Data from: Epigaeic and hypogaeic ant abundance data from 20 sites spanning a 1000 km gradient in Northern Australia

Studies using climatic gradients play a key role in our understanding of
the importance of rainfall and temperature as factors regulating species
diversity and distribution, and thus of likely responses to climate
change. However, such studies currently consider above-ground species
only, ignoring the diverse hypogaeic (subterranean) invertebrate fauna.
Here, we assess the extent to which the responses of hypogaeic ant
assemblages to a rainfall gradient in the Australian seasonal tropics are
congruent with those of epigaeic (ground-dwelling) assemblages. We sampled
at 20 sites covering a gradient of over 1000 km and 1100 mm in mean annual
rainfall (MAR). We predicted that the different assemblages would display
contrasting patterns because the epigaeic fauna is highly arid-adapted
whereas the hypogaeic fauna is mesic-adapted in Australian savannas. We
collected 392 epigaeic and 17 hypogaeic species. Epigaeic ant abundance
and species diversity tended to increase with decreasing rainfall, whereas
the reverse was shown by hypogaeic species. In contrast, the phylogenetic
diversity (PD) of both epigaeic and hypogaeic assemblages showed only weak
or no variation with rainfall. The low response of PD reflected the fact
that additional species tended to come from the same rather than
additional genera: genus-level diversity did not change with MAR. Epigaeic
species composition formed three distinct clusters, corresponding to low,
moderate and high MAR, whereas hypogaeic ants did not. Our findings show
that ant assemblages can have stratum-specific responses to climatic
gradients, reflecting different evolutionary histories of their
constituent taxa. This may be true for other taxa, and has important
implications for predicting responses to climate change. Lastly, we also
show that different levels and facets of diversity have contrasting
responses to climatic gradients. We thus advocate for ecological research
simultaneously assessing assemblages of several strata, as well as varying
levels and facets of their diversity. This dataset consists of ant records
collected along the Northen Australian Tropical Transect (NATT) in 2023.
Ants were sampled every 50 km along a 1000 km transect. Two methods were
used at each site: pitfall and subterranean baited traps. In total, 20
sites were sampled with 400 pitfall and 800 subterranean traps. These
traps were left open for 4 days to collect ants. No ethics or sampling
permits were required to collect this data. The dataset contains site
name, location and environmental attributes (collected from Worldclim). It
also contains ant species abundance for each trap used in the
study.