Biology — Population Ecology (Density, Growth & Carrying Capacity)

What is a population?

a group of individuals of the same species living in the same general area

What is population density?

the number of individuals in a specific area

What is dispersion?

how individuals are spread throughout their habitat

What is clumped dispersion?

when individuals are packed closely together into groups (like a school of fish)

What is uniform dispersion?

when individuals are spaced evenly apart (like gannet nests in a colony)

What is random dispersion?

when individuals are spread unpredictably (like wind-dispersed dandelion seeds)

Why might a population show clumped dispersion?

for protection warmth finding food or avoiding predators

Why might a population show uniform dispersion?

competition for limited resources spaces individuals evenly

Why might a population show random dispersion?

there is no strong reason to group so spacing is left to chance

When does a population grow from births and deaths?

when the birth rate is greater than the death rate

When does a population decline from births and deaths?

when the death rate is greater than the birth rate

What is immigration?

individuals moving into a population from elsewhere

What is emigration?

individuals leaving a population

When does a population grow from movement?

when immigration is greater than emigration

When does a population decline from movement?

when emigration is greater than immigration

What is exponential growth?

growth by a fixed percentage each period so the bigger the population the faster it grows

What curve shape does exponential growth produce?

a J-shaped curve

When does exponential growth usually happen?

under optimal conditions with plentiful resources

What is the formula for exponential growth?

population = starting population times the growth factor raised to the number of periods

How do you turn a growth rate percentage into a growth factor?

add it to 1 (a 10% rate becomes 1.1)

A population of 1000 grows 10% per month. What is its size after 2 months?

1210 (1000 times 1.1 squared)

What is logistic growth?

growth that is exponential at first then slows and levels off

What curve shape does logistic growth produce?

an S-shaped curve

When does logistic growth usually happen?

as resources become scarce and competition increases

Why can no population grow exponentially forever?

natural resources are limited

What does a population growth model describe?

how a population changes over a specific period of time

Are populations static or dynamic?

dynamic (they cycle through growth stability and decline)

What is carrying capacity (K)?

the maximum population size an environment can support

What does a population do around its carrying capacity?

it often fluctuates just above and below K

What are limiting factors?

abiotic and biotic factors that control population growth

What are density-independent limiting factors?

factors that limit growth regardless of density such as natural catastrophes

Give examples of density-independent factors?

volcanic eruptions earthquakes fires droughts floods tsunamis and hurricanes

What are density-dependent limiting factors?

factors that affect growth more strongly as density rises

Give examples of density-dependent factors?

competition predation herbivory disease parasitism and overcrowding stress

Can an environment's carrying capacity change?

yes through changing seasons natural disasters or human activity

What happens if carrying capacity rises?

populations may grow

What happens if carrying capacity falls very low?

populations can die out

What is a species' life history?

its lifespan behaviour and reproductive strategy

What are r-selected traits?

short lifespan many offspring and little or no parental care

What are K-selected traits?

long lifespan fewer offspring and more parental care

Give examples of r-selected species?

jellyfish insects rodents and frogs

Give examples of K-selected species?

large mammals such as elephants horses and primates

What growth pattern do r-selected species often show?

rapid boom-bust growth that overshoots then crashes

What growth pattern do K-selected species often show?

slow sustained growth that stabilises near carrying capacity

What environments suit r-selected species?

variable or unstable environments

What environments suit K-selected species?

stable consistent environments

Is any species purely r-selected or K-selected?

no most have a mix of both kinds of traits

What is a memory aid for r and K selection?

r is rapid reproduction with many offspring and K is staying near carrying capacity