A Stroll Along Australian Ecosystems: Using Bioclimatic Transects to Examine Environmental Drivers of Community Assembly in Birds

Abstract

Aim

Variation in community composition along environmental gradients provides crucial information for identifying zones where species turnover is rapid and to ascertain whether compositional changes occur gradually or rather abruptly. We examined changes in bird community composition along three bioclimatic transects in Australia to test whether drivers of species turnover are consistent, rather than spatially contingent, across biologically contrasting ecosystems. We also detected potential transition zones associated with environmental thresholds and determined whether certain abiotic conditions promote a higher rate of community compositional turnover.

Location

Mainland Australia.

Taxon

Terrestrial birds.

Methods

We applied multivariate community analysis, generalised dissimilarity modelling (GDM) and threshold indicator taxa analysis (TITAN).

Results

We observed that environmental variables are better predictors of community composition than spatial distance, which indicates that species sorting, rather than dispersal, plays a key role in structuring Australian avian communities. Annual precipitation constitutes a key driver of species turnover regardless of the analysed transect. The most humid landscapes and those with a higher tree canopy show lower spatial heterogeneity in community composition compared to those with less benign environmental conditions (e.g., dryer environments). TITAN detected significant transition points and supported the results obtained using GDM, which suggests that bird composition change along the gradients is not monotonic.

Main Conclusions

Our results suggest that avian beta diversity increases with increasing environmental harshness, presumably through changes in the relative importance of stochastic versus deterministic processes. The obtained findings show that open forests and woodlands are extremely important ecosystems on this continent and deserve special attention in terms of conservation due to their vulnerability to global change. Lastly, this study exemplifies the value of combining community- and taxon-based analyses to identify and interpret community thresholds, which can serve to pinpoint targets for preserving biodiversity.