Abstract:
In savannas, grazing is an important disturbance that modifies the grass layer structure
and composition. Habitat structural complexity influences species diversity and
assemblage functioning. By using a combination of natural sites and manipulated
experiments, we explored how habitat structure (grazing lawns and adjacent bunch
grass) affects ant diversity and foraging behaviour, specifically the efficiency of resource
acquisition, resource monopolisation and ant body size. We found that in the natural
sites there was no difference in the amount of time ants took to locate resources, but
in the manipulated experiments, ants were faster at locating resources and were more
abundant in the simple treatments than in the more complex treatments. Ant body
size was only affected by the manipulated experiments, with smaller ants found in the
more complex treatments. In both the grazing lawn and bunch grass habitats there were
differences in assemblage patterns of ants discovering resources and those dominating
them. Seasonality, which was predicted to affect the speed at which ants discovered
resources and the intensity of resource monopolisation, also played a role. We show
that ants in winter monopolised more baits and discovered resources at a slower rate,
but only at certain times within the experiment. Grazing in conjunction with season
thus had a significant effect on ant diversity and foraging behaviour, with dominant
ants promoted where habitat complexity was simplified when temperatures were low.
Our results indicate that structural complexity plays a major role in determining ant
assemblage structure and function in African savannas.
