Living on the edge – why should we bother conserving edge-of-range populations?

In a world with looming mass extinction due to climate change, extensive land conversion and deforestation, global economic crisis, growing human population and rising questions of food security, why should we spend the limited funding available for conservation on peripheral populations at the edge of a species’ distribution?

Edge populations are often less abundance and more vulnerable to extinction than populations at the centre of the species’ range (Curnutt et al. 1996). When the edge of a species range coincides with a political boundary, the species may receive high conservation priority within that country even if it is abundant and widespread internationally. It is always sad to hear about the disappearance of a species from a country, especially when it is the result of human activities, but are these edge populations of wider conservation importance?

Grey long-eared bat in flight

Grey long-eared bat in flight

I spent the past four and a half years studying the edge population of the grey long-eared bat, Plecotus austriacus, one of the rarest UK mammals. The grey long-eared bat is relatively common and widespread in southern Europe, but extremely rare at the northern edge of its range. In the UK this bat is restricted to the southern coast of England and the south-west tip of Wales.

Last week my research was in the news (e.g. http://www.bbc.co.uk/news/science-environment-23519010 ) warning that the grey long-eared bat may disappear from the UK. The UK population was estimated at around 1000 individuals and it appears to have declined dramatically in the past century and become fragmented as a result of changes in farming practices and the loss of lowland semi-natural grasslands (meadows and marshlands). These findings were outlined in a Conservation Management Plan that calls to award the grey long-eared bat a priority conservation status and to adopt a landscape-scale approach to the conservation of this bat, focusing on habitat management around roosts and increasing landscape connectivity between roosts.

One question I was repeatedly asked when interviewed by radio presenters and journalists was: ‘why should we care if this bat disappears from the UK?’. For this bolg I want to lay out the case for the conservation of edge populations and explain how it can be connected to wider conservation issues and benefit biodiversity in general.

The moral / ethical argument

Without getting into a deep philosophical discussion, most people will agree that biodiversity holds an intrinsic value and a single species has the right to exist. Due to the effects of humans on biodiversity, there is a moral argument stating that we have a duty to maintain habitats and conserve other species regardless of their importance for human use. What will be the moral consequence of losing a species from the UK? Perhaps not detrimental. Just over 20 years ago the greater mouse-eared bat, Myotis myotis, was officially declare locally extinct in the UK and our societal values did not crumble. However, where do we draw the line and which species do we decide to conserve, knowing that most species are also found outside the UK?

For a review of ethical arguments behind wildlife conservation see: Ethics of wildlife conservation

Climate change and the conservation value of edge populations

Genetically unique edge populations can contribute to the evolutionary potential of the species and future speciation events (Lesica and Allendorf 1994). Our research (Razgour et al. 2013) has shown that the UK grey long-eared bat population forms two unique genetic clusters, separated from European populations, and contains unique haplotypes. Therefore its conservation is important for maintaining the genetic diversity of the species as a whole.

Under future climate change, edge population are particularly valuable. Having evolved in marginal atypical environments, edge populations may be better able to respond to environmental changes and expand into new habitats (Hunter & Hutchinson 1994), two important qualities for leading range shifts in response to climate change. Indeed with future climate change some range margins may become more suitable than the current centre of the range. Our research on the grey long-eared bat (Razgour et al. 2013) shows that by the end of the century most of the UK is predicted to become climatically suitable, while most of southern Europe will become unsuitable for this bat. The north-western shift in suitable conditions means that the UK edge population is important for spearheading range shifts and the future spread of genetic diversity. Because range shifts and successful population establishment depends not only on suitable climatic conditions but also on the availability of roosting and foraging habitats, actions taken now to conserve edge populations and their habitats are important for the future of the species as a whole.

Edge populations as part of the wider ecosystem

Because bad news often makes the news, the conservation plight of edge populations on the brink of local extinction can receive media coverage (as has been the case with the grey long-eared bat). This media attention and interest from the general public can be used to raise awareness for the conservation of other species and biodiversity in general. In our management plan we recommend using the grey long-eared bat as a flagship species to promote the conservation of its main foraging habitat, lowland semi-natural grasslands (Razgour et al. 2011a), one of the most threatened habitats in the UK. Semi-natural grasslands contain a high proportion of plant, invertebrate and bird species of high conservation concern, and therefore addressing the stark decline of this habitat is an important conservation priority (State of Nature Report).

The grey long-eared bat represents the requirements of lower trophic levels, including arthropods and plants, as well as other bats, birds, reptiles and small mammals that are likely to benefit from conservation measured aimed at improving foraging habitats and landscape connectivity for the grey long-eared bat. Beyond semi-natural grasslands, grey long-eared bats rely on woody riparian vegetation, edge of deciduous woodlands and well-developed woody hedgerows or tree stands found along arable fields and pasture (Razgour et al. 2011a). All these landscape elements are commonly used by bats and other wildlife for foraging and commuting.

Bats play important ecological roles, and insectivorous bats in particular provide ecosystem service by controlling nocturnal insect populations, including some agricultural pests (Kunz et al. 2011). The grey long-eared bat consumes agricultural pests, like the cranefly Tipula oleracea (leatherjackets) and the moths Autographa gamma (silver Y) and Agrotis ipsilon (dark sword-grass / black cutworm) (Razgour et al. 2011b). Therefore, encouraging these bats in the farmed landscape may benefit the wider farming community, though the population will have to grow substantially before it has a considerable impact on insect pests.

——-

The arguments surrounding the conservation of edge population are part of a wider debate in conservation biology and a general paradigm shift away from single-species conservation to landscape scale ecosystem management and the maintenance of ecosystem services. I believe that the ecosystem approach can be used as a framework for studying and managing single species and populations within the wider community and landscape context, and the grey long-eared bat UK population may offer an example of how this can be done.

Catching grey long=eared bats in Jersey

Catching grey long-eared bats in Jersey

References

Curnutt JL, Pimm SL, Maurer BA (1996) Population variability of sparrows in space and time. Oikos 76, 131-144.

Hunter ML, Hutchinson A (1994) The virtues and shortcomings of parochialism: conserving species that are locally rare, but globally common. Conservation Biology 8, 1163-1165.

Lesica P, Allendorf FW (1995) When are peripheral populations valuable for conservation? Conservation Biology 9, 753-760.

Razgour O, Hanmer J, Jones G (2011a) Using multi–scale modelling to predict habitat suitability for species of conservation concern: the grey long–eared bat as a case study. Biological Conservation 144, 2922-2930.

Razgour O, Clare EL, Zeale MRK, Hanmer J, Bærholm Schnell I, Rasmussen M, Gilbert MTP, Jones G (2011b) High-throughput sequencing offers insight into mechanisms of resource partitioning in cryptic bat species. Ecology and Evolution 1, 556-570.

Razgour O, Juste J, Ibáñez C, Kiefer A, Rebelo H, Puechmaille SJ, Arlettaz R, Burke T, Dawson DA, Beaumont M, Jones G (2013) The shaping of genetic variation in edge-of-range populations under past and future climate change. Ecology Letters DOI: 10.1111/ele.12158

3 Comments on “Living on the edge – why should we bother conserving edge-of-range populations?

  1. Glad to hear you covered the topic in your journal club. Morphological variation is quite difficult to quantify in these bats as they are part of a cryptic species complex with little variation between species. This summer I measured many grey long-eared bats in Spain expecting to find some morphological differences from the UK population, but found no differences in wing, size, coloration and other common measurements. Many bat species tend to show regional variation in echolocation calls, which is one aspect I have not measured. – From Dr. Orly Razgour

  2. Awesome blog! Do you have any helpful hints
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