The reasons for the extinction of a species and for the rapid rates
of change in our environment are currently the focus of much scientific
research. An individual species' susceptibility to extinction depends on at
least two things: the taxon (the biological group—kingdom, phylum, class,
(5) order, family, or genus) to which a species belongs, and the overall rate
of environmental change. Fossil evidence shows that more mammals and
birds become extinct than do mollusks or insects. Studies of the extinction
of the dinosaurs and other reptiles during the Cretaceous Period show
that a changing environment affects different taxa in different ways. Some
(10) may be dramatically affected, others less so.
The best way to answer the question of what causes anextinction is
to combine fields of inquiry and a variety of viewpoints. Using the fossil
record and historical documentation, the different rates of the extinction
of various taxa and different responses to environmental change can be
(15) detected. Then the evolutionary development of the different species
can be compared, and traits that may be disadvantageous can be singled
out. Finally, researchers can use mathematical formulae to determine
whether a population is likely to adapt itself to the changing environment
or disappear. Hopefully, as more of this information is collected, specialists
(20) in different fieldse.g. physiological and behavioral ecology, population
ecology, community ecology, evolutionary biology and systematics,
biogeography, and paleobiology — will work together to make predictions
about the changes that might occur in the ecosystem.
1. Which of the following is the main topic of the passage?