Longhorn beetles in Sweden – changes in distribution and abundance over the last two hundred years

• The abandonment of traditional agricultural practices and the introduction of large-scale industrial forestry has transformed landscapes and changed the conditions for wood-living organisms. This study examines changes in distribution and abundance of the 118 species of longhorn beetles (Col. Cerambycidae) recorded from natural habitat in Sweden over the 19th and 20th centuries, based on extensive surveys of museums, private collections and information in the literature, all in all more than 57 000 specific records compiled by 1400 collectors. The primary results are presented as maps of species’ distributions (-1900; 1901-1950; 1951-1975, and 1976-2000), population size indices (PSI s) based on species frequencies in subsets of the total material obtained by comparable collection methods, and estimates of abundance compiled from a succession of insect faunas spanning two centuries. Changing practices and preferences of collectors are examined in order to interpret the maps and indices and separate real changes of distribution and/or abundance from artefacts due to sampling biases. Appendices include the phenology of individual species and sources of data in the literature. Distributions of most species have changed little during our period of study, and 45 of 103 species are still assigned to the same category of abundance today as in the faunas from the early 19th century. Similarly, tests and interpretations of the PSIs indicate that the abundances of 31 out of 76 analysed species have been quite stable since the 1950s. Other species seem to increase - 32 are considered more abundant today than in the early 19th century faunas, and 17 of the 76 analysed species appear to have become more common since the 1950s. However, there have also been substantial negative changes: 26 species are categorised as less abundant today than in the early 19th century, and 5-10 of these have probably gone extinct. Furthermore, tests and interpretations of the PSI s indicate that 16 of 76 analysed species have decreased in abundance over the last fifty years. Some of these are associated with burnt trees, a handful develop in large diameter sun-exposed dead oak wood, others utilise dead wood of lime, a couple live in open, grazed coniferous forests, two species mainly develop in old construction wood and one species is primarily found in old-growth spruce forests. Close to half of all Swedish species of longhorn beetles are red-listed. However, our analyses indicate that few red-listed species meet the IUCN thresholds for population decline, suggesting that the thresholds are set too high to detect declining longhorn beetles (and perhaps insects more generally), but also that some red-listed species seem to increase and should be removed from the list. Our results also indicate that red-listed species whose narrow distributions have been the same for a long time may be limited by other factors than substrate availability, and therefore be more resilient to habitat change than their red-list classification suggests. Conversely, species with recently contracting ranges of distribution may be even more at risk than their threat categories imply. A final section briefly discusses monitoring of future trends and gives some suggestions on how conservation measures may be designed to better meet regional conservation needs

Ämnesord

LANTBRUKSVETENSKAPER  -- Annan lantbruksvetenskap -- Miljö- och naturvårdsvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Other Agricultural Sciences -- Environmental Sciences related to Agriculture and Land-use (hsv//eng)

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