Slide Set 4 Population Growth Part 1

What is a population?

Individuals of the same species living in the same geographical area

What questions are asked when studying patterns of population growth?

How population size and composition change and what ecological and evolutionary causes drive those changes

How do populations of species vary?

They vary over space and time

What are population attributes concerned with changes in population size?

Density, natality, mortality, immigration, and emigration

What drives population dynamics?

Resources, natality, mortality, immigration, and emigration

What is population dynamics?

The change in population density through time and space

What is population density?

The number of individuals per unit area or volume

How can population density be measured?

Total counts, sub-sampling methods, and indirect indicators

What are total counts?

Counting all individuals in a population

Why are total counts often impractical?

Populations are too large or difficult to observe

What are sub-sampling methods?

Estimating density using quadrats, line transects, and mark–recapture

What is mark–recapture used for?

Estimating total population size

What was the trout mark–recapture example result?

27 trout

How is total population size calculated in mark–recapture?

M/C = M1/N

What was the correct answer to the trout example?

27

What are indirect indicators of population density?

Nests, fecal droppings, eggs, tracks

What is dispersion?

The spacing of individuals within the geographic range of a population

What is clumped dispersion?

Individuals distributed in discrete groups

Why is clumped dispersion common?

Unequal resources and social behavior

What is uniform dispersion?

Individuals evenly spaced due to interactions

What is random dispersion?

Distribution without regard to other individuals

How does dispersion change?

It changes with spatial scale

What is natality?

The number of offspring produced per unit time

How does natality vary among organisms?

Oysters produce millions of eggs; birds and mammals produce fewer offspring

What is per capita birth rate?

Number of births divided by reproductive population size

What is the formula for per capita birth rate?

px = bx / nx

What was the robin birth rate example answer?

0.10

What is mortality?

The number of offspring dying per unit time

Is natural senescence common?

No, most organisms die from predation, disease, or hazards

What is per capita death rate?

Number of deaths divided by population at risk

What is the formula for per capita death rate?

qx = dx / nx

What was the zebra mortality example answer?

0.01

What is immigration rate?

Number of individuals moving into an area per unit time

What is emigration rate?

Number of individuals moving out of an area per unit time

Why is movement important to population dynamics?

It affects population persistence

When is movement most important to populations?

At small spatial and temporal scales

What methods are used to study population size changes?

Demography

What demographic methods are used?

Direct observation, life tables, survivorship curves, and models

What are survivorship curve types?

Type I, Type II, Type III

What is Type I survivorship?

Low mortality early, high late (humans)

What is Type II survivorship?

Constant mortality (birds)

What is Type III survivorship?

High early mortality (plants and fishes)

Why are mathematical models useful?

They apply broadly and work for hard-to-observe populations

What is the basic population growth equation?

Nt = N0 + B − D + I − E

What does Nt represent?

Population size at time t

What does N0 represent?

Population size at time 0

What does B represent?

Number of births

What does D represent?

Number of deaths

What does I represent?

Number of immigrants

What does E represent?

Number of emigrants

When does a population increase?

When B + I > D + E

When does a population decrease?

When B + I < D + E

What is exponential growth?

Population growth at a constant per capita rate

Do all populations have potential for exponential growth?

Yes

What conditions allow exponential growth?

Unlimited resources and constant environment

What is the differential equation for exponential growth?

dN/dt = rN

What does r represent?

Per capita growth rate

How is r calculated?

r = b − d

What happens when r > 0?

Population increases

What happens when r = 0?

Population size remains constant

What happens when r < 0?

Population decreases

What population grows faster?

The one with higher r

What was the South Sudan human growth rate example?

4.65% per year

How many new individuals were added in the 4% growth example?

40

How many individuals were present at the start of year 2?

1030

How often does the human population double at this rate?

Every ~25 years

What real-world example shows short-term exponential growth?

COVID-19

When did the COVID-19 outbreak begin?

December 2019

When was COVID-19 declared a pandemic?

March 11, 2020

What limits long-term exponential growth?

Resource limitation and environmental resistance

What invasive species example showed exponential growth?

European rabbits in Australia

How many rabbits were introduced?

24 rabbits

When were rabbits introduced?

1859

How fast can rabbits reproduce?

Up to 20 offspring per female per year

How large did the rabbit population become by 1940?

600 million

What control method failed for rabbits?

Australia’s rabbit-proof fence

What disease was introduced to control rabbits in 1950?

Myxomatosis

What later disease was used for rabbit control?

Rabbit Hemorrhagic Disease Virus (RHDV)