Epsilon Archive for Student Projects

Abstract

The understanding of species’ ecology and their trophic interactions, are crucial in the work of
conservation. A population decline in a predatory species may be a result of a decline in their
food source, a trophic level down. Then an understanding of why the predator’s food source
has declined is needed, to be able to pinpoint conservation actions. In Swedish forests one
such trophic interaction is between dead wood, saproxylic insects and woodpeckers. Modern
forestry of clear cuttings and monoculture plantations of coniferous trees, has changed many
Swedish forests to be less diverse in tree species, age classes of trees, types of dead wood,
denser and hence also deficits in dead deciduous wood. As a result, insects in Swedish forests
have declined. Most longhorn beetle species (Cerambycidae) larvae are saproxylic and have
different niches. Niches such as specific host trees, age classes of trees, types of wood and
different succession stages of decomposed dead wood. Of the 118 species of longhorn beetles
in Sweden, 46 were red listed in the 2020 Swedish red list evaluation. Lesser spotted
woodpecker (Dryobates minor) is a small woodpecker preferring open broadleaf forests.
Between 1975-1991 the Swedish population decreased by approximately 50% and today D.
minor is classified as Near Threatened, according to the 2020 Swedish red list evaluation.
Studies in southern Sweden have shown that the most important factor influencing
reproduction success in D. minor is the prey density several weeks to months before breeding.
During that time they feed on wood living insect larvae, mainly in dead thin twigs on living
deciduous trees. Longhorn beetle larvae and pupae are probably the most important food
source. In order to understand why D. minor is threatened, their food source has to be
understood as well. In this study I used pheromone traps to monitor longhorn beetles in 34
areas between May-July, in the counties of Skåne, Blekinge, Småland and Västergötland in
southern Sweden. Pheromone-based trapping is an effective method to monitor otherwise
elusive species and in this study pheromone blends attracting mainly Pyrrhidium sanguineum,
Phymatodes testaceus, Poecilium alni and Plagionotus arcuatus were used. The areas
monitored in this study, had been inventoried 2019-2020 by “project lesser spotted
woodpecker at Lund University”, giving occurrence information about D. minor. In this study
I found no differences in longhorn beetle abundance or longhorn beetle biodiversity between
areas inhabited or uninhabited by D. minor. Hence, no evidence was found that D. minor
habitat choice depend on the longhorn beetles studied. A strong positive association was,
however, seen between P. sanguineum and P. alni and large dissimilarities between P.
testaceus and P. alni as well as between P. sanguineum and Anaglyptus mysticus. These
associations between the species could perhaps be used in future identification of indicator
species. I also found a negative correlation between the biodiversity of longhorn beetles and
increasing latitudes, but the factors affecting longhorn beetles are not clear. Lastly, several
new localities with red listed species were found and my findings suggest that P. sanguineum,
P. alni and perhaps also A. mysticus distributions are underestimated.