Human Population (4.6)

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Define ecology.

Ecology is the study of the mutual interactions among living organisms and between living organisms and their environment.

Define population ecology.

Population ecology is the branch of ecology that studies factors influencing population size, population growth, growth forms and the distribution of individuals within a population.

Define an individual.

A single organism that forms part of a species.

Define a species.

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

Define a population.

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

Define a community.

A group of populations living and interacting in the same area.

Define an ecosystem.

A unit consisting of living (biotic) organisms interacting with one another and with the non-living (abiotic) environment.

Define environment.

The external biotic and abiotic factors surrounding an organism that influence its survival and development.

Define habitat.

The specific environment or natural home in which an organism normally lives.

Define population size.

The total number of individuals in a population.

Define population density.

The number of individuals per unit area.

Define natality.

The birth rate of a population; the number of births per thousand individuals per year.

Define mortality.

The death rate of a population; the number of deaths per thousand individuals per year.

Define immigration.

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

Define emigration.

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

Define carrying capacity.

The maximum number of individuals that an environment can support sustainably.

Define environmental resistance.

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

Define limiting factors.

Factors that prevent unlimited population growth, such as food shortages, disease, water shortages, shelter shortages and lack of space.

Define density-dependent factors.

Factors whose effects increase as population size or density increases.

Give examples of density-dependent factors.

Food supply, disease, competition, shelter, living space and predation.

Define density-independent factors.

Factors that affect populations regardless of population size.

Give examples of density-independent factors.

Droughts, floods, fires, earthquakes, tsunamis and extreme temperatures.

Define ecological footprint (EF).

The amount of biologically productive land and water required to provide resources and absorb the waste generated by a population.

Define biocapacity.

The amount of productive land and water available to provide resources and absorb waste.

Define ecological overshoot.

A situation where humans use resources faster than Earth can regenerate them.

In what units are ecological footprint and biocapacity measured?

Global hectares (gha).

Define geometric growth.

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

Define logistic growth.

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

Define a population pyramid.

A graph showing the age and gender distribution of a population.

Define age structure.

The number of individuals in each age group within a population.

Which four parameters affect population size?

• Natality • Mortality • Immigration • Emigration

Which factors increase population size?

• Natality • Immigration

Which factors decrease population size?

• Mortality • Emigration

Draw the population size relationship.

Population Size = (+ Natality) (+ Immigration) (− Mortality) (− Emigration)

Name two direct methods of determining population size.

• Census • Aerial counts/photographs

Name two indirect methods of determining population size.

• Mark-recapture • Quadrat sampling

When is mark-recapture used?

For mobile organisms that move around.

Steps in mark-recapture.

Capture organisms. Count them. Mark them harmlessly. Release them. Allow mixing. Capture a second sample. Count marked individuals. Calculate estimated population size.

Formula for mark-recapture.

$P=\frac{M \times S}{T}$ Where: P = estimated population size M = first sample marked S = second sample size T = marked individuals recaptured

Requirements for mark-recapture.

• Marking must not harm organisms. • Marking must not affect movement. • Organisms must be released where captured. • Sufficient mixing must occur before recapture.

When is quadrat sampling used?

For sessile or slow-moving organisms.

Examples of organisms sampled using quadrats.

• Grass • Sunflowers • Shellfish • Barnacles

Formula for quadrat sampling.

Population size = Average number per quadrat × (Total area ÷ Quadrat area)

Which organisms on a quadrat boundary are counted?

Organisms mostly inside the quadrat.

What are the two main population growth curves?

• Geometric (J-shaped) • Logistic (S-shaped)

Describe geometric growth.

• Starts slowly. • Rapid exponential increase. • Little environmental resistance. • Resources abundant. • Produces J-shaped curve.

Why does geometric growth occur?

• Plenty of food • Plenty of water • Plenty of space • Little disease • Low competition

When is geometric growth commonly observed?

• New habitats • Newly introduced species • Bacteria • Rodents • Insects

Describe logistic growth.

• Starts slowly. • Exponential increase. • Growth slows. • Population stabilises around carrying capacity. • Produces S-shaped curve.

What causes a population to level off?

Environmental resistance creates a carrying capacity.

Name the four phases of logistic growth.

A: Lag phase Exponential phase Decelerating (transitional) phase Plateau (stationary/equilibrium) phase

Describe the lag phase.

• Few breeding individuals • Population establishing itself • Slow growth

Describe the exponential phase.

• Many resources available • Rapid reproduction • Natality exceeds mortality • Maximum growth rate

Describe the decelerating phase.

• Environmental resistance increases • Resources become limited • Growth rate slows

Describe the plateau/stationary phase.

• Population fluctuates around carrying capacity • Natality approximately equals mortality • Stable population

What is an overshoot?

When a population temporarily exceeds carrying capacity.

What usually happens after an overshoot?

• Population declines • Population recovers • Population stabilises near carrying capacity

What happens if carrying capacity continues to decrease after an overshoot?

• Population declines • Extinction may occur

Differentiate between carrying capacity and environmental resistance.

Carrying Capacity: Maximum number of organisms supported. Environmental Resistance: Factors that create the carrying capacity by limiting growth.

Can carrying capacity change?

Yes.

When does carrying capacity increase?

• More habitat • More food • More water • More shelter

When does carrying capacity decrease?

• Habitat destruction • Food shortages • Disease outbreaks • Environmental degradation

Why was human population growth slow before 1750?

• High mortality rates • Disease • Plagues • Poor medical care

Around which year did exponential human population growth begin?

Around 1750.

What medical advances contributed to exponential population growth?

• Better disease treatment • Vaccinations • Improved healthcare

What agricultural advances contributed to exponential population growth?

• Fertilisers • Improved farming methods • Disease-resistant crops

Which countries generally have higher population growth rates?

Less-developed countries (LDCs).

Which countries generally have lower population growth rates?

More-developed countries (MDCs).

What does the x-axis of a population pyramid represent?

Number of individuals.

What does the y-axis represent?

Age groups.

What do the two sides represent?

• Males • Females

What shape indicates rapid population growth?

Wide base and narrow top.

Why does a rapidly growing population have a wide base?

• High birth rate • Limited contraception • Lower education levels

Why does a rapidly growing population have a narrow top?

• High death rate • Poor healthcare • Poor nutrition

Which countries typically show rapid-growth pyramids?

Less-developed countries.

What shape indicates stable population growth?

Rectangular or almost square.

Why do stable populations have lower birth rates?

• Family planning • Education • Economic planning

Why do stable populations have lower death rates?

• Good healthcare • Good nutrition • High standard of living

What shape indicates negative population growth?

Narrow base compared to reproductive age groups.

What causes negative population growth?

• Low birth rate • Stable death rate • High emigration

What trend is seen in South Africa's population growth?

Growth rate is slowing down.

What contributed significantly to slower population growth in South Africa?

HIV/AIDS-related deaths.

What population transition is South Africa experiencing?

Moving from rapid growth towards a more stable growth pattern.

Why is South Africa moving towards a more stable growth pattern?

• Improved education • Better healthcare • Improved living standards • Lower birth rates

What does ecological footprint measure?

Human demand on Earth's productive land and water.

What was the average global ecological footprint?

About 2.6 gha per person.

What was the average global biocapacity?

About 1.8 gha per person.

What does ecological overshoot indicate?

Humans are using resources faster than Earth can replace them.

Consequences of ecological overshoot.

• Collapse of fish stocks • Deforestation • Water shortages • Climate change • Pollution accumulation

Why do MDCs have larger ecological footprints?

• More electricity use • More vehicles • More consumption • More waste production

Why do LDCs generally have smaller ecological footprints?

• Lower consumption • Lower incomes • Simpler lifestyles

Define predation.

An interaction where a predator hunts, kills and eats a prey organism.

What happens to predator numbers when prey numbers increase?

Predator numbers increase after a short delay.

What happens when predator numbers increase?

Prey numbers decrease.

What happens when prey numbers decrease?

Predator numbers decrease because food becomes scarce.

Which graph peaks first in a predator-prey graph?

The prey population graph.

Do predator and prey peaks occur at the same time?

No. Predator peaks occur shortly after prey peaks.

Why is predation density-dependent?

The effect depends on prey population density.

South African predator-prey example.

Lion and zebra.

Biological control definition.

Using a natural enemy to control a pest population without pesticides.