Population Ecology Deck (4)

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What is ecology?

The study of the interactions among living organisms and between living organisms and their physical and biological environment.

What is population ecology?

The branch of ecology that studies population size, growth, distribution and the factors that regulate changes in populations.

What is an individual?

A single organism that forms part of a species.

What is a species?

A group of organisms with similar characteristics that can interbreed naturally and produce fertile offspring.

What is a population?

A group of organisms of the same species living in the same area at the same time and capable of interbreeding.

What is a community?

All the populations of different species living and interacting in a particular area.

What is an ecosystem?

A community of living organisms interacting with one another and with the abiotic environment.

What is the environment?

All the living (biotic) and non-living (abiotic) factors surrounding an organism that influence its survival and development.

What is a habitat?

The specific place or environment in which an organism normally lives.

What is population size?

The total number of individuals in a population.

What is population density?

The number of individuals of a population per unit area or volume.

What are population parameters?

Natality, mortality, immigration and emigration — the factors that affect population size.

What is natality?

The birth rate of a population, usually expressed as the number of live births per thousand individuals per year.

What is mortality?

The death rate of a population, usually expressed as the number of deaths per thousand individuals per year.

What is immigration?

The one-way movement of organisms into a population where they become established.

What is emigration?

The one-way movement of organisms out of a population to become established elsewhere.

What is a closed population?

A population in which immigration and emigration do not occur.

What is a census?

A direct counting method in which every individual in a population is counted.

What is direct population estimation?

A method involving counting every individual in the population.

What is indirect population estimation?

A method that estimates population size by counting only a sample of the population.

What is a quadrat?

A square frame of known area used to sample organisms.

What are sessile organisms?

Organisms that are permanently attached to a surface and cannot move from place to place.

What is the mark-recapture method?

An indirect sampling method used to estimate the size of mobile animal populations by capturing, marking, releasing and later recapturing individuals.

What is carrying capacity (K)?

The maximum population size that an environment can support sustainably.

What is environmental resistance?

The combined effect of limiting factors that restrict population growth and create the carrying capacity.

What is a limiting factor?

Any factor that restricts population growth and prevents unlimited population increase.

What is a density-dependent factor?

A limiting factor whose effect increases as population density increases.

What is a density-independent factor?

A factor that affects populations regardless of their size or density.

What is population overshoot?

When a population temporarily exceeds its carrying capacity.

What is a stable population?

A population whose numbers fluctuate around carrying capacity.

What is an unstable population?

A population that greatly exceeds carrying capacity and may experience rapid decline.

Distinguish between population size and population density.

Population size = total number of individuals. Population density = number of individuals per unit area or volume.

Which population parameters increase population size?

Natality and immigration.

Which population parameters decrease population size?

Mortality and emigration.

Which population parameters affect a closed population?

Natality and mortality only.

What effect does natality have on population size?

It increases population size.

What effect does mortality have on population size?

It decreases population size.

What effect does immigration have on population size?

It increases population size.

What effect does emigration have on population size?

It decreases population size.

What is the population-size relationship?

Population size increases through natality and immigration and decreases through mortality and emigration.

What are the three main methods used to estimate population size?

Direct counting/census, quadrat sampling and mark-recapture.

When is direct counting most suitable?

For small populations, small study areas, and organisms that are stationary or slow-moving.

How can large populations sometimes be counted directly?

Using aerial photographs, drones, helicopters or aircraft surveys.

When is quadrat sampling used?

For plants, sessile organisms and slow-moving organisms.

Why must quadrats be placed randomly?

To avoid bias and obtain a representative sample.

How are organisms on the border of a quadrat counted?

Count organisms that are mostly inside the quadrat.

What determines the reliability of quadrat sampling?

Accurate counting, random placement, suitable quadrat size and an adequate number of quadrats.

State the quadrat formula.

Population size = Average number per quadrat × (Total habitat area ÷ Area of one quadrat).

What is the correct sequence for quadrat sampling?

Measure the study area → place quadrats randomly → count organisms → calculate the average number per quadrat → estimate total population.

When is mark-recapture used?

For mobile animals that are difficult to count directly.

State the mark-recapture formula.

P = (M × C) ÷ R, where P = estimated population size, M = number marked in first capture, C = total caught in second capture, R = marked individuals recaptured.

What are the steps of mark-recapture?

Capture first sample → count and mark individuals → release them → allow them to mix → capture second sample → count total and marked individuals → calculate population size.

What must be true about the marking?

It must not harm the organism, affect survival, or change its behaviour/movement, and it must remain visible.

Why must marked organisms be released back into the same habitat?

So they can mix with the original population and make the second sample representative.

Why must sufficient time be allowed for mixing?

To ensure marked individuals are randomly distributed throughout the population.

Why should the population remain closed during mark-recapture?

Immigration and emigration would alter population size and reduce accuracy.

Why should sampling occur over a short period?

To minimise the effects of births and deaths on population size.

What other assumption is required for accurate mark-recapture?

All individuals should have an approximately equal chance of being captured.

What should you do if a population estimate contains a decimal?

Round down to the nearest whole number because partial organisms cannot exist.

A researcher marks 200 fish, later catches 150 fish, and 30 are marked. Estimate the population size.

P = (200 × 150) ÷ 30 = 1,000 fish.

What is population growth?

The increase in the number of individuals in a population over time.

What is geometric growth?

Population growth where the population doubles at regular intervals, producing a J-shaped curve.

What is exponential growth?

Rapid population growth occurring when resources are unlimited and environmental resistance is absent or very low.

What is logistic growth?

Population growth that slows as environmental resistance increases and eventually stabilises around carrying capacity, producing an S-shaped curve.

What is intrinsic rate of natural increase (r)?

The potential growth rate of a population under ideal conditions, calculated as birth rate minus death rate.

What does a high value of r indicate?

A population capable of growing rapidly.

What does a low value of r indicate?

A population that grows slowly.

What are the two main population growth curves?

Geometric/exponential growth = J-shaped. Logistic growth = S-shaped.

What conditions are required for exponential growth?

Unlimited food, water and space, little competition, little predation and minimal disease.

What shape does exponential growth produce?

A J-shaped curve.

Why is growth initially slow on a J-shaped curve?

Few individuals are present to reproduce.

Why does growth become very rapid later?

Increasing numbers of breeding individuals reproduce simultaneously.

What birth and death rates occur during exponential growth?

High birth rate and low death rate.

Where is exponential growth commonly observed?

New habitats, newly introduced species, bacterial populations, rodents and insect outbreaks.

Why is exponential growth rarely maintained in nature?

Resources eventually become limited.

What may happen after rapid exponential growth?

A sudden population crash or decline due to resource depletion.

What shape does logistic growth produce?

An S-shaped/sigmoid curve.

Why is logistic growth more realistic than exponential growth?

Natural populations experience limiting factors and environmental resistance.

What causes a J-shaped curve to become S-shaped?

Environmental resistance caused by limiting factors.

What happens as a population approaches carrying capacity?

Growth slows because resources become limiting.

What are the four phases of logistic growth?

Lag phase → exponential phase → decelerating/transitional phase → equilibrium/stationary/plateau phase.

What is the lag phase?

A period of slow growth when few individuals are reproducing and the population is becoming established.

Why is growth slow during the lag phase?

There are few breeding individuals, the population is establishing itself, and reproduction takes time.

What is the exponential/accelerating phase?

A period of rapid population increase due to abundant resources and many reproducing individuals.

Why does rapid growth occur during the exponential phase?

Resources are abundant, competition is low and birth rate exceeds death rate.

What is the decelerating/transitional phase?

The phase where population growth slows as resources become limited.

Why does growth slow during the decelerating phase?

Competition increases; food, water and space become limited; environmental resistance increases.

What is the equilibrium/stationary/plateau phase?

The phase where population size fluctuates around carrying capacity.

Why is population size relatively stable during the equilibrium phase?

Birth rate approximately equals death rate.

What does the plateau on a logistic graph indicate?

The population has reached carrying capacity.

What must always be labelled on a population-growth graph?

X-axis = Time. Y-axis = Population size.

What line is usually shown on a logistic growth graph?

The carrying capacity (K).

Which population growth model is most commonly found in nature?

Logistic growth, because resources are limited.

What creates carrying capacity?

Environmental resistance.

Distinguish between carrying capacity and environmental resistance.

Carrying capacity = the maximum population size the environment can support. Environmental resistance = the factors that limit growth and create that carrying capacity.

Can carrying capacity change?

Yes.

When can carrying capacity increase?

When resources, habitat or environmental conditions improve.

Give factors that can increase carrying capacity.

More food, water, habitat and shelter; expansion of habitat; reduced competition.

When can carrying capacity decrease?

When resources decline or habitat is damaged.

Give factors that can decrease carrying capacity.

Habitat destruction, resource depletion, food shortages, disease outbreaks and environmental degradation.