Ant thermal preference and behavioural dominance in a grassland
Caswell Munyai, Nokubonga Thabethe , Stefan Foord , Caswell Munyai
School of Life Science, University of KwaZulu-Natal, Pietermaritzburg, South Africa; School of Life Science, University of KwaZulu-Natal, Pietermaritzburg, South Africa ; SARChI-Chair on Biodiversity Value and Change, Department of Zoology, School of Mathematical and Natural Science, University of Venda, Thohoyandou, South Africa ; School of Life Science, University of KwaZulu-Natal, Pietermaritzburg, South Africa
In ant ecology, competition is one of the factors thought to structure ant assemblages, and this has shown evidence of a trade-off between thermal preference and dominance. Previous studies have observed ant competitive interactions at baits to classify them into dominance hierarchies. The aim of the study was to define a dominance hierarchy for ant community at baits and quantify their thermal preference in a grassland. The specific objectives were to quantify the temperatures at which different ant species are active, and to quantify the trade-off between ant dominance and thermal preference. The study was conducted in a grassland site at the University of KwaZulu-Natal, in Pietermaritzburg, KwaZulu-Natal. Ant baiting was done across all four seasons of the year, three days in each season. Ant activities were observed at five bait types (cat food, sugar water, oil, water and a peanut-jam mixture). A 70m long transect was laid out, with 15 baiting stations 5m apart. Ground surface temperature was recorded for each baiting station. A combination of numerical and behavioural dominance matrices were used to rank ant species. Dominant ants were numerically and behaviourally dominant at baits. Subdominant and subordinate ant species foraged below the temperature range of dominant ants avoiding dominant ants. Dominant ants were more active at baits in the early hours of the day, with subdominant in the afternoon and subordinate ants more abundant also in the morning at a different temperature range. There was a positive relationship between dominance index and temperature range, dominance index and maximum temperature. Dominant ants foraged at intermediate temperatures, while subdominant and subordinate ant species foraged at lower or higher temperatures. This may have some important implications on the impacts of climate change, meaning subdominant and subordinate ants may be under a lot of pressure in the future.