Transcript Lecture 06 Ecosystem Productivity and Nutrient Cycling

Energy and Living Things
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Outline
Energy Sources
Solar-Powered Biosphere
Photosynthetic Pathways
Using Organic Molecules
Chemical Composition and Nutrient
Requirements
Using Inorganic Molecules
Energy Limitation
Food Density and Animal Functional
Response
Optimal Foraging Theory
Energy Flows Through Living Systems
Heterotrophs
Plants=
Autotrophs
• Autotroph: ‘self feeder’ - an organism that
can gather energy (usually from light) … to
store in organic molecules
– Photosynthesis
– chemosynthesis
• Heterotroph: An organism that must rely
on other organisms to capture light energy
… must rely on breakdown of organic
molecules produced by an autotroph as an
energy source
– Classified by trophic level
Law of the minimum- ecosystems
must adapt to it.
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Light in ocean floor
Water in desert
Heat on mountain top
Matter is also limiting, thus have limiting
nutrients that allow for life
Flow of energy and nutrients
• Photosynthesis
• Metabolism
Photosynthesis
• Capture and transfer light energy to chemical
bonds
• Occurs in:
– Plants
– Algae
– Certain Bacteria
• Not a perfect process – some energy is lost entropy
How Photosynthesis Works
• Light strikes leaf
• Energy absorbed by
chemical pigments
• Absorbed energy drives
chemical processes to
convert CO2 into larger
molecules
– Energy absorbed in building
larger molecules, released as
they are broken down
Only certain Wavelengths of Light are Used in
Photosynthesis
• Light Energy Used = ‘Photosynthetically Active
Radiation’ or PAR
– How Much is absorbed: Number of light energy
(photons) striking square meter surface each second.
• Chlorophyll absorbs light as photons.
• Landscapes, water, and organisms can all change the
amount and quality of light reaching an area.
• Light not absorbed is reflected
– Some in PAR + all in green and yellow wavelengths
Wavelengths most
useful in driving
photosynthesis
Absorption
spectra of
chlorophylls
and
carotenoids
Wavelengths not
used - reflected
Fall color
• In many
plants
production of
chlorophyll
ceases with
cooler
temperatures
and
decreasing
light
• other
pigments
become
visible
C3 Photosynthesis
CO2 enters passively
so stomata have to be
open for long periods
of time
Why C3 Photosynthesis Doesn’t always
work out CO2 must enter though stomata
• stomata (sing., stoma)
are tiny holes on the
undersides of leaves
• CO2 enters and moisture
is released
• In hot, dry climates, this
moisture loss is a
problem
• Producers
Food Web
• Herbivores
– Green plants and algae
– Use solar energy to build
energy-rich carbohydrates
– Animals that eat plants
– The primary consumers
of ecosystems
• Carnivores
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Animals that eat herbivores
The secondary consumers of ecosystems
Omnivores are animals that eat both plants and animals
Tertiary consumers are animals that eat other carnivores
• Detritivores
– Organisms
that eat dead
organisms
• Decomposers
– Organisms that
break down organic
substances
Thermodynamics
 Total
amount of energy kept constant
 Energy can be converted
Transfer of Energy with
Ecosystems
• Board notes
• Three Feeding Methods of Heterotrophs:
– Herbivores: Feed on plants.
– Carnivores: Feed on animal flesh.
– Detritivores: Feed on non-living organic matter.
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Classes of Herbivores
Grazers – leafy material
Browsers – woody material
Granivores – seed
Frugivores – fruit
Others – nectar and sap feeders
– Humming birds, moths, aphids, sap suckers
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Herbivores
• Substantial nutritional chemistry problems.
– Low nitrogen concentrations – difficulty
extracting needed protein/amino acids from
source.
– Require 20 amino acids to make proteins ~ 14
are must come from diet
How do plants respond to feeding pressures
by herbivores?
• Mechanical defenses – spines
• Chemical defenses
– Digestion disrupting chemicals – tannins,
silica, oxalic acid
– Toxins – alkaloids
• More common in tropical species
How do animals respond?
– Detoxify
– Excrete
– Chemical conversions – use as nutrient
Carnivores
• Predators must catch and subdue prey size selection.
– Usually eliminate more conspicuous members
of a population (less adaptive).
– act as selective agents for prey species.
Adaptations of Prey to being preyed upon
• Predator and prey species are engaged in
a co-evolutionary race.
• Avoid being eaten – avoid
starving/becoming extinct
• Defenses:
– Run fast
– Be toxic – and make it known
– Pretend to be toxic
• Predators learn to avoid
Carnivores
• Consume nutritionally-rich prey.
– Cannot choose prey at will.
• Prey Defenses:
– Aposomatic Coloring - Warning colors.
– Mullerian mimicry: Comimicry among several species of
noxious organisms.
– Batesian mimicry: Harmless species mimic noxious species.
Mullerian mimicry: Comimicry
Batesian mimicry: Harmless
species mimic noxious species
Aposomatic Coloring - Warning colors
Detritivores
• Consume food rich in carbon and energy,
but poor in nitrogen.
– Dead leaves may have half nitrogen content
of living leaves.
• Fresh detritus may still have considerable
chemical defenses present.
Detritivores and decomposers
productivity
• Refers to the production of food
• Primary production = total gross primary
production
• Activity- Compare ecosystems p. 26
Optimal Foraging Theory
• Assures if energy supplies are limited,
organisms cannot simultaneously
maximize all life functions.
– Must compromise between competing
demands for resources.
• Principle of Allocation
• Fittest individuals survive based on ability
to meet requirements principle of
allocation
Optimal Foraging Theory
• All other things being equal,more
abundant prey yields larger energy return.
Must consider energy expended during:
• Search for prey
• Handling time
• Tend to maximize rate of energy intake.
• What would a starving man do at an all
you can eat buffet?
Optimal Foraging in Bluegill Sunfish
Cycles of matter
• Nitrogen
• Carbon
Nutrient Cycling and Retention
Chapter 19
Nitrogen Cycle
• Includes major atmospheric pool - N2.
– Only nitrogen fixers can use atmospheric
supply directly.
• Energy-demanding process.
– N2 reduced to ammonia (NH3).
• Once N is fixed it is available to organisms.
– Upon death of an organism, N can be released by fungi
and bacteria during decomposition.
Nitrogen fixation
Biological Nitrogen Fixation (BNF) occurs
when atmospheric nitrogen is converted to
ammonia by a pair of bacterial enzymes
N2
+ 8H+ + 8e− + 16 ATP → 2NH3 + H2 + 16ADP + 16 Pi
Microbes Denitrification NO3(nitrate) → NO2- → NO →
N2O → N2 gas
Nitrogen Cycle
Carbon Cycle
• Moves between organisms and
atmosphere as a consequence of
photosynthesis and respiration.
– In aquatic ecosystems, CO2 must first
dissolve into water before being used by
primary producers.
– Although some C cycles rapidly, some
remains sequestered in unavailable forms for
long periods of time.
Carbon Cycle
Animals and Nutrient Cycling in
Terrestrial Ecosystems
• Huntley and Inouye found pocket gophers
altered N cycle by bringing N-poor subsoil
to the surface.
• MacNaughton found a positive relationship
between grazing intensity and rate of
turnover in plant biomass in Serengeti
Plain.
– Without grazing, nutrient cycling occurs more
slowly through decomposition and feeding of
small herbivores.
Animals and Nutrient Cycling in
Terrestrial Ecosystems
Plants and Ecosystem Nutrient
Dynamics
• Fynbos is a temperate shrub/woodland
known for high plant diversity and low soil
fertility.
– Two species of Acacia used to stabilize
shifting sand dunes.
• Witkowski compared nutrient dynamics
under canopy of native shrub and
introduced acacia.
– Amount of litter was similar, but nutrient
content was significantly different.
– Acacia - N fixer
Biotic communities
Climate and weather