Biology (Unit 1): Population Dynamics

What is population density?

the number of individuals in a given area

What is dispersion?

the way individuals are spread out in an area

What are the three dispersion patterns?

clumped, uniform, and random

What is clumped dispersion?

individuals gather in groups, often for protection or where resources are patchy

What is uniform dispersion?

individuals are evenly spaced, often due to competition for resources

What is random dispersion?

individuals are spread with no pattern, often where resources are even and plentiful

What four processes change a population's size?

births, deaths, immigration, and emigration

When does a population grow?

when births plus immigration are greater than deaths plus emigration

What is immigration?

individuals moving into a population

What is emigration?

individuals moving out of a population

What is exponential growth?

growth that speeds up as the population gets bigger, shown by a J-shaped curve

When does exponential growth tend to happen?

when resources are unlimited, often early in a population's growth

What is logistic growth?

growth that slows and levels off at carrying capacity, shown by an S-shaped curve

What is the difference between exponential and logistic growth?

exponential keeps accelerating, while logistic slows and levels off at a limit

What is carrying capacity?

the maximum population size an environment can support

Can a population exceed its carrying capacity?

yes, but it then usually crashes back down

What is overshoot and dieback?

when a population grows past carrying capacity and then crashes as resources run out

What is a limiting factor?

something that slows or caps population growth

What is a density-dependent limiting factor?

one whose effect gets stronger as the population gets denser, like disease or competition

What is a density-independent limiting factor?

one that affects a population regardless of its density, like a flood or fire

What is the difference between density-dependent and density-independent factors?

density-dependent factors depend on crowding, while density-independent ones do not

Give a few examples of density-dependent factors?

competition, predation, and disease

Give a few examples of density-independent factors?

floods, fires, and extreme weather

What is an r-selected species?

one that produces many offspring with little care, suited to unstable environments

What is a K-selected species?

one that produces few offspring with much care, suited to stable environments

What is the difference between r-selected and K-selected species?

r-selected favour quantity in changing conditions, while K-selected favour quality in stable ones

How do predator and prey populations affect each other over time?

they rise and fall in a linked cycle, with the predator lagging behind the prey

Why does the predator population lag behind the prey?

predators increase only after their prey food supply has grown