Abstract
Human-induced ecological and climatic changes have led to the decline and even local extinction of many formerly widely distributed temperate and cold-adapted species. Determining the exact causes of this decline remains difficult. Bryodemella tuberculata was a widely distributed orthopteran species before the mid-19th century. Since then, many European populations have suffered drastic declines and are now considered extinct or critically endangered. We used ecological niche modelling based on a large dataset of extant and extinct occurrence data to investigate whether poor climatic suitability in the periphery of its global range was a possible cause of the local extinction of the European populations of B. tuberculata. We also used population genetics based on the COI marker to estimate and compare the genetic diversity of extant populations. We found that Europe still provides highly suitable habitats close to the climatic optimum, contradicting the assumption of climate change as major driver of this decline. Instead, changes in land-cover and other anthropogenic modifications of the habitats at the local scale seem to be the major reasons for local extinctions. Genetic analysis suggests Central Asia as center of diversity with a stable population size, whereas the effective sizes of the remaining European populations are decreasing. We found European genetic lineages nested within Central Asian lineages, suggesting a Central Asian source distribution area. Our results suggest that the declining European populations represent relics of a formerly wider distribution, which was fragmented by changes in land-use. These relics are now threatened by limited connectivity and small effective population sizes. Specific conservation actions, such as the restoration of former or potential new habitats, and translocation of individuals from extant populations to these restored sites may help slow, stall, or even revert the extinction process.
Highlights
Biodiversity decline, insect decline, has been recognized as a major threat to global ecosystems (Dirzo et al 2014; Conrad et al 2006; Hallmann et al 2017)
Hutchinson’s concept of the ecological niche (Hutchinson 1957) divides the multidimensional parameter space of habitat variation roughly into two regions: (1) the region in which the number of local births exceeds that of local deaths, close to the optimum niche of the species, and a source of emigration; and (2) the region in which the number of deaths exceeds that of local births, typically far from the environmental optimum of the species, where populations are maintained by immigration from source populations (Holt 1996)
The northernmost location was found in Siberia (Russia) at 67°N; the southernmost location was in Tibet (China) at 28°N
Summary
Biodiversity decline, insect decline, has been recognized as a major threat to global ecosystems (Dirzo et al 2014; Conrad et al 2006; Hallmann et al 2017). Species are affected differently by environmental change depending on their ecological tolerance and other species-specific life history traits, determining the likelihood of decline and local extinction (Cahill et al 2013). The extinction of local populations depends on the combination of the geographic location of the population within the distribution range, the ecological tolerance of the species and shifts in habitat conditions (Lawton 1994; Cahill et al 2013). Known as center-periphery hypothesis, this concept has provided a baseline for many studies of population dynamics and genetic variability at species distribution limits
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