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Effects of disturbance on beetle and spider assemblages in a Mediterranean woodland
Titre : Effects of disturbance on beetle and spider assemblages in a Mediterranean woodland
Auteur : Angel, Noa
Université de soutenance : Ben-Gurion University of the Negev
Grade : Master of Science 2009
Résumé
In Mt. Meron Nature Reserve landscape is becoming homogeneous following tree
encroachment. Understory vegetation encompasses lower herbaceous plant species
richness than adjacent open patches which are scarcely shaded or modulated by the
canopy. This study aimed to examine the canopy effects on higher trophic groups. The
research tested whether beetle and spider species diversity was higher in the open
patches, following herbaceous species richness, or if it is positively affected by the
filtering of the trees, and therefore higher in areas with higher tree cover.
I tested two main hypotheses in which the spider and beetle richness in the
woody patches are expected to increase with a decrease in canopy area. The Landscape
Modulator-filtering hypothesis postulated that trees modulate their environment thus
allowing the existence of woody-affiliated species. With the decrease in tree cover,
beetle and spider species richness in the woody patch was predicted to decrease. The
taxonomic diversity hypothesis postulates a direct relationship between plant species
richness and arthropod species richness thus predicting an increase in beetle and spider
species richness as a function of herbaceous species richness. Open patches-affiliated
species were predicted to have a positive relation with both herbaceous plant richness
and increased open area.
. I examined these hypotheses through the use of two disturbance forms of
management affecting the woody patch. Tree removal was used to decrease the tree
cover, or increase the open area and cattle grazing was introduced in order to test its
disturbance effects through grazing and browsing on regenerating trees.
The results of this study partially supported the landscape modulator-filtering
hypothesis. Ground-dwelling predator and detritivore species diversity decreased in
their diversity with decreased tree cover. The taxonomic diversity hypothesis was also
only partially supported. Herbivore species richness increased only in open patches as a
function of herbaceous richness.
Disturbance effects were attributed mostly to tree removal which had a large
effect on beetle and spider diversity patterns and composition while grazing had little to
no effect. The interaction between grazing and removal decreased diversity of grounddwelling
spiders and beetles in the woody patches. Removal with no grazing generally
increased vegetation-dwelling beetle and spider richness and abundance. Removal
changed the assemblage composition of ground-dwelling spiders and beetles and
removed woody patches were more similar in their composition to open patches than to
woody unremoved patches. Vegetation-dwelling beetles exhibited different
communities in the two patch types with and without removal.
My study shows that beetle and spider diversity and composition is influenced
more through the effect of the tree as a dominant landscape modulator than the change
in herbaceous plant richness. Removal can be used as an effective land-use management
tool in order to manipulate the landscape patch mosaic.
Mots Clés : Beetles — Ecology — Merron(Israel). — Grazing — Environmental aspects — Spiders — Ecology — Tree felling
Page publiée le 10 janvier 2012, mise à jour le 22 novembre 2018