Factors contributing to the decline of an endangered flightless longhorn beetle: A 20‐year study

Abstract

World‐wide decreases of insect abundance and diversity are of major concern because of their importance for ecosystem functioning and the stability of ecosystems. Various studies reported dramatic declines of butterflies, wild bees and beetles in agricultural areas. Yet, evidence for decreasing abundance in cryptic insect species is scarce. Using a transect‐count technique, we monitored the relative population size of the endangered flightless grassland longhorn beetle Iberodorcardion fuliginator in 13 dry, semi‐natural grassland sites in the border region of Switzerland, France, and Germany at yearly intervals over 20 years (1999–2018). To disentangle potential causes for changes in I. fuliginator abundance over time, we recorded quantitatively the plant communities in all sites in 2004 and 2017 and changes in other habitat characteristics. We found that the overall abundance of I. fuliginator individuals decreased by 90% over 20 years: at one site the population went extinct, at five sites the populations were critically decreasing, at four sites the populations were decreasing and at only three sites population size remained stable. Linear models revealed that the factor ‘change in plant species composition’ is the main driver for the decrease in beetle abundance. Alternative models indicated that – in addition to vegetation changes – area of suitable habitat and low heat load affected the probability of decreasing population size. Our study shows that gradual habitat deterioration measured as reduction in grass cover and change in plant species composition negatively affect the abundance of the highly specialised beetle I. fuliginator.

Integrated modelling of insect population dynamics at two temporal scales

“…Our models confirmed a serious decline of the beetle total annual abundance over the 19 years of study. A simple linear regression of the total annual abundance (in Figure 3) on year suggested a decline by about 98% (from approximately 9900 individuals to only about 250) which is comparable with findings in Baur et al (2020), who suggest that habitat deterioration may be responsible for the decline of this specialised species. Although the time-series of counts are statistically-speaking short, there appears to be a difference between the two annual cohorts, with a potentially stronger decline and more even trajectory for the even-year cohorts whereas, in contrast, the odd-year cohorts hardly appear to exhibit a long-term trend, but show more pronounced annual fluctuations.…”

Further evidence for a global decline of the entomofauna

“…For example, abundance of the endangered flightless longhorn beetle Iberodorcardion fuliginator decreased by 90% in 13 semi‐natural grassland sites around Basel (Switzerland) over 1999–2018 (Baur et al . 2020). Changes in plant species composition and decreasing grass cover are key factors for this decline, as both adults and larvae feed on various grasses and their roots.…”

A Fine-Scale Hotspot at the Edge: Epigean Arthropods from the Atacama Coast (Paposo-Taltal, Antofagasta Region, Chile)

“…However, much more field work on the coast is needed for disentangling those relationships, especially in El Niño years. The potential effects of climate change are already under observation in different coastal regions of Latin America [89] and hotspots worldwide [90,91], but much needs to be done especially in the field, considering that the changes in plant species composition seem to drastically affect endangered insects [92]. All these are crucial aspects that will certainly drive entomological surveying and monitoring in our current times of ecological crises.…”