As a population continually adapts to its environment, the accumulation of these adaptations over time makes the organism different enough for it to become its own species. There are many ways to define a species and many ways for a species to form. Organisms must constantly change as the environment changes, so constant speciation is natural and inevitable.
Speciation: The formation of a new species.
Allopatric Speciation: When two populations of organisms from the same species are physically separated, each of the two organisms adapts to their respective environments.
Sympatric Speciation: When a new species arises even without geographic separation occurring between two populations of the same species.
Coevolution: When two species evolve based on their interactions with and effects on one another.
Gradualism: A model where evolutionary changes occur at a slow and steady pace.
Punctuated Equilibrium: A model where there are long periods of little evolutionary changes and short bursts of rapid changes.
There are many things called “species concept” to consider when defining a species. We are only going to look at four, but a species does not need to match all the species concept defined here to be considered a species. However, it should match at least one.
Ecological species concept: This species concept looks at the role of two different organisms within their environment and the ecological niche that they fulfill. For example, if one of the organisms is prey, and the other organism is a predator, then we know that these organisms are obviously not the same species (unless they are cannibalistic, but this is pretty rare) that happen to share an environment.
Speciation can occur for several reasons. Geographic separation is important in allopatric speciation.
Speciation can occur even if two populations are not geographically separated. Sympatric speciation can occur due to other types of isolating mechanisms. For example, two populations of the same species may evolve reproductive barriers. The two populations may no longer mate at the same times or may have developed different mating rituals.
Coevolution often occurs with species in symbiotic relationships.
Macroevolution can occur slowly or quickly, depending on changes in climate and geologic conditions.