Random Change
Genetic Drift – changes to allele frequency as a result of chance; such changes are much more pronounced in small populations
1.
Bottleneck – a dramatic, often temporary, reduction in population size usually resulting in significant genetic drift.
Example: cheetahs have famously low levels of genetic variation. This can probably be attributed to a population bottleneck they experienced around 10,000 years ago, barely avoiding extinction at the end of the last ice age.
2.
Founder Effect – genetic drift that results when a small number of individuals separate from their original population and find a new population
Example: a few seeds carried by a bird or by wind to distant volcanic island may germinate and rapidly establish a large population. With self-pollinating plants, an entire population can be established from a single fertile seed
2.10 Pathways of Evolution
Adaptive Radiation
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When a single species evolves into a number of distinct but closely related species
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Each new species fills a different ecological niche
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Occurs when a new resource that is not being used by other species becomes available
Example: Darwin’s finches – 13 species that live on the Galapagos Islands evolved from a single species

Divergent Evolution
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Occurs when two or more species evolve increasingly different traits, resulting from differing selective pressures or genetic drift.
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Large-scale evolution of a group into many different forms
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Ontario has over 20 species of closely related rodents
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All of these species evolved from a single common ancestor that existed millions of years ago. Species include (a) deer mouse, (b) flying squirrel, (c) porcupine, and (d) beaver.
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Sometimes divergent evolution occurs in rapid succession, or simultaneously, among a number of populations. This process, known as adaptive radiation, results in one species giving rise to three or more species (example: Darwin’s finches).
Convergent Evolution
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Occurs when two different species evolve to occupy similar ecological niches.
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The evolution of similar traits in distantly related species.
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Cacti (a) and euphorbia (b) have evolved similar features in response to their hot dry environment.
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Sharks and dolphins are another example of convergent evolution, both have evolved very similar streamline bodies well suited for high speed carnivorous behaviour.
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Same body shapes in two very distantly related species
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Complex eyes have evolved independently in many animal groups including insects (a), arachnids (b), mollusks (c), and vertebrates (d)
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Traits that are similar in appearance but that have different evolutionary origins are referred to as homoplasies (also known as analogous features)

Coevolution
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A process in which one species evolves in response to the evolution of another species.
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Certain plants have evolved hard protective shells to protect seeds, while some seed-
 eating mammals have evolved powerful jaws and teeth for chewing through hard shells.
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One or both species may become increasingly dependent on the other.
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In extreme cases the extinction of one species can lead to the extinction of the other.
The Madagascar long-spurred orchid is pollinated by a hawk math (b) whose tongue is about
30 cm long.
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Natural selection has selected long spurs because the moth have to spend more time and effort to get the nectar, making them more likely to pick up pollen.