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Ecosystems – Species Diversity & Environmental Interactions. After this unit you should be able to : Explain the process of natural selection and cite evidence for this process Describe the ways in which evolution influences biodiversity
After this unit you should be able to:
How evolution influences biodiversity
Reasons for species extinction
Species = a population or group of populations
Whose members share characteristics
They can breed with one another and produce fertile offspring
Population = a group of individuals of a species that live in the same area
Evolution = means change over time
Biological evolution: genetic change in populations over time
Genetic changes lead to changes in appearance, functioning or behavior over generations
Evolution may be seen as random
directed by natural selection
Natural Selection = traits that enhance survival and reproduction
Are passed on more frequently to future generations
those that do not lead to survival, disappear in the gene pool.
Premises of natural selection:
Organisms struggle to survive and reproduce
Organisms produce more offspring than can survive
Individuals of a species vary in their characteristics due to genes and the environment
Some individuals are better suited to their environment and reproduce more effectively
Natural selection acts on genetic variation
Adaptation = the process where, over time, characteristics (traits) that lead to better reproductive success
Become more prevalent in the population
Adaptive trait (leads to adaptation) = a trait that promotes reproductive success
Mutations = accidental changes in DNA that may be passed on to the next generation
Non-lethal mutations provide the genetic variation on which natural selection acts
Sexual reproduction = also leads to variation through mating preferences.
Natural selection changes characteristics through:
Directional selection = drives a feature in one direction
Stabilizing selection = favors intermediate traits
Preserving the status quo
Disruptive selection = traits diverge in two or more directions
It is evident in every adaptation of every organism
Artificial Selection = the process of selection conducted under human direction
Producing the great variety of dog breeds and food crops
Speciation produces new types of organisms
The process of generating new species from a single species
Where changes and isolations within the environment and habitat cause new species to form.
Allopatric speciation: species formation due to physical separation of populations
The main mode of speciation
Populations can be separated by glaciers, rivers, mountains
Each population gets its own set of mutations
Sympatric speciation= species form from populations that become reproductively isolated within the same area
Feed in different areas or eat different foods.
Mate in different seasons or because of mating rituals.
Hybridization between two species
Bird dances: rifle bird ; moonwalk.
How do major groups diverge over time?
Phylogenetic trees(cladograms) = show relationships among species, groups, genes, etc.
Scientists can trace how certain traits evolved
Extinction = the disappearance of a species from Earth
Species last 1-10 million years
Biological diversity is now being lost at an astounding rate
This loss of species is irreversible
Number of species = speciation - extinction
Humans profoundly affect rates of extinction
Biodiversity loss affects people directly
Food, fiber, medicine, ecosystem services
Extinction occurs when the environment changes rapidly
Natural selection can not keep up
Many factors cause extinction:
Severe weather, climate change, changing sea levels
New species, small populations
Endemic species = a species only exists in a certain, specialized area
Very susceptible to extinction
These species usually have small populations
Some U.S. salamander species live on top of single mountains
In 1964, Golden toads were discovered in Monteverde, Costa Rica
The mountainous cloud forest has a perfect climate for amphibians
They became extinct within 25 years
Climate change’s drying effect on the forest
A lethal fungus