6.6.05 The Ecosystem and Human Interference

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Transcript 6.6.05 The Ecosystem and Human Interference

The Layout Of Life (from BIG to small)
Biosphere (planet earth: water, land and sky)
Biomes (Tundra, Taiga, Dessert, Ocean, Lake)
(all of the plants and animals in a community
that live together in a particular biome)
Climate and the Biosphere
Our “Biosphere” = EARTH
Climate refers to the prevailing weather
conditions in an area as dictated by
temperature, rainfall, and these factors:
Variations in solar radiation due to a spherical earth;
The tilt of the earth’s axis as it rotates about the sun;
Distribution of land masses and oceans; and
Topography (landscape) features.
Distribution of solar energy
Biomes of the World
• A biome is a large biogeographical unit of the
biosphere that has a particular mix of plants and
animals that are adapted to living under certain
environmental conditions.
• Terrestrial: Tundra, Taiga, Coniferous and
Deciduous Forests, Temperate Rain Forests,
Grasslands, Shrublands (Chaparrel), Desert,
• Aquatic: Freshwater (lakes), Saltwater (Ocean),
Estuaries (salt and fresh combined)
• A community consists of all the various
populations in an area.
• An ecosystem is the community plus its
nonliving habitat, including abiotic (nonliving:
the soil, rocks, etc.) and biotic (living: plants and
animals) components.
• Ecology is the study of these ecosystems!
• Ecology is the study of these ecosystems!
• Ecology is not just about plants, animals and
their environmets……
………………..it’s also about the humans!
(as our lives tend to affect all other lives
Ecological levels in a coral reef
Community Composition and
• The composition of a community is a
listing of populations present.
• The diversity of a community adds in the
relative abundance of individuals.
• Ecologists have ideas about why
populations assemble together in the
same place at the same time.
• The interactive model of community
structure views the community as a stable
assemblage that remains the same over
• The individualistic model views a
community as a collection of species
where each responds to its own
requirements and tolerance factors.
Two terrestrial communities
Patterns of distribution within a
• Abiotic factors such as water, temperature, and
availability of organic nutrients often determine
a population’s distribution and density.
• Biotic factors, such as the availability of food, or
presence of disease, affect the distribution of
Patterns of Population Growth
• Each population has a particular pattern of
• The per capita rate of increase is calculated by
subtracting the number of deaths from the
number of births and dividing by the number of
individuals in the population.
• It is assumed that immigration and emigration
are equal. (that is: MOVE IN = MOVE OUT)
Population Growth and Density
(one is dependent on the other)
• Environmental resistance occurs when most
environments restrict growth, and exponential
growth cannot continue indefinitely.
• When the population reaches carrying capacity,
the population stops growing because
environmental resistance opposes biotic potential
How are population numbers kept in check?
1. Competition:
• Competition occurs when two species try to use
a resource that is in limited supply.
• According to the competitive exclusion principle,
no two species can occupy the same ecological
niche at the same time when resources are
• Resource partitioning occurs when resources
are partitioned between two or more species.
2. Predation
• Predation occurs when one living organism, the
predator, feeds on another, the prey.
• Predators include lions, whales that filter feed,
parasites that draw blood from hosts, and
herbivores that eat grass, trees, and shrubs.
Predator-Prey Population Dynamics
• Predator-prey interactions between two species
are influenced by environmental factors.
• Cycling of population densities may occur, as in
the case of the Canadian lynx and hare;
predators kill off prey and then the predator
population declines when food is in short supply.
• Predator-prey systems are not usually simple
two-species systems.
Predator-prey interaction: lynx and snowshoe hare
3. Prey Defenses
• Prey defenses against predation take many
forms: camouflage, use of fright, and warning
coloration are three prey defense mechanisms.
• Coevolution occurs when two species adapt to
selective pressures of each other.
Antipredator (Prey) defenses
4. Symbiosis
• Symbiosis refers to close interactions between
members of two populations.
• Three types of symbiosis occur: parasitism,
commensalism, and mutualism.
• Symbiotic associations do not necessarily fall
neatly into these three categoties.
• In the symbiotic relationship called parasitism,
the parasite benefits and the host is harmed.
• Parasites derive nourishment from their host
and the effect can be mild or fatal to the host.
• Many parasites use a secondary host to
disperse or complete their stages of
development, as is the case in the life cycle of a
deer tick.
• In commensalism, one species benefits and
the other is neither benefited nor harmed.
• Often a host provides a home or transportation
for another species.
• For example, barnacles attach to backs of
whales, remoras attach to sharks, clown fishes
live within the tentacles of sea anemones, and
cattle egrets eat insects off large grazing
Egret symbiosis
• In mutualism, both members benefit.
• Cleaning symbiosis involves crustaceans, fish,
and birds that act as cleaners of a variety of
vertebrate clients.
• In some cases, the cleaners may exploit the
situation and feed on host tissues, but cleaning
appears to improve the fitness of the client.
Cleaning symbiosis
Human Population Growth
• The human population is expanding
• The doubling time is the length of time it takes
for a population to double, currently estimated at
53 years.
• Only when birthrate equals death rate will there
be zero population growth.
More-Developed Versus Less-Developed
• Most of the expected increase in human
population will occur in certain less-developed
countries (LDCs) of Africa, Asia, and Latin
• Doubling time in more-developed countries
(MDCs) is about 100 years because a decrease
in death rate due to medical advances was
followed by a decrease in birth rates.
World population growth
• Despite introduction of medical care, LDCs still
have twice the MDC growth rate.
• Support for family planning, social progress,
and delayed childbearing could help prevent an
expected increase in population size.
• So what?!?! So……..the natural balance of all
the ecosystems cannot support continued
exponential growth of the human population !!!!RESOURCES ARE LIMITED and we are
depleting them without restoring them!!!
Age Distributions
• Many MDCs have a stable age structure, but
most LDCs have a youthful profile—a large
proportion of the population is younger than age
of 15.
• This means their populations will expand greatly
in the near future. (so we’d better get ready!)
• Zero population growth or replacement
reproduction does not occur when each couple
has only two children because there is
momentum from younger women entering
reproductive years.
Chapter 34: Ecosystems and
Human Interferences
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The Nature of Ecosystems: FRAGILE!
• An ecosystem contains biotic (living)
components and abiotic (nonliving)
• The biotic components of ecosystems are
the populations of organisms.
• The abiotic components include inorganic
nutrients, water, temperature, and
prevailing wind.
Biotic Components of an
• Autotrophs are producers that produce
food for themselves and for consumers.
• Most are photosynthetic organisms but
some chemosynthetic bacteria are
• Heterotrophs are consumers that take in
preformed food.
Biotic components
• Consumers may be:
• Herbivores – animals that eat plants,
• Carnivores – animals that eat other
• Omnivores, such as humans, that eat plants
and animals, or
• Decomposers, bacteria and fungi, that
break down dead organic waste.
• Detritus is partially decomposed organic
matter in the soil and water; beetles,
earthworms, and termites are detritus
Energy Flow and Chemical Cycling
Every ecosystem is characterized by two
1) Energy flows in one direction from the
sun to producers through several levels
of consumers, and
2) Chemicals cycle when inorganic
nutrients pass from producers through
consumers and returned to the
atmosphere or soil.
Nature of an ecosystem
• Only a small portion of energy and nutrients
made by autotrophs is passed on to
heterotrophs, and only a small amount is
passed to each succeeding consumer; much
energy is used at each level for cellular
respiration and much is lost as heat.
• Ecosystems are dependent on a continual
supply of solar energy.
• The laws of thermodynamics support the
concept that energy flows through an
Energy balances
Energy Flow
• The feeding relationships in an ecosystem are
interconnected in a food web.
Forest food webs
Food chain
Ecological Pyramids
• The shortness of food chains can be attributed
to the loss of energy between trophic levels.
• Generally, only about 10% of the energy in one
trophic level is available to the next trophic level.
• This relationship explains why so few carnivores
can be supported in a food web.
Ecological pyramid
Global Biogeochemical Cycles
• All organisms require a variety of organic and
inorganic nutrients.
• Since pathways by which chemicals cycle
through ecosystems involve both biotic and
abiotic components, they are known as
biogeochemical cycles.
• Biogeochemical cycles often contain reservoirs,
such as fossil fuels, sediments, and rocks that
contain elements available on a limited basis to
living things.
• Nutrients flow between terrestrial and
aquatic ecosystems.
Model for chemical cycling
The Water Cycle
• In the water, or hydrologic cycle, the sun’s
rays cause fresh water to evaporate from
the oceans, leaving the salts behind.
• Vaporized fresh water rises into the
atmosphere, cools, and falls as rain over
oceans and land.
• Precipitation, as rain and snow, over land
results in bodies of fresh water plus
groundwater, including aquifers.
• Water is held in lakes, ponds, streams,
and groundwater.
• Evaporation from terrestrial ecosystems
includes transpiration from plants.
• Eventually all water returns to the oceans.
• Groundwater “mining” in the arid West and
southern Florida is removing water faster
than underground sources can be
The water cycle
The Carbon Cycle
• In the carbon cycle, a gaseous cycle,
organisms exchange carbon dioxide with the
• Shells in ocean sediments, organic
compounds in living and dead organisms,
and fossil fuels are all reservoirs for carbon.
• Fossil fuels were formed during the
Carboniferous period, 286 to 360 million
years ago.
The carbon cycle
Carbon Dioxide and Global
• The transfer rate , the amount of a nutrient
that moves from one compartment of the
environment to another, can be altered by
human activities, allowing more carbon
dioxide to be added to the atmosphere.
• Atmospheric carbon dioxide has risen from
280 ppm to 350 ppm due to burning of fossil
fuels and forests.
• Besides CO2, nitrous oxide and methane are
also greenhouse gases.
• Similar to the panes of a greenhouse, these
gases allow the sun’s rays to pass through
but hinder the escape of infrared (heat)
• Buildup of more of these “greenhouse
gases” could lead to more global warming.
• The effects of global warming could include
a rise in sea level, affecting coastal cities,
and a change in global climate patterns with
disastrous effects.
Earth’s radiation balances
The Nitrogen Cycle
• Nitrogen makes up 78% of the atmosphere
but plants are unable to make use of this
nitrogen gas and need a supply of
ammonium or nitrate.
• The nitrogen cycle, a gaseous cycle, is
dependent upon a number of bacteria.
• During nitrogen fixation, nitrogen-fixing
bacteria living in nodules on the roots of
legumes convert atmospheric nitrogen to
nitrogen-containing organic compounds
available to a host plant.
• Cyanobacteria in aquatic ecosystems and
free-living bacteria in the soil also fix
nitrogen gas.
• Bacteria in soil carry out nitrification when
they convert ammonium to nitrate in a twostep process: first, nitrite-producing bacteria
convert ammonium to nitrite and then
nitrate-producing bacteria convert nitrite to
• During denitrification, denitrifying bacteria in
soil convert nitrate back to nitrogen gas but
this does not quite balance nitrogen fixation.
The nitrogen cycle
Nitrogen and Air Pollution
• Human activities convert atmospheric
nitrogen to fertilizer which when broken
down by soil bacteria adds nitrogen
oxides to the atmosphere at three times
the normal rate.
• Humans also burn fossil fuels which put
nitrogen oxides (NOx) and sulfur dioxide
(SO2) in the atmosphere.
• Nitrogen oxides and sulfur dioxide react
with water vapor to form acids that
contribute to acid deposition.
• Acid deposition is killing lakes and forests
and also corrodes marble, metal, and
• Nitrogen oxides and hydrocarbons (HC)
react to form photochemical smog, which
contains ozone and PAN
(peroxyacetylnitrate), oxidants harmful to
animal and plant life.
Acid deposition
• A thermal inversion, where these
pollutants are trapped under warm,
stagnant air concentrates pollutants to
dangerous levels.
• Nitrous oxide is not only a greenhouse
gas, but contributes to the breakdown of
the ozone shield that protects surface life
from harmful levels of solar radiation.
Thermal inversion
The Phosphorus Cycle
• The phosphorus cycle is a sedimentary
• Only limited quantities are made available to
plants by the weathering of sedimentary
rocks; phosphorus is a limiting inorganic
• The biotic community recycles phosphorus
back to the producers, temporarily
incorporating it into ATP, nucleotides, teeth,
bone and shells, and then returning it to the
ecosystem via decomposition.
The phosphorus cycle
Phosphorus and Water Pollution
• Phosphates are mined for fertilizer
production; when phosphates and nitrates
enter lakes and ponds, eutrophication
• Many kinds of wastes enter rivers which
flow to the oceans; oceans are now
degraded from added pollutants.
• If pollutants are not decomposed, they may
increase in concentration as they pass up
the food chain, a process called biological
Chapter Summary
• An ecosystem includes autotrophs that
make their own food and heterotrophs that
take in preformed food.
• Solar energy enters biotic communities via
photosynthesis, and as organic molecule
pass from one organism to another, heat is
returned to the atmosphere.
• Chemicals cycle within and between
ecosystems in global biogeochemical
• Biogeochemical cycles are gaseous
(carbon cycle, nitrogen cycle) or
sedimentary (phosphorus cycle).
• The addition of carbon dioxide (and other
gases) to the atmosphere is associated
with global warming.
• The production of fertilizers from nitrogen
gas is associated with acid deposition,
photochemical smog, and temperature
• Fertilizer also contains mined phosphate;
fertilizer runoff is associated with water
• Certain pollutants undergo biological
magnification as they pass through the
food chain.
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