Transcript Understanding Our Environment

Chapter 25
Lecture Outline
Ecology
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Outline

Plants and the Environment

Life Histories

Natural Cycles

Succession

The Impacts of Humans on Plant Communities

Global Warming

Erosion

Aquifer Depletion

Loss of Biodiversity

At the Regional Level

Restoration of the Land
Plants and the Environment

Ecology - Involves the relationships of
organisms to each other and to their
environment
• Determines whether or not a species or individual
member of a species can survive and reproduce
in a particular habitat

Environment of each habitat determined by
biotic (living) and abiotic (nonliving) factors.
• Biotic - Other organisms in habitat
• Abiotic - Wind, rain, sunlight, soil, temperatures
Plants and the Environment

Populations - Groups of individuals of the
same species
• May vary in numbers, in density, in genetic
diversity and in total mass of individuals
• Ways to investigate populations:
–
Count number of individuals
–
Estimate population density - Number of individuals per
unit volume
–
Calculate biomass - Total mass of living individuals
present
Plants and the Environment

Plant community - Unit composed of all
species of plants in a given area
• If include other organisms = biotic community
• Within a region, similar environments have
similar species composition.
• However, each species distributed according to
own responses to changes in physical and biotic
environment.
• Species composition of a community determined
by local availability of species, by unique
historical events, and by chance.
Plants and the Environment

Plant community
• Practical reasons to analyze and classify plant
communities (vegetation maps):
–
Land-use planning
–
Natural resource management
–
Biological conservation
–
Landscape restoration
–
Analyze changes in vegetation over time
–
Infer qualities of environment
Plants and the Environment

Ecosystems - Communities and their
physical environments, which interact and
are interconnected by physical, chemical
and biological processes
• Distribution of a plant species in an ecosystem
controlled mostly by temperature, precipitation,
soil type, and effects of other organisms.
–
Mineral content of soil
–
Competition for resources
–
Herbivory
–
Dispersal by animal community
–
Pattern of available water
Plants and the Environment

Ecosystems may be sustained entirely through
photosynthetic activity, energy flow through food
chains, and nutrient recycling.

Producers - Photosynthesize and store produced
energy
•

Primary consumers - Feed on producers
•

Cows, caribou, caterpillars
Secondary consumers - Feed on primary consumers
•

Plants, algae
Tigers, toads
Decomposers - Break down organic material to forms
that can be reassimilated by producers
•
Bacteria, fungi
Plants and the Environment

Ecosystems:
• Producers and
consumers
interact, forming
food chains or
food webs.
–
Determine flow
of energy
through different
levels
Plants and the Environment

Ecosystems:
• Trophic efficiency - Percentage of available energy
actually transferred from one trophic level to next
–
Available energy
to secondary
consumers
quickly drops off.
–
Sharp reduction
in numbers of
individuals and in
total mass at
each level of food
chain
Plants and the Environment

Interactions among plants, herbivores and other
organisms:
• Allelopathy - Production of chemicals that inhibit growth
of other plants
• Phytoalexins - Chemicals that kill or inhibit disease fungi
or bacteria
• Some bacteria and fungi limit plant growth by producing
inhibitory compounds.
• Some plants do not produce chlorophyll and depend on
plant hosts for energy.
• Plants have mutualistic relationship with mycorrhizal
fungi.
• Herbivores and plants involved in co-evolution.
Plants and the Environment

Association between
Acacia and ants:
• Ants live in hollow
thorns.
Special
bodies at
leaflet tips
• Ants feed on sugar,
fats and proteins
from petiolar
nectaries and from
special bodies at
tips of leaflets.
• Ants attack other
organisms that
come into contact
with plant.
Hollow thorns
Life Histories

A species life history is composed of traits that
control its survival and reproduction.
• Big bang reproduction - Devote all resources to growth for
most of life until favorable conditions and then energy goes
into single reproductive burst
–
Desert agave plants
• Repeated reproduction - Produce seeds throughout lifetime
–
Most trees
• Annuals - Grow, reproduce and then die at end of season
• Biennials - Grow for one year, reproduce second year and
die after seeds produced
• Perennials - Produce vegetative structures that survive for
many years
Life Histories

Life histories also described in functional terms:
• Habitats with low stress and little disturbance select
for traits that confer competitive advantage:
–
Large, persistent, fast growing, slow to reproduce
• Habitats with high stress, but little disturbance select
for stress tolerance:
–
Small, slow growing, limited reproductive ability, do not
respond to nutrients
• Habitats with low stress, but substantial disturbance
select for weedy traits:
–
Fast growing, small, annual, reproduce quickly
Life Histories

Phenology - Timing of crucial life events:
germination, bud burst, flowering, seed
production
• Photoperiod or light quality trigger germination
and flowering in some species.
• Growth rates controlled by available moisture and
temperature.
–
Effect of global warming
Natural Cycles

The water cycle:
• Earth’s water is constantly being recycled; total
amount remains stable.
–
98% of water in oceans, rivers, lakes.
–
Remaining water in living organisms, glaciers, polar ice,
water vapor and soil.
–
Rainfall percolates down through soil to water table, while
water is evaporated from bodies of water and is transpired
by plants.
–
Water vapor rises into atmosphere, condenses, and falls
back to earth in the form of rain, snow and hail.
–
Water cycle disrupted by humans.
o
Aquifer depletion, creation of reservoirs, irrigation, global
warming
Natural Cycles

The water cycle:
Natural Cycles

The carbon cycle:
• Plant life uses CO2 for photosynthesis.
–
CO2 = 0.038% of atmosphere.
• Respiration from all living things replace CO2.
–
As much as 90% produced by bacteria and fungi.
• Burning of fossil fuels significantly increases amount
of CO2 in air.
–
C3 plants increase growth with increased CO2 levels, but
C4 plants do not.
o
–
May give C3 plants competitive advantage and effect C4
crops
Oceans become more acid, making shelled organisms
vulnerable.
Natural Cycles

The carbon cycle:
Natural Cycles

The nitrogen cycle:
• Most nitrogen in living organisms is in protoplasmic
proteins of cells.
• Nitrogen in air unavailable to plants and animals.
• Most of nitrogen supply of plants derived from soil in
form of inorganic compounds and ions taken up by
roots.
–
Nitrogen-fixing bacteria convert nitrogen from air to ammonia
or other nitrogenous compounds.
o
Some plant species, particularly legumes, produce root
nodules in which these bacteria multiply.
• Constant flow of nitrogen from dead organisms into
soil and from soil back to plants
Natural Cycles

The nitrogen cycle:
Natural Cycles

The nitrogen cycle:
• Large amounts of nitrogen leach out of soil by erosion
of topsoil.
• Nitrogen lost by crop harvests.
• To offset loss, nitrogenous fertilizers added to
artificially increase soil nitrogen content.
–
Large amounts of energy expended to produce
inorganic fertilizer, with much lost by erosion.
–
If organic matter not added to soil at same time as
inorganic fertilizers added, then hardpan soil created.
Succession

Occurs wherever there has been disturbance of
natural areas
• Initially no signs of life
• Living organisms appear and alter environment as they
carry on metabolism and reproduction.
• Accumulation of wastes, dead organic material and
inorganic debris and other changes favor different
species.
• These, in turn, alter environment until further changes in
species composition occur.
• Communities are constantly changing in response to
array of disturbances.
–
May help to enhance species diversity
Succession

Primary succession - Involves formation of soil
in beginning stages
• On bare rocks and lava:
–
Tiny cracks permit plants to invade.
Fern spores blow into
cracks of bare lava
Succession

Primary succession:
• On bare rocks and lava:
–
Lichens and mosses become established on surfaces.
o
Contribute to organic matter and small amount of soil
builds up
–
Other species become established.
–
As soil buildup continues, larger plants take over.
–
Eventually vegetation reaches equilibrium of a stable
plant community = climax community.
o
Communities can differ in response to available
species and chance events.
Succession

Primary succession:
• In wet habitats - Ponds
and lakes left behind by
retreating glaciers, like
those in northern parts
of Midwestern states
–
Grow a bit smaller each
year as a result of
succession
–
Algae carried in by wind
or on feet of waterfowl.
–
Algae concentrated along water margins
and dead parts of algae sink to bottom.
–
Duckweeds form band around body of
water just offshore.
Duckweeds
floating on pond
Succession

Primary succession:
• In wet habitats - Ponds and lakes left behind retreating glaciers:
–
Peat mosses encroach and become dominant floating plants.
–
Water lilies and other rooted plants with floating leaves
become established.
–
Accumulating organic matter turns to muck.
–
Cattails and other plants take root in muck around edges.
–
Algae, duckweeds and peat mosses move farther out.
–
Surface area of exposed water diminishes.
–
Floating mat may form.
–
Sedges, herbaceous plants and shrubby plants move in.
–
Coniferous trees eventually grow across entire site and pond
or lake disappears.
Succession

Primary succession:
• In wet habitats - Stream-fed lakes and ponds:
–
Eventually become filled with silt and debris
–
Nutrient content (particularly nitrogen and phosphorus)
of water rises = eutrophication.
–
Eutrophication facilitates growth of algae and other
organisms.
–
Eutrophication accelerated by:
o
Sewage and other pollutants
o
Clearing trees from land - Land erodes, carrying soil
into water.
Succession

Secondary succession:
• May take place if soil is already present and there are
surviving species in vicinity
• On burned or logged land:
–
Grasses and other herbaceous plants become
established.
–
Followed by trees with widely dispersed seeds
–
Ending in climax community
• Fewer stages than primary succession
Succession

Fire ecology:
• Natural fires, started primarily by lightning, have occurred
for thousands of years.
• In the Western US, forest burned on average of every 6-7
years.
• Trying to eliminate fires
disrupts natural habitats.
• Fire plays role in
composition of forests.
–
–
Many species
repeatedly replace
themselves after fires.
Seeds of some species
must be exposed to fire
in order to germinate.
Succession

Fire ecology:
• Fires benefit grasslands, chaparral and forests by
converting accumulated dead organic material to
mineral ash, whose nutrients are recycled within
ecosystem.
• In prairies of Midwest, grasses better adapted to fire
than woody plants.
–
Some of North American grasslands originated and
maintained by fire.
–
Since fire has been controlled, many areas invaded by
shrubs.
The Impacts of Humans on Plant Communities

At the global level:
• Many problems are global in scope and have
long-lasting impacts.
–
Climatic changes
–
Stratospheric ozone depletion
–
Loss of biodiversity
• These problems traced to human activities.
Global Warming

Human activities are accelerating the rate at
which global warming is occurring.
• Glaciers shrinking.
• Permafrost disappearing.
• Sea levels rising.
• Greenhouse effect - Accumulation in atmosphere
of gases that permit radiation from sun to reach
earth’s surface, but prevent heat from escaping
back into space
• Gases involved - Carbon dioxide, methane and
others, such as chlorofluorocarbons
Global Warming – Carbon Dioxide

Carbon dioxide emissions from transportation and
burning fossil fuels are increasing dramatically.
• From 1990 to 2008 - CO2 emissions increased globally by
over 25%.
• Since1850, CO2 increased by 37%.
• Resulting unwelcome events:
–
Sea level rising, resulting in flooding
–
More extreme storms
–
Huge swings between wet and drought years
–
Rapidly expanding deserts
–
Dramatic drops in crop yields
–
Massive extinctions due to habitat changes
–
Expansion of vector-borne diseases
Global Warming – Methane

Methane is a greenhouse gas 23 times as potent
as CO2.

Produced by:
• Anaerobic bacteria in swamps and wetlands
• Animal digestive processes
• Wood-digesting organisms in guts of termites
–
Termites increasing as tropical rainforests are cleared.
• Melting of permafrost that releases trapped methane
Global Warming – Ozone Depletion

Methane gas and chlorofluorocarbons (CFCs)
(refrigeration and industry) - Broken down into
active compounds by sunlight at high altitudes
• Breakdown products destroy ozone in the
stratosphere.

–
Ozone provides natural shield against UV radiation.
–
Increased UV radiation increases skin cancers.
Halons (bromine-based), found in electronic
equipment, reported to be 3-10 times more
destructive than chlorofluorocarbons.
• Increased 20% per year between 1980 and 1986
Erosion

Wind and water remove productive soil and degrade
land.

Soil erosion is most significant limitation to
sustainable agriculture productivity.

Erosion removes topsoil faster than ever before.
• Takes away organic matter that makes soil fertile
• Ability to soak up water lost, so water runs off land,
increasing erosion.
• Runoff carries fertilizers and pesticides into streams and
lakes.

Direct result of overgrazing, clearing land for
urbanization and roads, and plowing
Aquifer Depletion

Overpumping of aquifers is probably the most
underestimated ecological problem in the world.
• Water pumped from underground for:

–
Irrigation - 70%
–
Industry - 20%
–
Homes - 10%
Demands for water is growing, while sustainable
yield of aquifers is fixed.
Loss of Biodiversity

When natural habitats are destroyed, a few species
may be able to adapt, but most are not capable and
ultimately perish.

Extinction rates have accelerated enormously over
past 50 years as many types of habitats have been
damaged or destroyed.

Keeping crops from succumbing to diseases often
depends on our ability to breed new diseaseresistant strains by tapping into gene pools of wild
relatives.

Loss of biodiversity in an ecosystem reduces
efficiency of production and nutrient use, and makes
the ecosystem less resistant to disturbances.
At the Regional Level

Acid deposition
• Burning fossil fuels releases sulfur and nitrogen
compounds into the atmosphere.
–
Chemical reactions with sunlight and rain convert the
compounds into nitric acid (HNO3) and sulfuric acid
(H2SO4).
–
Acid rain adversely effects living organisms.
o
Mycorrhizal fungi susceptible.
o
Trees die.
–
Alters soil fertility
–
Large amounts of nitrogen accumulate - Eutrophication
o
Increases soil fertility - Loss of plant species due to
competition
At the Regional Level

Water contamination
• Pollution in lakes and streams
–
Dumping toxic wastes
–
Runoff over polluted land
–
Pesticide spraying
–
Exhaust from aircraft and ships
–
Combustion of fossil fuels
• Ground-water supplies
–
Pesticides
–
Wastes from septic tanks
–
Fertilizers
At the Regional Level

Wetlands - Swamps, marshes, bogs, lagoons, river
margins, estuaries, floodplains
• Wetlands historically regarded as wastelands and routinely
drained and converted to agricultural land.
• One hectare of tidal wetland can perform same recycling
functions that wastewater treatment equipment capable of.
• Wetlands also:
–
Provide habitat for a
wide variety of wildlife
–
Purify streams and
lakes
–
Reduce erosion
–
Reduce flooding
At the Regional Level

Hazardous Waste
• Earlier generations routinely disposed of toxic
industrial wastes in a casual fashion.
• Even under increased regulations, serious
accidents and spills occur.
• At most solid waste dumps, it is now illegal to
dispose of almost any form of hazardous material.
• Promise for future - Genetically engineered
bacteria that can dismantle and render harmless
many types of wastes
At the Regional Level

Invasion of foreign species
• Often aggressive weeds
–
Reproduce quickly and crowd out native plants
–
Have no natural pests or herbivores, thus selection for
reproduction and less for defense, allowing
outcompetition of native plants
–
More phenotypic plasticity
–
More genetic differentiation (rapid evolution)
Restoration of the Land

Restoration ecology assumes that much of
environmental damage can be mitigated.
• Applies successional concepts to assist and
accelerate recovery process
Restoration ecology “is the means to end the
great extinction spasm. The next century will,
I believe, be the era of restoration in ecology.”
E. O Wilson
Review

Plants and the Environment

Life Histories

Natural Cycles

Succession

The Impacts of Humans on Plant Communities

Global Warming

Erosion

Aquifer Depletion

Loss of Biodiversity

At the Regional Level

Restoration of the Land