Richness‐environment relationships in epigaeic ants across the Subantarctic‐Patagonian transition zone

Abstract

Abstract. 1. We analysed ant species richness-environment relationships across theSubantartic-Patagonian transition, in southern South America. We tested the predictionsof the (i) thermal limitation hypothesis: temperature limits ant species richness,(ii) the productivity hypothesis: ant richness is driven by the indirect effect of climate(temperature and precipitation) mediated by changes in plant environment (plantcover and litter accumulation). We also evaluated the effects of (iii) plant speciesrichness, and (iv) habitat use by cattle on richness.2. We collected ants using 450 pitfall traps within a 150 · 150 km area. We usedpath analysis to evaluate the associations of ant richness with environmental predictors.We evaluated the influence of local abundance variation on richness-environmentrelationships; we applied principal co-ordinates of neighbour matrices tomodel the spatial autocorrelation in the data and combined spatial and ecologicaldescriptors of ant richness into partial regression.3. Ant richness responded positively to indirect effects of precipitation mediatedby shrub cover and tree cover, towards the west, and by litter accumulation, towardsthe east of the transition. Direct climatic effects on richness were negative or weakthroughout. The local increase in plant species richness and habitat disturbance bycattle promoted an increase in ant richness, mostly towards the east of the transition.These results were not seriously affected by variation in local abundance and the spatialautocorrelation in the data.4. We suggest that climate, either directly or indirectly, through its biological effecton plant environment interacts with micro-spatial variation in habitat heterogeneityand disturbance to account for ant species diversity across this transition.