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Assignment 3: Are we facing a sixth mass ? KEY

Many scientists claim we are on the verge of a sixth mass extinction comparable in scale to the 5 past mass extinction events. Your assignment is to discuss this topic by defining mass extinction events, discuss their causes, and presenting evidence for and against the hypothesis that we are facing a 6th mass . Your answer should clearly address the following points:

1) Define what is meant by a mass extinction event, using past mass to characterize the and scope of such an event. Barnosky et al. (2011) defined this as a loss of > 75% of in a short period (a few million or less)

2) What have been the primary causes of recent anthropogenic extinctions (past 500 years)? What causes are expected to be important in the next few decades? According to Lomolino et al. (2010), habitat loss and fragmentation has been the biggest cause in this period. According to McCauley et al. (2015), overharvesting has been a primary cause of marine extinctions or threats, and this will continue in the near future, with playing an increasing role. Both McCauley et al. (2015) and Barnosky et al. (2011) identify acidification and as becoming more important threats in the near future.

3) What are some of the possible causes for past mass extinctions over the past 600 million years of ’s History? Which of these past causes might resemble current ones, and which might be different? Climate change is implicated in virtually all past mass-extinctions. For some (e.g. K-T transition), bolide impacts were important causes. Marine anoxia and atmospheric change (e.g. high levels of CO2 and H2S), along with (e.g. from volcanism) were likely contributors in some cases. Tectonic shifts, , and release of methane clathrates are all additional possibilities [see table in Barnosky et al. 2011 for details]. Of these, increasing atmospheric CO2, ocean acidification, climate change, ocean anoxia and eutrophication all resemble current threats to species survival and are likely to be important causes of mass extinction in the near future. Bolide impacts and extensive volcanism are examples of less likely current causes.

4) Conclude by summarizing the evidence for and against the argument that we are on the verge of a 6th mass extinction and listing at least one possible means of avoiding a mass extinction. While not yet at a level of past mass extinctions, if all threated species were lost (a possibility over the next few hundred years), we would have attained the level of a mass extinction (Barnosky et al. 2011). So we can say we are “on the edge” of a mass extinction, most immediately for terrestrial species, with marine species losses not yet as severe (McCauley et al. 2015). On the other hand, expected changes from ocean acidification and marine habitat destruction could readily push marine systems over the edge in the near future (unless several key steps are taken) (McCauley et al. 2015). Means to avoid mass extinctions include better management of marine ecosystems (less , habitat destruction, and implementation of MPAs), avoiding habitat destruction, and reducing CO2 and other greenhouse gas emissions (Barnosky et al. 2011, and McCauley et al. 2015)

Grading Scheme: Your answer will be graded on content (did you fully address the topics above?) and clarity (was your essay well-written, concise, and did it follow the proper citation format?).

Page limit: Each question above should be answered with a short paragraph, with the total page length to be about 1 page (single-spaced 12-point, times roman font). Note that references are not included in this page limit.

In answering these questions, use the articles below and your textbook (Lomolino et al. 2010) as primary sources. Be sure to cite all sources (both in the text, and by providing full bibliographic references at the end), using proper citation format protocols (APA Style). For further information on the APA citation format, see http://guides.library.ualberta.ca/apa (or other similar reference).

References:

Barnosky AD, et al. (2011) Has the Earth’s sixth mass extinction already arrived? Nature 471:51-57, doi:10.1038/nature09678 Lomolino et al. 2010 , 4th Edition. Sinauer associates. Sunderland MA. McCauley DJ, et al. (2015) Marine : loss in the global ocean. Science 347 (6219):247, 1255641-1 doi:10.1126/science.1255641