Community diversity and composition of ground-dwelling arthropods in major habitat types of the KwaZulu-Natal Sandstone Sourveld.
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Date
2023
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Abstract
Grasslands constitute over 25% of the global land surface and close to one-third of southern Africa.
Natural and semi-natural grasslands are recognized globally for their high biodiversity value and
their important contribution to the provision of ecosystem services, including provisioning
services such as carbon sequestration, water catchments, and grazing for livestock and wildlife.
Nonetheless, grasslands are consistently reduced and threatened by anthropogenic activities and
invasive alien plants. Invasive alien plants may hinder the growth of natural vegetation by
overconsumption of resources. The impact of invasive alien plants on natural vegetation may
indirectly affect plant-to-animal interactions such as specialized pollination and seed dispersal
syndromes which may ultimately disturb ecosystem processes. The Sandstone Sourveld in
KwaZulu-Natal province of South Africa is a threatened grassland ecosystem as a result of various
anthropogenic disturbances. Knowledge of arthropod response to differences in habitat types may
be essential for an improved understanding of the structure and functioning of ecosystems, which
is relevant for informing conservation practice. The aim of this study was to investigate the
composition and diversity patterns of ground-dwelling arthropods (ants, beetles, Orthopterans, and
spiders) in three habitat types (forest, intact grassland, and disturbed grassland) at Springside and
Tanglewood Nature Reserves, which occur in the KwaZulu-Natal Sandstone Sourveld (KZNSS).
The objectives were: (i) to document the response of the ground-dwelling arthropod community
in different habitat types, (ii) to determine the impacts of seasonal change on the abundance and
richness of ground-dwelling arthropods at the two sites, and (iii) to determine the correlation
between the distribution of ground-dwelling arthropods and soil characteristics in the KZNSS.
Ground-dwelling arthropods were sampled in Springside and Tanglewood Nature Reserves using
pitfall traps in each habitat type. Soil parameters in the habitats were also assessed. Analysis of
variance was used to test for differences in arthropod morphospecies richness and abundance across the habitat types and between seasons. The Shannon-Weiner diversity index was computed
and used to compare the diversity of ground-dwelling arthropods between the two sites and among
habitat types. Ground-dwelling arthropods showed varying patterns in response to habitat
characteristics and the disturbance gradient at Springside and Tanglewood. Intact grassland was
the most diverse habitat in both Springside and Tanglewood. In Tanglewood, the abundance of
ants was greater in disturbed grassland which consisted of a variety of alien invasive shrubs, the
high abundance was explained by the “intermediate disturbance hypothesis”. However, alien
invasion showed more negative than positive impacts on the abundance and composition of
ground-dwelling arthropods when there was a significant decrease in the abundance and
composition of ants, beetles and spiders. Species richness of ants and beetles was higher in the wet
than dry season whereas Orthopterans and spiders showed no significant difference between
seasons. In all arthropod groups, a greater number of species were correlated to soil potassium,
soil pH, and soil bulk density. Overall, the intact grassland had the highest species richness and
abundance followed by the forest and lastly the disturbed grassland. The greater abundance of
ants, beetles, and spiders in the pristine grasslands of KZNSS shows that there is still a need to
conserve the remnants of the KZNSS vegetation. Therefore, the conservancy management is urged
to consider the eradication of alien invasive plants. Future studies are recommended to consider
the volant and vegetation canopy arthropods as they are all interdependent with ground-dwelling
arthropods to form a whole community of arthropods in an ecosystem.
Description
Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.