Ecology

The BiospherePopulation EcologyCommunity Ecology

Ecosystems

Introduction to Ecology and the Biosphere

Chapter 50

Abiotic Factors of the Biosphere

Climate– Water/Rainfall –Light– Temperature –Wind

Rocks and Soil– Particle size –Mineral composition– pH

Periodic Disturbances– Catastrophic events: fire, flood, earthquake, etc.

Global Climate Patterns

Determined by:– input of solar energy

• Shape of earth—latitudinal variation• 23.5° tilt of earth’s axis—seasonal variation

– earth’s movement in space

Global Air Circulation, Precipitation, and

Winds

Local and Seasonal Effects on Climate

Proximity to bodies of water– Oceanic currents along continental coasts– Large inland bodies of water—lakes

Topographic features– Mountain ranges

Rain Shadows

Seasonal Turnover of Lakes/Ponds

Lake stratification and biannual mixing– Temperature water densest at 4°C,– Density it sinks below water that is

warmer or colder

Chapter 52

Population Ecology

Overview: Earth’s Fluctuating Populations

To understand human population growth, we must consider general principles of population ecology

Population ecology = study of populations relative to environment, including environmental influences on density and distribution, age structure, and population size

Population = group of individuals of a single species living in the same general area

Density and Dispersion

Density is the number of individuals per unit area or volume Dispersion is the pattern of spacing among individuals

within the boundaries of the population– Environmental and social factors influence spacing of individuals

in a population

Clumped distribution may be influenced by resource availability (living in groups increases the effectiveness of hunting, spreads the work of protecting and caring for young)

Uniform distribution may be influenced by social interactions such as territoriality

Random distribution—the position of each individual is independent of other individuals

Demography

Study of theory and statistics behind population growth and decline

N = size of the population

Demographic Statistics

Birth rate = number of offspring produced per time period

Death rate = number of deaths per time period

Sex ratio = proportion of males and females in a population

Generation time = time needed for individuals to reach reproductive maturity

Demographic Statistics

Age structure = statistic that compares the relative number of individuals in the population from each age group

Immigration rate = rate at which individuals relocate into a given population

Emigration rate = rate which individuals relocate out of a give population

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Demographic Statistics

These statistics together determine the size and growth rate of a given population

Population Growth = (Births + immigration) - (deaths + emigration)

If birth rates are greater than death rates:

Population Growth Fictional "Tribbles" from

Star Trek: Defining characteristic of the

Tribbles is their extreme reproductive rate. Over half of a Tribbles metabolism is devoted to reproduction, allowing them to bear a litter of young every twelve hours. 

With an average litter of ten, a single Tribble can therefore create a population of 1,771,561 within three days, and an amazing 304,481,639,541,400,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 in thirty days! 

Short generation time = faster rate of population growth

Population Growth and Size

Biotic potential = maximum growth rate of a population given unlimited resources, unlimited space, and lack of competition or predators– Rate varies from species to species

Carrying capacity = maximum number of individuals that a population can sustain in a given environment without destroying the habitat

Density-dependent factors come into play when population approaches and/or passes the carrying capacity– Food supplies, waste products, population-

crowding diseases Density-independent factors have nothing

to do with the population size– Floods, droughts, earthquakes, other natural

disasters and weather conditions

Limiting Factors Control Population Sizes

Population Growth Exponential Growth =

population grows as if there are no limitations as to how large it can get (biotic potential)

A population increases slowly at first (the "lag phase") and then grows increasingly rapidly as time passes (the "log phase"). When numbers are low, a doubling does not produce much addition to the population, but as numbers increase, each successive doubling adds larger and larger increments.

Population Growth

Logistic Growth = population growth slows to zero and population size tends to stabilize because of environmental resistance (limiting factors)

Exponential growth can be represented by the following equation:

dN/dt = rNwhere:

– dN/dt is the instantaneous rate of change in population size– r is the intrinsic rate of increase of the population– N is population size at any given point in time

The S-shaped (sigmoid) curve that shows the effect of environmental resistance upon population growth can be represented by the following equation, often referred to as the logistic equation:

dN/dt = rN (K-N) / K where K is the carrying capacity (maximum value of

N for a given set of environmental conditions)

Point of Maximum growth (K/2)

Number of generations

Po

pu

lati

on

siz

e (N

)

K = 1,5001,500

2,000

1,000

500

1510500

Logistic growth

Exponentialgrowth

= 1.0NdNdt

= 1.0NdNdt

1,500 – N1,500

Carrying Capacity

Life History Strategies

K-selected populations are of a roughly constant size whose members have low reproductive rates.– Offspring require extensive postnatal care until

sufficiently matured (humans) R-selected populations experience rapid

growth– Offspring are numerous, mature rapidly, and

require little postnatal care (bacteria)

Predator-Prey Cycling

Many populations undergo boom-and-bust cycles

Boom-and-bust cycles are influenced by complex interactions between biotic and abiotic factors

Community EcologyChapter 53

Interactions Between Populations of Different Species

Interspecific interactions—occur b/w populations of different species

Coevolution—a change in one species acts as a selective force on another species

Interactions Between Populations of Different Species

Predation (+/–)—consumption of one organism by another– Predator eats prey– Parasitism (+/–)—specialized

predator (parasite) lives on/in its host, not killed immediately

• Endoparasitism—live inside host (tapeworms/viruses)

• Ectoparasitism—live on surface of host (mosquitoes/aphids)

– Herbivory (+/–)—herbivores consume plants

Plant Defenses Against Hebivores

Physical defenses– thorns, hooks/spines on

leaves Chemical defenses

– Make plant distasteful or poisonous

• Morphine from opium poppy

• Nicotine from tobacco

Animal Defenses Against Predators Behavioral defenses

– Alarm cries– Distraction displays

Cryptic coloration/shape (camouflage)

– Blend in with environment– Asposematic coloration

• Red/black; yellow/black

Mechanical/chemical defenses– Quills, spines, and other similar structures– Toxins—distasteful or poisonous

• Monarch butterfly stores toxin of milkweed as larvae• Poisonous toads secrete toxin

Animal Defenses Against Predators Mimicry—prey resembles species that cannot

be eaten– Batesian mimicry: Imitate color patterns or

appearance of more dangerous organisms Mimicry can be used to lure prey

– Snapping turtle wriggles tongue like a worm to attract and capture small fish

Interspecific Competition (–/–)

Competition occurs when 2 or more populations overlap in their niches– Limiting resources

• Food

• Space

• Mates

Generally, one will out-compete the other

Competitive Exclusion Principle Two species cannot coexist in a community if

their niches are identical

Competition in Nature Two possible Outcomes

1. Weaker competitor becomes extinct

2. One or both species may evolve enough to use a different set of resources

Competition cannot operate for long periods of time

Evolution Drives Reduced Niche Overlap

0

2

4

6

8

10

12

2 4 6 8 10 12 14 16 18 20

Height of nesting site in apple trees

Num

ber

of in

divi

dual

s

Population 1Population 2

0

2

4

6

8

10

12

2 4 6 8 10 12 14 16 18 20

Resource Partitioning

Character Displacement

Joseph H. Connell Study

Symbiotic Relationships

Non-Beneficial– Parasitism (+/–)—host harmed

Beneficial– Commensalism (+/0)—one partner benefits

while not harming the other• Cattle egrets—egrets eat ectoparasites/cattle are

groomed

– Mutualism (+/+)—both partners benefit• Lichens-association b/w fungus and algae• Nitrogen-fixing bacteria and legumes

Community Structure Predators can moderate competition among its

prey species Keystone species can alter the whole community

Effects of a Keystone Predator:Sea Star (Pisaster)

0

5

10

15

20

25

1963

1964

1965

1966

1967

1968

1969

1970

1971

1972

Year

Num

ber

of S

peci

es

Pre

sent With Pisaster

Without Pisaster

Community Structure Introduction of a species (exotic species)

into a community can have drastic affects on the existing community members

Habitats that are more varied can support a more diverse community – provides more ecological niches

Nonequilibrium and Disturbances in a Community

Storms, fire, floods, droughts, overgrazing, or detrimental human activities:– Remove organisms – Alter resource availability

Create opportunities for new species that have not previously occupied the habitat

Humans are the biggest disturbance– Logging, agriculture, overgrazing

Ecological Succession Primary succession

– Begins in a virtually lifeless area where soil has not formed

– Lichens and mosses colonize first

– Soil gradually forms and small plants and shrubs take root

Secondary succession– Occurs where an existing community has been cleared

by some disturbance that leaves soil in tact

– Earliest plants to recolonize are often those that grow from wind-blown or animal-borne seeds

Ecological Succession

Competition among early species shape the succession of an area

Tolerance to abiotic conditions determines early species

EcosystemsChapter 54

Trophic Relationships Ecosystems divided into trophic levels

(feeding levels)– Primary producers—autotrophs (mostly

photosynthetic)– Primary consumers—herbivores– Secondary consumers—carnivores that eat

herbivores– Tertiary consumers—carnivores that eat other

carnivores– Detrivores—consumers that eat dead or

decaying matter

Food Webs Feeding

relationships woven into elaborate interconnections between species

Energy Flow in Ecosystems Each level in a food web contains a

different quantity of stored chemical energy When consumers eats producers or 2

consumers eat 1 producers, some energy is lost in the each transfer from one level to the next– Gross primary productivity= [total chemical

energy generated by producers]– Net primary productivity= [total chemical

energy – respiration by plants]

Pyramid of Net Productivity:

10% of energy at each level converted

to new biomass

Pyramids of Standing Crop

Biomass

Sharp decrease in biomass at

successively higher levels

Small crop of 1 producers

support larger crop of 1 consumers

Pyramid of Numbers:In higher trophic levels, the

small amount of biomass contained in a few organisms

Biogeochemical Cycles Chemical elements available only in limited

amounts Movement of essential elements between

the biotic and abiotic environment

Carbon Cycle Nitrogen Cycle Phosphorus Cycle Water Cycle

Carbon Cycle

*

Human Impacts

Greenhouse Effect– Increase of atmospheric CO2

• Combustion of fossil fuels• Burning of wood from deforestation

– Increase in numbers of C3 plants in areas previously inhabited by C4 plants

– Increase in global temperature

Nitrogen Cycle

*

Human Impacts

Agricultural effects– Cultivation—turns up soil and increases rate of

decomposition of organic matter; Releases more nitrogen

– Harvesting removes nitrogen from ecosystem– Adding industrially synthesized fertilizers to

soil has resulted in doubling globe’s supply• Excess nitrogen leeches into soil and into rivers,

streams, and lakes and ground water—

– high amounts are toxic to aquatic organisms and humans

– Algal blooms in lakes speed up eutrophication

Phosphorus Cycle

*

Water Cycle

The human population is disrupting chemical cycles throughout the biosphere

As the human population has grown, our activities have disrupted the trophic structure, energy flow, and chemical cycling of many ecosystems

Nutrient Enrichment

In addition to transporting nutrients from one location to another, humans have added new materials, some of them toxins, to ecosystems

Agriculture and Nitrogen Cycling

Agriculture removes nutrients from ecosystems that would ordinarily be cycled back into the soil

Nitrogen is the main nutrient lost through agriculture; thus, agriculture greatly impacts the nitrogen cycle

Industrially produced fertilizer is typically used to replace lost nitrogen, but effects on an ecosystem can be harmful

Contamination of Aquatic Ecosystems

Critical load for a nutrient is the amount that plants can absorb without damaging the ecosystem

When excess nutrients are added to an ecosystem, the critical load is exceeded

Remaining nutrients can contaminate groundwater and freshwater and marine ecosystems

Sewage runoff causes cultural eutrophication, excessive algal growth that can greatly harm freshwater ecosystems

Acid Precipitation Combustion of fossil

fuels is the main cause of acid precipitation

North American and European ecosystems downwind from industrial regions have been damaged by rain and snow containing nitric and sulfuric acid

North America

Europe

4.3 4.6

4.14.34.6

4.34.6

4.6

Field pH

5.35.2–5.35.1–5.25.0–5.14.9–5.04.8–4.94.7–4.84.6–4.74.5–4.64.4–4.54.3–4.4<4.3

5.3

5.3

5.35.3

5.3 5.3

5.3

5.2

5.3

5.6

5.9

5.4

5.2

5.2

5.2

5.2

5.4

5.56.0

5.0

5.4

6.3

5.3

5.3

6.1

5.5

5.4

5.4

5.4

5.4

5.6

5.5

5.5

5.6

5.65.2

5.1

5.15.74.9

5.7

5.0

5.0

5.0

5.04.9

4.9

4.9

4.9

4.14.3

4.3

4.34.4

4.44.4

4.4

4.4

4.5

4.54.5

4.54.5

4.54.5

4.5

4.5

4.54.5

4.5

4.5

4.5

4.54.5

4.5

4.54.5

4.5

4.5

4.64.6

4.64.6

4.6

4.6

4.64.6

4.64.64.6

4.64.6

4.6

4.7

4.7

4.74.74.7

4.7

4.7

4.74.7

4.7

4.74.7

4.7

4.7

4.7

4.84.8

4.8

4.8

4.8

4.8

4.8

4.8

4.8

5.0

5.0

5.3

5.2

5.1

5.1

5.1

5.1

5.2

5.25.2

5.3

5.4

5.4

5.5

5.5

4.74.7

4.7

4.7

4.7

4.7

4.7

4.9

4.8

4.8

4.64.7

4.7

4.7

4.84.8

4.8

4.8

4.9

4.9

4.9

5.0

5.0

5.0

5.1

5.1

5.0

5.0 5.05.1

5.2

5.3

5.45.4

5.7

By the year 2000, acid precipitation affected the entire contiguous United States

Environmental regulations and new technologies have allowed many developed countries to reduce sulfur dioxide emissions

Toxins in the Environment

In some cases, harmful substances persist for long periods in an ecosystem

One reason toxins are harmful is that they become more concentrated in successive trophic levels

In biological magnification, toxins concentrate at higher trophic levels, where biomass is lower

Zooplankton0.123 ppm

Phytoplankton0.025 ppm

Lake trout4.83 ppm

Smelt1.04 ppm

Herringgull eggs124 ppm

Co

nc

en

tra

tio

n o

f P

CB

s

Atmospheric Carbon Dioxide

One pressing problem caused by human activities is the rising level of atmospheric carbon dioxide

Rising Atmospheric CO2

Due to the burning of fossil fuels and other human activities, the concentration of atmospheric CO2 has been steadily increasing

The Greenhouse Effect and Global Warming

The greenhouse effect caused by atmospheric CO2 keeps Earth’s surface at a habitable temperature

Increased levels of atmospheric CO2 are magnifying the greenhouse effect, which could cause global warming and climatic change

Depletion of Atmospheric Ozone

Life on Earth is protected from damaging effects of UV radiation by a protective layer or ozone molecules in the atmosphere

Satellite studies suggest that the ozone layer has been gradually thinning since 1975 O

zon

e l

ay

er

thic

kn

es

s (

Do

bs

on

un

its

) 350

300

250

200

150

100

50

0196019651970197519801985 199019952000 2005

Year (Average for the month of October)1955

Destruction of atmospheric ozone probably results from chlorine-releasing pollutants produced by human activity

Chlorine atoms

O3Chlorine

Cl2O2

CIO

O2

O2

CIO

Chlorine from CFCs interacts with ozone (O3), forming chlorine monoxide (CIO) and oxygen (O2).

Sunlight causes Cl2O2 to break down into O2 and free chlorine atoms. The chlorine atoms can begin the cycle again.

Two CIO molecules react, forming chlorine peroxide (Cl2O2).

Sunlight

Scientists first described an “ozone hole” over Antarctica in 1985; it has increased in size as ozone depletion has increased

October 1979 October 2000