Resource: An Origin of Species

The term evolution refers to the cumulative change that occurs in populations of organisms over time. Sometimes evolutionary change is so dramatic that different populations of the same species diverge to become two or more distinct species. In the case of a group of birds called honeycreepers, for example, a single species that colonized the Hawaiʻian Islands about 5 million years ago ultimately diverged into 57 different species.

This process, which evolutionary biologists call speciation or adaptive radiation, can happen anywhere. However, it is most clearly demonstrated on geologically young land masses, such as newly formed islands or mountains. In these environments a population of organisms will typically find a set of environmental opportunities and pressures very different from the conditions they experienced in their place of origin. These environmental differences come in many forms and often cause sweeping evolutionary changes in a founding population.

Several environmental factors affect the process of speciation. The structural habitat of an area determines the ease with which creatures are able to move around and find shelter from weather and other organisms. Food, both the type and its availability, dictates the ease with which animals are able to acquire the energy they need to survive and reproduce.

Competition for various resources is another factor that can drive the process of speciation. Competitive pressure can come from organisms of the same species or from organisms of different species. Generally, in highly competitive environments, traits that minimize competition — traits that, for example, allow two different populations to feed on very different types of food — are advantageous.

Another factor that can influence speciation is predation. Predators typically reduce the rate of speciation because they limit other organisms' access to resources. On newly formed land masses, however, the number of predators is typically lower than on older continents. These younger environments, therefore, provide more opportunities for species to evolve into new and different species.

Describe some of the physical changes in the pollenpeeper species.

What are some of the environmental factors that influence the passing of varying traits from generation to generation?

Where did the greatest change in the species occur? Why?