Invertebrate species turnover and body size patterns across an altitudinal gradient
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University of Pretoria
Abstract
Understanding patterns of biodiversity over geographical gradients is an important aspect of
conservation science. Latitudinal and altitudinal gradients are among the preferred gradients selected
to study due to their ecological significance. Studying diversity along these gradients may assist in
understanding why some areas are more species rich than others. A similarity in climatic conditions
can be observed between latitudinal and altitudinal gradients in terms of both gradients representing a
climatic cline. However, within an altitudinal gradient a faster rate of change within environmental
variables e.g. temperature can be observed compared to latitudinal gradients. As a result, altitudinal
studies may be a preferred choice to investigate patterns in biodiversity.
Climate change is a topic that has received considerable research attention due to its uncertain
impacts on taxa. One species may respond positively to the changes while another may respond
negatively. Altitudinal gradients can be used to investigate these possible responses of species under
changes in temperature.
Many studies have investigated species richness patterns across altitudinal gradients, while
species turnover and body size patterns have received less attention, especially in South Africa.
Abstract
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Furthermore, few studies have focussed on comparing species richness and turnover patterns between
taxa. The aim of this study was to investigate and compare species richness and species turnover
patterns of spiders and ants across an altitudinal gradient in the Drakensberg Mountains. The
altitudinal gradient studied ranged from 900 to 3 000 m.a.s.l. Overall, a clear difference in spider and
ant species richness patterns was observed, ant species richness decreased significantly with
increasing altitude, while no spider species richness pattern was detected. Spider species turnover was
higher than the ant species turnover across the altitudinal gradient, between seasons, and between
sampling occasions. I also investigated spider body size patterns in relation to Bergmann’s rule at an
inter-and intraspecific level. Bergmann’s rule states that the body size of populations and species
within a broadly distributed taxonomic clade is of a larger size in cooler climates than their
small-bodied relatives found in warmer regions. No significant relationship between spider body size
and altitude was observed when using a midpoint or mean body size method. At the intraspecific
level, a weak but significant relationship was observed, as spider body size increased with altitude.
This study has provided some valuable insights into spider and ant diversity across an altitudinal
gradient and has provided further insights into spider body size patterns in relation to altitude.
Keywords: Altitude, Spiders, Ants, Species Richness, Species Turnover, Body Size
Description
Dissertation (MSc (Entomology))--University of Pretoria, 2014.
Keywords
Altitude, Spiders, Ants, Richness, Species turnover, UCTD
Sustainable Development Goals
Citation
Jansen, W 2014, Invertebrate species turnover and body size patterns across an altitudinal gradient, MSc Dissertation, University of Pretoria, Pretoria, viewed yymmdd <http://hdl.handle.net/2263/41119>