Background/Aims
Patterns of phylogenetic and morphological diversity can offer insights into the processes underlying the organisation of species assemblages, such as environmental filtering, competitive exclusion, and limiting similarity. Here, we examine the phylogenetic and morphological relationships of 220 Australian freshwater fish species across 245 river basins.
Methods
We explore spatial structure in these diversity patterns using spatial autocorrelation, and employ spatial regression analyses to investigate how diversity is influenced by temperature and precipitation variables.
Results
Overall, we find that patterns in both phylogenetic and morphological diversity exhibit strong spatial structuring. We find that freshwater fish communities across Australia are generally phylogenetically clustered, with clustering strongest in basins with colder minimum annual temperatures. Morphological diversity patterns are more variable, with widespread clustering at high latitudes and overdispersion more prevalent nearer the tropics. Consistent with this observed latitudinal gradient, we find that morphological diversity increases with increasing minimum and maximum annual temperatures, as well as increases in minimum monthly precipitation and precipitation seasonality. The presence of strong phylogenetic and morphological clustering in much of Tasmania and southern mainland Australia is indicative of environmental filtering operating on phylogenetically conserved traits, while morphological overdispersion and phylogenetic clustering in the tropics suggests that competitive exclusion is operating where the most competitive traits are phylogenetically conserved.
Conclusions
Our findings suggest that environmental factors play a larger role in structuring communities in harsher climates with stronger selection pressures, while ecological interactions contribute more to community structuring where environmental constraints are weaker.