Transcript ecosystem

ECOLOGY
Part 2
What is “Ecology”?
The study of biological organization “at and above the level of
the organism”. (one definition)
Ecology
What are “levels of organization”?
Biosphere
Ecosystem
Community
Population
Organism
Organ
Tissue
Cell
Organelle
Molecule
Note: “species” is not on this list
2-7
Ecosystem
Community
Population 1
Abiotic Environment
Light, nutrients,
substrate, etc.
Pop 2
Pop 3 etc.
Organism (sp. 1)
2
3
Populations/Communities
Similar species can co-exist more readily if they
utilize different portions of shared niche axes
– have different niches (determined by traits)
Coastal wetland
So, an organism’s integrated traits (genes) allow success or
determine failure of a population in any particular ecosystem
Both the possibilities and limits for survival
Communities
What “organizes” biology above the level of the population?
Communities & Ecosystems - Primarily the interactions of
populations with each other and the abiotic environment
(another definition of ecology).
Most common interaction? Eating.
In economics – “follow the money”, in ecology, “follow the food”
Communities
Community – the array of
interacting populations in a
place.
Major insight – to a
large extent, the
question is
- who eats who?
Communities are analyzed
by the network of eating
interactions, ultimately the
overall food web or
trophic structure.
2-16/2-18 A marine food web
Species Interactions classified by pairwise effects – (+,-, 0)
Competition (-/-) use same resource, depletion or combat
Predation (+/-) one eats(kills) the other
Parasitism (+/-) one eats (partially) the other
Mutualism (+/+) each benefits from the other
Commensalism (+/0) hard to verify, e.g. epiphytes
(0,0) meaningless, seldom see (-,0) why?
Eating still the key underlying theme – competition,
predation, parasitism obvious.
Even mutualism often
about eating (or not being
eaten) – usually involves a
trade (food, defense)
Plants – major mutualisms
- nutrition – myccorhizae
(fungus), nitrogen fixers
(bacteria), trade nutrient and
carbohydrate
4-4/4-2
Flowers – mutualism?
Angiosperm flowers attract
insects with “rewards”, often
food (nectar, pollen), gain
reproduction
In some flowers, the rewards
are questionable
Many mutualisms reveal these
kinds of subtle “antagonisms”
when studied closely.
Communities
A food web consists of a
complex set of interconnected
transformations. Similar in
this way to a biochemical
pathway.
Communities
A food web consists of a
complex set of interconnected
transformations. Similar in
this way to a biochemical
pathway.
One important difference is,
there is currently no evidence
that natural selection operates on
the overall food web as it does
on whole organisms. A
community is more like a “free
market” economy, structured
only by the interactions.
Communities are “assembled” by the component species
Note potential for “re-assembly”
Around my barn - Dillon Bustin
When the hound begins to howl
And I’ve not heard a hooting owl
When the chickens begin to squawk
That’s the time I’ll take a walk
Down in the cornfield see the deer
Each one chewing on a yellow ear
And every squirrel that’s ever been born
Wants to make a living off the little corn
That I get to my barn, get to my barnyard
Refrain: around my barn, around my barnyard
Could be the wind in the trees
Could be a rabbit or a groundhog sneeze
Eating the peppers in my garden spot
He’d better hope that I am not
All the milk that my milk cow makes
Gets drunk up by a long milk snake
You may not believe what I say is true
But he ain’t eating mice I’m telling you
Around my barn, around my barnyard
Out in my barn, out in my barnyard
Could be a cloud across the moon
Could be a fox or a sly raccoon
Coming down to make a meal
He don’t know the way I feel
Lindy tells me treat them like brothers
I told her let them eat each other
It’s what they done before I come
What they’ll do before I’m done
About my barn, about my barnyard
With my barn, done with my barnyard
You ask me what’s dirty trick
Skinny old weasel in among the chicks
And when he’s done gnawing their legs
An old skunk come and he’ll suck the eggs
Well I never expected life to be
Simple or easy or completely free
But I did not think that I’d have to fight
To get one drink or a single bite
That are left in my barn, left in my barnyard
Of food from my barn, food from my barnyard
Communities
Types of eating:
Herbivory – plant eating
Carnivory – meat eating
Omnivory – mixed diets
Detritivory – eating dead stuff
Photosynthesis – “sun eating”
Major insight – different food
webs share a general structure,
with photosynthesizers as the
foundation
The rest of the food web
depends on the
photosynthesizers
This led to the concept of ecosystem
Communities/Ecosystems
Simplified web – “food chain”
Photosynthesizers called
producers, herbivores &
carnivores called consumers
2-15/2-17
Ecosystem ecologists aggregate (simplify) webs
to focus on key dynamics and system properties
Ecosystems
Generalization called
attention to a major
component of the
ecosystem previously
ignored - decomposers
The unasked question:
where does all the dead
stuff go?
and incidentally – what
are plants eating?
Why do decomposers exist?
2-13/2-14
Ecosystems
The most general concept of
ecosystem includes decomposers
as main component
Also “chemicals”, or
nutrients (since this
is mostly food for
the producers)
Note the
difference in
emphasis
compared to the
food web
2-14/2-15
Ecosystems
This is a dynamic equilibrium
(outputs ≈ inputs)
Components may
stay fairly stable,
but…
Energy flows
through the
ecosystem, driving
Material cycles
within
Resource use by
individuals
(eating) drives
these dynamics
This is a basic picture of an ecosystem
Energy
Materials
Both energy and materials
are transferred together…
Heat
Consumers
Heat
Decomposers
Heat
Producers
…except here
Nutrients
Sun
To a decent first approximation, you can stick our kingdoms
into this basic picture of ecosystems
Animals &
Protists
Animals
Bacteria &
Fungi
Bacteria &
Fungi
Algae &
Plants
Cyanobacteria
Nutrients
Sun
Terrestrial (land-based)
Nutrients
Sun
Aquatic (water-based)
This suggests a deep connection between evolution and ecology
Ecosystems – nutrient cycling
Decomposers are a complex of
many species in an OM matrix
Terrestrial ecosystems - soil
Rock particles &
organic matter
Aquatic systems
Dissolved organic
matter (DOM) &
Sediments
Soils & sediments can take
100s of years to develop
7-A/2-22
Ecosystems – nutrient cycling
What are nutrients?
In addition to CO2, light and water, producers also need various
other essential elements – Nitrogen (N), Phosphorus (P),
Potassium (K), Magnesium (Mg), Calcium (Ca) and various
others (Iron, Boron, Nickel, etc.) – Why?
What controls nutrients?
Chlorophyll
Ecosystems –nutrient cycling
Nutrient Cycling
Reservoirs. Most elements originally come from rock – the
earth’s crust, via weathering. Except Nitrogen - atmosphere
In most systems, most elements used by producers come from
decomposition which recycles the nutrients.
Nutrients have both long and
short term cycles
Short term (fast) – community to
dead organic matter (detritus;
OM) via decomposition to the
nutrient pool back to community
Long term (slow) – from
system to reservoir, back to
system
Consumers
Decomposers
OM
Producers
Nutrients
Reservoir
Ecosystems – nutrient cycling
In addition to water and carbon cycles, life creates cycles
within ecosystems of essential nutrients for producers
Phosphorus cycle is typical of most elements – rock reservoir,
organic matter derived available pool (also K, Ca, Mg, etc.)
Consumers
Decomposers
OM
Producers
Nutrients
Reservoir
2-22/2-28
Ecosystems – nutrient cycling
Nitrogen Cycle
Reservoir – N2 gas in atmosphere – 79%
Nitrogen fixation (certain bacteria) – converts N2 to organic form
energetically expensive
Decomposition releases nitrogen to available
forms (ammonium (NH4) and nitrate (NO3))
Producers take up available N so convert it back to organic
Nitrogen – completing the short cycle
Consumers
Decomposers
OM
Producers
Nutrients
Reservoir
N2 => OrgN => Available N
Ecosystems – nutrient cycling
Some bacteria use NO3 for energy, releasing N2 gas –
Denitrification. This is the cause of our N2 atmosphere
Percent Composition of the Atmosphere
CO2
O2
N2
Venus
96.5
trace
3.5
Mars
95
0.13
2.7
Earth
(w/o life)
98
0.0
1.9
Earth
(w/ life)
0.03
21
79
Consumers
This creates the longer cycle
Decomposers
OM
Producers
Nutrients
N2 => OrgN => Available N => N2
Reservoir
Ecosystems – nitrogen cycling
Consumers
Decomposers
OM
Producers
Nutrients
Reservoir
2-21/2-27
Ecosystems – nutrient cycling
Consumers
These nutrient cycles can be added to the water
and carbon/oxygen cycles covered earlier.
Decomposers
OM
Producers
Nutrients
Reservoir
2-20/2-26
photosynthesis
O2
CH2O
CO2, H2O
respiration
Together they describe the global fluxes of major
materials regulating ecosystem production
2-19/2-25
Ecosystems
Trophic Structure – The energy pyramid
Energy flows through the ecosystem
– from sun to space
Heat
Consumers
Energy is transformed by
photosynthesis from light to
Heat
chemicals (e.g., sugar)
Producers
Energy of chemicals is
transformed from producers to
consumers and to decomposers Sun
Heat
Decomposers
Nutrients
Energy is lost in all transformations as heat, generating EM waves
-Respiration (can be >90% of energy taken in)
-The energy transformations are not 100% efficient
Ecosystems - energy
The flow of energy “up”
is a diminishing one
Only a portion of energy
flowing into a trophic
level is transferred to the
next higher level.
Ecological Efficiency
about 10% (2-40%)
This limits trophic levels
to 4 or 5
2-17/2-19
Ecosystems
Primary Productivity
Ecosystems depend on producers for energy
Primary productivity is variable throughout the world
What controls this variability?
Global chlorophyll levels –winter 2004
Ecosystems - productivity
Net Primary Productivity (NPP)
= Gross Primary Productivity
(GPP) – Respiration (R)
NPP measures the ecosystem’s
capacity to support life (producers,
consumers, decomposers)
Units: kcal/m2/year
energy/area/time
Ecosystems - productivity
2-18/2-21
Ecosystems differ in NPP – area of systems not shown (e.g., ocean)
Why?
Biomes
Globally, there is a strong
correlation between NPP,
total plant biomass, and
precipitation.
We know that NPP is
dependent on temperature,
water, light, CO2 and many
nutrients.
Why is water so important?
Biomes
How plants work:
Leaf – light, CO2
Root – water, nutrients
But – water is lost in taking up CO2
more water = more CO2
And – water increases decomposition rate in soil
more water = more nutrients
Result: Water is both a resource and a controller of CO2
and nutrients. More rain has several benefits.
Temperature?
higher temp = more water lost per C
lower temp = shorter growing season (less liquid water)
air
soil
Biomes
In general: NPP controlled by light and water.
Light is relatively un-varying; water is variable
Variation in NPP primarily due to water
Biomes
Biomes
So precipitation and temperature are the
master controllers of plant production (NPP)
Distribution of
climates.
Precipitation and temperature = climate
Biomes
Climate controls NPP
Distribution
of
chlorophyll
Biomes
“niche diagram”
3-6/3-7
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Ecology summary
The biosphere consists of diverse linked ecosystems
Eating by individual organisms, including
photosynthesis, drives primary production, trophic
structure, and decomposition. The ‘balance of
nature’ reflects a balance of conflicting interests of
individuals.
Ecosystems consist of 4 main components:
producers, consumers, decomposers, nutrients. Fit
of kingdoms to these compartments suggests a deep
connection of evolution and ecology.
Energy flows from the sun through the ecosystems
and into space, powering materials (elemental)
cycles within ecosystems.
In terrestrial systems, variation in climate controls
variation in NPP, and therefore biome distribution.
End Ecology
End Ecology