The history of life on Earth is punctuated by mass extinctions, which are relatively sudden events in which many or even most of the planet’s species die out. Causes of mass extinctions in Earth’s past include asteroid impacts, massive volcanic eruptions, and major climatic shifts. As greater numbers of species go extinct under a human-dominated planet, an important question worth asking is whether we are currently causing a new mass extinction.
In order to understand to what degree humans drive extinction, we need to take a closer look at how different organisms adapt, evolve and recover. One way to do this is to look at the intrinsic risk of certain organisms to go extinct under “normal” environmental variations, as discussed in a paper by Finnegan et al. (2015). Intrinsic risk is calculated for a particular group of organisms (i.e., marine mammals or corals) by identifying the diversity of species in specific areas over the past 23 million years. By mapping the distribution of genera over time, scientists can identify geographic distribution of species reduction. High intrinsic risk -- or high extinction risk -- identifies areas with fauna that are strongly affected by human activity or climate change (both natural and anthropogenic). Finnegan et al. (2015) looked at intrinsic risk for six groups of marine organisms and were able to conclude that tropical areas of the Western Atlantic and Indo-Pacific have the highest intrinsic risk. This pattern is likely driven by regional, organismal requirements requiring specific habitat and food sources for survival, which makes tropical species more vulnerable to even small perturbations in their ecosystems. The Finnegan et al. (2015) study finds marine mammals, which includes dolphins, seals, whales, and others, have the highest intrinsic risk. On the one hand, this means that significant extinctions could be expected within this group even without human activity. However, their overall extinction risk is even higher with human activity, as we cause additional stressors of habitat loss, overfishing, and pollution. Mapping geographic regions with high intrinsic risk and comparing them with areas currently experiencing extreme stress from human activities, as well as areas predicted to experience dramatic effects of human-caused climate change, gives us some sense of what to expect in the near-future. For instance, the Western Atlantic is an area with high direct human impact, whereas the Indo-Pacific is especially sensitive to future climate change. Due to the high intrinsic risk in these areas, scientists expect the overall magnitude of extinction to be particularly severe. In addition to understanding extinction, the geologic record can tell us how systems recover from abrupt change. A recent study by Moffitt et al. (2015) analysed how seafloor community ecology changed in response to episodes of climate change since the Last Glacial Maximum (20,000 years ago). Surprisingly, this study found that although seafloor communities can change very rapidly (<100 years) in response to prevailing seafloor conditions, it may take a much longer time (>1000 years) for ecosystems to recover if favorable conditions return. A sobering lesson from this study is that changes humans make to our climate and environment may have quick, lasting impacts which may not be easily reversible on short timescales. Although extinctions are a part of Earth history, on human timescales they may have devastating effects on ecosystems that we depend upon for our daily lives. The papers we explored in our class show that many of the areas to be affected by anthropogenic climate change are already predisposed to experience significant extinctions, and when extinctions do happen, it can take the lifespan of many human generations for ecosystems to recover. As a result, we have to work to conserve what we can, and also begin to think of ways to respond and adapt to extinctions that are already taking place and may be unavoidable. Comments are closed.
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ArchiveSea Levels: Past, Present and Future
How has El Niño changed in the past? Lessons from paleoclimate archives Paleoclimate into Policy: is there a bright future for learning from the past AuthorsWritten by the members of UC Davis GEL 232: K. Barclay, R. Banker, P. Edwards, C. Fish, K. Hewett, T. Hill, G. Hollyday, C. Livsey, H. Palmer, P. Shukla, D. Vasey. Categories
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