Measuring Species and Extinction

Scientists studying biodiversity must determine the number of species on the Earth and the numbers being lost to extinction. Biodiversity studies therefore rely on solid estimates of the population size of species, which is aff ected by species behavior, migrations, breeding cycles, and the size and distribution of habitats. All of these assessments can be rather diffi cult to make, especially when studying biota that live largely mysterious lifestyles in remote places.

Biodiversity measurements involve fi ve main challenges. Th e fi rst challenge comes from the diffi culty of determining the number of species on Earth. Second, molecular biology is constantly revealing more about the genetic makeup of species—how they are related and why they are similar or dissimilar. Sometimes a species does not succumb to extinction, but rather it acquires genes that help it adapt to changes in the environment. Th ird, the characteristics that certain species require in their habitat may not be fully understood, and this makes it diffi cult to assess
the status of a species when a habitat is altered. Fourth, not all species on Earth have been discovered, and science has no way of knowing whether or when these species go extinct or their role while they inhabit the Earth. Finally, animals oft en move around. Biologists must determine whether an animal’s population is declining or whether the species has simply migrated to a new place. A useful adage in biodiversity studies is the following: “Every animal is rare somewhere.”