Population Growth & Species Regulation – Lecture Review

These flashcards cover definitions, formulas, factors, growth models, reproductive strategies, life tables, survivorship curves, and age-structure concepts introduced in the lecture on Population Growth and Species Regulation.

What is the definition of a population in ecology?

A group of individuals of the same species inhabiting the same area (habitat).

What does ecology study?

The interactions of organisms with each other and with their environment.

What is population ecology?

The branch of ecology that studies the structure and dynamics of populations.

How does human demography define a population?

As a set of humans living in a given area.

What is a population in genetics?

A group of interbreeding individuals of the same species isolated from other groups.

Name any four key characteristics of a population.

Size, density, distribution/dispersion, and age structure (others include natality, mortality, and growth rate).

Differentiate crude density from ecological density.

Crude density is the number (or biomass) of individuals per total unit space, whereas ecological density counts only the habitat space that can actually be colonised.

What is natality?

The birth rate within a population.

What is mortality?

The death rate within a population.

Define immigration and emigration in population dynamics.

Immigration is the movement of organisms into a population’s area; emigration is the movement out of the area.

What is a density-dependent limiting factor?

Any factor that influences population growth more strongly as population size or density increases.

Give two examples of density-dependent factors.

Competition for space or food, predation pressure, disease, or stress due to overcrowding.

What is a density-independent factor?

A factor that reduces population size by roughly the same percentage regardless of population density, often acting by chance.

Provide two examples of density-independent factors.

Weather extremes, climate events, or natural disasters such as floods and fires.

Define biotic potential (r).

The maximum rate at which a population can increase under ideal conditions.

State two biological reasons why species differ in biotic potential.

Variation in reproductive span, frequency of reproduction (semelparous vs. iteroparous), litter size, or offspring survival rates.

Distinguish semelparous from iteroparous reproduction.

Semelparous species reproduce once in a lifetime; iteroparous species reproduce multiple times.

Write the basic exponential growth equation for population size.

Nt = N0 e^(rt) where Nt is population at time t, N0 is initial population, r is growth rate, and e ≈ 2.71.

What does the expression dN/dt = rN represent?

The rate of change in population size (growth) under exponential conditions, proportional to size and intrinsic growth rate r.

What graphical shape does exponential growth produce?

A J-shaped curve.

Define carrying capacity (K).

The maximum number of individuals an environment can sustain without long-term degradation.

Give the logistic growth equation.

dN/dt = rN[(K – N)/K].

What shape characterises logistic growth?

An S-shaped (sigmoidal) curve.

How do r-selected species generally differ from K-selected species with respect to reproduction?

r-selected species have high reproductive rates with many small offspring and little parental care; K-selected species produce fewer, larger offspring with high parental investment.

List three typical traits of r-strategists.

Short life, early maturity, rapid growth, many small offspring, little parental care.

List three typical traits of K-strategists.

Long life, late maturity, slower growth, fewer large offspring, high parental care.

What is a life table?

A record of survival and reproductive rates in a population, broken down by age, size, or developmental stage.

Define a survivorship curve.

A plot showing the number of individuals from a cohort that survive to different ages, derived from life-table data.

Describe a Type I survivorship curve and give an example.

Low mortality early and mid-life with high mortality in old age; example: humans, large mammals.

Describe a Type II survivorship curve and give an example.

Constant mortality rate throughout life; example: many birds, some reptiles.

Describe a Type III survivorship curve and give an example.

Very high mortality of young with survivors living long; example: oysters, many plants, invertebrates.

What is meant by an expanding age structure?

A ‘bottom-heavy’ population pyramid where a large proportion of individuals are pre-reproductive, indicating potential for rapid growth.

What characterises a stable age structure?

Each age class is roughly replacing itself; the population size remains steady.

What is indicated by a declining age structure?

‘Top-heavy’ pyramid where natality has fallen below replacement; population is likely to shrink.

Why must ecologists consider human population trends when studying other species?

Because humans compete for resources, alter environments, add pollutants, and can both harm and benefit other species, affecting their survival and reproduction.