Transcript Ecology

Ecology
Introduction
• Ecology is the study
of interactions
between species and
with the non-living
environment.
Levels
• Population: all members of one species living in a given
area.
• Community: all living organisms (many different species)
living in a given area
• Ecosystem: the organisms in a given area along with the
non-living environment (rain, temperature, soil, etc.).
– large scale ecosystems are called biomes.
• Biosphere: the entire living world and its non-living
environment. The portion of Earth that supports life.
Roughly 2 miles below the surface to 6 miles above the
surface, over the entire planet.
Population Dynamics
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How a species is distributed and how it
changes over time.
populations can stay steady with time
or, they can undergo exponential
growth (a J-shaped curve, 1-2-4-8-1632-...). Ends up increasing very
quickly, but the rate can vary. The
doubling time of a population is the
critical parameter: How long it takes to
double the population size.
or, they can grow exponentially for a
while and then level off as limits are
approached (logistic growth).
carrying capacity : how many of a
species can a given area support. If
the population grows much past the
carrying capacity, it will have a die off.
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limiting factors: food, waste disposal,
predators, nesting/mating sites
Population Age Structure
• Relative number of
individuals of different
ages and sexes.
• How many are of
reproductive age vs.
before it or after it?
• predicts future structure:
groups move up in age
but relative sizes of
groups stays the same.
r-Selected vs. K-Selected Species
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Two fundamentally different strategies.
K-selected, or equilibrium species.
Produce a small number of offspring,
enough to replace each generation or
have a slow population growth rate.
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Lots of energy into each offspring.
Late maturity, many live to old age,
parents care for their offspring.
Population size stays near the carrying
capacity of the environment.
Humans and most other large
mammals are K-selected.
r-selected, or opportunist species.
Produce vastly more offspring than
can survive.
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If times are good, many will survive and
if times are bad only a few will survive.
Allows rapid exploitation of new
resources.
Small organisms, early maturity. cheap
to make, short life expectancy, no
parental care.
Mosquitoes, flies, many fish
Community Interactions
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A community is all the organisms that live is a
particular region.
Habitat: physical surroundings inhabited by a
community of organisms. The type of place
where they live. Influenced by temperature,
soil, rainfall, etc.
Niche. How an individual species makes a
living: What it eats, where it lives, how it
competes with other species. its food resources,
mating and offspring rearing resources,
defenses against predators and diseases.
– All species in a community share a common
habitat, but each species has its own niche.
– fundamental niche vs. realized niche.
Fundamental niche is what a species could
occupy in the absence of competition and other
constraints. realized niche is the niche the
species actually sues. realized niches change
over time as the species responds to pressures.
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The important thing about the niche is that it is
heavily influenced by interactions between
species.
Competition
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Different species often have
similar requirements for
resources, but never as similar as
members of the same species.
– competition within a species is the
driving force in microevolution:
individuals with more fit alleles
take over the population.
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competitive exclusion: each niche
can have only 1 occupying
species. Others will be driven out.
– the diagram: 2 species of
paramecium will grow well alone,
but one dies of if they are mixed.
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resource partitioning: dividing up a
niche as a method of co-existing
Predation and Parasitism
• predator-prey cycles: too
many predators means
prey population size
crashes, leading to
predator crash.
• successful parasites don’t
kill all of their hosts.
• large amount of
evolutionary change
driven by arms race
between predators (or
parasites) and prey
Evolutionary Arms Race
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Co-evolution: species influence
each other’s ability to survive and
reproduce.
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Camouflage: hiding from
predators
Defenses: painful sting, sharp
claws, bad taste.
Warning coloration: Warn the
predator about prey’s defenses so
it learns to stay away.
Mimicry as a tool: fool predators
by looking like another species
that is unpleasant or dangerous to
attack.
Of course, predators evolve ways
to get around these defenses:
sharper senses, chemical
detoxification.
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Mutually Beneficial Interactions
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Symbiosis: two species living together.
Some symbioses are mutually
beneficial and others (parasitism) are
not.
mutualism: both species benefit.
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Pollination of flowers is a good
example: the flower supplies nectar
(sugary nutrients) and the bee spreads
the flower’s pollen from one individual
to another. Many such interactions
between flowering plants and their
pollinators.
Nitrogen-fixing bacteria invade root
nodules on certain plants: the plants
get fixed nitrogen and the bacteria get
nutrients and shelter from oxygen,
which would kill them.
commensalism: one benefits, the other
neither gains nor loses.
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Birds nesting in trees. The birds
benefit, but the trees are unaffected.
Community Succession
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How does a community come into
existence?
Classical model of succession:
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a barren lifeless area starts out with a
few very tough species
These pioneer organisms improve
conditions so that other species can
move in.
a series of different communities takes
over in turn, each one improving
conditions for the following community
ends in a steady state, self-sustaining
climax community
Example:
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bare rock is colonized by lichens and
mosses. As they decay, they build up a
thin layer of soil.
Grasses and other small plants can
grow on this thin soil.
They in turn improve the soil, allowing
shrubs to grow.
These are followed by small trees which
shade the ground.
Other trees can grow well in the shade,
and they eventually take over.
More on Succession
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primary vs. secondary.
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Primary succession is taking over a
lifeless area: new land formed after
volcanic eruption or a glacier’s retreat.
Secondary succession is an area
whose climax community has been
disrupted, such as after a fire, or an
abandoned farm field. Starts with some
life already present. Many
communities require periodic fires to
stay healthy.
The environment doesn’t stay stable
forever: no climax community lasts
forever.
New species can radically alter a
community.
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grasslands are now farmlands
exotic species can take over an area:
zebra mussels, kudzu, chestnut blight,
starlings, and many more.
Energy Flow in Ecosystems
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Energy flow is a one-way process: from
high quality sunlight to low quality waste
heat. Energy is lost to heat at every
step.
Three basic actors:
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primary producers: convert energy from
sunlight into chemical bond energy in
sugars and other organic molecules.
Consumers: eat plants and each other.
Herbivores eat plants, carnivores eat other
animals.
Decomposers eat dead organisms.
Trophic levels. We can classify
organisms according to a hierarchy of
feeding relationships: who eats who.
How close an organism is to the primary
producers.
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Several levels of consumer, starting with
primary consumers (herbivores), then
several levels of predator, ending at a toplevel predator.
Similar levels among the decomposers,
starting with large decomposers such as
carrion-eating birds, then going down
through insects, fungi and finally bacteria.
Energy Pyramid
• Each level of
consumption above the
primary producers
involves about a 90%
loss of energy. This
implies that the
biomass at each stage
is 1/10 the biomass of
the stage below it.
• Different areas of the
world have different
levels of primary
productivity, which is
the rate at which
biomass accumulates.
Nutrient Cycles
• Unlike the one-way flow of energy, matter is continuously
recycled.
• Elements such as carbon and nitrogen often change
their state: for instance carbon can exist as organic
compounds, as carbon dioxide in the atmosphere, or as
calcium carbonate rock.
• Environmental reservoirs, especially geological
reservoirs, can hold large amounts of nutrients for very
long times
• Nutrients cycle very rapidly through living organisms
• We are going to talk about a few cycles, but every
element used in living organisms has a cycle.
Carbon Cycle
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Most of the carbon on Earth is found
in rocks, as calcium carbonate or as
coal and oil.
The next largest pool of carbon is the
oceans, where carbon dioxide is
dissolved in the water.
The atmosphere holds a significant
amount as carbon dioxide
Plants and cyanobacteria (especially
in the oceans) convert carbon dioxide
into organic carbon compounds.
Other organisms convert organic
compounds back into carbon dioxide.
Also, significant amounts of organic
carbon is converted to carbon dioxide
by humans burning fuel.
The carbon dioxide level is increasing
in the atmosphere. Since carbon
dioxide reflects heat back to the
surface (it’s a greenhouse gas), the
Earth’s temperature is slowly
increasing.
Nitrogen Cycle
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The largest pool of nitrogen is in the
atmosphere, which is about 80%
nitrogen gas.
Nitrogen is “fixed”, converted to a form
usable by living organisms, by
nitrogen-fixing bacteria. Several
different types of bacteria interconvert
three main forms of fixed nitrogen:
ammonia, nitrate and nitrite.
Lightning in the atmosphere fixes
some nitrogen.
Artificial nitrogen fixation: the industrial
production of fertilizer, is also an
important factor.
Most living organisms keep nitrogen in
fixed form. However, denitrifying
bacteria convert it back into nitrogen
gas.
Nitrogen fertilizer leaching out of fields
into ground water sometimes ends up
over-fertilizing bodies of water. This
leads to blooms of algae which use up
all the oxygen in the water and kill
most other organisms.
Hydrological Cycle
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Water is composed of oxygen and
hydrogen, but it can be considered as a
single cycle for the most part.
Water evaporates from the oceans and
other surfaces, then precipitates out as
rain or snow.
Some of it goes into the ground, but
eventually nearly all of it ends up in
bodies of water and ultimately the
oceans.
The primary problem: getting enough
fresh (non-salty) water to where it is
needed.
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One obvious solution: don’t live in the
desert.
However, water does decompose into
hydrogen and oxygen. Hydrogen gas is
very light, and at the top of the
atmosphere hydrogen gas is slowly
escaping into space.
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Because the Moon has less gravity, most
of its hydrogen has already escaped.
This lack of hydrogen is the primary
difficulty that any Moon colony will face.
Climate and Atmosphere
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Our climate is created by interactions of the
atmosphere, the oceans, and the land.
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Mountains create rain shadows: winds blowing
over them have to release their water before the
air can get over the top. Thus the far side is often
very dry: a major cause of deserts.
Monsoons: dry land in tropical places gets heated
by the sun. Warm air is low pressure, and this
draws in moisture-laden air from surrounding
oceans.
Bodies of water increase the amount of moisture
in the air and moderate temperature changes.
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the Sun heats the equatorial region more than the
poles.
the Earth rotates
land absorbs and gives up heat faster than the
oceans
It is colder in the winter and warmer in the summer
here in DeKalb than it is near Chicago
Chicago’s lake effect snow: warm moisture-laden air
meets cold air over the lake and water precipitates
out.
At our latitude (roughly 42o North of the equator)
the winds mostly blow from the west. Other
latitudes have different directions of prevailing
winds.
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Big effects on yearly temperatures and precipitation
Ocean Circulation
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Water in the oceans moves more slowly
than air in the atmosphere, but water
circulates much more heat throughout the
world.
Also, ocean currents move nutrients and
oxygen around the world.
The oceans are one continuous body of
water: Earth is more water than land.
The ocean waters flow in a continuous
conveyor belt powered by temperature and
salt content.
Warm, less salty water flows near the
surface.
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The Gulf Stream is part of this: warm water
from tropical America keeps Europe warm.
For instance, London England is a t51oN.
That latitude is about 700 miles north of us, a
very cold part of Canada.
As it reaches colder areas near Greenland
and Antarctica, it sinks down to become a
cold, saltier current.
The cold current picks up nutrients from the
ocean bottom. The oceans at high latitudes
(north and south) are very productive.
The warm current picks up oxygen from the
atmosphere and mixes it in with all ocean
water
Terrestrial Biomes
• We are now going to briefly examine several of the major
ecosystems on Earth, the biomes.
• Each biome has characteristic temperature and rainfall
levels, and corresponding characteristic plant life and
productivity.
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tundra
taiga (boreal forest)
temperate forest
grasslands
tropical rain forest
desert
Tundra
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tundra: cold, low lying.
Far north and high on mountains.
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going south, Antarctica is mostly
covered in ice, and the tips of South
America, Australia, and Africa are not
far enough away from the equator
Cold is the dominating factor.
Also dryness: less than 10 inches of
rain per year.
Dominated by lichens, low shrubs,
grasses. Low productivity, short
growing season.
Animals have adaptations to the cold,
including antifreeze in the bodily fluids
of some insects.
Massive blooms of mosquitoes and
biting flies in the summer.
Permafrost (permanently frozen
ground) just under the surface: leads
to soggy melted zone on top in
summer.
Taiga
• Also called “boreal forest”.
• Cold, less dry than tundra.
Some of it quite swampy even.
• Dominated by conifer forests.
– Not losing their needles
means thy can do
photosynthesis whenever it is
warm and sunny enough, not
just during a short growing
season.
– Needles covered with wax to
prevent drying out.
• A number of large mammals.
• Harsh in winter: animals either
migrate south or hibernate.
Temperate Forest
• Also called deciduous
forest, meaning that the
trees lose their leaves in
the winter.
• Our local biome,
stretching eastward to the
Atlantic Ocean.
• Hot in the summer, cold
in the winter, abundant
rainfall. Relatively long
growing season, but not
year-round.
• Many animal species.
And plants too. Very rich
habitat easily inhabited by
humans.
Grasslands
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Also called prairie, steppes, pampas,
veldt: different names for the same
phenomenon.
Drier than forested regions.
Plants need to survive droughts.
Fire is another problem: it’s dry.
Grasses survive fire much better than
trees because the growing point of
grasses is below the ground.
Stretches west from Illinois to the
Rocky Mountains, gradually getting
drier.
Dominated by grasses.
Largely converted to farming in many
areas, due to very fertile soil.
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Add some trees and shrubs =
savannah, dry shrublands, dry
woodlands
Tropical Rain Forest
• Heavy rain, lots of
vegetation.
• Continuous canopy of
trees, with very little light
reaching the ground.
• Soil is very poor: all the
nutrients are tied up in
living things.
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animal species never go
down to the ground
because there is so much
nutrition available up high.
• Very high species
diversity and productivity.
Desert
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Less than 10 inches of rain per
year—very dry.
Some are hot (such as the Sahara
or the Mohave in California) and
some are cold (such as the Gobi
desert in Mongolia).
Sparse vegetation, but it can grow
very quickly in response to rain.
Adaptations to saving water: thick
fleshy plant leaves, animals often
live underground, are most active
at night, and have urineconcentrating mechanisms.
– some use for crops: Imperial
Valley in California. But irrigation
is necessary and the soil tends to
get salty.
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Deserts usually have grasslands
next to them, as rainfall levels
increase.
Aquatic Ecosystems
• freshwater: lakes, rivers, wetlands
• estuaries: river meets ocean, giving water
that is less salty than sea water.
• oceans
• Freshwater ecosystems are often very
productive
Oceans
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Intertidal and coastal zones. The most
productive parts of the ocean are near the
shore, due to wave action carrying in fresh
nutrients and lots of sunlight
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Ocean surface: lots of sunlight, but little
nutrients in many places. Most productive in
polar regions.
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also coral reefs (secreted by cnidarian
animals) are very rich communities.
Photosynthesis by “phytoplankton” = algae,
seaweed.
Fed upon by “zooplankton”, mostly
crustaceans and the larval stages of ocean
invertebrates.
Fish and sea mammals and birds prey on
zooplankton.
Deep ocean: unlighted below 100 meters, so
all nutrients fall from above.
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Very low productivity. Almost all organisms
are decomposers or predators.
But, there are thermal vents that release high
energy inorganic compounds that Archaea
and other chemotrophs can use. These form
the basis of communities in the ocean deeps.