2.6.1 4,2.1.7

2.6.1-.4, 2.1.7 Population

Dynamics

5/11/2013 Author -Guru IB/ESS 1

Population Dynamics

A look at the factors that tend to increase or

decrease the size of a population.


The population size of a species in a given space at a given time is determined by the interplay between BIOTIC POTENTIAL and ENVIRONMENTAL RESISTANCE.

Biotic potential = growth rate with unlimited resources.

Environmental resistance = all the factors acting jointly to limit population growth.


POPULATION SIZE

Growth factors (biotic potential)

Favorable light Favorable temperature Favorable chemical environment (optimal level of critical nutrients)

Abiotic

Biotic High reproductive rate

Generalized niche

Adequate food supply

Suitable habitat

Ability to compete for resources

Ability to hide from or defend against predators

Ability to resist diseases and parasites

Ability to migrate and live in other habitats

Ability to adapt to environmental change

Decrease factors (environmental resistance)

Too much or too little light Temperature too high or too low Unfavorable chemical environment (too much or too little of critical nutrients)

Abiotic

Biotic Low reproductive rate

Specialized niche

Inadequate food supply

Unsuitable or destroyed habitat

Too many competitors

Insufficient ability to hide from or defend

against predators

Inability to resist diseases and parasites

Inability to migrate and live in other

habitats

Inability to adapt to environmental

change


Four variables change population size:

1. NATALITY = birth rate

2. MORTALITY = death rate

3. IMMIGRATION = rate of organisms moving in

4. EMIGRATION = rate of organisms moving out


Nu

mb

er

of

ind

ivid

uals

Time

Carrying capacity

K species;

experience

K selection

r species;

experience

r selection

K

REPRODUCTIVE STRATEGIES


Opportunistic or r-Selected Species

cockroach dandelion

Many small offspring

Little or no parental care and protection of offspring

Early reproductive age

Most offspring die before reaching reproductive age

Small adults

Adapted to unstable climate and environmental

conditions

High population growth rate (r)

Population size fluctuates wildly above and below

carrying capacity (K)

Generalist niche

Low ability to compete

Early successional species


Fewer, larger offspring

High parental care and protection of offspring

Later reproductive age

Most offspring survive to reproductive age

Larger adults

Adapted to stable climate and environmental

conditions

Lower population growth rate (r)

Population size fairly stable and usually close

to carrying capacity (K)

Specialist niche

High ability to compete

Late successional species

elephant saguaro

Competitor or K-Selected Species


SURVIVORSHIP CURVES


Population density affects population growth.


DENSITY INDEPENDENT FACTORS = affect a

populations’ size regardless of its population density.

1. Weather

2. Earthquakes

3. Floods

4. Fires

. . . Natural disasters

R-strategists populations are most affected by these.


DENSITY DEPENDENT FACTORS = affect a

populations’ size depending on its population density.

1. Predation

2. Disease

3. Availability of food and water

4. Space

Negative Feedback!!


INTERNAL FACTORS = might include density-dependent fertility or size of breeding territory.

EXTERNAL FACTORS = might include predation and disease.


Species interactions influence population growth and carrying capacity = SYMBIOSIS

Competition for resources.

High

Low

Rela

tive p

op

ula

tio

n d

en

sit

y

0 2 4 6 8 10 12 14 16 18

Days

Each species grown alone

Paramecium

aurelia

Paramecium

caudatum

High

Low

Re

lati

ve

po

pu

lati

on

de

ns

ity

0 2 4 6 8 10 12 14 16 18

Days

Both species grown together

Paramecium

aurelia

Paramecium

caudatum


Resource Portioning


PREDATION

PREY

POPULATION

PREDATOR

POPULATION


Span worm Bombardier beetle

Viceroy butterfly mimics

monarch butterfly

Foul-tasting monarch

butterfly

Poison dart frog When touched, the

snake caterpillar

changes shape to look

like the head of a snake

Wandering leaf insect

Hind wings of io moth

resemble eyes of a

much larger animal

Avoiding predators


Parasitism


Mutualism

Oxpeckers and black rhinoceros Clown fish and sea anemone


Shark and ramora


Cleaning station

Sabertooth blenny

Cleaner blenny


Commensalism


Herbivory


Education

2.6.1 4,2.1.7