Population Ecology, Growth Models, and Evolutionary Concepts in Biology

Define population ecology.

The study of how biotic and abiotic factors influence the density, distribution, and size/age structure of populations.

What are the four primary factors that change population size?

Births, deaths, immigration, and emigration.

What are the four key properties used to describe a population?

Size, density, dispersion, and rate of change in size over time.

What are the three common patterns of population dispersion?

Random, clumped, and uniform.

What is a life table?

An age-specific summary of the vital statistics (birth and death rates) of a population.

Describe a Type I survivorship curve.

Low death rates during early and midlife, followed by a steep drop in survival during older age.

Describe a Type II survivorship curve.

Constant mortality rate throughout the organism's entire lifespan.

Describe a Type III survivorship curve.

High mortality in early life, with death rates declining significantly for those that survive to later life.

Define a gene pool.

The total collection of all copies of every allele at all loci in all members of a population.

What does it mean for a population to be monomorphic?

The population has only one allele for a specific gene, meaning that allele is fixed.

What are the five conditions required for a population to be in Hardy-Weinberg equilibrium (no evolution)?

No mutations, random mating, large population size, no gene flow (migration), and no natural selection.

What is the difference between allelic frequency and genotypic frequency?

Allelic frequency refers to the proportion of a specific allele in the gene pool, while genotypic frequency refers to the proportion of individuals with a specific genotype.

Define evolution in terms of genetics.

A change in allele frequencies within a population over generations.

What is gene flow?

The movement of alleles between populations due to the migration of individuals.

What is the primary effect of gene flow on different populations?

It tends to make populations more genetically similar over time.

What is adaptive introgression?

The process where hybridization and backcrossing allow beneficial genes from one species to transfer to another, increasing the recipient's fitness.

Define genetic drift.

A change in allele frequencies over generations due to random chance.

What is the difference between microevolution and macroevolution?

Microevolution refers to changes in allele frequencies within populations, while macroevolution refers to broad patterns of evolutionary change above the species level.

What is the biological species concept?

The definition of a species as a group of populations whose members have the potential to interbreed and produce viable, fertile offspring, but are reproductively isolated from other groups.

What is the primary disadvantage of the morphospecies concept?

It is subjective, can misidentify polymorphic species, and often misses cryptic species.

What is the phylogenetic species concept?

Defining a species as the smallest monophyletic group on a phylogenetic tree.

What are prezygotic barriers?

Biological factors that prevent different species from mating or hinder fertilization if mating is attempted.

Give three examples of prezygotic barriers.

Habitat isolation, temporal isolation, and behavioral isolation.

What are postzygotic barriers?

Factors that prevent a hybrid zygote from developing into a viable, fertile adult.

What is hybrid inviability?

A postzygotic barrier where genetic incompatibility causes hybrid offspring to be weak or fail to survive to reproductive age.

Why are mules considered an example of reduced hybrid fertility?

They are the sterile offspring of a horse and a donkey, often due to mismatched chromosome numbers that prevent proper meiosis.

What is the primary limitation of the morphospecies concept?

It is subjective and cannot identify cryptic species that differ in non-morphological traits.

What is the main difference between allopatric and sympatric speciation?

Allopatric speciation involves physical geographic separation, while sympatric speciation occurs within the same location.

What is polyploidy and how does it relate to speciation?

It is the possession of more than two complete sets of chromosomes; it can result in speciation within one generation, particularly in plants.

What are the four primary processes that change population size?

Births, deaths, immigration, and emigration.

What does the variable 'r' represent in population growth equations?

The per capita growth rate, calculated as births minus deaths.

Why is exponential growth rarely sustained in nature?

Because it requires unlimited resources, no predators, no disease, and no competition, which are conditions that do not last indefinitely.

What is the definition of carrying capacity (K)?

The maximum population size that a specific environment can support based on available resources.

In the logistic growth model, what does the term (K-N)/K represent?

The fraction of the carrying capacity that is still available for population growth.

What is the difference between population density and dispersion?

Density refers to the number of individuals per unit area, while dispersion refers to the spatial pattern of how they are arranged.

List three density-dependent factors that regulate population size.

Competition, disease, and predation.

At what population size (N) does the maximum sustainable yield (MSY) occur?

When N equals K/2.

What is the primary difference between exponential and logistic growth models?

Exponential growth assumes unlimited resources, while the logistic model incorporates carrying capacity to limit growth as the population increases.

How does territoriality act as a density-dependent factor?

It limits the number of individuals that can occupy a specific area, thereby restricting population density.

What are common methods biologists use to estimate population size?

Quadrat sampling, mark-recapture, and transects.

What is the 'terminal investment' strategy in life history evolution?

When individuals facing reduced future survival prospects increase their current reproductive effort to maximize lifetime fitness.

How do trade-offs influence life history strategies?

Because resources are finite, organisms must allocate energy between competing needs like survival, growth, and reproduction.

What is the evolutionary theory of aging regarding reproductive success?

Alleles that increase early-life reproductive success often reduce late-life survival.

True or False: A population with a positive 'r' value will always grow exponentially.

True, in the context of the exponential growth model, though it is limited by environmental factors in reality.

What is the mathematical equation for exponential population growth?

dN/dt = rN

What is the mathematical equation for logistic population growth?

dN/dt = rN[(K - N) / K]

How does habitat differentiation contribute to sympatric speciation?

It occurs when a subpopulation begins to exploit a habitat or resource not used by the parent population.

What are intrinsic factors in population regulation?

Physiological factors within the population, such as the accumulation of toxic waste, that regulate size.

Why is the logistic growth curve 'S-shaped'?

Because growth is rapid when the population is small but slows down as it approaches the carrying capacity.

What is the effect of increased testosterone on life history trade-offs?

It can increase growth rate and muscle mass but may decrease parental care and increase risk-taking behaviors.

What is the difference between a population's rate of change and its density?

Rate of change is the speed at which the population size shifts over time, while density is a measure of crowding per unit area.

What is the primary driver of allopatric speciation?

Geographic barriers that prevent gene flow between subpopulations.

What does a Type I survivorship curve represent?

High survival rates throughout most of the lifespan, followed by a rapid decline in survival in old age (e.g., humans, elephants).

What does a Type II survivorship curve represent?

A relatively constant probability of death at any age throughout the lifespan (e.g., many birds, some reptiles).

What does a Type III survivorship curve represent?

High mortality rates in the early stages of life, with few individuals surviving to adulthood (e.g., fish, plants, insects).

What is the definition of survivorship (Ix)?

The proportion of the original population still alive at a given age, used to standardize data for comparing populations of different sizes.

What is a cohort in population ecology?

A group of individuals born at the same time, which is tracked through time in a life table.

What is the core principle behind life history trade-offs?

Energy is limited, so organisms must allocate resources between competing needs like survival, reproduction, and growth.

How do environmental conditions influence reproductive strategies?

Unstable/high-risk environments favor early reproduction and many offspring (r-selection), while stable/competitive environments favor fewer offspring with higher investment (K-selection).

What is the primary difference between an allele and a genotype?

An allele is a specific version of a gene (e.g., A or a), while a genotype is the combination of alleles an individual possesses (e.g., AA, Aa, aa).

How is evolution defined in terms of a population's gene pool?

Evolution is the change in allele frequencies within a population over generations.

Why do populations evolve rather than individuals?

Individuals live or die based on selection, but evolution is a phenomenon that only manifests as changes in the genetic makeup of a population over time.

What are the Hardy-Weinberg equations and what do the variables represent?

p + q = 1 (allele frequencies) and p² + 2pq + q² = 1 (genotype frequencies), where p is the dominant allele frequency and q is the recessive allele frequency.

What are the five conditions required for a population to be in Hardy-Weinberg equilibrium?

No mutation, no natural selection, no gene flow, infinite population size (no genetic drift), and random mating.

What is the biological significance of the Hardy-Weinberg principle?

It serves as a null model to detect if a population is evolving; if observed frequencies deviate from expected values, evolution is occurring.

What is genetic drift?

Random changes in allele frequencies that have a more pronounced effect in small populations.

How does mutation relate to natural selection?

Mutation creates new genetic variation (randomly), while natural selection acts as a filter that selects among those variations (non-randomly).

If the frequency of the homozygous recessive genotype (q²) is 0.16, what is the frequency of the recessive allele (q)?

q = 0.4 (the square root of 0.16).

Does dominance imply that an allele is 'better' or 'stronger' in terms of fitness?

No, dominance refers only to how an allele is expressed in the phenotype, not its fitness value.

What are the four primary mechanisms of evolution?

Mutation, natural selection, genetic drift, and gene flow.

What is the difference between r-selection and K-selection regarding timing?

r-selection involves early reproduction due to environmental uncertainty, while K-selection involves delayed reproduction due to stable, competitive environments.

Why is Type III survivorship considered very common in nature?

Many species produce a high volume of offspring with low individual investment, leading to high juvenile mortality.

What is the purpose of a life table?

To track a cohort through time by recording the number of survivors at each age interval to calculate mortality and survivorship.

What does '2pq' represent in the Hardy-Weinberg equation?

The frequency of the heterozygous genotype in the population.

Why does population size matter for genetic drift?

In small populations, random events have a larger statistical impact on allele frequencies, whereas large populations are more resistant to random fluctuations.

What is the definition of a gene pool?

The total collection of all alleles present in a population at a given time.

Can a population be in Hardy-Weinberg equilibrium in reality?

No, it is a theoretical baseline model; real populations are almost always subject to some evolutionary forces.

What is the relationship between gene flow and populations?

Gene flow is the movement of alleles between populations, which can change allele frequencies and influence the evolutionary trajectory of those populations.

How does genetic drift differ from natural selection?

Genetic drift is driven by chance events and is non-directional, whereas natural selection is driven by fitness differences and is directional.

Why is genetic drift more impactful in small populations?

In small populations, chance events have a larger relative impact on the gene pool, whereas in large populations, these effects are averaged out.

What is the founder effect?

A type of genetic drift where a new population is established by a small number of individuals who do not represent the full genetic diversity of the source population.

What is the bottleneck effect?

A type of genetic drift occurring when a population size is drastically reduced by a chance event, causing remaining allele frequencies to change randomly.

What are the long-term consequences of genetic drift on genetic variation?

Genetic drift typically reduces genetic variation, leading to the loss of some alleles and the fixation of others.

Does random mating change allele frequencies?

No, random mating reshuffles existing alleles into new genotype combinations but does not change the overall frequency of those alleles.

In the Hardy-Weinberg equation p² + 2pq + q² = 1, what do the variables represent?

p² is the frequency of homozygous dominant individuals, 2pq is the frequency of heterozygotes, and q² is the frequency of homozygous recessive individuals.

What does it mean if an allele reaches 'fixation'?

It means the allele frequency has reached 1.0 (100%), meaning every individual in the population carries that allele.

Why is genetic drift considered a threat to conservation?

It can reduce genetic diversity and fix harmful alleles, potentially pushing small or endangered populations toward extinction.

How does gene flow differ from genetic drift?

Genetic drift is a random change in allele frequency within a population; gene flow is the movement of alleles between populations.

What is the primary effect of gene flow on populations?

Gene flow tends to make different populations more genetically similar to one another.

How does gene flow affect genetic variation within a single population?

Gene flow typically increases genetic variation within a population by introducing new alleles from other populations.

How does genetic drift affect genetic variation among different populations?

Genetic drift tends to make populations more different from each other as they randomly lose or fix different alleles.

What are the three main mechanisms of evolution mentioned in the text?

Genetic drift (random), gene flow (movement), and natural selection (fitness-based).

Why is the Hardy-Weinberg principle considered a 'null model'?

It provides a baseline of expected frequencies under ideal conditions (no evolution) that real populations almost never meet.

What does the X-axis and Y-axis represent on an allele frequency graph?

The X-axis represents generations, and the Y-axis represents the frequency of a specific allele.

What is the difference between a hypothesis and a prediction?

A hypothesis is a testable explanation for an observation, while a prediction is a specific, measurable outcome expected in an experiment.

What is the purpose of an ANOVA test in evolutionary studies?

It compares variation within groups versus variation between groups to determine if observed differences are statistically significant or due to chance.

Does drift always decrease fitness?

No, drift is random; it can increase, decrease, or have no effect on fitness.

What does 'within' vs 'among' populations mean in the context of genetic variation?

'Within' refers to diversity inside a single group, while 'among' refers to differences between distinct groups.

Why do humans have relatively low genetic diversity?

Due to past population bottlenecks and our relatively recent origin as a species.

What is the relationship between p and q in the Hardy-Weinberg equation?

p + q = 1, representing the sum of all allele frequencies for a two-allele system.