Cane toads are large, nonnative, poisonous toads in Australia. After cane
toads entered Australia, scientists observed that the average head size in a
population of toad-eating snakes was getting smaller. Snakes with smaller
heads are not able to eat the large cane toads. What is this situation called?
A. Directional selection
B. Stabilizing selection
C. Fitness
D. Species richness

One statements is an example of a scientific observation. another statement is an example of a scientific explanation. identify the correct statement for each category to illustrate how scientific explanations are inferred from scientific observations.

Examine the two squirrel populations in the accompanying figure. the populations are separated by a geographic barrier. if after a long period of time the two species are no longer separated, what evidence is needed to determine if speciation has occurred? the figure shows two populations of squirrels separated by a geographic barrier. examine the two squirrel populations in the accompanying figure. the populations are separated by a geographic barrier. if after a long period of time the two species are no longer separated, what evidence is needed to determine if speciation has occurred? the figure shows two populations of squirrels separated by a geographic barrier. polyploidy is creating new species. the two populations are not interbreeding freely. hybrid offspring of the two populations begin to appear. one species will increase into a population size twice as large as the other species.

Explain how paleontologists use trilobite fossils as index fossils for various geologic time periods.