From the readings for a previous post, Diamond’s comment (2002) about unpredictable climate inspired me to investigate further the influence of climate change on extinctions and the part it plays in contributing to the movement of invasive species. This next post will look at evidence to suggest the role of climate change in contributing to extinction events as well as how it will influence invasive alien species in the future.
There are arguments that humans have only had a significant impact on climate since 1800 AD (Crutzen and Stoermer, 2000) as this has been identified as when atmospheric concentrations of atmospheric CO2 and CH4 have started to increase above previous longer-term levels. However there is also evidence to back up arguments that anthropogenic activities, in fact, have had significant impacts on climate many thousands of years before (Ruddiman, 2003). Ruddiman (2003) compiles evidence to show that changes in atmospheric concentrations of greenhouses gases cannot be explained by natural events, such as orbital forcing and that the Holocene CO2 concentration trend does not match any other trend seen in previous interglacial periods. These ‘anomalies’ have been attributed to agricultural techniques such as rice farming in Asia from 7500 BP and natural loses in terrestrial biomass associated with deforestation (Ruddiman, 2003). Putting the direct impact deforestation has on species and the landscape aside, these actions have indirectly influenced species composition and ecological interactions, by creating/expanding existing environmental conditions and decreasing others.
McLaughlin et al., (2002) do however state there have been few extinctions directly linked ‘mechanistically’ to climate change, it is usually a combination of habitat fragmentation as well as climate change that induces extinction. This therefore shows that climate change is a contributory factor and is not a direct cause of extinction in its own right, it will push species to the edge of their ecological limits, but it requires a combination of factors for the species to then become extinct. These factors could include increased predation, hunting or removal by humans, landscape changes through activities such as farming or settlement. Decline in possible habitats through anthropogenic activities is therefore a more important factor as it reduces the range in which the species can exist if the one it is currently present in becomes uninhabitable. McLaughlin et al., (2002) discuss this with respect to two different populations of checkerspot butterfly where climate change caused variability in precipitation. When modelled with butterfly populations, this effect was seen to amplify population fluctuations, leading to rapid extinctions. However with global warming predicted to dramatically increase over the next 40-50 years, if mitigation actions are not implemented, then future predictions of the effect of climate change on extinction rates need to be considered. Thomas et al., (2004) predicted that, from sample regions that cover about 20% of the world, between 15-37% of species within those regions would be extinct, or committed to extinction, without any possibility of recovery if action is not taken. These calculations were made on the basis of a mid-range climate-climate warming scenario for 2050 (Thomas et al., 2004).
It is therefore important to think about the impact climate change could potentially have on invasive species. They have been broken down into five categories (change in pathways, change in environmental constraints, change in distributions, change in impacts and change in management effectiveness) (Hellmann et al., 2008), shown in figure 1.
Figure 1: the 5 responses by invasive species to climate change (Hellmann et al., 2008)
The predominant issue in relation to invasive species and climate change is that changes are subtler and take place over a longer period of time, compared to the current issues surrounding invasive species. This means that resource managers have a difficult time knowing when to start addressing the issue. However, using the five categories described in Figure 1 as a platform, these changes to invasive species would then lead to a totally different approach to how to manage them. These would require research that integrates invasions and climate-change biology (Hellmann et al., 2008). It will take more time to observe and understand, through wider research, how invasive species will respond to climate change as well as understanding which new species will become invasive.
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