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Extreme Events

CTBCC Project: Climate change and the impacts of extreme events on biodiversity




The primary aim of this research program is to create an understanding of ecological responses to extreme climatic events. This is paramount for predicting the future impacts of climate change on natural ecosystems and for preserving our unique biodiversity in this century and beyond.

Our research program entails a model ecosystem (Australian Wet Tropics bioregion), known to be under threat from climate change (Williams et al. 2003), and on a model taxonomic group (flying-foxes, or fruitbats, Pteropus spp.), known to be vulnerable to extreme climatic events (Welbergen et al. 2008). We choose this approach because a comprehensive mechanistic understanding of the ecological impacts of extreme climatic events requires the integration of information on the drivers of vulnerability across different levels of biological organisation, and across a whole range of spatiotemporal scales.

Our research focuses on the following three main areas:

  1. Ecosystem-wide analysis of vulnerability of Wet Tropics biota,

  2. Detailed assessment of drivers of vulnerability in Australian flying-fox species,

  3. Development of a generalised analytical toolkit for assessing vulnerability to extreme climatic events.


Black SaturdayWhile changes in the long-term mean state of climate will have numerous effects on a range of environmental, social, and economic sectors, many significant impacts of climate change will emerge through shifts in the intensity and the frequency of extreme weather and climate events, including heat waves, fires, flooding rain, and cyclones (IPCC 2007b). Such extreme events represent the way in which our communities, animals and plants will strongly experience climate change (BoM-CSIRO 2006). Emerging evidence strongly suggests that changes in the frequency, duration and intensity of climatic extremes will be even more important than gradual increases in climatic means in driving ecological responses to climatic change. At present our understanding of the biological impacts of changes in the regimes of extreme events is very limited at best, and there is clearly a need for quantitative, spatially-explicit research into the vulnerability of biodiversity (Hughes et al. 2009).

Extreme temperature events are of special concern to biodiversity conservation (Hughes et al. 2009; Kapos et al. 2008), both because of their direct impacts on organismal health, but also because of their effects on water demand and evaporative losses and the frequency and intensity of droughts and wildfires (e.g. IPCC 2007a). They can directly result in mass die-offs (Welbergen et al. 2008) and already contribute significantly to determining which species occur in which ecosystems (Parmesan 2006; Parmesan et al. 2000). Since the frequency, duration and severity of extreme temperature events are rising faster than the means (Easterling et al. 2000; Katz & Brown 1992; Schär et al. 2004; Tebaldi et al. 2006), they will continue to gain significance as mechanistic drivers of ecological responses to climatic change (Hughes et al. 2009; Kapos et al. 2008). However, despite their clear importance for our understanding of climate change impacts (and hence adaptation action), very little is known about their effects on biodiversity.


Lemuroid Ringtail PossumVulnerability of Australia’s wet tropics biota to temperature extremes

Tropical rainforests are the hotbed of the world’s biodiversity; yet, the vulnerability of tropical rainforest biota to extreme temperature events is largely unknown (Williams et al. 2008). This is of concern because although the increase in temperature variability is expected to be most pronounced at high latitudes, tropical species may already be living closer to their maximum thermal tolerances so that even small temperature changes could have disproportionally large impacts (Deutsch et al. 2008; Huey et al. 2009; Tewksbury et al. 2008). Australia’s Wet Tropics bioregion is the world’s best understood tropical system (Stork & Turton 2008). At CTBCC we have access to detailed biodiversity distribution data collected systematically in the bioregion over the last 19 years (Williams 2006; Williams et al. 2010). The dataset is recognised as one of the world’s most comprehensive ecological and environmental information sources available, and is unique for any tropical region. In addition, we have an extremely accurate description of the thermal environment in the Wet Tropics since the 1950s, including hourly temperature traces for the most commonly used microhabitats. Thus, the Wet Tropics provide a singular opportunity for assessing for predicting impacts across an entire high-biodiversity ecosystem.


Heat-stressed grey-headed flying-foxesVulnerability of flying-foxes to temperature extremes

Flying-foxes roost in very large colonies sometimes containing tens of thousands of individuals among the exposed branches of canopy trees. Our research has shown these species are highly susceptible to temperature extremes, with temperatures beyond a threshold of 42ºC causing wide-spread mortality (Welbergen et al. 2008). Currently, these mass mortality events occur between 0-5 times per year; however, there is only anecdotal evidence for three die-offs before 1994, suggesting that these events are becoming increasingly frequent (Welbergen et al. 2008). Because of their roosting habits, flying-foxes allow for easy examinations of exposure and sensitivity on both individual and population-wide levels of organisation; and are therefore convenient study subjects (or ‘canaries in the coalmine’) for determining vulnerability. The study uses colonies of three species of which we have known colony locations within their well-defined distributions down the Australian east coast [i.e. the spectacled flying-fox, P. conspicillatus, black flying-fox, P. alecto and grey-headed flying-fox, P. poliocephalus, respectively (Hall & Richards 2000)]. Here, our combined methodology will provide the first comprehensive assessment of the vulnerability of a single taxon to impacts of extreme climatic events.