Ant community structure along an extended rain forest–savanna gradient in tropical Australia

Abstract

In mixed tropical landscapes, savanna and rain-forest vegetation often support contrasting biotas, and this is the case for ant communities in tropical Australia. Such a contrast is especially pronounced in monsoonal north-western Australia, where boundaries between rain forest and savanna are often extremely abrupt. However, in the humid tropics of north-eastern Queensland there is often an extended gradient between rain forest and savanna through eucalypt-dominated tall open forest. It is not known if ant community structure varies continuously along this gradient, or, if there is a major disjunction, where it occurs. We address this issue by sampling ants at ten sites distributed along a 6-km environmental gradient from rain forest to savanna, encompassing the crest and slopes of Mt. Lewis in North Queensland. Sampling was conducted using ground and baited arboreal pitfall traps, and yielded a total of 95 ant species. Mean trap species richness was identical in rain forest and rain-forest regrowth, somewhat higher in tall open forest, and twice as high again in savanna woodland. The great majority (78%) of the 58 species from savanna woodland were recorded only in this habitat type. MDS ordination of sites based on ant species composition showed a continuum from rain forest through rain-forest regrowth to tall open forest, and then a discontinuity between these habitat types and savanna woodland. These findings indicate that the contrast between rain forest and savanna ant communities in tropical Australia is an extreme manifestation of a broader forest-savanna disjunction.

Ants as ecological indicators of rainforest restoration: Community convergence and the development of an Ant Forest Indicator Index in the Australian wet tropics

“…Ant communities in AWT rainforests have distinctive species composition that contrasts with that in adjacent open sclerophyll habitats (van Ingen, Campos, & Andersen, ). The thermophilic species of Iridomyrmex (functional group: Dominant Dolichoderinae) that dominate ant communities of open habitats throughout Australia are absent from rainforest habitats.…”

Assembling an ant community: species functional traits reflect environmental filtering

“…Ant assemblages provide an ideal study system for examining trait-environment relationships as they commonly vary in composition along environmental gradients (Gotelli and Ellison 2002;Hill et al 2008;Spiesman and Cumming 2008;van Ingen et al 2008). The role of environmental Wltering in this pattern is supported by Wndings showing that some individual ant species have speciWc traits that correlate with environmental conditions (e.g., Hölldobler and Wilson 1990;Menke and Holway 2006;Schilman et al 2007).…”

Rainforest ants of the Tiwi Islands: a remarkable centre of endemism in Australia’s monsoonal tropics

“…These faunas are dominated numerically by broadly adapted functional groups (Generalised Myrmicinae and Opportunists), and lack the behaviourally dominant dolichoderines and other thermophilic taxa that characterise the faunas of adjacent savanna (Reichel and Andersen, 1996;Andersen et al, 2006;van Ingen et al, 2008). Indeed, our surveys revealed no records at all of Dominant Dolichoderinae, and there was only one species of Hot-climate specialists (Meranoplus sp.…”

“…Savanna ant communities are similar to those throughout arid Australia in that they are comprised almost exclusively of ground-nesting species, experience high levels of behavioural dominance, and include numerous specialist thermophiles and granivores (Andersen, 2003). In contrast, rainforest ant communities are rich in litter and arboreal specialists, experience low levels of behavioural dominance, and are dominated numerically by highly generalised species (Andersen et al, 2006;van Ingen et al, 2008).…”