limits to distribution

Why some species are widely distributed over a variety of climates whereas others have a very small distribution range, is a question of great interest to physiologists. Often it is likely to be a number of interacting factors, such as weather or competition. However, the main driver of distribution ranges is probably energy, whether an individual can obtain enough energy to stay alive and to reproduce. Importantly, physiological data on what limits the distribution of species can shed light on how readily they can adapt to a changing climate or if they will not be able to adapt at all. Such information is critical in terms of constructing models for future scenarios and thus to develop informed management plans. To date, this research has involved quantifying the physiology of Australian bat species with both large and small distribution ranges. Norway provides a great natural setting for this research, as it encompasses a large latitudinal and climatic range. Therefore, we are currently working on a project on bat species with varying distribution ranges throughout Norway. 

The figure below reveals how populations of the same species, here the eastern long-eared bat (Nyctophilus bifax), can show differences in physiological traits due to local climate conditions. The trait represented here is the threshold ambient temperature at which bats begin to defend their body temperature so it does not decrease any further. As it is not often very cold in tropical areas, there has been no selection pressure on this population for this threshold to be as low as it is in temperate populations.

Figure taken from: Stawski C (2012) Comparison of variables of torpor between populations of a hibernating subtropical/tropical bat at different latitudes. Pp 99-108 In: Ruf T, Bieber C, Arnold W, Millesi E (eds). Living in a seasonal world: thermoregulatory and metabolic adaptations. Springer, Heidelberg.

Figure 3 IHS.JPG
Iluka Nature Reserve, subtropical rainforest
Tam O'Shanter National Park, tropical rainforest
Armidale, temperate eucalypt woodland

Tropical field site at Tam O'Shanter National Park, QLD, Australia. Copyright Clare Stawski

Subtropical field site at Iluka Nature Reserve, NSW, Australia. Copyright Clare Stawski

Temperate field site at Armidale, NSW, Australia. Copyright Clare Stawski