Evolutionary Biology: Hardy-Weinberg and Selection

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Questions and Answers

What characterizes a random distribution of individuals in an area?

Uniform spacing among individuals

Positive interactions between individuals

Equal probability of being anywhere (correct)

Clustering in resource-rich areas

Which distribution is characterized by individuals that avoid one another and are systematically spaced?

Random distribution

Regular distribution (correct)

Clumped distribution

Overdispersed distribution

What is a key factor in the clumped distribution of desert shrubs, according to recent studies?

Adequate resource sharing among all individuals

Uniform competition for soil nutrients

Seeds germinate at safe sites with nurse plants (correct)

Sequential use of resources leading to uniform spacing

In a regular distribution, what type of interactions generally occur between individuals?

Negative interactions due to competition Signup and view all the answers

Which statement accurately describes clumped distribution?

Individuals show positive interactions and cluster together. Signup and view all the answers

Which term describes a group of a single species in a specific area?

Population Signup and view all the answers

What does the term 'niche' primarily summarize?

Environmental factors influencing growth, survival, and reproduction Signup and view all the answers

What factor does NOT influence species distribution according to climate?

Predation Signup and view all the answers

Which of the following describes the realized niche?

Affected by interactions like competition and predation Signup and view all the answers

How does ecological variability affect distributions?

It can cause seasonal changes in distributions. Signup and view all the answers

Which of the following statements is true about fundamental and realized niches?

Fundamental niche represents potential living conditions. Signup and view all the answers

What limitations do environmental constraints impose on species distribution?

They combine physical environment with biotic factors. Signup and view all the answers

Which statement about the distributions of Encelia species is correct?

E.far and E.fr are adapted to completely different environments despite overlapping ranges. Signup and view all the answers

What does a Type 1 survivorship curve indicate about survival rates?

High survival for young to middle-aged individuals and low survival for the old. Signup and view all the answers

Which of the following is true about an unstable population indicated by age distribution?

It primarily consists of older trees with no young recruits. Signup and view all the answers

What does the term 'meta-population' refer to?

A collection of interacting sub-populations within a larger area. Signup and view all the answers

What is the implication of gaps in an age distribution of a population?

It indicates a recent disturbance such as drought. Signup and view all the answers

How is net reproductive rate calculated in life tables?

Log of net reproductive rate divided by generation time. Signup and view all the answers

Which environmental factor can cause a change in the survivorship curve?

Natural disasters like droughts and rainfall. Signup and view all the answers

What does it suggest if a population is described as having 'many young trees' in its age distribution?

The population is stable or growing. Signup and view all the answers

If most trees in a population are remnants from past recruitment, what can be inferred about their age structure?

The population is unstable with few young recruits. Signup and view all the answers

What does the variable 'B' represent in the population size equation Nt= Nt-1 + B + I - D - E?

Birth rate Signup and view all the answers

Which type of growth occurs when populations grow geometrically?

With abundant resources and few limiting factors Signup and view all the answers

What happens to population growth when it reaches carrying capacity (K)?

Population growth slows and eventually stops Signup and view all the answers

In the equation dN/dt, what does 'N' represent?

Population size Signup and view all the answers

What condition can cause exponential growth to slow down?

Limited space and resources Signup and view all the answers

What characterizes logistic population growth?

It follows an S-shaped curve Signup and view all the answers

Which factor is NOT included in the equation Nt= Nt-1 + B + I - D - E?

Population density Signup and view all the answers

Which is a likely reason for the rapid growth of populations after receding glaciers?

Exposed new habitats without competition Signup and view all the answers

What principle states that allele frequencies will remain constant in a population mating at random in the absence of evolutionary forces?

Hardy Weinberg Principle Signup and view all the answers

Which of the following is NOT a condition necessary for Hardy Weinberg equilibrium?

Rapid evolution Signup and view all the answers

How does genetic drift primarily affect small populations?

Changes allele frequencies due to chance events Signup and view all the answers

What type of selection acts against extreme phenotypes, favoring the average ones?

Stabilizing Selection Signup and view all the answers

Under which form of selection do extreme phenotypes thrive, leading to a bimodal distribution?

Disruptive Selection Signup and view all the answers

What is the potential consequence of inbreeding in small populations?

Reduced juvenile survival Signup and view all the answers

Which of the following describes the founder effect?

Genetic variation due to random sampling in a small population Signup and view all the answers

What does heritability (h^2) indicate when it is calculated as 0.6 for a trait?

Genetic variation contributes 60% to the phenotype Signup and view all the answers

How does natural selection influence allele frequencies in a population?

By favoring individuals with advantageous traits Signup and view all the answers

Which of the following scenarios exemplifies directional selection?

Longer beaks become more common in response to fruit size changes Signup and view all the answers

What results from the use of antibiotics in agriculture regarding evolutionary consequences?

Rapid evolution of resistance in populations Signup and view all the answers

Which of these factors greatly enhances the potential for evolutionary change in natural populations?

Isolation of geographical clusters Signup and view all the answers

Why is genetic variation typically lower in island populations?

Limited mating options and smaller population sizes Signup and view all the answers

What leads to a bottleneck effect in populations?

Significant environmental changes or disasters Signup and view all the answers

Study Notes

Hardy-Weinberg Principle

A null model used to identify evolutionary forces that change gene frequencies.
Assumes random mating and the absence of evolutionary forces.
States allele frequencies will remain constant in a population meeting these conditions.
Conditions necessary for Hardy-Weinberg equilibrium:
- Random mating
- No mutations
- Large population size
- No immigration
- Equitable fitness between all genotypes.
It is likely that at least one of these conditions won't be met, leading to changes in allele frequencies.
Indicates the potential for evolutionary change in natural populations is significant.

Genetic Drift

Change in allele frequencies due to chance or random events.
Reduces genetic diversity over time by increasing some alleles and reducing or eliminating others.
More impactful in smaller populations.
Examples include endangered species, founder effects, and bottlenecks.

Natural Selection

Differential survival and reproduction among phenotypes.
Some individuals possess phenotypic characteristics that provide higher survival rates and increased offspring production.
The fitness of an individual is measured by their relative contribution of offspring, or genes, to future generations.
Natural selection can favor, disfavor, or conserve the genetic makeup of populations.

Stabilizing Selection

Acts to impede changes in the population by favoring average phenotypes and acting against extreme phenotypes.
Extreme phenotypes have lower reproductive and survival rates, resulting in the average phenotype remaining the most common across generations.

Directional Selection

Drives changes in phenotypes by favoring one extreme phenotype over others in the population.
Extreme phenotypes experience higher rates of reproduction and survival, causing the population average to shift in that direction over time.

Disruptive Selection

Creates a bimodal distribution by favoring two or more extreme phenotypes over the average phenotype.
Average phenotypes have lower reproductive and survival rates compared to the extremes.
Over time, average phenotypes become less common, leading to increased phenotypic diversity in the population.

Heritability and Evolution

Natural selection can alter genotypic and phenotypic frequencies in populations, potentially leading to adaptation.
Heritability of traits is crucial for evolutionary change:
- h^2 = G/(G+E), where G is the genetic variance and E is the environmental variance.
- Phenotypic variance is influenced by both genetics and environmental factors.

Examples of Evolutionary Processes

Soapberry bugs:
- A classic example of directional selection through beak length adaptation based on fruit size.
Darwin's finches:
- Demonstrate disruptive selection where two distinct beak sizes are favored, highlighting the importance of beak morphology for food acquisition.
Chihuahua Spruce:
- Shows evidence of genetic drift in smaller populations, illustrating the impact of reduced genetic diversity.

Island Populations

Tend to harbor lower genetic variation compared to mainland populations.
This is likely due to limited gene flow and founder effects, which can lead to inbreeding and reduced diversity.

Genetic Diversity and Extinction

Inbreeding can drive extinction in small populations.
Reduced fecundity, juvenile survival, and lifespan are associated with inbreeding, leading to population decline.
The Glanville fritillary butterfly study highlights the relationship between inbreeding and extinction risks.

Evolution and Agriculture

Artificial selection is the breeding of domesticated organisms, selecting for desirable traits.
Genetic engineering involves the introduction or deletion of genes, creating genetically modified organisms (GMOs).

Unintended Evolutionary Consequences

Agricultural practices can have unintended evolutionary consequences.
Plant and animal pests may evolve resistance to pesticides and herbicides, leading to increasing challenges in controlling populations.
The emergence of antibiotic-resistant strains like MRSA illustrates the rapid evolution of populations in response to selective pressures.

Understanding Populations

A population refers to all individuals of a single species occupying a specific area at a particular time.
Key aspects of population study:
- Number of individuals
- Density
- Distribution
- Abundance.
- Age structure
- Growth rates

Environmental Constraints

The geographic distribution of species is limited by both physical and biotic factors.
Organisms have limits in their ability to compensate for environmental variations.
Niche: A concept describing the biophysical environmental factors influencing a species' growth, survival, and reproduction.

Fundamental vs. Realized Niche

Fundamental niche: The theoretical range of conditions where an organism could live.
Realized niche: The actual range of conditions occupied by a species, which is often limited by biotic interactions such as competition, predation, or diseases.

Distribution on Small Scales

Random dispersion: Individuals have an equal probability of occurring anywhere within an area.
Regular dispersion: Individuals are evenly spaced throughout the environment, often indicating competitive interactions.
Clumped dispersion: Individuals are grouped in areas of high local abundance, suggesting positive interactions or resource concentration.

Examples of Distribution

Desert Shrubs:
- Traditionally, it was thought that desert shrubs were regularly spaced due to competition.
- Research by Phillips and MacMahon suggests that clumped distribution is more common, potentially driven by factors such as seed germination at safe sites, limited seed dispersal, and nurse plant relationships.

Population Dynamics

Population size (Nt) can be described by:
- Nt = Nt-1 + B + I - D - E
  - Nt is the population size at a given time.
  - Nt-1 is the population size at the previous time step.
  - B is the birth rate.
  - I is the immigration rate.
  - D is the death rate.
  - E is the emigration rate.

Geometric Population Growth

Occurs when populations have abundant resources and experience minimal limiting factors.
Successive generations differ in size by a constant ratio.

Exponential Population Growth

Models unlimited population growth when generations are not discrete.
Change in population size over time (dN/dt) is a function of per capita increase and the number of individuals.
Paleo- ecological examples:
- Receding glaciers exposing new habitats with limited competition and abundant resources.

Logistic Population Growth

Occurs when exponential growth slows down due to environmental limitations such as resource depletion, competition, predation, or disease.
The carrying capacity or K represents the maximum population size that the environment can support.
Population growth slows as it approaches the carrying capacity, leading to an S-shaped or sigmoidal growth curve.

Survivorship Curves

Type 1: High survival rates for young and middle-aged individuals with low survival rates for older individuals.
Type 2: Constant survival rates across all ages.
Type 3: Extremely low survival rates for juveniles with high survival rates for older individuals.

Age Distribution

Can be assessed by aging individuals in a population.
Provides insights into population stability or growth.
For example, a population with many young individuals suggests future growth.

Life Tables

Used to track mortality and reproduction rates over time for a population.
Calculations include:
- l x m = lm (Proportion of individuals surviving to a certain age x reproduction rate at that age = net reproductive rate)
- log(net reproductive rate)/ generation time

Summary

Understanding population dynamics requires considering factors such as dispersal rate, metapopulation structure, survivorship curves, age distribution, and life tables.
Population growth models, including geometric, exponential, and logistic growth, provide insights into the relationship between population size and environmental factors.
Evolutionary processes shape populations through mechanisms like genetic drift, natural selection, and artificial selection.
The study of population biology is essential for managing populations, conserving biodiversity, and addressing challenges related to environmental change.

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Description

Explore key concepts in evolutionary biology, including the Hardy-Weinberg principle, genetic drift, and natural selection. This quiz will test your understanding of how these mechanisms affect gene frequencies and genetic diversity in populations. Perfect for students studying genetics and evolution.