Evolution of Biodiversity

Readings

•Evolution

*Chapter 5

*Species Diversity*Ecosystem species (# species in an area) genetic diversity

(within a population)

*We have classified 2 million species, but there is an estimated 10 million

*Species richness is the number of species in a given area (pond, tree canopy)

*Species evenness looks at individual proportions of species to see which are numerically dominant

*High species evenness if all species are represented equally

*Human development often disturb both of these

*Creating Genetic Diversity*Biodiversity results from evolution, the change in genetic

composition of a population over time

*Genes from a cell determine all possible traits of an organism (physical or behavioral)

*Complete set of genes is called the genotype. Phenotype is actual set of traits in an individual (what individual actually looks like)

*Two processes that create genetic diversity

*Mutations – DNA copies it self millions of times as cells divide. Occasionally there is a mistake.*Mutations can hurt organisms (often die before born) or they can help

organisms (mutation that makes an insect less vulnerable to insecticides)

*Recombination – Chromosomes are duplicated during reproductive cell division and a piece can break off and attach to another chromosome

*Does not create new genes, but creates new combinations of traits

*Might combine to give humans new immune system

*Evolution by Artificial Selection*Three main way evolution occurs: artificial selection, natural

selection, and random process

*Artificial selection is when humans determine which individuals will breed

*All dogs came from the gray wolf

*Most crops artificially selected

*Can lead to resistance (bacteria, pesticides)

*Natural selection is survival of the fittest

*Recombination and mutations give members of the same species different traits, some which may help them survive

*Traits get passed on and determine ability to survive and reproduce

*Adaptations are behavior changes

*Evolution by Random Process*Evolution by random process occurs in 4-ways:

1. Mutation – mutation can arise in a population and increase over time as it mates

2. Genetic drift – when genotypes are lost by chance (mouse population of 5 has 4 black mice and 1 white mouse. If that white mouse finds no one to mate with, the white mouse population will disappear)

3. Bottleneck effect – when a population is reduced, some genotypes are lost. Harder to survive because less helpful mutations available

4. Founder effect – when a small number of individuals determine characteristics of future generations (two birds get blown off course and end up on a new island. The future generations depend 100% on their traits)

*Allopatric vs Sympatric Speciation

*Geographic isolation can lead to evolution

*If two habitats have different conditions, different phenotypes will be favored among the same species (new island, lake split, volcano)

*Eventually they become so different, they can’t breed. Called reproductive isolation

*The whole process of geographic isolation leading to reproductive isolation is called allopatric speciation (Darwin’s finches)

*New islands, continents moving, rivers forming

*Each population gets its own set of mutations

*Sympatric speciation is when one species evolves into two without geographic isolation

*Feed in different areas, mate in different seasons

*The Pace of Evolution*Evolution can take from hundreds to millions years

*Factors that affect rate of change

*Rate of environmental change (faster change = less evolution)

*Genetic variation - more phenotypes which means quicker evolution (more genetic variation = more evolution)

*Population size – large populations means more genetic diversity, but a mutation in a small population can spread more quickly (smaller population equals more diversity)

*Generation time – quicker species becomes reproductively mature, the quicker they evolve (more generations over short period of time)

*We can genetically engineer to get the traits we desire

HUMAN IMPACTS ON TERRESTRIAL BIODIVERSITY

We have depleted and degraded some of the earth’s biodiversity and these threats are expected to increase.

*Niches*Range of tolerance is the limit of abiotic factors an organism

can tolerate (temp, salinity, pH)

*The further away from ideal conditions, the less of an organism you may find

*Beyond the range of tolerance, organisms will die

*The fundamental niche is the combination of ideal abiotic conditions

*Biotic conditions can further limit a niche (competitors, predators, diseases)

*Realized niche is based on the combination of biotic and abiotic factors

*Generalists have broad niche

*Specialists have a narrow niche

*Environmental Change and Species Distribution and

Extinction*Environmental changes change species distribution (last ice age to present)

*Try to predict distribution of future species as climate changes

*Most species can’t adapt to significant changes for three major reasons1. No favorable environment to move to (polar bear)

2. May be too much competition in new env

3. Environmental changes may happen to quickly

*Avg lifespan for a species is 1-10 million

*99% of the species ever on this planet are extinct

*Mass Extinctions*5 mass extinctions have occurred

*Last one (dinosaurs) occurred because meteor

*We are currently experiencing the sixth major extinction. Because of human activity

*Habitat destruction, overharvesting, invasive species, climate change, and emerging disease

Causes and consequences of biodiversity loss