Beetles, butterflies and how pole-ward migration works

The movement of species towards the poles is not as simple as individual organisms migrating further north. The actual phenomenon involves a decrease in population in the southern ends of a distribution of species (extinction due to warmer temperatures) and an increase in colonisation rates of the same species in the northern end of a distribution (including new areas which are now warm enough to host these species) [1]. This shows a gradual shift in the population of a species which correlates which global temperature rise. This pole-ward migration is likely to affect all types of species, however, airborne species are far more likely to be able to shift northward than slower land moving species due to habitat fragmentation. For example, animals such as birds are likely to be able to cross boundaries such as barren land (increasing with climate change!) and urban areas to habitats more suitable to live in. Slow moving creatures such as snails, for example, may find moving their distribution northwards a much more difficult task.

Butterflies are a good example as many species have already shown a great northward movement – however, other species may find it more difficult to move north due to how delicate and sensitive they are to habitat fragmentation (and not being able to fly long distances). In a study of 35 UK butterflies, 63% were found to have moved north significantly in the last century (35 – 240km) [1]. However, some scientists have been looking at ‘assisted colonisation’ of certain butterfly species. This term means that humans can help to relocate declining butterfly species into new habitats which are suitable for colonisation but they may not naturally be able to reach [2]. This is one way we may be able to reduce the loss of biodiversity from the impact of climate change over the next few decades.

Lastly, it is not such a bleak future for our bio diverse world. There are some species which will expand their range northward without contracting their southern range – increasing their distribution into new areas without their loss in others. An example of this is a species of ground beetle called Agonum viridicupreum which has been found to have expanded its range northward by about 100km in the last century without any loss of population in the southern range [3].

References:
[1] Parmesan et al 1999, 'Poleward shifts in geographical ranges of butterfly species associated with regional warming', Nature, 399, 579 – 583.
[2] http://planetearth.nerc.ac.uk
[3] Drees et al 2011, ‘Poleward range expansion without a southern contraction in the ground beetle Agonum viridicupreum (Coleoptera, Carabidae)’, ZooKeys, 100, 333-352.