Response of carabid and cicindelid beetles to various types of landscape disturbances.
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Date
1998
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Abstract
A study of carabids and cicindelids was carried out in eastern South Africa using the same
methodology as has been used in the northern hemisphere to obtain a southern hemisphere
perspective. The study used the macroecology approach to compare patterns and responses of
these animals to anthropogenic disturbances in visually similar habitats (forests, grasslands).
Although this is essentially a local component of a larger macroecological study, it is shown that
even though species and identities differ between the north and southern hemispheres, the
general patterns of community response to anthropogenic disturbances are surprisingly similar.
Changes in carabid assemblages were assessed across eight sites or landscape elements
experiencing a range of disturbance types, both regular and irregular (such as mowing, fire,
irrigation, fertilizers, pesticides, forestry). Direct comparisons were made with similar studies
in the Palaearctic. Species diversity, seasonal population variations, population phenology,
spatial patterns and mean body size of species assemblages relative to the landscape elements
are described. As in the north, intensively disturbed biotopes were impoverished, and natural
patches of moist forest acted as habitat sources for these disturbed sinks. Roadside verges were
species-rich analogues of natural habitats. The mean body size of carabid assemblages in forest
and grassland sites decreased with increasing intensity of disturbance. One contrary comparison
with the north was that a plantation, in this case macadamia, was exceptionally rich in carabid
species and individuals.
Classification and ordination methods identified and characterised the eight sites to six
ecological meaningful biotopes for carabids and cicindelids. This also allowed inferences as to
how the various landscape disturbances in natural forests, planted pine forests, macadamia
plantation, recreational park, road verge grasslands and hayfields affect carabid and cicindelid
species richness and abundance. Species assemblages that responded to these anthropogenic
impacts were potential indicator groups that can assist in the planning and management of forest
and grassland landscapes for conservation of biodiversity. Some management recommendations
for these landscapes are given.
Individual species-environment relations were investigated using both univariate and
multivariate analyses. The solutions to these analyses were then used to describe how species are distributed along major environmental gradients. It was shown that soil characteristics (pH,
moisture, twig and/or leaf litter) determine carabid and cicindelid assemblages. Land-use and
management regimes influence these patterns. The effect of altitude is masked by the presence
of soil characteristics in a multivariate analysis, and more so in the presence of pH and moist
soil-sand gradients with changing altitude. In the absence of soil characteristics and in univariate
analysis, altitude becomes very important. Altitude has therefore an indirect effect in that it
determines climate, which, in turn, determines soil and vegetation type which then determines
species presence and abundance.
It is concluded that the macroecological approach has great potential for teasing apart local
effects from global ones, and can contribute to the conservation of biodiversity at both small and
large scales.
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1998.
Keywords
Beetles--Ecology., Insect populations., Insects--Habitat--Protection., Biodiversity conservation., Natural areas--KwaZulu-Natal--Pietermaritzburg., Theses--Entomology.