Ant Diversity and Distribution along Elevation Gradients in the Australian Wet Tropics: The Importance of Seasonal Moisture Stability

Abstract

The threat of anthropogenic climate change has seen a renewed focus on understanding contemporary patterns of species distribution. This is especially the case for the biota of tropical mountains, because tropical species often have particularly narrow elevational ranges and there are high levels of short-range endemism. Here we describe geographic patterns of ant diversity and distribution in the World Heritage-listed rainforests of the Australian Wet Tropics (AWT), revealing seasonal moisture stability to be an important environmental correlate of elevational patterns of species composition. We sampled ants in leaf litter, on the litter surface and on tree trunks at 26 sites from six subregions spanning five degrees of latitude and elevation ranges from 100–1,300 m. A total of 296 species from 63 genera were recorded. Species richness showed a slight peak at mid elevations, and did not vary significantly with latitude. Species composition varied substantially between subregions, and many species have highly localised distributions. There was very marked species turnover with elevation, with a particularly striking compositional disjunction between 600 m and 800 m at each subregion. This disjunction coincides with a strong environmental threshold of seasonal stability in moisture associated with cloud ‘stripping’. Our study therefore provides further support for climatic stability as a potential mechanism underlying patterns of diversity. The average height of orographic cloud layers is predicted to rise under global warming, and associated shifts in seasonal moisture stability may exacerbate biotic change caused by rising temperature alone.

Forest structure determines spatial changes in avian communities along an elevational gradient in tropical Africa

“…We suggest that this might indicate the importance of mists for bird distribution (cf. Nowrouzi et al, ). The mist zone is generally a cool, wet and dark environment, which is then reflected in vegetation structure and could lead to uniformity of the environment between 1,500 and 1,850 m. Although we do not have enough data to support such an idea, we speculate that clouds can serve as an overlooked but important barrier for the elevational distribution of birds.…”

The truncated bell: an enigmatic but pervasive elevational diversity pattern in Middle American ants

“…Ferro (2013) found discrete lowland, mid-elevation, and upland communities of mammals in the Argentinian Andes. Multiple studies of ant richness and composition on elevation gradients have emphasized abrupt transitions between lowland and cloud forest habitats (Samson et al 1997, Fisher 1998, 1999b, Brühl et al 1999, Burwell and Nakamura 2011, Nowrouzi et al 2016. Likewise in Middle America there is an ecotonal shift from lowland rainforest to cloud forest, but somewhat higher, around 1000 m elevation.…”

Resource use and food preferences in understory ant communities along a complete elevational gradient in Papua New Guinea

“…, Nowrouzi et al . , Szewczyk & McCain ). Ant species distributions are highly sensitive to climatic variables, and temperature appears as one of the main factors influencing species diversity along elevational gradients (Sanders et al .…”

“…Given their dominance and ecosystem-level effects, ants constitute an ideal group to study the response to elevational gradients (Samson et al 1997, Malsch et al 2008, Longino et al 2015, Nowrouzi et al 2016, Szewczyk & McCain 2016. Ant species distributions are highly sensitive to climatic variables, and temperature appears as one of the main factors influencing species diversity along elevational gradients (Sanders et al 2007).…”