ENDY 6013 - ENVIRONMENTAL DYNAMICS

HOMEWORK ASSIGNMENT #6 - "IT'S A GOOD DAY TO DIE"

DUE FRIDAY, 10 NOVEMBER 2006

During the last decade, there has been increasing concern over the state of Earth's biosphere. In particular, biologists have focused on biodiversity and the "quantity" of biodiversity within the biosphere. While there is no doubt that human activity has been responsible for the extinction of a number of species, is there justification for the claim that humans are effecting a "mass extinction" event? (Note: Paleontologists characterize mass extinctions as events where significant numbers of organism families and orders, not species or even genera, become extinct).

PART A:

Using the Fossil Plot data base in MS Excel, copy the 'Compendium' tab and place in a new worksheet. Note also that the Fossil Plot tab 'AbsDate' provides a detailed geological time scale that is used in the data base. This time scale is informative for those of you unfamiliar with the nomenclature of the time scale and the known temporal boundaries of geologic intervals. This part of the exercise will require the greatest effort, so don't procrastinate!

Using the copied 'Compendium' file, sort your data by the LAD column (Last Appearance Datum, which is the extinction age for each genus in the compendium). Next determine the number of genera and orders that became extinct during both the Permian and Cretaceous-Teritiary (K-T) events. Compare these extinction numbers to the number of extant genera and orders immediately preceding each extinction event. What percentage of extant genera and orders became extinct during each event?

PART B:

From the Fossil Plot database, choose any three orders of organisms and create a plot showing their diversity through time using the '@EpochDOX' plot in Fossil Plot. For each order, find at least one image from the Internet showing an example of these organisms, and prepare a half-page description of the group including a description of their geologic range and biological associations (related organisms, environment in which they lived, ecological function, etc.). This part of the exercise is primarily for those of you who do not have extensive experience with the fossil record and will give you an opportunity to learn a little bit about some of the remarkable creatures that have inhabited our planet through time.

PART C:

Lomborg (2001) suggests the background extinction rate might be on the order of 1 species per decade, and concedes that the present extinction rate might be as high as 1 species per year (i.e. an order of magnitude greater than his claimed background extinction rate). Boggs and Roughgarden (2000) suggest that locally, extinction rates may be 10,000 times the background rate, though most estimates place the number somewhere between 100 and 1,000 times the background rate. Let's do a thought experiment: Let's assume Lomborg's (2001) background extinction rate of 1 species per decade and that present extinction might be 100 to 1,000 times the background rate and consider these values as global rates.

To be complete, we should attempt to determine what the present background rate of speciation is. Oddly, this number seems far more difficult to obtain than those for extinction rates. However, Boggs and Roughgarden (2000) provide an example of a "hotbed" of speciation - East African Rift lakes. Here, they suggest that approximately 300 species of cichlid fish may have originated during the last 12,000 years (i.e. 1 new species every 40 years). However, some entomologists suggest that insect species might be emerging at rates between 1 and 100 species per year. Since we don't have any good estimates for speciation, let's assume a middle magnitude for speciation of 10 species per year as an estimate of the global background rate of speciation.

Finally, we need to estimate a quantity for biodiversity (i.e. number of species) for the biosphere on the whole. Estimates of this number range from 1 million to 100 million. Let's be conservative and pick a number of mid-magnitude, 10 million.

Calculate the following:

    1. Using the above values for extinction and speciation, what is the global net annual change in biodiversity?
    2. Using an extinction rate 100 times Lomborg's background estimate, how many years would it take to reduce biodiversity by 50% (which most paleontologists would agree amounts to a mass extinction event).
    3. Using an extinction rate 1,000 times Lomborg's background estimate, how many years would it take to reduce biodiversity by 50% (which most paleontologists would agree amounts to a mass extinction event).
    4. What is the probability that human activity might maintain these extinction rates for the interval necessary to declare a mass extinction has occurred?
    5. Can these numbers be trusted to conclude that there is a mass extinction underway? Use your knowledge of the biosphere to evaluate the claim of an ongoing mass extinction event.