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Questions and Answers
What is a characteristic of directional selection?
What is a characteristic of directional selection?
Which of the following is NOT one of the postulates for natural selection?
Which of the following is NOT one of the postulates for natural selection?
What does sexual dimorphism refer to?
What does sexual dimorphism refer to?
Which type of selection favors the average phenotype over extremes?
Which type of selection favors the average phenotype over extremes?
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What is intrasexual selection characterized by?
What is intrasexual selection characterized by?
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Which statement about female choice in sexual selection is true?
Which statement about female choice in sexual selection is true?
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What does runaway selection lead to in terms of male attributes?
What does runaway selection lead to in terms of male attributes?
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What is the primary reason that facilitates natural selection?
What is the primary reason that facilitates natural selection?
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Which selection process is primarily influenced by environmental conditions with low predation?
Which selection process is primarily influenced by environmental conditions with low predation?
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What is the main consequence of the bottleneck effect on a population's gene pool?
What is the main consequence of the bottleneck effect on a population's gene pool?
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Which type of speciation involves geographic isolation leading to the divergence of two species?
Which type of speciation involves geographic isolation leading to the divergence of two species?
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What mechanism prevents two species from successfully mating due to differences in mating rituals?
What mechanism prevents two species from successfully mating due to differences in mating rituals?
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Which of the following is an example of postzygotic reproductive isolation?
Which of the following is an example of postzygotic reproductive isolation?
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What type of mimicry involves a non-toxic organism resembling a toxic one?
What type of mimicry involves a non-toxic organism resembling a toxic one?
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Which type of adaptation is exemplified by bears hibernating during winter months?
Which type of adaptation is exemplified by bears hibernating during winter months?
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What is a benefit of resource partitioning in ecosystems?
What is a benefit of resource partitioning in ecosystems?
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Which condition describes the founder effect in a population?
Which condition describes the founder effect in a population?
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Which of the following adaptations relates directly to an organism's physical traits?
Which of the following adaptations relates directly to an organism's physical traits?
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What does punctuated equilibrium describe in evolutionary changes?
What does punctuated equilibrium describe in evolutionary changes?
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Intra-specific competition primarily involves competition between members of?
Intra-specific competition primarily involves competition between members of?
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What term describes anatomical structures that have different ancestors but serve similar functions?
What term describes anatomical structures that have different ancestors but serve similar functions?
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What is a characteristic feature of geographical isolation?
What is a characteristic feature of geographical isolation?
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Study Notes
Natural Selection
- Definition: The process where heritable traits that improve survival and reproduction become more common in a population over time, changing the population's genetic makeup.
- Mechanism: Organisms adapt to environmental pressures; those with advantageous traits survive and reproduce, passing on those genes.
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Four Postulates:
- Individuals within a population exhibit genetic variation.
- This variation is heritable.
- More offspring are produced than can survive, leading to competition.
- Individuals with favorable traits survive and reproduce more successfully.
Types of Natural Selection
- Directional Selection: Favors one extreme phenotype. Individuals with that extreme have higher fitness.
- Disruptive Selection: Favors both extreme phenotypes. Individuals with extreme traits have higher fitness.
- Stabilizing Selection: Favors the intermediate phenotype. Individuals with the average trait have higher fitness.
Sexual Selection
- Definition: A special form of natural selection focused on mating success.
- Intrasexual Selection: Competition within the same sex (e.g., males fighting for mates).
- Intersexual Selection: Choice by one sex (often females) of mates based on traits or behaviors of the other (often males).
- Sexual Dimorphism: Differences in appearance between males and females of a species, often due to intrasexual competition and female choice.
- Female Choice: Females' higher reproductive investment leads them to be selective in mate choice.
- Male Ornamentation: Costly displays signify good health and genes, attracting females.
- Runaway Selection: Female preference for exaggerated male traits can lead to their constant enhancement, but only under specific conditions (low predation, unlimited resources).
- Natural Constraints: Natural selection usually limits the exaggeration of such traits.
Genetic Drift
- Definition: Random changes in gene frequencies in a population.
- Effect: Usually leads to a loss of genetic variation.
- Impact of Population Size: Smaller populations are more strongly affected by genetic drift.
- Fitness vs. Luck: Survival isn't necessarily based on fitness, but sometimes on luck.
Specific Genetic Drift Examples
- Bottleneck Effect: Catastrophes drastically reduce population size, altering allele frequencies. Some alleles may increase, others disappear.
- Founder Effect: A few individuals from a population colonize a new area, establishing a new population with potentially skewed allele frequencies.
Punctuated Equilibrium
- Definition: Evolutionary change happening relatively quickly, often associated with speciation events.
- Environmental Changes: Environmental pressures can drive speciation events.
Speciation
- Definition: The process of forming new species, resulting in reproductively isolated populations.
- Reproductive Isolation: Mechanisms preventing successful reproduction between species.
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Prezygotic Isolation: Prevents mating or fertilization:
- Behavioral Isolation: Differences in mating rituals.
- Temporal Isolation: Different mating times.
- Geographic Isolation: Separation by physical barriers.
- Gametic Isolation: Egg and sperm are incompatible.
- Mechanical Isolation: Genitals are incompatible.
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Postzygotic Isolation: Prevents the formation of viable offspring after fertilization:
- Zygotic Mortality: Zygote fails to develop.
- Hybrid Inviability: Hybrid offspring don't survive to adulthood.
- Hybrid Infertility: Hybrid offspring are sterile.
Modes of Speciation
- Allopatric Speciation: Formation of new species following geographic isolation, leading to adaptation and reproductive isolation. Often linked to genetic drift.
- Peripatric Speciation: Similar to allopatric, but the isolated group is very small, leading to a rapid impact of genetic drift. Often related to the founder effect.
- Parapatric Speciation: No geographic barrier, but mating isn't random, e.g., different flowering times.
- Sympatric Speciation: Formation of new species within the same geographic area.
Defense Mechanisms
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Passive Defense: Mechanisms to avoid predation.
- Crypsis: Camouflage or hiding.
- Aposematism: Warning coloration.
- Camouflage: Matching the environment for concealment.
- Concealing coloration: Matching the environment's color.
- Distributive coloration: Breaking up body outlines.
- Disguise: Resembling something non-living.
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Mimicry: Resembling another organism.
- Batesian mimicry: A harmless organism mimicking a harmful one.
- Müllerian mimicry: Two or more harmful organisms mimicking each other.
Competition
- Interspecific Competition: Competition between different species for resources.
- Intraspecific Competition: Competition within the same species for resources, often more intense.
- Resource Partitioning: Species dividing resources to avoid competition and coexist.
- Benefits of Resource Partitioning: Increased survival for all species involved.
- Costs of Resource Partitioning: Potential reduction in population size for each species.
Adaptations
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Adaptations Types:
- Structural: Related to body parts (e.g., thick fur).
- Behavioral: Related to actions (e.g., hibernation).
- Physiological: Related to bodily functions (e.g., venom production).
Evolutionary Processes
- Analogous Structures: Anatomically different structures with similar functions in unrelated organisms, due to similar environmental pressures. (e.g., bird and bat wings)
- Convergent Evolution: Traits evolving similarly in unrelated species due to similar environmental pressures.
- Homologous Structures: Anatomically similar structures in related organisms, potentially with different functions, due to divergent evolution. (e.g., human forearm and dolphin flipper)
- Divergent Evolution: Traits diverging from a common ancestor due to differing selective pressures.
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Description
Explore the fundamentals of natural selection, including its definition and mechanisms. Learn about the four postulates of natural selection and the types, such as directional, disruptive, and stabilizing selection. Test your understanding of how these concepts shape populations over time.
