A study of climate change and land-use impacts on butterfly populations in England has revealed that persistence of a business as usual scenario will lead to widespread drought-sensitive butterfly population extinctions occurring as early as 2050.
Apart from climate change due to greenhouse gas emissions, diversion of semi natural habitat areas by fragmenting them for food and energy needs is another factor in drought sensitive butterfly population collapses. However, there is a 50 per cent probability of achieving persistence right through 2100 if landscape management (restoring the semi natural habitats to reduce fragmentation) is combined with a drastic reduction in emissions, notes a paper published recently in Nature Climate Change.
The study used extensive long-term butterfly population data from 129 sites of the UK Butterfly Monitoring Scheme to assess historical responses of 28 species to an extreme drought event in 1995. This was the most severe summer since records began in 1776.
Butterflies, though warmth-loving, can exhibit declines in population due to heat stress to larvae and absence of host plants under aridity conditions. The study calculated recovery rates by measuring population change in the four years following the drought and found that the recovery rate was greater in a semi natural habitat with large contiguous area unlike a highly fragmented one. When recovery times exceed return times of drought, it would lead to continual population erosion, and ultimately local extinction, the authors say.
The study authors refer to the extent of fragmentation as “edginess,” meaning that there are more edges in a fragmented habitat and the more the edges the more the population decline due to less soil moisture at the edges. Explaining this, the study’s lead author, Dr. Tom Oliver from the University of ReadingSchool of Biological Sciences, UK said in an email to this correspondent: “This is simply due to the physics that things tend to dry out at their edges first. The centres of woodlands, which are dense and shady, remain moist for longer. In contrast, the edges dry out quicker, probably because they receive more sunlight which dries out the forest floor and also there are more air currents which lead to higher rates of evaporation.”
In comparison to this scenario, populations on the brink of extinction can be rescued if there is improved connectivity to neighbouring fragments and populations. This rescue effect refers to the phenomenon whereby, when a population becomes locally extinct, it can be re-colonised by individuals from nearby populations.
However, individuals only tend to move across landscapes (and produce the rescue effect) when the landscapes are less hostile. In contrast, when there are larger amounts of favourable butterfly habitats in the intervening landscape (i.e. a well connected landscape), then individuals are more likely to move across it and lead to the rescue effect allowing recovery of the population that went locally extinct.
One possibility is that microevolution of drought tolerance could mitigate some future impacts. Although there are examples where evolution in response to climate change can occur rapidly, in Britain it may not occur because butterfly populations are small.
Source : The Hindu
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