Ecology and Human Concerns

Chapter 25

Ecology

Study of interactions of organisms

with one another and with the

physical environment

Ecological Terms• Habitat

• Community

• Niche

• Specialist species

• Generalist species

• Ecosystem

• Succession

• Primary succession

• Secondary succession

Simple Ecosystem

Modelenergy input from sun

nutrientcycling

PHOTOAUTOTROPHS(plants, other producers)

HETEROTROPHS(consumers, decomposers)

energy output (mainly heat)

Nature of EcosystemsAutotrophs

• Producers

Heterotrophs

• Consumers

• Detritivores

• Decomposers

• Omnivores

Tropic Levels

1 - Producers

2 - Herbivores

3 - Primary carnivores

4 - Secondary carnivores

Food Chain

• A straight-line

sequence of who

eats whom

• Simple food chains

are rare in nature

MARSH HAWK

UPLAND SANDPIPER

GARTER SNAKE

CUTWORM

FoodWeb

Primary Productivity

• Gross primary productivity is

ecosystem’s total rate of photosynthesis

• Net primary productivity is rate at which

producers store energy in tissues in

excess of their aerobic respiration

Ecological Pyramids

5,060

decomposers/detritivores21

383

3,368

20,810

top carnivores

carnivoresherbivores

producers

• Producers form base

• Biomass pyramid

• Energy pyramid

Energy pyramid for Silver Springs

Biogeochemical Cycle

• The flow of a nutrient from the

environment to living organisms and

back to the environment

• Main reservoir for the nutrient is in the

environment

Three Categories

• Hydrologic cycle

– Water

• Atmospheric cycles

– Nitrogen and carbon

• Sedimentary cycles

– Phosphorus and sulfur

Hydrologic Cycle

evaporation from ocean

425,000

precipitation into ocean 385,000

evaporation from land plants

(evapotranspiration) 71,000

precipitation onto land 111,000

wind-driven water vapor40,000

surface and groundwater flow

40,000

Atmosphere

Oceans Land

Phosphorus Cycle

• Phosphorus is part of phospholipids and

all nucleotides

• It is the most prevalent limiting factor in

ecosystems

• Main reservoir is Earth’s crust; no

gaseous phase

Phosphorus Cycle

GUANO

FERTILIZER

ROCKS

LAND FOOD WEBS

DISSOLVED IN OCEAN

WATER

MARINE FOOD WEBS

MARINE SEDIMENTS

excretion

weathering

mining

agriculture

uptake by autotrophs

death, decomposition

sedimentation settling out leaching, runoff

weathering

uplifting over geologic time

DISSOLVED IN SOIL WATER,

LAKES, RIVERS

uptake by autotrophs

death, decomposition

Human Effects

• In tropical countries, clearing lands for

agriculture may deplete phosphorus-

poor soils

• In developed countries, phosphorus

runoff is causing eutrophication of

waterways

Carbon Cycle

• Carbon moves through the atmosphere

and food webs on its way to and from

the ocean, sediments, and rocks

• Sediments and rocks are the main

reservoir

Carbon Cycle

photosynthesisTERRESTRIAL

ROCKS

volcanic action

weathering

diffusion

Bicarbonate, carbonate

Marine food webs

Marine sediments

Atmosphere

Terrestrialrocks

Soil waterPeat, fossil

fuels

Land food webs

Carbon in Atmosphere

• Atmospheric carbon is mainly carbon dioxide

• Carbon dioxide is added to atmosphere– Aerobic respiration, volcanic action,

burning fossil fuels

• Removed by photosynthesis

Greenhouse Effect

• Greenhouse gases impede the escape

of heat from Earth’s surface

Carbon Dioxide Increase

• Carbon dioxide levels fluctuate

seasonally

• The average level is steadily increasing

• Burning of fossil fuels and deforestation

are contributing to the increase

Other Greenhouse Gases

• CFCs - synthetic gases used in plastics

and refrigeration

• Methane - produced by termites and

bacteria

• Nitrous oxide - released by bacteria,

fertilizers, and animal wastes

Nitrogen Cycle

• Nitrogen is used in amino acids and

nucleic acids

• Main reservoir is nitrogen gas in the

atmosphere

Nitrogen Cycle

NO3-

IN SOIL

NITROGEN FIXATION

by industry for agriculture

FERTILIZERS

FOOD WEBS ON LAND

NH3-, NH4

+

IN SOIL

1. NITRIFICATION

loss by leaching

uptake by autotrophs

excretion, death,

decomposition

uptake by autotrophs

NITROGEN FIXATION

loss by leaching

AMMONIFICATION

2. NITRIFICATION

NITROGENOUS WASTES, REMAINS IN SOIL

GASEOUS NITROGEN (N2)

IN ATMOSPHERE

NO2-

IN SOIL

Biological Magnification

A nondegradable or slowly degradable

substance becomes more and more

concentrated in the tissues of

organisms at higher trophic levels

of a food web

Human Population Growth

• Population now exceeds 6 billion

• Rates of increase vary among countries

• Average annual increase is 1.26 percent

• Population continues to increase

exponentially

Side-Stepping Controls

• Expanded into new habitats

• Agriculture increased carrying capacity;

use of fossil fuels aided increase

• Hygiene and medicine lessened effects

of density-dependent controls

Limiting Factors

• Any essential resource that is in

short supply

• All limiting factors acting on a

population dictate sustainable

population size

Logistic Growth

• As size of the population increases, rate of reproduction decreases

• When the population reaches carrying capacity, population growth ceases

carrying capacity

Time

Density-Dependent Controls

• Logistic-growth equation deals with

density-dependent controls

• Limiting factors become more

intense as population size increases

• Disease, competition, parasites,

toxic effects of waste products

Air Pollutants

• Carbon oxides

• Sulfur oxides

• Nitrogen oxides

• Volatile organic compounds

• Photochemical oxidants

• Suspended particles

Industrial Smog

• Gray-air smog

• Forms over cities that burn large

amounts of coal and heavy fuel oils;

mainly in developing countries

• Main components are sulfur oxides and

suspended particles

Photochemical Smog

• Brown-air smog

• Forms when sunlight interacts with

components from automobile exhaust

• Nitrogen oxides are the main culprits

• Hot days contribute to formation

Ozone Thinning

• In early spring and

summer, ozone

layer over

Antarctica thins

• Seasonal loss of

ozone is at highest

level ever recorded

SouthAmerica

Antarctica

Effect of Ozone Thinning

• Increased amount of UV radiation

reaches Earth’s surface

• UV damages DNA and negatively

affects human health

• UV also affects plants, lowers

primary productivity

Water Use and Scarcity

• Most of Earth’s water is too salty for

human consumption

• Desalinization is expensive and

requires large energy inputs

• Irrigation of crops is the main use

of freshwater

Negative Effects of Irrigation

• Salinization, mineral buildup in soil

• Elevation of the water table and

waterlogging

• Depletion of aquifers

Generating Garbage

• Developed countries generate huge

amounts of waste

• Paper products account for half the

total volume

• Recycling can reduce pollutants, save

energy, ease pressure on landfills

Desertification

• Conversion of large tracts of grassland

to desertlike conditions

• Conversions of cropland that result in

more than 10 percent decline in

productivity

Effects of Deforestation

• Increased leaching and soil erosion

• Increased flooding and

sedimentation of downstream rivers

• Regional precipitation declines

• Possible amplification of the

greenhouse effect

Regions of Deforestation

• Rates of forest loss are greatest in

Brazil, Indonesia, Mexico, and Columbia

• Highly mechanized logging is

proceeding in temperate forests of the

United States and Canada

Reversing Deforestation

• Coalition of groups dedicated to saving

Brazil’s remaining forests

• Smokeless wood stoves have saved

firewood in India

• Kenyan women have planted millions

of trees

Fossil Fuels

• Coal, oil, natural gas

• Main energy source of developed

countries

• Burning of fossil fuels contributes to

global warming

Nuclear Energy

• Used extensively in some energy-poor developed countries

• Little support in the United States

• Emits fewer air pollutants than burning coal, but creates radioactive wastes

• Potential for meltdown

Chernobyl Accident - 1986

• Core meltdown at a nuclear power plant in the Ukraine

• 31 immediate deaths, radiation sickness and death for others

• Cloud of radiation spread by winds across Europe

• Long-term health impacts downwind

Wind Energy

• An indirect use of solar energy

• Wind farms are arrays of turbines

• Can supplement needs of some

regions but is not dependable

enough on its own

Solar-Hydrogen Energy

• Photovoltaic cells use sunlight

energy to split water

• Hydrogen gas produced in this way

can be used as fuel or to generate

electricity

• Clean, renewable technology

Deforestation

• Removal of all trees from large tracts

of land

• 38 million acres logged each year

• Wood is used for fuel, lumber

• Land is cleared for grazing or crops