Natural Selection and Diversity Photo by Harvey Barrison

Natural Selection Every ecosystem contains a finite amount of resources. Some ecosystems can support large amounts of life, but even the most fertile ecosystems have limits. The largest population size that an ecosystem can support is the population’s carrying capacity. Photo by Eckhard Jakob at the German language Wikipedia

Natural Selection Populations tend to produce more offspring than the ecosystem can support. This may seems harmful, but it helps to drive natural selection.

Natural Selection When a population exceeds its carrying capacity, the organisms with the best adaptations are most likely to survive and reproduce. This helps increase the frequency of beneficial alleles within the population.

Natural Selection If two populations become separated, they may be forced to adapt to different environments. This may cause natural selection to favor different alleles in each population.

A mutation creates a new green allele which increases in frequency. Natural Selection Mutations may also introduce new alleles into one population that are not present in the other. Over time, natural selection can increase the diversity that is found within a species. A mutation creates a new green allele which increases in frequency.

Natural Selection As long as the members of two populations continue to interbreed, they are considered part of the same species. A species contains all of the organisms that reproduce and create fertile offspring. While these spiders look very different, they are all a part of the same species and can reproduce with each other. Photos courtesy of Rosemary Gillespie, UC Berkeley

Two species of squirrel that adapted to different regions. Natural Selection Sometimes, two populations become adapted to different environmental conditions, and the variations within the populations will cause them to no longer interbreed. When this happens, the two populations are considered different species! Two species of squirrel that adapted to different regions.

Speciation When a new species is formed, it is called speciation. Speciation is usually the result of populations becoming adapted to different environmental conditions.

Finches Finches are a type of bird in the Galapagos Islands. Because the islands are close enough for the birds to reach, small population of finches migrated to new islands. However, each island had slightly different resources.

Different types of seeds and insects made different alleles more favorable based on the niche each population filled on an island. Photo by Harvey Barrison Photo by Mark Putney Photo by Mark Putney Photo by Michael Dvorak

Finches Because each population faced different conditions and filled different niches, natural selection favored different alleles for size and beak shape. Photo by Harvey Barrison Photo by Mark Putney Photo by Mark Putney Photo by Michael Dvorak

Finches Over time, the variations between finch populations increased as each population became more adapted to its island. Natural selection increased the diversity because different alleles helped these finches survive and reproduce. Photo by Harvey Barrison Photo by Mark Putney Photo by Mark Putney Photo by Michael Dvorak

Finches Each population became so adapted to its niche that today none of these populations interbreed. Each population of finch is considered to be its own species. The formation of these new species is what we call speciation! Galapagos Islands