Download Chapter 12: Evolution and Extinction A Tropical Murder Mystery

Chapter 12: Evolution and Extinction
A Tropical Murder Mystery: Finding the Missing Birds of Guam
Story Abstract and Additional Information
This chapter explores the variety of life on Earth that is a result of natural selection favoring those
individuals within populations that are best able to survive in their particular environment. Given
enough time, some populations may be able to adapt to environmental changes. Extinction is a natural
part of this process, as less adapted populations are eliminated by better competitors or are lost due to
natural disasters. Human activities can introduce changes so quickly that some populations of other
species cannot adapt fast enough to survive and may go extinct.
Here are some of the key points in the story for this chapter:
What is evolution?

Evolution occurs when a population has experienced a change in gene frequencies from one
generation to the next. Gene frequencies are the assortment and abundance of particular
variants of genes relative to each other within a population. Here are twelve different examples
of evolution: http://www.wired.com/wiredscience/2008/12/evolutionexampl/.

Selective pressure on the population—a nonrandom influence affecting who survives or
reproduces—favors individuals with certain inherited traits over others (such as better
camouflage, tolerance for drought, or enhanced sense of smell). The traits that an environment
favors are called adaptations, and the process by which organisms best adapted to the
environment survive to pass on their traits is known as natural selection. Here are ten different
examples of natural selection: http://curiosity.discovery.com/topic/ecology-and-evolution/10examples-natural-selection.htm.
How are humans impacting evolution and extinction?

In addition to genetic diversity, the size of the population also makes a difference in how quickly
natural selection can produce a change in a population: beneficial traits can spread more quickly
in smaller populations simply because it is more likely that the individuals with the trait will find
each other and mate. Reproductive rate and generation time also influence how quickly a
population can adapt to changes. The strength of the selective pressure also affects how quickly
natural selection might produce a change in a population. Read about how humans are
continuing to evolve: http://www.time.com/time/health/article/0,8599,1931757,00.html.

Extinction is nothing new on Earth. It is as constant and as common as evolution; by most
estimates, more than 99% of all species that ever lived on the planet have gone extinct. But
these kinds of events often lead to the emergence of new species, as other populations adapt to
the open niches that are left. Today, most scientists agree that swelling human populations have
triggered a sixth major extinction event, one that we are witnessing right now:
http://www.scientificamerican.com/article.cfm?id=could-re-wilding-avert-6th-great-extinction.
What factors are currently contributing to species endangerment?

The world’s biodiversity faces threats on several fronts. If a species faces a very high risk of
extinction in the immediate future, scientists classify that species as endangered. When a
species is likely to become endangered in the near future, they say it is threatened. The
International Union for Conservation of Nature (IUCN) classifies a species as endangered when it
suffers a population loss of 80% or greater in a three-year period. Read about how conservation
efforts in the Philippines led to a green turtle nesting boom:
http://www.iucn.org/about/work/programmes/species/?9201/Green-Turtle-nesting-boom-inPhilippines.

Globally, the IUCN estimates that 40% of all known species face extinction. Recent studies
indicate that there are only about 3,200 tigers, 720 mountain gorillas, and 60 Javan rhinoceros
left in the wild. But the fight for survival is not confined to large, furry mammals. In fact, the
majority of listed endangered species are plants, not animals, and this could impact us directly.
Of the 70,000 or so flowering and nonflowering plants with known medicinal value, more than
15,000 are endangered. Read about efforts in India to save the Guggul tree, whose gum-resin is
used to treat bone fractures, arthritis, inflammation, obesity, and heart problems:
http://iucn.org/about/work/programmes/species/our_work/plants/plantsnews/?3032/endange
red-indian-medicinal-plant.
Additional information about other topics from this chapter:
Brown Tree Snake in Guam

Things are looking up for birds in Guam. Thanks to efforts by the Guam Department of
Agriculture and the U.S. Department of Agriculture Wildlife Services, brown tree snakes are
being controlled to allow bird populations to recover. Read more about efforts to control this
population: http://www.aphis.usda.gov/lpa/pubs/fsheet_faq_notice/fs_wsbtsnake.html.