Lecture 10
Chapter 19
The biosphere is the sphere of life and organic activity that
extends from the ocean floor to 5 miles altitude into the atmosphere. Biosphere includes many ecosystems. These are open systems for solar energy and
matter.
HUMANS ARE THE EARTH’S MOST INFLUENTIAL BIOTIC AGENT.
There have been 6 major extinctions in the history of
earth. Number 5 was 65 million years ago
and the 6th is NOW. This is
the first one of biotic origin (What does that mean?)
Ecosystems have biotic and abiotic components. Energy from sunlight and from chemical
reactions (in caves and ocean floor.)
Ecosystems have subsystems:
biotic (producers, consumer and decomposers) and abiotic (flows of the gaseous,
hydrologic and mineral cycles.)
Communities can be identified by physical appearance, species
(and population), complexity of interdependence and trophic structure. Habitats have limits and required
nutrients. Species have trophic and
reproductive niches. No two species can
occupy the same niche in a stable community (competitive exclusion
principle.) Symbiotic relationships
create mutualism, allowing both species to survive. Parasitic relationships kill the host. Is humanity’s relationship with earth
symbiotic or parasitic?
Plants are the essential biotic component. They are the critical link between solar
energy and the biosphere. All life rests
upon the process of plants’ ability to capture sunlight. Vascular plants (270,000 known species) have
tissues and roots that transport nutrients and water. Only 20 species of plants provide 90% of the
world’s food supply.
Carbon dioxide, oxygen, water and sunlight enter and exit the
plant through the leaf surface (through pores called stomata.) Water leaves through the stomata- this works
like a straw. The process of photosynthesis
manufactures starches and sugars; releasing oxygen and producing food for the
plant. The results of this is
competition within the plant community for light.
Why is vegetation green?
Chlorophyll absorbs the orange-red and violet-blue wavelengths and
reflects green. KNOW EQUATION ON PAGE 592:
Carbon dioxide + water + sunlight --> glucose, carbohydrate and oxygen
Respiration (consumption of energy) is the
reverse of photosynthesis. The
compensation point is the break-even point between production and
conusmption. Each leaf must produce or
it is eliminated. Add up all
photosynthesis for a plany community to get the net primary productivity
(amount of stored chemical energy.) The
DRY weight of organic material is biomass.
Net primary productivity measured as fixed carbon (m2/year.) Highest between Tropic of Cancer and
Capricorn at sea level. Precipitation is
postiviely correlated with productivity.
In oceans productivity is limited by nutrients. Upwelling (west coast) currents bring nutrients. Carbon production (fixing) varies with
seasons.
Net productivity is the most important aspect of a community.
The flow of energy and the cycling of nutrients and water is
critical. Solar energy powers
ecosystems. It enters via photosynthesis. About 1% of energy is fixed by photosynthesis
as chemical energy (stored as carbohydrates.)
Plants have adapted their flowering and germination patterns to the
seasonal changes of insolation. Air and
soil temperatures are also important.
Water cycle (availability) and quality are important. Regional climate affects vegetation patterns
and in the long-term influences soil development.
Life zones have their own temperature, precipitation and
insolation relations. Ecosystems also
have microclimates. Forests have 5% more
humidity (that nonforested), moderated temperatures and fewer winds. Slope and exposure (away from sun are moister
and more vegetated) are translated into differences in temperature and moisture
regimes (moister slopes face north.)
Most abundant elements in living matter are hydrogen, oxygen and
carbon. Key chemical cycles include the
gaseous (atmosphere) and sedimentary (mineral and solid phases- nitrogen,
phosphorus, etc.) cycles. Photosynthesis
and respiration tie oxygen and carbon cycles.
Atmosphere is the link between the 2 cycles. Lots of oxygen in the earth’s crust-
unavailable to us for use. Same with
carbon, except lots of it in ocean (comes from phytoplankton
photosynthesis.)
In atmosphere plant and animal respiration, volcanoes and fossil
fuel consumption produce carbon dioxide.
Humans have increased 25% more carbon dioxide to the atmosphere between
1880 and 1970.
Nitrogen in atmosphere is not available to us. It is part of make up of organic molecules
(essential to living processes.) It is
made available to us through nitrogen-fixing bacteria, which are symbiotic with
certain plants. These are called
legumes, such as clover, alfalfa, soybeans, peas, beans and peanuts. Plants use this nitrogen to make organic
matter. Nitrogen in waste is freed back
into the atmosphere by bacteria. Humans
fix more nitrogen than any other organism (fertilizer for agriculture.) Too much nitrogen has accumulated into the
environment. Excessive nitrogen
encourages over-growth of algae resulting in diminished oxygen reserves
(hypoxic- oxygen depleted.) Look up
Elevation limits growth
Lack of water
Too much water
Change in salinity
Lack of iron in oceans
Low phosphorus
Lack of chlorophyll (above 20,000 feet)
PRECIPITATION IS THE NUMBER ONE LIMITING FACTOR
Some animals can detect the earth’s magnetic field, through tiny
amounts of sensitive particles inside them (like a compass.) Who are these animals?
Abiotic system: energy, atmosphere, water, weather, climate and
minerals
Nature of an ecosystem determined by: energy flow, nutrient
cycling and trophic relationships. Sun
replenishes energy. Nutrients are a
closed system and must be recycled.
Autotrophs: Essential producers that capture
light energy, then convert it to chemical energy, incorporate carbon, form
biomass and free oxygen. Solar energy
enters each food chain through plants.
Review page 602.
Important idea: Weak, secondary interaction in complex food webs
is the glue that hold the communities together
Food Web Efficiency: 10% of calories in plant matter
survive from primary to secondary trophic levels. Eating meat instead of grain is very
inefficient and results in greater biomass loss. Our
diet is expensive in terms of biomass and energy. Half of the cultivated acres in
The study of food webs is a study of what and where things eat
and are eaten. Different environments
have different food web structures.
Compare grassland to temperate forest (why is forest base so
narrow?) Metabolism: the way in which a
community uses energy and produces food for operations. It is the sum of all chemical processes. Given this, pollutants can become
concentrated in the food web (biological amplification.)
Succession: Biotic Sphere is dynamic, the same ideas of dynamic
equilibrium apply as previous chapters.
Growth, death and change are constant, sometimes in balance and
sometimes thrown out of balance (diversity is the key word.) Tendency to remain stable (inertial
stability) does not insure the ability to recover from change (resilience). An entertaining discussion (you can actually
learn while you read) of this is in the sequel to Jurassic Park, The Lost World. Ecosystems have different levels of
resilience. Rain forests are not very
resilient (the key here is in understanding microclimates.) Grasslands tend to be resilient (but does
HUMANS ELIMINATE BIODIVERSITY THROUGH AGRICULTURE. One disease or pest can wipe out an entire
crop (monoculture). This also creates a
great demand for energy, chemical pesticides, fertilizer and water.
Most scientists accept global warming. Studies show that colder climate are getting
greener. How fast can plants adapt to
new climates or move to shifting habitats (succession?) Adaptation is the key to evolution, but can
species adapt over decade instead of millions of years? If change takes place too fast, not enough of
a species may migrate to the new habitat to insure survival of the
species. What other factors may
influence this? Think of human demand
for resources and land and climate change.
Ecological Succession: older communities replaced by newer. Nature is in constant adaptation and
non-equilibrium. Ecosystems are a
patchwork of mosaic of communities- striving for optimal range and low
environmental stress (study is called patch dynamics.) Succession is the
interaction in structure and form among patches. Look at patches on top of patches in
landscapes. How is this the case in
Think through example of forest growth- trees blocking sunlight
for grasses, giving way to hardwood trees that like shade, etc.
Aquatic succession
characterized by nutrient levels.
Lakes and ponds are temporary landscape features. They fill with nutrients and sediments, turning
into bogs and swamps and eventually meadows, etc. Eutrophic means high in nutrients
Ecosystem
Ecology
Community
Habitat
Niche
Photosynthesis
Net primary productivity
Biomass
Life zone
Biogeochemical cycles
Limiting factor
Autotroph (producer-plant-carbon fixer through photosynthesis)
Heterotroph (consumer- feed on others)
Producers/consumers
Food chain/food web
Herbivore/carnivore/omnivore/detrivore
Biodiversity
Ecological/primary/secondary succession
Fire ecology
Definitions: ecosystem, biomass, biogeochemical cycles,
producers, food chain & biodiversity
Questions: 11, 14, 16 & 17