1 of 80

Population Dynamics

Unit 4, Lesson 1

Exploration 2

2 of 80

Population Density and Dispersion

3 of 80

Pigeon Populations

4 of 80

Vocabulary

Population Dispersion - How organisms are spread out (clumped, uniform or random)

Survivorship Curve- Graph showing survival rates by age. (Humans are Type 1 - most die at an old age)

Exponential Growth- Fast, unlimited population growth. J-shaped curve

Logistic Growth - Growth slows as resources run out. S-shaped curve

Carrying Capacity - Max population the environment supports.

5 of 80

Vocabulary

Density Dependent L. F. - Affects big populations more (like competition or disease).

Density Independent L. F.- Affects all populations (like natural disasters or pollution).

Biotic Factor - Living parts of the environment (plants, animals, fungi)

Abiotic Factor - Nonliving parts (water, air, sunlight).

Habitat - Where an organism lives

6 of 80

Vocabulary

Ecological Niche - An organism’s role in its environment (what it eats, where it lives, how it survives)

Predation- One organism hunts and eats another organism

7 of 80

Vocabulary

Keystone Species - A species that has a big impact on its ecosystem; if it’s removed, the whole ecosystem can change.

Biodiversity - The variety of living things in an area.

Symbiosis- close relationship between two different organisms, which can help, harm, or not affect one of them.

Mutualism- relationship where both organisms benefit.

8 of 80

Vocabulary cont.

Commensalism - relationship where one organism benefits and the other is not helped or harmed.

Parasitism- relationship where one organism benefits and the other is harmed.

Competition- When organisms fight for the same resource.

Predation- One animal hunts, kills, and eats another animal.

9 of 80

Invasive Species

Invasive species are non-native organisms that cause harm to the ecosystem they enter. They often:

Outcompete native species for food and space
Spread disease or parasites
Change habitat structure

10 of 80

Brown Marmorated Stink Bugs

Silver Carp

Native to E. Asia
First documented in US in 2001
Possibly arrived in shipping crates
Now in 38 states

Native to E. Asia
Introduced in 1973 to control algae & parasite growth.
Eventually escaped to Mississippi River

11 of 80

Kudzu

Cane Toads

13 of 80

European Rabbits in Australia

24 wild rabbits were introduced for hunting by wealthy settlers in 1859
By the 1920s the rabbit population reached 10 billion.
Currently, around 200 million inhabit Australia.

14 of 80

Populations in the Greater Yellowstone Ecosystem

The reintroduction of wolves into Yellowstone National Park has caused both direct and indirect changes in populations of many other species within their ecosystem.

16 of 80

Ecosystem - a biological community of interacting organisms and their physical environment.

Trophic Cascade - indirect interactions that can control entire ecosystems, occurring when a trophic level in a food web is suppressed.

17 of 80

Keystone Species

Keystone species have an unusually large effect on their ecosystem.

Many other species depend on them.

Without keystone species, an ecosystem would be dramatically different.

18 of 80

Keystone Species:

Wolves in Yellowstone National Park

Environment is ideal for wolves
Human impact began to hurt the wolf population.
1926, last wolf pack eliminated
1995, program developed for reintroduction of the wolves to the park

20 of 80

Population size is the # of individuals in a population.

Population density is the average # of individuals in a population per unit of area.

21 of 80

Population Density and Dispersion

How can scientists determine if a population is healthy or not?

Look at population stability over time

Population Density= # individuals 200 deer

Unit of area 10 mi²

= 20 deer/mi²

22 of 80

Population Density Example

Population density is calculated using the formula:

Population Density = Population ÷ Area

Elizabethtown:

34,024 people / 72 km² ≈ 472 people per km²

Louisville:

617,638 people / 1032 km² ≈ 598 people per km²

New York City:

8,992,908 people / 783.8 km² ≈ 11,470 people per km²

23 of 80

Population Dispersion describes the way a population is spread out in a given area.

24 of 80

Population Dispersion

3 main patterns of population dispersion

Clumped - Resources spread unevenly in ecosystem, organisms cluster around resource - helps protect organism and makes finding a mate easier
Uniform - Individuals must compete for limited resources and territory
Random - Resources evenly distributed - organisms spread randomly within the ecosystem

25 of 80

	Clumped	Uniform	Random
Draw
Why?	Resources are patchy Search for food	Competition for limited resources and territory	Environment is uniform Individuals are solitary
Example

27 of 80

Measuring Population Size

A population consists of all the organisms of a given species that live in a particular area.

How can we measure the size of a population without counting every single individual?

28 of 80

Quadrat Sampling

Quadrats are grids used to collect data about a population in a small area to help determine the population of a larger area.

Works best with species that do not move, such as plants and corals.

29 of 80

2. Mark-recapture

Technique used to measure the size of a population. Biologists capture individuals in a population, tag them, and release them.
After a period of time, a second sample is captured, and biologists compare the number tagged to the number recaptured.

30 of 80

3. GPS

Animals are marked with a radio collar, or GPS tag and released into the wild.

31 of 80

Population Growth Patterns

Unit 4, Lesson 1

Exploration 2

32 of 80

33 of 80

What would happen if you left an apple in your locker over winter break?

How fast would the population rise?

When would the population’s growth rate begin to slow down?

34 of 80

The size of a population changes based on how many individuals are added or are removed.

To accurately track the population over time, they would need to account for four factors:

Births
Deaths
Immigration (move INTO the population)
Emigration (EXITING the population)

Population Growth

35 of 80

Immigration & Emigration

Immigration (Into)

Occurs when organisms move into a population

Emigration (Exit)

Occurs when organisms move out of a population.

If a population has more births than deaths, and immigration and emigration rates are equal, then the population will grow.

Growth rate can be zero, positive, or negative

36 of 80

r = (b + i) – (d + e)

Use the equation determine the growth rate of the bear population

(“r” = growth rate)

37 of 80

Survivorship Curves

A survivorship curve shows graphically the relative survival rates of individuals at different ages.

There are three types of survivorship curves:

Type I
Type II
Type III

38 of 80

Type I individuals survive well early in life and generally live many years.

At an advanced age, the death rate increases dramatically.

Examples include large mammals.

39 of 80

Type II - survivorship rate is equal at all stages of life -

Individuals have a death rate that is relatively constant at any age.

Examples include lizards, hydra, and some small mammals.

41 of 80

Type III very high birth rate, very high infant mortality

Those that do survive may live to an advanced age.

Examples include many fish and other marine organisms.

43 of 80

Growth Rate Graphs

These graphs represent how the number of individuals in a population changes over time.

Two main types

Exponential growth
Logistic growth

44 of 80

Exponential Growth (J-Shaped)

Almost any species in ideal conditions (available resource, space, protection from predators and disease…) will rapidly increase in population size
Under these conditions, the population will grow exponentially.

45 of 80

Exponential Growth (J-Shaped)

When you graph exponential growth, the graph appears in the shape of a “J”.

When a species moves into a new habitat, its population grows exponentially for a time.

46 of 80

Example of Exponential Growth

A deer herd in a forest will grow exponentially at first.

Locust populations can erupt exponentially when conditions are favorable.

Bacteria

47 of 80

Overpopulation can lead to

Insufficient supply of water
Starvation and malnutrition or poor diet
Unhygienic living conditions.
Higher risk for infectious disease
Disturbance of ecosystems

Populations in the real world don’t grow exponentially for very long.

Sooner, or later, the population growth will slow down.

48 of 80

�

Density Dependent Factors-

Resources that are limited because the rate at which they become depleted depends on the density of the population that uses them.

Examples:

Food

Water

Shelter

Can limit the population size!

49 of 80

Exponential vs. Logistic Growth

Exponential Growth happens when a population grows rapidly with unlimited resources.
Logistic Growth starts rapidly but slows down as the population reaches the carrying capacity (K).
Carrying Capacity (K) is the maximum number of individuals the environment can support.

50 of 80

Logistic Growth

51 of 80

Logistic Growth (S-Shaped)

As resources become scarce, population growth will slow or stop.
This forms an “S” shaped curve.
Population size is capped at the carrying capacity

This model of population growth considers the carrying capacity (K) and is limited by density-dependent factors.

52 of 80

Carrying Capacity

Number of individuals that the environment can support in a given area.

Can change based on available resources.

53 of 80

Example of Logistic Growth

As the population increases, food sources become limited, and predators may take their toll. This will slow down the growth rate and eventually lead to a stable population size around the carrying capacity of the environment.

As locust numbers increase, they will eventually deplete food sources, and diseases or predators can play a role in bringing the population back down to a more sustainable level.

Yeast used in bread making can multiply rapidly in a warm, sugary environment, exhibiting exponential growth until resources are depleted.

54 of 80

Limiting Factors

A limiting factor is something that causes population growth to decrease.

55 of 80

Density Independent Factors-

Factors that do not depend on the size of the population, but can affect it nonetheless.

Examples

Weather

Climate

Can reduce a population size, but it is completely random and does not consider how dense the population is.

56 of 80

Density Dependent Limiting Factors

Depend on population size
Become limiting only when population density reaches a certain level
Doesn’t affect small, scattered populations

Competition
Predation
Parasitism & disease

Affect populations regardless of their size

Weather
Natural disasters
Human activity

Density Independent Limiting Factors

Population Limiting Factors

58 of 80

SYMBIOSIS

Sym- together

Bio- life/living

Osis- Condition of

59 of 80

SYMBIOSIS

A relationship in which two species live closely together is called symbiosis.

Biologists recognize three main classes of symbiotic relationships in nature:

Mutualism
Parasitism
Commensalism

60 of 80

MUTUALISM

A relationship in which both organisms benefit.

62 of 80

Ant Army Defends Tree

63 of 80

COMMENSALISM

Commensalism is a relationship in which one organism benefits and the other is neither helped nor harmed.

Human Our eyelashes are home to tiny mites

that feast on oil secretions and dead skin. Without harming us, up to 20 mites may be living in one eyelash follicle.

Demodicids Eyelash mites find all they need to survive in the tiny follicles

of eyelashes. Magnified here 225 times, these creatures measure 0.4 mm in length and can be seen only with a microscope.

Organism benefits

Organism is not affected

Commensalism

65 of 80

EXAMPLE OF COMMENSALISM

Small marine animals called barnacles often attach themselves to a whale’s skin.
The barnacles have no effect on the whale.
They benefit from the constant movement of water and food particles past the swimming whale.

66 of 80

Remora Fish & Whale Shark

67 of 80

Eyelash Mites

68 of 80

PARASITISM

Parasitism is a relationship in which an organism lives inside or on another organism.
The parasite obtains all or part of its nutrients from the host organism.
Parasites weaken but usually do not kill their hosts.

Organism benefits

Organism is not affected

Hornworm caterpillar

The host hornworm will eventually die as its organs are consumed

by wasp larvae.

Braconid wasp

Braconid larvae feed on their host and release themselves shortly before reaching

the pupae stage of development.

Parasitism

69 of 80

Parasitic Wasp

70 of 80

EXAMPLE OF PARASITISM

Ticks live on the bodies of mammals, feeding on their blood and skin.

71 of 80

Botfly Invasion

72 of 80

Toxoplasmosis

75 of 80