Ecology Chapter 6: Evolution

fixation

-allele frequency of 100%

Evolution can alter ecological interactions

-evolutionary changes that occur over long time scales also affect ecological interactions

Alleles

-two or more forms of a given gene that results in the production of different versions of the protein that the gene encodes

4 Mechanisms of evolution

1- Mutation 2-natural selection 3-gene flow 4-genetic drift

Two ways in which new species can form

1-genetic divergence 2- when members of 2 different species produce fertile hybrid offspring

Ecological trade-offs of adaptive evolution

-ability to perform one function reduces the ability to perform the other;

Genetic drift: results from chance events

-alters allele frequencies significantly over short periods of time in SMALL POPULATIONS

Why are adaptations not perfect?

-an organism's environment is not static because abiotic and biotic componenets of the environment change over time.

Genes

-composed of DNA and specify how to encode proteins

Relationship between ecology and evolution

-ecology is the study of the abundance and distribution of organisms; factors affecting abundance and distribution are also important in evolution

Adaptive radiation

-event in which a group of organisms gives rise to many new species that expand into new habitats or new ecological roles in a short amount of time

Mutations...

-generate the raw material for evolution -change in the DNA of a gene

Natural selection can result from differences between populations

-if 2 populations experience different environmental conditions, individuals with one set of characterisitics may be favored by natural selection in one population

Lack of genetic variation in adaptive evolution

-if none of the individuals in a population has a beneficial allele of a particular gene that influences survival and reproduction, adaptive evolution cannot occur at that gene

Evolutionary history of adaptive evolution

-if the necessary genetic variation is present, natural selection works by modifying the traits already present in an organism; doesn't craft the adaptations of an organism from scratch

Disruptive selection

-individuals with a phenotype at either extreme is favored

Stabilizing selection

-individuals with an intermediate phenotype are favored

Mass extinction

-large proportions of earth's species were driven to extinction worldwide in a relatively short time -greatly increases the diversity of some of the surviving groups of organisms by removing competitor groups

Genotype

-letters that represent the individuals two copies of each gene

What shapes long term patterns of evolution?

-mass extinctions and adaptive radiations

Why are mutations a weak agent of allele frequency change?

-occur too rarely

Descent with Modification

-populations accumulate differences over time, so when a new species forms it differs from its ancestors -also resembles its ancestors and continues to share many characteristics with them

Natural Selection

-process by which individuals with certain heritable characteristics survive and reproduce more successfully than other individuals -responsible for the modification part of descent with modification

Speciation

-process by which one species splits into two or more species -most commonly occurs when a barrier prevents gene flow between two or more populations of a species

Species and geographic variation

-represent natural groupings; structure of small groups interconnected by highways can lead to geographic variation

Gene flow

-transfer of alleles between populations -via the movement of individuals or gametes

Hardy- Weinberg: the falsifiable model

-used to test whether or not a population is evolving at one or more genes -predicts no change in allele frequencies in large, randomly mating populations if there is no mutation, migration, selection, or genetic drift

Directional selection

-when individuals with one extreme of a heritable phenotypic trait are favored over other individuals

Gene flow can limit local adaptation

-whenever alleles are transferred between populations that live in different environments, the extent to which adaptive evolution occurs in each population depends on whether natural selection is strong enough to overcome the effects of ongoing gene flow

Mutations and recombination(production of offspring that have combinations of alleles that differ from those in either of the parents

-work together to provide the genetic variation on which evolution depends -

Evolution (2 main parts)

1- is an allele frequency change in a population over time 2- is descent with modification

Natural selection increases frequency of advantageous alleles 3 TYPES

1-Directional selection 2-Stabilizing selection 3-Disruptive selection

Constraints on adaptive evolution

1-Lack of genetic variation 2-Evolutionary history 3-Ecological trade-offs

4 effects of genetic drift

1-can cause allele frequencies to fluctuate randomly in small populations over time 2- can cause alleles to be lost from a population, reducing the genetic variation of a population 3- can increase the frequency of a harmful allele; can overrule the effects of natural selection causing the harmful allele to increase or decrease in frequency based on chance. 4-can increase genetic differences between populations; can cause an allele to reach fixation in a population or be lost in another population

Ecological interactions can cause evolutionary change

1-predator-prey interactions 2-studies of speciation shows this 3-effect of ecology on evolution is clear from studies of relatively small evolutionary changes in populations

Two effects of gene flow

1-tends to make a population more similar to another genetically 2-can introduce new alleles into a population