1. Changes in vegetation community composition, such as a transition from grassland to shrubland (woody encroachment), are associated with reductions in plant cover and increases in bare ground. Encroachment-driven changes in surface cover at small spatial scales can alter ant community assemblages by changing their foraging behaviour and their ability to locate and monopolise resources.2. Artificial arenas with three levels of complexity were used to examine changes in ant foraging efficiency, body size and ability to monopolise food. The three levels of complexity included a control (no substrate), low-complexity treatment (woody debris) and high-complexity treatment (leaf litter).3. No difference was found in ant species composition within the complexity arenas between grassland and shrubland, but ant functional groups 'generalised Myrmicinae' and 'subordinate Camponotini' were more abundant in grassland arenas, whereas 'opportunists' were more abundant in shrubland arenas. Ants took twice as long to find baits in high-complexity treatments, and 1.5 times as long in low-complexity treatments, than in control treatments, which were bare arenas with no substrate. Ant body size declined with increasing surface complexity, suggesting that larger ants are discouraged from foraging in complex habitats.4. There was also significantly greater monopolisation of the protein bait (tuna) in low-and high-complexity treatments, but there were no differences between tuna and carbohydrate (honey) in the control treatment. Consistently, no differences were found in ant behaviour between grasslands and shrublands.5. The present study shows that ants are more responsive to small-scale alterations in soil surface complexity than to changes in vegetation community composition. Changes in soil surface complexity select for ants based on body size, which in turn influences their foraging success. Changes in vegetation complexity at small spatial scales are therefore likely to influence ant behaviour and abundance of some functional groups, potentially having an effect on the many ecosystem functions carried out by ants.

Secondary seed dispersal by ants (myrmecochory) is an important process in semi-arid environments where seeds are transported from the soil surface to an ant nest. Microsites from which ants often remove seeds are the small pits and depressions made by native and exotic animals that forage in the soil. Previous studies have demonstrated greater seed retention in the pits of native than exotic animals, but little is known about how biotic factors such as secondary seed dispersal by ants affect seed removal and therefore retention in these foraging pits. We used an experimental approach to examine how the morphology of burrowing bettong (Bettongia lesueur), greater bilby (Macrotis lagotis), short-beaked echidna (Tachyglossus aculeatus) and European rabbit (Oryctolagus cuniculus) foraging pits and ant body size influenced ant locomotion and seed removal from pits along an aridity gradient. Ants took 3.7-times longer to emerge from echidna pits (19.6 s) and six-times longer to emerge from bettong pits (30.5 s) than from rabbit pits (5.2 s), resulting in lower seed removal from bettong pits than other pit types. Fewer seeds were removed from pits when cages were used to exclude large body-sized (>2 mm) ants. Few seeds were removed from the pits or surface up to aridity values of 0.5 (humid and dry sub-humid), but removal increased rapidly in semi-arid and arid zones. Our study demonstrates that mammal foraging pit morphology significantly affects ant locomotion, the ability of ants to retrieve seeds, and therefore the likelihood that seeds will be retained within foraging pits.

Increases in the cover or density of woody plants (encroachment) and overgrazing by European livestock are 2 major drivers of ecosystem structure and function in drylands and are often associated with land degradation. Although the effects of encroachment and overgrazing on vascular plants are relatively well known, little is known about their effects on arthropods such as ants. We examined ant community composition at sites ranging in shrub cover in a wooded dryland in eastern Australia, testing the notion that increasing shrub cover and grazing intensity would alter ant assemblages and functional group composition. We used ants because they are abundant, diverse, and respond to small‐scale environmental changes. Increasing shrub cover had no effect on ant richness, diversity, or evenness but increased the abundance of Subordinate Camponotini. Larger shrubs tended to have greater ant richness, and abundance of Cold Climate Specialists, but fewer Generalized Myrmicinae and Hot Climate Specialists. More intense grazing was associated with greater ant richness, diversity, and evenness; a greater abundance of Hot Climate Specialists and Dominant Dolichoridae; and lower abundance of Subordinate Camponotini. Our study indicates that changes in grazing intensity had stronger effects on ant richness than any increase in shrub cover. The effects of grazing likely resulted from changes in soil surface complexity such as barer ground associated with grazing‐induced degradation.