Page 85 - University of Pretoria RESEARCH REVIEW 2016

MOUNTAIN ANTS
AS BIOINDICATORS
Understanding the effects of temperature change on the diversity and activity patterns of ants is a continent-spanning research project that collects data on abundance, body size and colouration, and on the internal physiology of mountain ants.
Invertebrates, especially ants, are useful bioindicators as they are sensitive to environmental change. Dr Tom Rhys Bishop and Professor Mark Robertson in the Department of Zoology and Entomology study the lives of ants in mountainous regions to gain a better understanding of global patterns in biodiversity. Over several years they have used a research site in the Sani Pass of the Maloti-Drakensberg Mountains and, in 2016, made two important advances in understanding how temperature may limit the diversity and activity patterns of ants.
The first step was to gather information on the abundances of different ant species at different elevations (from 900 to 3 000 metres above sea level) in the Sani Pass, and to supplement this with data
on the body size and colour of each ant species. The project was extended to collaborators in South Africa, Argentina and Australia to generate a continent- spanning dataset of ant abundance, body size and colouration.
A key finding was that in cold environments, the most common ants tended to have larger bodies
and darker colours while in warmer temperatures, the most common ants were smaller and paler. These findings make sense in terms of how ants
are thought to regulate body temperature. Large bodies help retain heat due to the small surface area to volume ratio, while dark colours absorb more incoming solar radiation than lighter colours. As a result, it is beneficial to have a large body and a dark colour in cold climate conditions. This advantage is so strong that the dominant ants at a given site change, depending on the environment: large, dark ants prevail in colder years while the smaller and paler ones are much more common in the warm years.
Bishop and Robinson’s second area of interest
has been whether the internal physiology of ant species occupying different elevations matches the temperature regimes that they experience. In order to address this question, and working in the Sani Pass at highland and lowland sites with collaborators from the United Kingdom and Australia, they collected data on the upper and lower thermal limits of a range of ant species.
There were several interesting findings. They
found that the average lower temperature limit of ant species decreased with increasing elevation.
Ants occupying the cold mountaintop also had an internal physiology to match. When the researchers linked these estimates of thermal physiology to activity patterns through time, they found that ants that have adapted to withstand the cold were not influenced by changing temperatures over the years and seasons. The activity of ants that could not
cope with low temperatures, however, was limited
to periods when it was warm. Their research shows that it is the ability of ants to adapt to cold conditions that drives patterns of ant activity in this mountain environment, a result that has important implications for understanding the possible impacts of climate change in mountain ecosystems.
Mark Robertson and Tom Rhys Bishop
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