Triple jeopardy in the tropics: assessing extinction risk in Australia's freshwater hotspot

A project undertaken at the Department of Zoology, University of Melbourne, and supervised by Dr Stephen Swearer

Freshwater ecosystems worldwide are experiencing a period of unprecedented biodiversity loss. Effective conservation efforts require accurate estimates of biodiversity and knowledge of risks of extinction. Predicting extinction risk is challenging, as rarity is a multi-faceted concept. Species which have small ranges, small population sizes and narrow ecological niches due to specialisation are thought to be subject to a 'triple jeopardy' risk of extinction.

The Kimberley region in remote northwestern Australia is a hotspot of freshwater fish biodiversity, but one that has been poorly characterized. At least 18 (~40%) of the region’s diverse freshwater fish species are found nowhere else and many of these endemics are extremely range-restricted. The aim of our project was to uncover the true freshwater fish biodiversity in the Kimberley and to determine whether range restricted endemic species are more prone to extinction than more widespread species because they are less abundant, have specialized niche requirements (in terms of habitat, diet, and physiology), and/or life histories that are invariant or maladaptive to predicted environmental change.

Our freshwater fish surveys have been the most extensive in the Kimberley region to date; covering 76 locations across 18 rivers. Two of these rivers (the Moran and Glenelg) were surveyed for the first time. We have found 15 morphologically and genetically distinct candidate species from the families Terapontidae and Eleotridae, which we are currently describing. Significant range extensions were also recorded for a further 22 species. With the inclusion of these candidate new species, the Kimberley has the highest number of endemic species of any freshwater biogeographic province in Australia.

We created and analysed a database of range size, body size, and abundance data for all Australian freshwater fish. We found a positive relationship between geographic range size and body size, and species that are conservation listed have a range size an order of magnitude lower than similarly size unlisted species. There is a negative relationship between abundance and body size, and no relationship between abundance and range size. Our results also indicate that abundance alone is likely a poor proxy for conservation status. The study has highlighted a suite of unlisted species that share characteristics with conservation listed species. Many of these potentially vulnerable species are found in either the wet tropics or the Kimberley region, indicating that northern Australia should be the focus of future freshwater fish conservation efforts.

Our analysis of diet, life-history traits, and habitat data continues to shed light on the differences in ecological niche breadth between range-restricted species and their widespread counterparts. Notably, highly specialized diets (single food types) appear to be a common thread among range-restricted species, while widespread species exhibit far more generalist diets. We are currently evaluating physiological capacity of Kimberley endemic species to assess their vulnerability to climate change, which will provide greater resolution of extinction risk in Australia’s last freshwater frontier.

Publication

Le Feuvre, M.C., Dempster, T. Shelley, J.D. and Swearer, S.E. (2015). Macroecological relationships reveal conservation hotspots and extinction-prone species in Australia's freshwater fishes. Global Ecol. Biogeogr. doi: 10.1111/geb.12397

 
Figure 1. An x-ray of a candidate new species. This allows us to look at internal characters (e.g. number of vertebrae) that are required for formal species description.

Figure 2. A candidate new species from the family Terapontidae

Figure 3. A candidate new species from the family Eleotridae

Figure 4. Study site on the Mitchell River

Figure 5. Setting a fyke net to trap fish on the King Edward River

Figure 6. Study site on the Fitzroy River