Transcript Document

Ecosystems & biodiversity
Feedbacks through biota
Chapters 9, 13, & 18
Evolution of life & biogeochemistry
• Biota mediate the cycles of many elements that cycle between
various reservoirs with different residence times
• Biology – transfer energy through food chains/webs
• Geochemistry – lead to steady state systems far from chemical
equilibrium
• Records on Earth – atm composition, sediments
• Diversity of microbial metabolisms
– Higher organisms mostly aerobic
– Present day cycles can deviate from rock record
Complex processes cycle elements
among different reservoirs
- involves biology
- has geochemical consequences
Different communities store and cycle
material and energy differently
- diversity differences
- different biogeochemical results
- different storage of biomass
What it means to be Alive
•
Auto conservation
– The main function of every living organism is making sure that it can continue it's
existence.
•
Auto reproduction
– Any living system can reproduce or proceeds from a reproduction.
•
Storage of information
– Each organism contains genetic information. This appears stored in DNA, and is
read and translated by proteins according to a universal genetic code, which is
common to all creatures.
•
Breathing-fermentation
– Every living being must have a metabolism that will transform energy and matter
taken from the environment into energy and compounds that can be used by the
different parts of the living organism.
•
Stability
– Through the creation and control of it's own internal environment, all creatures
remain stable in front of the perturbations of the external world.
•
Control
– The distinct parts of an organism contribute to the survival of a group and,
therefore, to the conservation of it's identity.
•
Evolution
– The mutations in the hereditary material and natural selection permit the
perfection, adaptation and complexity of living beings. For many, life is a mere
product of evolution.
•
Death
What it Means to be Alive
• Capable of transforming
energy
– Photosynthesis and respiration
• For homeostasis
• For growth
• For reproduction
• Life and the second law of
thermodynamics
– Transformation of energy
leads to disorder
– Life requires the maintenance
of order
– Homeostasis, growth and
reproduction occur at the
expense of increased disorder
(entropy) of the whole system
• Life is characterized by:
– Cells
– Common metabolic pathways
– Common genetic code
• Living things include
–
–
–
–
Bacteria
Algae
Plants
Animals
• Non-living things include
– Viruses
– Prions
– Organic molecules
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•
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Proteins and amino acids
Nucleic acids
Fats
Sugars
The Origin of Life on Earth
• The earth is 4.6 billion years
old
• Life on earth has existed for
more than 3.8 billion years
• All life requires liquid water
• The basic molecules of life
can be made from a
primitive reducing
atmosphere
– Methane, ammonia water,
hydrogen, and energy
– No oxygen - anoxic
The Origin of Life
• Growing evidence supports the idea that the
emergence of catalytic RNA was a crucial early step.
How that RNA came into being remains unknown.
• Catalysts are essential for the chemistry of life
• RNA acts as a genetic ‘messenger’ in modern cells
• The ‘Central Dogma’ of Modern Biology
– DNA makes RNA, RNA makes protein, proteins are the
common biological source of enzymatic catalysis
Two Critical Steps in the Origin and
Evolution of Life
• Organic catalysis and self-replication
– Catalytic RNA?
• Photosynthesis
– A mechanism for capturing energy and converting
it into food
Structure of the biosphere
• Hierarchy
– Species – reproductive group
– Population – members of a single species that
live in a given area
– Community – assemblage of interacting species
in a given area
– Biome – a region with a characteristic plant
community (e.g. rainforest, desert)
– Ecosystem – a community of animals, plants,
microbes, etc, together with the physical
environment that supports it
Structure of the biosphere
• Ecosystem
– Assemblage of organisms that interact with each other and the
environment
– Some can be defined by their environment (rain forest, desert)
• Interactions between organism and environment
– Daisyworld example
• Alteration of environments can impact ecosystems
– ENSO events – food web effects
– Cessation of upwelling – food web effects
• Physiological versus ecological growth optima
– Not always the same – optimal niche versus realized niche
– High productivity oceanic regions are often high latitude or upwelling
– Related to ocean physics and nutrient availability rather than growth
optima; compromise between mixing (promoting nutrient availability) and
temperature (promoting stratification)
Fig. 9-1
Environments
• Many ecosystems defined by the
environment
• Organisms subdivide that environment
• Organisms that share habitats find niches
within those habitats
– Strategies and living habits
Productivity
• High productivity
– Upwelling; low latitudes
• Low productivity
– Central gyres; downwelling
ENSO
La Nina
Upwelling – productive
No upwelling - collapse
El Nino
Western
Fig. 15-13 & 14
Productivity
• Nt = Noekt
• Add resource limitation to set limits to
population size (Nt)
• Oh, and life pollutes…
Phytoplankton growth in the ocean
0
Temperature optima in the lab are 20-25 deg
Highest productivity at higher latitudes!
Ecological growth optimum is 8 deg C – due to ocean physics and nutrient availability
Phytoplankton productivity
• Related to physics, light, & nutrient supply
• If surface waters are too warm, water
stratifies & limits nutrient resupply from
bottom waters
• High turbulence increases mixing up of
nutrients
• Compromise between nutrients & temp
Light
• On land, photosynthesis proceeds just above
ground level
• In water, communities may be vertically
stratified
• In the water, photosynthesis proceeds to
considerable depths, depending on
– Water clarity
– Sun angle
– Sea state
Light
• Unlike the atmosphere, water attenuates light,
especially green and red
• The depth to which light penetrates depends on the
amount and nature of dissolved and suspended
constituents
• Oceanic waters contain few particles and are blue
• Coastal waters contain high phytoplankton
populations and are green
• Estuarine waters contain lots of suspended
sediments and look brown
• Light penetrates
deepest in oceanic
waters
• Blue light
penetrates best
• Red light is rapidly
attenuated
• Light penetration is shallower in
plankton-rich coastal waters
• Phytoplankton absorb blue light for
photosynthesis
• Water absorbs red light
• Coastal ocean looks green
Light Penetration in Coastal Waters
Photosynthesis
• Depends on the amount of light up to
saturation
• Depends on the color of light – not all
photons are equivalent
• Most efficient with blue and red light, least
efficient with green light
Layers of
the ocean
defined by
light
Temperature
• Ocean temperature varies with
– Depth
– Latitude
• Temperature controls rate of chemical reactions
– Slower at low temperature because molecules carry less energy
• Fewer collisions
• Less energy per collision
– Metabolism is defined by chemical reactions
• Most organisms are ectothermic – don’t regulate body temperature
• Some organisms are endothermic – regulation of body temperature
requires
– lots of energy
– good insulation
Salinity
• Salinity can vary with rainfall and
evaporation
• Changes in salinity (up or down) can affect
metabolic function, energy consumption
and cell viability.
• Different organisms have very different
salinity tolerances
Marine Communities are Highly
Productive
Marine Communities Store Less
Organic Carbon and Turnover Rates
are Faster than Terrestrial
Communities
Ocean Productivity Observed from Space
Trophic Relationships
• Energy Transfer
• Primary Producers are
Autotrophs
– harvest sunlight
• Heterotrophs are
Consumers
– eat organic matter
The Trophic Pyramid:
A Model of Consumption
Food Webs Illustrate Complex Trophic
Relationships
Exploitation efficiency
• Autotroph – plants & microbes
– Photosynthesis or chemosynthesis
– Produce organic matter from inorganic C
sources
• Heterotroph – accelerate chem reactions to
gain energy
– Herbivores - ~ 20%
– Carnivores - ~ 0.2% (not very efficient at
converting food to biomass!)
Symbioses
• Mutualism – both organisms benefit
That’s biology but… biodiversity
• Linked to ecosystem health and stability
– Number of species per unit area or ecosystem
• Often think of deforestation
– Destruction of tropical habitats
Biodiversity
• Number of species
in a community
• Diversity indices
– Simpson diversity =
1 – [(proportion of
species A)2 +
(proportion of
species B)2 + …..]
Biodiversity over time
• Natural changes in diversity due to
evolution and extinction of species
• General increase in diversity over time
• Interupted by extinction events
– 26 my periodicity in extinction events?
– Extraterrestrial cause?
• Extinction is natural
– Over 90% of species that have evolved are
extinct
26 my periodicity
etc.
Figs. 13-4 & 13-10
Recent changes in biodiversity
• Present day rates exceed geological rates of
extinction
• Present day extinction is across the board – affects
many groups
• Other extinction events affected species within
particular groups – other groups survived
– Example is K-T extinction of dinosaurs; mammals and
plants survived to reradiate
• Modern extinction associated with spread of human
populations
– Over hunting/fishing
– Habitat destruction – deforestation & coral bleaching
Fig. 18-1 - Extinction of
large mammals and birds
corresponds to the spread
of human populations
Deforestation & biodiversity
• Poster child
• The tropics is the area of greatest rate of
species loss
• Concern for more than biodiversity
– Addition of CO2
– Loss of CO2 uptake mechanism
• Impact on regional climate
Deforestation and soil nutrients
• Distinct differences in storage of biomass &
nutrient cycling between temperate & tropical
forests
• Temperate forests have thick, rich topsoils
– Humus layer of organic detritus on top of subsoil
– Nutrients stored in soils
• Tropical soils are highly weathered (lots of rain)
– Lateritic clays depleted in nutrients
– Thin humus layer
– Nutrients stored in biomass
Tropical above ground
storage of biomass & nutrients
Model results – decrease forest cover, increase albedo,
decrease winter temperatures, increase sea ice,
increase albedo, decrease temperatures….
Deforestation and recovery
• Rainforests – loss of rainforest trees leads to
loss of nutrients & changes in the water
cycle
• Temperate forests recover because nutrients
retained in the soils
Deforestation & water cycle & climate
• Elimination of tropical rainforests disrupts regional
water cycle
– Minimizes evapotranspiration (source of H2O to atm)
– Decreases soil moisture and increases runoff
• Increases erosion rates
– Soils form slowly
– 200-1500 yrs to form 2.5 cm of topsoil from bedrock
• General circulation models to predict
– Net temperature increase
– Decrease in soil moisture
The water cycle of the Amazonian
rain forest
Tropical rain forests - high Net Primary Production but low
nutrient residence times (as compared to other biomes)
High recycling sustains high productivity
decreases
(change in albedo)
Decrease forest cover
Increase runoff
Decrease nutrient supply
Decrease forest cover
Decrease forest cover decreases
Increase albedo
Decrease net radiation
Decrease temp
Decrease evapotranspiration
Increase temperature
Decrease clouds
Increase temperatures
Biodiversity and deforestation in tropical
areas
• Half of the living species are found in rainforests
• Forest plants have medical value
– Treatment of diseases
• Forest plants have agricultural value
– Need genetic diversity for long-term health (Darwinian
evolution)
– Need variety to limit vulnerability to diseases and pests
– Modern agricultural practices limit diversities
– Centers of genetic diversity for crops come from areas
threatened by development, population pressures,
deforestation
– Seed banks
Biodiversity and ecosystem stability
• Relationship is complex
– In some settings environmental stability leads to high
diversity
– In others, high diversity is thought to result from
disturbances of intermediate frequency and intensity
• How does loss of biodiversity impact ecosystem?
– Remove enough species and ecosystem collapses (removal
of predators; invasive species)
– May be that some species aren’t necessary – system
maintained by a few keystone species
Causes of deforestation
• Social, political, and economic drivers
• Economic arguments – people and countries
need hard currency (Nepal)
– Motivation not to
– Who will bear the costs of not exploiting
resources?
• Earth will recover, will humans survive?
Biodiversity over time - geologic
• Natural changes due to new species
evolving and extinction
• General increase that should theoretically
occur over time
– Extinction events – cleans the slate
– Natural extinction – 90% of species ever alive
are extint now
26 my periodicity
etc.
Fig. 13-4
Darwin’s main points
• In any population, more offspring are produced
that can survive to reproduction
• Genetic variation occurs in populations
• Some inherited traits increase the probability of
survival
• Bearers of those traits are more likely to leave
offspring to the next generation – those traits
accumulate
• Environmental conditions determines which traits
are favorable
Biogeochemical Cycles
• Elements cycle between organisms, the water, the
sediments and the land
• The maintenance of life requires continued access to
these elements
• Only a few are of biogeochemical significance
• C, N, P, Si, Fe
• Elemental ratios in living organisms are fairly
constant
• Redfield Ratio C:N:P 106:16:1
The Elements of Life
• In addition to energy, life
requires certain material
substances
• All organisms require 23
basic elements
• Availability of these
elements can limit growth
and survival
The Carbon Cycle
• A basic building block of life
• Largest of all biogeochemical cycles
• Availability rarely limits marine productivity
– Seagrasses are important exceptions
The Nitrogen Cycle
• N is a critical component of proteins, nucleic
acids and pigments (e.g. chlorophyll)
• Traditionally viewed as the most limiting
nutrient in the sea
• Liebig’s Law of the Minimum –
– Growth is limited NOT BY THE TOTAL
RESOURCES AVAILABLE but by the single
resource in shortest supply,
The Nitrogen Cycle
• Free N2 comprises 80% of the atmosphere
– Not generally biologically available
– Biological availability requires FIXATION
– For most of earth’s history, N fixation was mediated by
small microbes – cyanobacteria - and was generally in short
supply
– Cyanobacteria are photosynthetic but N2 fixation is
inhibited by oxygen. How can this be?
– Humans now use industrial processes to FIX more N2 than
nature on an annual basis
– Most of the anthropogenically fixed N ultimately winds up
in our rivers, estuaries & coastal waters where it promotes
HARMFUL ALGAL BLOOMS
The Nitrogen Cycle
The Phosphorus and Silicon Cycles
• Phosphorus is necessary for nucleic acids
(DNA, RNA, ATP etc.), bone, teeth and some
shells
• Silicon (NOT silicone) is used by diatoms and
radiolarians to make their skeletons
P and Si cycles involve 3 loops
• Most rapid cycle involved daily feeding, death
and decay of organisms
• Some organisms fall below the pycnocline
where it can take hundreds of years to return to
the sunlit portion of the sea
• Some organisms get buried in the sediments; it
may take millions of years –and tectonic
activity to return the Si to the surface water
Iron and other trace metals
• Used in minute quantities
• Long thought to be in excess supply
– Iron is very abundant but not very soluble
– Iron ships and sampling gear contaminated early samples
• John Martin first showed that iron could limit ocean
productivity
• High nutrient – low chlorophyll (HNLC) areas limited by
iron
– Subarctic Pacific
– Equatorial Pacific
– Antarctic convergence
Continental dust is a major source of
iron to ocean waters
HNLC areas are far from iron inputs
from land runoff or continental dust