What Happens Outside Refugia?

There has been a lot of focus and debate over what happens to species when isolated inside refugia, however, I have not yet mentioned anything about the fate of populations outside refugial areas – something which was brought to my attention whilst reading Stewart et al (2010).

Benettet al (1991) investigated the pollen record of North European forest trees and concluded that trees which expanded their ranges from Southern Europe during warmer interglacials became extinct in the Northern part of their ranges with the onset of the last glaciation, not retreating south at the end of the interglacial. In a corresponding study, Dalén at el (2007) put forward data to suggest that the Arctic fox populations in mid-latitude Europe became extinct at the end of the Pleistocene and was incapable of traking Northern habitat shifts. This population did not, therefore, contribute to the genetic make up of present day populations of Arctic fox.

According to Stewart et al (2010), these two studies show that populations that once occupied widespread ranges when conditions were favourable became extinct instead of ‘traking retreting habitats by physically moving into the refugium’. This means that the species in long-term refugia have descended in-situ from those already in that refugial location, rather than species outside the area (who, consequently, make no contribution to the refugial populations). Studies on species outside of refugial areas, however, are rare so perhaps this is an area that needs more attention? We do know, however, that ‘the ultimate fate of a species in a contraction phase may be complete extinction’, and ‘because species’ ranges tend to contract in the direction of their refugia, the long-term refugial areas will often be the eventual location of the terminal populations’ (Stewart et al 2010).