Biological Isolation, Natural Selection, and Reproductive Strategies

ethological isolation

*behavorial* differences that reduce or prevent interbreeding between individuals of different species (including pheromones and other attractants)

Mechanical isolation

Morphological differences can prevent successful mating

Ecological isolation

species occur in the same area, but they occupy different habitats and rarely encounter each other

Temporal isolation

form of reproductive isolation in which two populations reproduce at different times

geographic isolation

form of reproductive isolation in which two populations are separated physically by geographic barriers such as rivers, mountains, or stretches of water

Genetic drift

A change in the allele frequency of a population as a result of chance events rather than natural selection.

Gene flow

Movement of alleles into or out of a population due to the migration of individuals to or from the population

Founder Effect

change in allele frequencies as a result of the migration of a small subgroup of a population

John Endler's famous experiments demonstrated that

sexual selection results in bright color guppies in low predation environments.

stabilizing selection

form of natural selection by which the center of the curve remains in its current position; occurs when individuals near the center of a distribution curve have higher fitness than individuals at either end

directional selection

Form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve

disruptive selection

form of natural selection in which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle

frequency-dependent selection

the fitness of a phenotype depends on how common it is in the population

sexual selection

A form of natural selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates.

Muller's ratchet

is a process by which the genomes of an asexual population accumulate deleterious (harmful) mutations in an irreversible manner.

Red Queen hypothesis

sexual selection allows hosts to evolve at a rate that counters the rapid evolution of parasites

negative frequency dependent selection

Phenotypes favored only when rare. Example is left-handed fighting ability

positive frequency dependent selection

Phenotypes are favored only when common. Example is warning coloration

polymorphic variation

More than one allele at frequencies greater than mutation alone

continuous variation

Variation measured on a continuum rather than in discrete units or categories (eg height in human beings).

negative assortative mating

Mate with individuals UNLIKE yourself. Increases heterozygotes, decreases homozygotes

ecogeographic variation

variation along a ecological or geographic gradient

-can occur as a cline

Ex: plant morphology along H2O gradient

quantitative variation

Phenotypic variation that is characterized by the distribution of continuous variation (expressed using a numerical measure) within a population (for example, in a bell curve).

Isogamy

sexual reproduction by the fusion of similar gametes

Anisogamy

Refers to a difference in gamete size in males and females. Eggs large and costly, sperm small and cheap

Oogamy

sexual reproduction in which one of the gametes (the egg) is large and nonmotile and the other gamete (the sperm) is smaller and motile

How to Calculate Relative Fitness

number of surviving offspring per individual of a particular genotype/number of surviving offspring per individual of the most successful genotype