Studied by 7 peopleAPES 2024
Factors that influence population size are either
density-dependent or density-independent
Desnity-dependent factor
influences an individualās 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 individualās 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
āExponential growth model (N t = N 0 e rt )
A growth model that estimates a populationās
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 environmentās 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
Note
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