Ecology CH3 Natural selection

Natural selection

differential survival and reproduction (fitness) of individuals with certain phenotypes compared with individuals of other phenotypes

Differential fitness will lead to ____

Change in allele frequency over time

Requirements for evolution by natural selection

Variability of a phenotype

Heritability of a phenotype

Differential survival and reproduction of a phenotype

Selection can occur without evolution. Why?

If a trait is not heritable and selection occurs, the trait will continue to appear in following generations despite the previous selection event

Evolution is possible without natural selection. Why?

Other mechanisms of evolution like genetic drift

Adaptation

The evolutionary process by which, over the course of generations, organisms are altered to become adapted to a particular environment with respect to features that affect survival or reproduction

a characteristic of an organism that evolved by natural selection

Having an adapted trait MUST

increase an individual’s fitness over those that do not have that trait/have a reduced form of that trait

Selection of vs. selection for

Selection for is active selection based on an environmental selection pressure (ex. small animals) selection of is what happens to go with the trait that is selected for (all small animals happen to be red)

Not all traits are adaptations. Why else might traits exist?

A trait may be a necessary consequence of physics/chemistry (ex our blood is red bc it has iron, not bc it is beneficial for it to be red)

A trait may have evolved from other mechanisms (such as drift) rather than by selection

The trait may have evolved not because it is an adaptive advantage, but because it is correlated with another trait that is an adaptation

May be a consequence of phylogenetic history (vestigial structure)

How to tell if something is an adaptation?

It is complex/well-designed

Use comparative experiments

Trade offs

Existence of both a fitness benefit and a fitness cost of a mutation or character state relative to another

Why have some adaptations not evolved?

Lack of suitable mutations/genetic variability

Phylogenetic constraints

Trade offs