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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.

At 17 sites in the European Alps (2l70-3310 m), the population density and seed production of the high alpine cushion plant Eritrichium nanum were investigated. Recruitment in this non-clonal species relies exclusively on seeds. The population density rose significantly with increasing altitude. A mean number of 368 seeds per m 2 was observed. Whereas the quantity of the generative rosettes (metamers) was relatively constant, the annual seed production strongly varied and was found vulnerable, particularly in 1996, when it was suppressed by unfavorable weather conditions. In 1997 seed production again reached the usual level, when about the same amounts of seeds were recorded as in previous years, indicating the strong resistance of elevated E. nanum populations against the severe climate at high altitudes. With rising population density, E. nanum produces distinctly higher seed numbers. This increasing amount of seeds seems essential for the persistence of its uppermost populations. Our results indicate that it is caused by the rising number of rosettes/ surface and not a higher reproduction by single rosettes. Compared to other alpine species, the seed weight of E. nanum (average 0.76 mg) is high. Most of its neighboring species are clonal, producing much lighter seeds. The strategy of producing heavy seeds favors successful recruitment and appears to be decisive for an obligatory seeder such as E. nanum.

Zoller H. and Lenzin H. 2006. Composed cushions and coexistence with neighbouring species promoting the persistence of Eritrichium nanum in high alpine vegetation. Cushions of high alpine plants may consist of several individuals, either of the same or of different species (composed cushions). To clarify the role of this coexistence for the life history of alpine plants, cushions of Eritrichium nanum (Boraginaceae) were investigated at 17 sites (2170-3320 m a.s.l.) distributed over the European Alps. We determined the age structure of large cushions using herbchronology, described their root systems, and recorded how frequently E. nanum directly coexists with other plant species. The maximum age of individual plants was 35-40 years, but cushions contained up to 25 individuals, including seedlings and juveniles, which suggests that composed cushions can become much older than individual plants. Unlike other cushion plants, E. nanum does not develop adventitious roots to take up nutrients trapped in the interior of cushions. Its root system consists of a primary axis bearing plenty of fine rootlets, two to four tap roots, and long plagiotropic side roots, which explore a large soil area and allow the effective exploitation of nutrients from humus-rich patches. About half of the surveyed plants grew individually on open soil, while the rest lived in close contact to other plants of the same or different species. When it coexisted with other species, E. nanum either acted as an epistratum, overgrowing dense cushion plants (63.5% of the contacts), or as a hypostratum, being overgrown by graminoids such as Festuca halleri. We conclude that at altitudes above 2500 m, E. nanum mainly profits from its coexistence with other species, which together with the joining of individuals into composed cushion seems to improve recruitment success and the persistence of stable populations.