Biology: Populations & Communities

What is population density?

the number of individuals in a specific area

What is dispersion?

how individuals are spread throughout their habitat

What are the three dispersion patterns?

clumped uniform and random

What is clumped dispersion?

individuals packed into groups such as a school of fish

What is uniform dispersion?

individuals spaced evenly such as gannet nests in a colony

What is random dispersion?

individuals spread unpredictably such as wind-blown seeds

Why might individuals clump together?

for protection warmth or finding food

When does a population grow from births and deaths?

when the birth rate is greater than the death rate

When does a population shrink from births and deaths?

when the death rate is greater than the birth rate

What is immigration?

individuals moving into a population

What is emigration?

individuals leaving a population

When does a population grow from movement?

when immigration is greater than emigration

What four processes change a population's size?

births deaths immigration and emigration

What is exponential growth?

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

What curve does exponential growth produce?

a J-shaped curve

When does exponential growth happen?

under ideal conditions with plentiful resources

What is the exponential growth formula?

population = starting size times the growth factor to the power of the number of periods

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

add it to 1 so 10% becomes 1.1

A population of 1000 grows 10% per month. What is it 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 does logistic growth produce?

an S-shaped curve

When does logistic growth happen?

as resources run short and competition rises

What is the difference between exponential and logistic growth?

exponential is an unlimited J-curve while logistic is an S-curve that levels off

Why can no population grow forever?

resources are limited

What is carrying capacity?

the maximum population an environment can support

What does a population do around its carrying capacity?

it fluctuates just above and below it

What are limiting factors?

abiotic and biotic factors that control population growth

What are density-independent factors?

factors that limit growth regardless of density such as natural catastrophes

Give examples of density-independent factors?

fires floods droughts and volcanic eruptions

What are density-dependent factors?

factors that affect growth more strongly as density rises

Give examples of density-dependent factors?

competition predation disease and overcrowding

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

density-dependent factors get stronger with crowding while density-independent ones hit no matter the density

What is a quick test for a density-independent factor?

ask if it would still harm a tiny spread-out population (yes means independent)

Can carrying capacity change?

yes through seasons natural disasters or human activity

What is a species' life history?

its lifespan behaviour and reproductive strategy

What are r-selected traits?

short life many offspring and little parental care

What are K-selected traits?

long life few offspring and much parental care

Give examples of r-selected species?

insects rodents and frogs

Give examples of K-selected species?

large mammals like elephants and primates

What growth pattern do r-selected species show?

fast boom-bust growth that overshoots then crashes

What growth pattern do K-selected species show?

slow steady growth that levels off near carrying capacity

What is a memory aid for r and K selection?

r is rapid with many offspring and K stays near carrying capacity

What is a community made of?

many different species interacting in an area

What is an intraspecific interaction?

one between individuals of the same species

What is an interspecific interaction?

one between individuals of different species

What is a memory aid for intra versus inter?

intramural means within your school so intra means within one species

What is competition?

individuals competing for the same limited resources

What is the outcome of competition for both sides?

both are harmed

What is the competitive exclusion principle?

two species cannot coexist if they compete for all the same resources

What is resource partitioning?

species dividing a resource by area time or type so they can coexist

What is predation?

a predator killing and eating prey

What is the outcome of predation?

good for the predator and bad for the prey

How do predator and prey populations behave over time?

they rise and fall in cycles with the predator lagging behind the prey

What is herbivory?

a non-plant species feeding on a plant

How does herbivory differ from predation?

it does not always kill since only part of the plant may be eaten

What is symbiosis?

a close long-term association between two or more species

What is mutualism?

a symbiosis where both species benefit

What is commensalism?

a symbiosis where one benefits and the other is unaffected

What is parasitism?

a parasite feeding on and harming its host

What is the difference between an endoparasite and an ectoparasite?

an endoparasite lives inside the host and an ectoparasite lives on the outside

Which interaction benefits both species?

mutualism

Which interaction harms both species?

competition

Which interactions benefit one species and harm the other?

predation herbivory and parasitism

Which interaction benefits one species and leaves the other unaffected?

commensalism