Extinction through time; were humans a factor in the past, too?

By Gloria Lima

It’s known that humans have played a large role in the extinction of many organisms. But does this mean we are the only cause? How is it possible for us to tell if we are the only factor or if we simply play a large role in the whole ordeal? Paleoecology offers clues, starting with which organisms went extinct, and which survived. We can look to paleontological data for patterns, like the body size of extinct species, or how those species interacted with their habitats.  By comparing fossil and modern animals, it is then possible to see how the organisms in the past interacted with their environments, by looking at the ecology of their surviving relatives.

picture one

Image courtesy of Smithsonian Magazine.

Much of what we know about extinction comes from carbon dating the remains of extinct animals. An example is seen in the article “Patterns of generic extinction in the fossil record.” The authors looked at many fossils from a wide range of genera to see if there was a common pattern in extinction among the organisms. If there was a trend, it’s then possible to see whether the environment played a large role in the extinction, compared to the biology of the organisms. If so, this could mean that the climate caused a change in the environment before the organisms were able to adapt to it.

 

There are a number of ways in which environmental change can cause a decline in organisms, such as declines in precipitation, declines in plant life or food availability, or the arrival of humans. When looking at how humans affected the population of many organisms, one is able to see that although they aren’t the only factor influencing species during the last hundred thousand years, humans are a large portion of “pie” that makes up an extinction.

In “Timing and dynamics of Late Pleistocene mammal extinctions in southwestern Australia”, the authors examined how extinction could be linked to humans. Smaller mammals in the area were able to survive while the larger animals were not, which is interpreted as an impact of human hunting. Through carbon dating, they showed that humans and the now-extinct mammals overlapped, and so you can’t rule out that there was interaction between humans and larger mammal species. This then begs the question: How did humans interact with these extinct organisms, and if they hunted them, were they a major predator for these larger mammals? The authors argue that humans are a major role player in the extinction of many mammals, yet the change in habitat and climate was the final straw the extinctions. We humans shouldn’t be shocked to find so many animal and plants extinctions, because we have played such a large role in their lives. This role may have been direct, such as hunting an animal to extinction, or indirect, such as setting fires in areas where the organism lived.

extinction

By T. McCracken

What are the consequences of extinctions? Modern ecologists are able to tell quite a lot about the relationship between organisms and how they may have interacted with their environments, including competition, predation, and parasitism. But how is it possible to see these relationships in fossil records? It’s actually pretty similar to how modern ecologist see these relationships, such as looking at bones for markings, or evidence in preserved stomach contents. Yet this can only go so far, that is when relation to modern ecology is necessary. Animal behavior is often similar through time, so modern relationships between animals and their environment can be linked to observed changes in past environments. The present can be the key to the past! In “Persistent predator-prey dynamics revealed by mass extinction,” the authors explain how you can identify a species interaction from evidence in the paleontological record. One issue is that predator-prey interactions are hard to identify, and are often mistaken as competition or factors caused by the environment. However, such connections are useful to identify, because once they are seen it is possible to see how the introduction of humans influences the interactions amongst other organisms.

 

Understanding what caused an extinction in the past may help conservationists find new ways to protect organisms that are endangered in the modern era. Many ecologists look toward the past to see how our future will be affected, and how many plants or animals will react to changes in the environment. Since there are many reasons why an organism may be dying off today, it must be understood that while ecosystem change plays a role, it just so happens that humans got the ball rolling for many extinctions throughout time. The combination of the two is often a stronger influence than either alone.

REFERENCES

Prideaux, Gavin J., et al. “Timing and dynamics of Late Pleistocene mammal extinctions in southwestern Australia.” Proceedings of the National Academy of Sciences 107.51 (2010): 22157-22162.

Raup, David M., and George E. Boyajian. “Patterns of generic extinction in the fossil record.” Paleobiology 14.2 (1988): 109-125.

Sallan, Lauren Cole, et al. “Persistent predator–prey dynamics revealed by mass extinction.” Proceedings of the National Academy of Sciences 108.20 (2011): 8335-8338.

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