11-22 Carrying capacity

APES 2024

Factors that influence population size are either

Factors that influence population size are either

density-dependent or density-independent

Desnity-dependent factor

influences an individual’s probability of survival and reproduction in a manner that depends on the size of the population (ex. disease)

Density-independent factor

has the same effect on an individual’s probability of survival and the amount of reproduction at any population size (ex. natural disasters)

When food is abundant

individuals are able to reproduce abundantly

Fecundity

ability to produce an abundance of offspring

High number of births and low number of deaths will produce a

high population growth rate

⊗Exponential growth model (N t = N 0 e rt )

A growth model that estimates a population’s
future size (N t ) after a period of time (t), based on the intrinsic growth rate (r) and the number of reproducing individuals currently in the population (N 0 )

When populations are not limited by resources,
their growth can be very rapid, more births occur with

each step in time, creating a J-shaped growth curve

Populations do not typically experience exponential
growth indefinitely, they are

limited by resources and carrying capacity

Limiting resource

A resource that a population cannot live without and that occurs in quantities lower than the population would require to increase in size

Carrying capacity (K)

The limit of how many individuals
in a population the environment can sustain

Carrying capacity is

more realistic because it incorporates environmental limits

A small population initially experiences exponential growth. As the population becomes larger, however, resources become scarcer, and

the growth rate slows

What happens when carrying capacity is reached

growth stops

Due to growth stopping

the pattern of population growth follows an S-shaped curve

S-shaped curve

The shape of the logistic growth model when graphed

If food becomes scarce or other conditions change

a population can experience fluctuations

Overshoot

When a population becomes larger than the environment’s carrying capacity

Environmental impacts of population overshoot

resource depletion

Die-off

A rapid decline in a population due to death

Die-back

often severe to catastrophic due to lack of available
resources leads to famine, disease and/or conflict

Population density

the number of individuals in a population per unit area

Large organisms typically have

low densities

Large organisms have low densities because

they need more resources to survive

High densities make it easier to

find mates

High densities increase

competition, vulnerability to predation, and transmission of diseases

Low densities make it harder to find a mate, but

but individuals enjoy plentiful resources and space

Random

no pattern to the location, ex. trees in a natural forest

Uniform

evenly spaced, ex. trees planted in a plantation

Clumped

large group provides better feeding opportunities or protection from predators, ex. schools of fish, flocking birds, herding animals

Corridor

strips of natural habitat that connect populations

Metapopulation

A group of spatially distinct populations that are
connected by occasional movements of individuals between them

Inbreeding depression

When individuals with similar genotypes - typically relatives - breed with each other and produce offspring that have an impaired ability to survive and reproduce

Age structure diagram

A visual representation of the number of individuals within specific age groups for a country, typically expressed for males and females

Population pyramid

An age structure diagram that is widest at the bottom and smallest at the top, typical of developing countries

Population momentum

Continued population growth after growth reduction measures have been implemented