population density

what is population density ?

individuals per unit area/volume

what factors effects population size ?

• Natality (birth rate)

• Mortality (death rate)

• Immigration – individuals entering a population

• Emigration – individuals leaving a population

Population increases when:

Births + Immigration > Deaths + Emigration

Population decreases when:

Deaths + Emigration > Births + Immigration

what is the geometric growth model

Geometric Growth

Also called exponential growth.

Characteristics:

• Unlimited resources

• Rapid growth

• J-shaped curve

Keywords:

• Exponential growth

• Geometric growth

• J-curve

• Ideal conditions

Exponential growth (J-curve): Unlimited resources → rapid population increase.

what is the logistic growth model?

Logistic Growth

Characteristics:

• Resources become limited

• Growth slows over time

• S-shaped curve

Keywords:

• Logistic growth

• S-curve

• Carrying capacity

• Environmental resistance

Logistic growth (S-curve): Limited resources → growth slows and levels off at carrying capacity.

what is carrying capacity?

Maximum population size an environment can sustainably support.

Symbol:

• K

what are density dependent factors?

Density-Dependent Factors

Effects become stronger as population density increases.

Examples:

• Competition

• Disease

• Predation

• Parasitism

what are density independant factors?

Affect populations regardless of density.

Examples:

• Drought

• Floods

• Fires

• Extreme temperatures

what is clumped dispersion and why does it occur?

Clumped Distribution

Definition: Individuals are grouped together in patches.

Examples

• Herds of deer

• Schools of fish

• Colonies of penguins

• Trees growing around a water source

Why does it occur?

• Resources (food, water, shelter) are concentrated in certain areas.

• Protection from predators.

• Social behaviour (living in groups).

• Increased mating opportunities.

Exam answer:

Clumped distribution occurs when resources are unevenly distributed or when organisms benefit from living together.

what is uniform dispersion and why does it occur?

Uniform Distribution

Definition: Individuals are evenly spaced apart.

Examples

• Nesting penguins keeping a fixed distance

• Desert shrubs spaced apart

• Territorial wolves or birds

Why does it occur?

• Competition for resources.

• Territorial behaviour.

• Aggression between individuals.

Exam answer:

Uniform distribution occurs because competition or territorial behaviour keeps individuals evenly spaced.

what is random dispersion and why does it occur?

Random Distribution

Definition: Individuals are scattered with no predictable pattern.

Examples

• Dandelions in a field

• Wildflowers in a meadow

• Trees in some natural forests (where resources are abundant)

Why does it occur?

• Resources are plentiful and evenly available.

• Individuals do not strongly attract or repel each other.

• Seeds or spores are dispersed randomly by wind or animals.

Exam answer:

Random distribution occurs when resources are abundant and individuals do not interact strongly with one another.

what is fecundity?

Fecundity

Definition:

Fecundity is the reproductive capacity of an organism, or the number of offspring it can produce.

There is usually a trade-off:

• High fecundity → many offspring, but fewer survive.

• Low fecundity → fewer offspring, but more parental care and higher survival.

give me the characteristics of the type 1 survivorship curve?

Type I Survivorship

Pattern:

High survival during early and middle life.

Most individuals die at old age.

Examples:

• Humans

• Elephants

• Whales

lots of parental care

give me the characteristics of the type 2 survivorship curve?

Type II species have a relatively constant mortality rate throughout their lives and moderate fecundity.

ex.) squirrels

mod perental care

give me the characteristics of the type 3 survivorship curve?

Type III species have very high fecundity and produce many offspring, but most die at a young age due to predation, disease, or competition.

ex.) flies

high fecundity no parental care, frogs,plants

Why do Type III species have high fecundity?

They produce many offspring because only a small proportion survive to adulthood, increasing the chance that some will reproduce.

birth rate is synonymous with what term?

natality

what is a limiting factor?

A limiting factor is any environmental factor that restricts the size or growth of a population.

density dependant and density independant factors are limiting factors

what is population sampling?

when Scientists estimate population size because counting every organism is impractical.

what is quadrate sampling and when is it used?

Quadrat Sampling Used for

Organisms that do not move.

Examples:

• Grass

• Flowers

• Moss

• Seaweed

Method:

• Place a square frame (quadrat) randomly.

• Count organisms inside.

• Repeat several times.

• Calculate average density.

✅ Best for plants and sessile organisms.

what is the mark and recapture method when is it used?

Used for

Animals that move around.

Examples:

• Fish

• Rabbits

• Birds

• Insects

Method:

1.Capture animals.

2. Mark them safely.

3. Release them.

4. Capture another sample later.

5. Count how many are marked.

• N = estimated population

• M = number marked first

• C = total caught second

• R = marked individuals recaptured

Assumptions

• Marks stay on.

• Marks don't affect survival.

• Population doesn't change much between samples.

• Marked individuals mix randomly.

name all community interactions?

competition

predation

mutualism

commensalism

parisitism

what is competition?

Both species are negatively affected because they compete for the same limited resources.

what is predation?

One organism benefits by killing and eating another.

Examples:

• Fox → rabbit

• Hawk → mouse

Predator benefits.
Prey is harmed.

what is mutualism?

Mutualism (+ / +)

Both species benefit.

Examples:

• Bees and flowers

• Clownfish and sea anemones

what is commensalism?

Commensalism (+ / 0)

One species benefits.
The other is unaffected.

Examples:

• Barnacles on whales

• Birds nesting in trees

what is parasitsm?

Parasitism (+ / -)

One organism benefits while the host is harmed, usually without being killed immediately.

Examples:

• Tick on a deer

• Tapeworm in humans

• Fleas on dogs

what are the 4 levels of ecological organization?

• Organism – A single individual living thing.

  • Example: One wolf.

• Population – A group of individuals of the same species living in the same area.

  • Example: All the wolves in a forest.

• Community – All the different populations (different species) living and interacting in an area.

  • Example: Wolves, deer, rabbits, birds, trees, and insects in the same forest.

• Ecosystem – The community plus the non-living (abiotic) environment.

  • Includes sunlight, water, soil, temperature, rocks, and air.

  • Example: A forest ecosystem.

what is the exponential growth rate formula?

type growth rate

type e^x on calc

multiply by time

multiply by start organsism

if population were to double would it be exponential or logistic growth?

The population doubles, meaning the increase gets larger over time rather than increasing by a fixed amount.

a population follows logistic growth . Explain what happens to :

• birth rate

• death rate

• resources
  as it approaches carrying capacity.

As a population approaches carrying capacity, the birth rate decreases while the death rate increases due to limited resources and increased competition. Resources become scarce, causing population growth to slow and eventually stabilize at carrying capacity.

what is the difference between a food chain and food web?

A food chain shows a single pathway of energy transfer from one organism to another. A food web consists of many interconnected food chains, showing multiple feeding relationships and providing a more accurate representation of an ecosystem.

In a mark–recapture experiment, researchers estimate a population of 500 birds.

Several weeks later they discover that the paint used for marking made the birds easier for predators to catch.

The estimated population is most likely:

A. Too high

B. Too low

C. Accurate

D. Impossible to determine

smaller r larger population