Ecology Day 2:

Populations and Human Influence

Populations

• members of the same species that reside

in the same area

Characteristics of populations

a. Geographic

distribution:

Where do they live?

b. Density:

How many are

found in a given unit

of area

c. Growth rate:

How quickly do they

grow? Daisy population

Factors affecting population growth?

1. Birth rate:

number of offspring per time period

2. Death rate:

number of deaths per time period

3. Migration rate

movement in and out of populations in a period of time

• Immigration: in

• Emigration: out

Exponential growth

• Occurs when

individuals in a

population reproduce

at a constant rate

• Only under ideal

conditions

Logistic growth • Occurs when a population’s growth rate slows or

stops, following a period of exponential (geometric)

growth

• Carrying capacity:

largest number

that a given

environment

can support

Click image to play video.

Limiting factors • cause population growth to stop

• Density-dependent factors depend upon

population size:

– Competition

– Predation

– Parasitism

– Disease

Competition • Occurs when 2 species occupies the same

niche & habitat

• What are some things they compete for?

Competition

• Using this 1990

census map of

US population

densities, what

can one deduce

at resource

competition

between the

different parts of

the country? How can competition explain

population size in nonhuman

species?

Predation

• Predator: one that consumes or exploits a particular species for self gain

• Prey: one that is consumed or exploited

• What would you expect to happen to prey populations if the predator numbers increased or if predator numbers decreased?

Figure 5-7 Wolf and Moose Populations

on Isle Royale

60

50

40

30

20

10

0 1955 1960 1965 1970 1975 1980 1985 1990 1995

2000

1600

1200

800

400

0

2400

Moose Wolves

Describe the relationship between the wolf and

moose populations shown in the graph.

Predator-Prey relationships

Parasitism and Disease

• Both deplete the

host organism of

vital minerals and

nutrients to sustain

life.

• Death of the

organism results in

the decline of

population size. Heart worms (roundworms) as

exposed by a veterinarian

Density-independent factors

• Limiting factors on

population size,

regardless of the

number of individuals

in the population

– Weather

– Natural disaster

– Seasonal cycles

– Human activities (habitat

destruction) Corals that have died from weather

changes, leading to increased

water temperature and pollution.

Historical Human Population Growth

Agriculture begins

Plowing and irrigation

Bubonic plague

Industrial Revolution begins

It took 500,000 years to reach 1 billion

& less than 200 years to reach 5 billion.

What might be some reasons why?

What’s the carrying capacity for the human

population?

What if it’s right here? ---------------------------

But, what if it’s right here? ---------------------------

(We do know it lowers when pollution occurs)

Age structure diagrams (population profiles):

graphs showing numbers of people in

different age groups in the population

U.S. Population Rwandan Population Males Males Females Females

What conclusions can be drawn from these graphs?

Why do the population growth curves

look different between developing and

developed countries?

Demography

• Study of human population size, density

and distribution, movement, and its birth

and death rates

• Birth rate is the number of live births

per 1000 population in a given year.

• Death rate is the number of deaths per

1000 population in a given year.

Calculating how fast populations

grow

• Birthrate – Death rate = Population Growth

Rate (PGR)

• If PGR > 0, then the population is growing.

• If PGR < 0, then the population is

declining.

Human activities that affect the

biosphere

• Hunting& Gathering

• Agriculture

• Industry

• Urban development

Types of resources

Nonrenewable resources:

• unable to be replenished through natural means

– Ex: fossil fuels, natural gas

Renewable resources:

• able to be replenished but is not unlimited

– Ex: freshwater

Sustainable development

• A way to use natural

resources without

causing long term

environmental

problems

• This plan takes into

consideration

environmental,

economic, and

community demands

Problems land resources face

Desertification

• the process of overusing land

and drought leading to the

formation of arid, desert lands

that cannot sustain agriculture

Soil erosion

• loss of topsoil layer from over farming

(plowing) lands

Deforestation • The process of cutting down (logging) forests for lumber and land.

• Leads to severe erosion during heavy rains.

• Which can lead to permanent changes to local soils and microclimates.

Overfishing

• Harvesting fish faster than they can be

replaced by reproduction.

• What happens to aquatic food webs if

overfishing continues to occur?

Aquaculture • raising water animals

for human use

• Pictured to the right

are tilapia fish farms

in Australia that then

export the fish to

markets.

• “Farm raised”

Air pollution

• Combustion of carbon

fuels released nitrogen

and sulfur that

combine with water to

form acid rain.

• Pollutant:

• any harmful substance

that enters the

biosphere from land,

air, or water

Acid rain

Why should we preserve

biodiversity? Biodiversity:

• sum total of

genetically based

variety of all

organisms in the

biosphere

–Ecosystem diversity

–Species

diversity

Why should we preserve

biodiversity?

• Biodiversity is one of Earth’s greatest

natural resources.

• Species of many kinds have provided us

with foods, industrial products, and

medicines – including painkillers,

antibiotics, heart drugs, antidepressants

and anticancer drugs.

Threats to species biodiversity

• Human activity can reduce

biodiversity by altering habitats,

hunting species to extinction,

introducing toxic compounds into food

webs, and introducing foreign species

to new environments.

Threats to species biodiversity

• Endangered:

species that is

declining in

population size

• Extinction:

species that

disappears from

all or part of its

range Endangered status:

Ailuropoda melanoleuca

Dodo Bird

• The dodo has been

extinct since the mid-

to-late 17th century.

• Its extinction occurred

during recorded human

history and was directly

attributable to human

activity

Habitat fragmentation

• When land is developed through or around

ecosystems, the species residing within

are impacted in what way?

Central Park in New

York City is a perfect

example of habitat

fragmentation.

DDT

• First synthesized in 1874, DDT's insecticidal

properties were not discovered until 1939, and it

was used with great success in the second half

of World War II to control malaria and typhus

among civilians and troops.

• After the war, DDT was used as an agricultural

insecticide, and soon its production and use

skyrocketed

• DDT was banned in most countries in 1972

Biomagnification:

• Increasing the concentration of harmful

materials up the food chain

Introduced species • Humans transport animal and plant species from

one part of the world to another.

• Many of these species can become invasive (non-native to a specific location; an introduced species); and has a tendency to spread).

Nutrias are native

to South America

but have become

pests in coastal US

cities.

Water Hyacinth

Hydrilla

Kudzu

Fire Ants

Conserving Biodiversity

• To conserve biodiversity and multi faceted

approach is best:

• Protection of species

• Protection of habitat

• Protection of biodiversity

Conserving Biodiversity Challenges

• Balancing :

• Public need and economics

• Public policy

• Conservation

Charting a Course for the Future

• Researchers are gathering data to monitor and evaluate the effects of human activities on important systems in the biosphere.

• Issues:

• Ozone depletion

• CO2 emissions

• Global warming

• Alternative fuels

• Alternative food sources

Ozone depletion

• Ozone: layer of

concentrated gas that

protects the Earth

from harmful UV rays

• O3

• 1970s, scientists

found a gap in the

ozone layer near

Antarctica.

NASA image

Global warming

• Compounding the

ozone depletion was

the buildup of CFCs

(chlorofluorocarbons)

from aerosols and

AC units with Freon.

• CFCs trap heat,

leading to a rise in the

global temperature.