more temperate ones).

But what’s so special about these refugia?

• The effect of the possible allopatric isolation within refugia and the process of re-colonisation from them have advanced understandings of aspects of evolution, including adaptation, speciation and extinction (Stewart et al 2010).
  
• We can possibly use understanding of how species reacted to climate change during the last cold stage to infer how species reacted to climate change during previous cold stages (Stewart and Lister 2001).
• If we can develop an understanding of how species reacted to climate change in the past, we may be able to predict responses to future changes in climatic conditions (Stewart et al 2010).
  
• It is interesting to see what role cryptic Northern refugia played in shaping the make-up of modern day flora and fauna (Stewart and Lister 2001).
• Modern populations of flora and fauna that have derived ‘in situ’ from cryptic Northern refugia could possibly have ‘different genetic signatures’ from those populations that re-colonised from further refugial locations (Stewart and Lister 2001). As a result of this, geneticists and palaeontologists can work together, advising each other about possible sampling site locations.
• As scientists carry out further investigations into cryptic Northern refugia, their understanding of ‘non-analogy fossil assemblages’ will hopefully become greater (Stewart and Lister 2001).