Origins of Life . The Earth developed in two phases:Chemical Evolution - organic molecules, bipolymers, and systems of chemical reactions formed the first protocellsBiological Evolution - from single-celled prokaryotic bacteria to single-cell eukaryotic organisms, then to multicellular organisms .
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1. Chapter 5 Evolution and Biodiversity; Origins, Niches, and Adaptation
2. Origins of Life The Earth developed in two phases:
Chemical Evolution - organic molecules, bipolymers, and systems of chemical reactions formed the first protocells
Biological Evolution - from single-celled prokaryotic bacteria to single-cell eukaryotic organisms, then to multicellular organisms
3. The “E Word” - Evolution Evolution - the change in a populations genetic makeup through successive generations.
Theory of Evolution - all species descended from earlier, ancestral species which explains how life changed over 3.7 billion years and why life is so diverse today.
4. Macro vs. Microevolution Microevolution - the small genetic changes that occur in a population.
Macroevolution - the long-term, large-scale evolutionary changes through which a new species is formed from ancestral species and other species are lost through extinction.
5. How Does Microevolution Work We need genetic variation for evolution to occur!
Microevolution is a change in the population’s gene pool over time.
Genes may have two or more different forms, alleles. Each individual has different combinations of alleles.
Mutations create changes in the genetic variability in a populations.
Mutations are random and unpredictable
Mutations must be passed onto offspring
Some are beneficial and some are harmful.
Beneficial mutations create better chances for an individual and their offspring under existing or changing conditions.
6. What Role Does Natural Selection Play? Natural Selection - occurs when some individuals in a population have genetically based traits that increase their chances of survival and their ability to produce offspring.
In order for evolution to occur, there must be:
Natural variability for a trait in a population
Trait must be heritable
The trait must lead to differential reproduction (individuals with the trait leave more offspring than other members of the population.)
7. What Does Natural Selection Do? An allele or set of alleles becomes more common in succeeding generations.
Other alleles become less common.
The beneficial allele is known as an adaptation or adaptive trait.
Heritable trait that enables organisms to better survive and reproduce under a given set of environmental circumstances.
8. If the environment changes, what choices do organisms have? Adapt to new conditions through natural selection (not a “choice”)
Migrate to an area with more favorable conditions
Become extinct (also, not a “choice”)
9. Three Types of Natural Selection Directional Natural Selection - where environmental changes cause allele frequencies to shift so that individuals with traits at one end of the normal range become more common than midrange forms.
10. Three Types of Natural Selection - Continued Stabilizing Natural Selection - tends to eliminate individuals on both ends of the genetic spectrum and favor individuals with an average genetic makeup.
11. Three Types of Natural Selection - Continued Diversifying Natural Selection - happens when environmental conditions favor individuals at both extremes of the genetic spectrum and eliminates or reduces the number of individuals in the normal or intermediate range.
12. What is an Ecological Niche? The species’ way or life or functional role in an ecosystem.
Includes their range of tolerance for physical and chemical conditions
Includes the types and amounts of resources used
Includes how it interacts with other living and non-living components of the ecosystem
Includes the role it plays in energy flow and matter cycling.
Why is it important to understand a species’ niche?
It can prevent premature extinction.
We can assess any environmental changes we make in different ecosystems.
13. Fundamental Niche Vs. Realized Niche Fundamental Niche - the full potential range of conditions and resources the species could theoretically use if there were no direct competition from other species.
Realized Niche - the actual amount of its fundamental niche that the species uses to survive and avoid competition
14. Generalist Vs. Specialist Generalist Species
Have broad niches
Live in different places
Eat a variety of foods
Tolerate a wide variety of environmental conditions
Have narrow niches
Use only one or a few types of food
Tolerate only a narrow range of climatic and environmental conditions
More prone to extinction
Better to be a generalist of a specialist?
Under constant conditions - a specialist has fewer competitors
Under changing conditions - a generalist has more choices.
15. What Limits Adaptation The trait needs to be present in the population!
Reproductive capacity - how quickly can organisms with the adaptive trait be produced.
Quick RC: change happens in a short amount of time.
Slow RC: organisms can take thousands of years to change
Even if the trait is present in a population, there has to be some impetus to allow the trait to predominate.
16. Speciation, Extinction, and Biodiversity Speciation - when natural selection leads to entirely new species
Geographic Isolation - groups of the same population between physically separated for long periods of time.
Reproductive Isolation - when mutation and natural selection happen independently in two geographically isolated populations and change the allele frequencies so that the populations can no longer interbreed.
17. Example Reproductive Speciation
18. Oh No! --Extinction If environmental conditions change, and a species does not evolve or move to a more favorable area, it will become extinct.
Major factors affecting extinction:
Gradual climate changes
Rapid climate changes caused by catastrophic events.
Background Extinction - as local environment changes, a certain number of species disappear at a low rate.
Mass Depletion - rates higher than normal
Mass Extinction - a significant rise above the background rates
19. What Happens After Mass Extinctions and Depletions Adaptive radiation - periods of recovery after earth’s mass extinctions and depletions.
Species evolve to fill ecological roles or niches in the changed environment.
20. Environmental Connection and Impact BIODIVERSITY, BIODIVERSTY, BIODIVERSTY!
Biodiversity = the planet’s genetic raw material for future evolution in response to changing environmental conditions.
Speciation - Extinction = Biodiversity
21. Environmental Connection and Impact Humans have been a major force in the premature extinction of species:
Extinction rates have increased by 100 - 1000 times the natural background rate
Over the next 50 years, human population and resource consumption might cause the premature extinction of 1/4 of the earth’s current species.