Biodiversity responds to increasing climatic extremes in a biome-specific manner
Graphical abstract
Introduction
Environmental changes during the 21st century are projected to be comparable in magnitude to those of the largest recorded global change that occurred 65 million years ago, and to increase at rates 10–100 fold faster (Diffenbaugh and Field, 2013). The unprecedented rate of global environmental change predicted for the next century is coupled with increases in the unpredictability of climatic events and increases in extreme weather (Urban, 2015). Ecosystem responses to these changes are highly uncertain and challenging to predict (Walther et al., 2002). A range of linear and non-linear ecosystem responses to environmental change potentially exist (Scheffer and Carpenter, 2003). Non-linear responses are characterised by large changes in ecosystem properties in response to a small range of environmental change, in contrast to relative insensitivity outside that critical range of environmental conditions. This threshold behavior is sometimes linked to hysteresis, allowing alternative stable states to persist under the same environmental conditions. ‘Regime shifts’ between such states may be triggered either by gradual environmental change until a threshold is reached, or by disturbance events (Scheffer and Carpenter, 2003). Ecosystems that display these kinds of responses are challenging to manage because points of change are difficult to predict and reversal of state changes could necessitate major manipulations that may not be feasible (Suding and Hobbs, 2009).
Long time-series of ecological data offer an opportunity to investigate drivers of change and to provide a meaningful context for interpreting trends. Time series data are also appropriate to explore beyond considerations of central tendencies (Pearson and Dawson, 2003) and are paramount for understanding how the extreme highs and lows of temperature or precipitation may drive biodiversity responses (Greenville et al., 2013; Wardle et al., 2013). Such understanding of ecosystem drivers and mechanisms of change is critical for developing more-reliable predictions about ecosystem structure and function in future (Keith et al., 2008, Keith et al., 2013). This, in turn, will better inform decisions on climate adaptation which, to be effective, must be cognisant of the likelihood of synergistic effects among existing processes and legacies from past events (Sala et al., 2012; Monger et al., 2015). It is therefore essential that investment in environmental monitoring programs be sophisticated enough to improve mechanistic knowledge, not simply detect change.
The world's climate has changed. Global mean temperatures have increased by 0.85 °C from 1880 to 2012 due to anthropogenic activities (IPCC, 2014), and these increases, combined with changes in global rainfall patterns, have changed disturbance regimes (Bowman et al., 2014). There has also been an increase in the frequency and magnitude of extreme climate events such as floods and heat waves (IPCC, 2014; CSIRO and Bureau of Meteorology, 2015). Understanding the effects of changes in climate and disturbance regimes on biota can only be provided by long time-series of ecological observations or experiments (Lindenmayer and Likens, 2010; Lindenmayer et al., 2012). Such insight will be vital for identifying species and ecosystems at risk of collapse and for informing mitigation measures.
Here, we use case studies drawn from the Australian Long Term Ecological Research Network (LTERN) to examine ecosystem responses to changes in climate and disturbance regimes. We first compare climatic variables recorded annually at each plot network during its period of operation, and place these in the context of long-term climatic trends. Then, we raise and test the following hypotheses:
- 1.
The number of extreme weather events recorded by each plot network has increased over the last decade;
- 2.
Trends in biodiversity will be associated with recent climate change, either directly or indirectly through climate-mediated disturbance (e.g., wildfire) responses. We examined biodiversity responses to environmental change for evidence of non-linear behavior.
Using insights gained from long-term datasets, we consider management implications for long-term monitoring in conservation organisations that seek to maintain species populations that are likely to face increases in extreme weather events and an increasingly unpredictable climate.
Section snippets
Methods
Long-term data (10–35 years) were obtained from five of the 12 Australian LTERN plot networks (Lindenmayer et al., 2014). These five plot networks monitor biodiversity in tropical savannas and heathlands, deserts, alpine systems, temperate heathlands and temperate woodlands, representing half of the major Australian biomes defined by Olson et al. (2001) (Fig. 1).
Climate
Across all plot networks, more survey years in the last decade experienced extreme climate events (10th and 90th percentile) than were recorded in the pre-2005 survey years. The increase in extreme climate events within the last decade occurred in all four biomes represented by the five plot networks. Frequency of extreme temperatures increased in all five plot networks, while three networks showed increased frequency of extreme rainfall events. In the Three Parks Savanna Fire-Effects Plot
Discussion
In general, trends in biodiversity were associated with recent climate change, either directly or indirectly through climate-mediated disturbance (wildfire) responses. However, we found no evidence of non-linear responses, suggesting either that tipping points may not exist in these ecosystems or that they have not yet been reached. Instead, the influence of the drivers was context-specific, with some species responding positively to climate variables or fire, and others responding negatively.
Acknowledgements
The authors wish to thank W. Blanchard for statistical advice and J. Stein for access to the ANUCLIM data. The Desert Ecology Plot Network thanks Bush Heritage Australia, H. Jukes, G. McDonald, D. Smith and G. Woods for allowing access to properties in the study region, members of the Desert Ecology Research Group, especially B. Tamayo, C.-L. Beh and D. Nelson, and many volunteers for valuable assistance in the field. The Alpine Plot Network thanks Mt. Hotham Alpine Resort for continuing access
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