Ecology Part 1
Chapter 2 – Principles
of Ecology
Ecosystems and
the Biosphere
Energy Transfer
• Autotrophs – organisms that can make
their own food
• Because autotrophs capture energy and
use it to make organic molecules, they
are called producers.
• Most are photosynthetic
• Chemosynthetic organisms do not use
sunlight as an energy source. They use
inorganic molecules to produce
carbohydrates.
• In terrestrial ecosystems, plants are the
major producers.
• In aquatic ecosystems, photosynthetic
protists and bacteria are the major
producers.
• Gross primary productivity is the rate at
which producers capture energy.
• Organic material in an ecosystem is known
as biomass.
• Producers add biomass to an ecosystem
by making organic molecules.
• Net primary productivity is the rate at
which biomass accumulates
• Usually expressed in units of energy per year
(kcal/m2/yr) or in units of mass per unit area
per year (g/m2/yr)
• Equals the gross primary productivity minus
the rate of respiration in producers.
• In terrestrial ecosystems, productivity is
determined by light, temperature, and
precipitation.
• In aquatic ecosystems, productivity is
determined by light and the availability of
nutrients.
Consumers
• Organisms that cannot manufacture their own
food are called heterotrophs
• Heterotrophs obtain energy by consuming
organic molecules made by other organisms.
They are know as consumers.
• Herbivores eat producers
• Carnivores eat other consumers
• Omnivores eat both producers and consumers
• Detritivores are consumers that feed on dead
and decaying matter.
• Decomposers are a type of detritivore. They cause
decay by breaking down complex molecules in dead
tissue into simpler molecules that can be recycled.
Energy Flow
• In an ecosystem, energy flows in one
direction only, from producers to
consumers.
• An organism’s trophic level shows the
organism’s position in the sequence of
energy transfers
• All producers belong to the first trophic
level.
• Herbivores belong to the second trophic
level
• Predators of herbivores belong to the
third trophic level.
• Most ecosystems contain only three or
four trophic levels.
• A food chain is a single pathway of
feeding relationships in an ecosystem
that results in energy transfer.
• Most food chains interlink.
• A food web shows the interrelated food
chains in an ecosystem.
Quantity of Energy Transfer
• Roughly 10% of the total energy in one
trophic level is available to the organisms
in the next level
• The rest of the energy is used for metabolism
and is lost as heat.
• Since the rate of energy transfer between
trophic levels is so low, ecosystems rarely
contain more than a few trophic levels.
• It takes many more producers to support
first, second, and third order consumers.
• If the first trophic level contained 50,000
kcal of energy, how much would be
available to the:
• First-order consumers?
• Second-order consumers?
• Third-order consumers?
Ecosystem Recycling
• Remember, energy flows through an
ecosystem (one direction only)
• Water and minerals like carbon, nitrogen,
calcium, and phosphorus are recycled and
reused.
• Biogeochemical cycles move substances
from the abiotic (non-living) part of the
environment, into living things, and back
again.
• We will look at the water cycle, carbon
cycle, and nitrogen cycle.
The Water Cycle
The Carbon Cycle
The Nitrogen Cycle
The Nitrogen Cycle
• Nitrogen gas, N2, is readily available in the
atmosphere.
• Most plants can use nitrogen only in the
form of nitrate.
• The process of converting nitrogen gas
into nitrate is called nitrogen fixation.
• Nitrogen-fixing bacteria convert nitrogen
gas into ammonia, then nitrite, and then
nitrate, which plants can use.
• Nitrogen-fixing bacteria live in the soil and in
the roots of some kinds of plants, like beans,
peas, clover, and alfalfa (a mutualistic
relationship)
• Decaying organisms release nitrogen as ammonia
in a process called ammonification
• Bacteria in the soil take up ammonia and oxidize
it into nitrates and nitrites in a process called
nitrification.
• Plants use nitrates to form amino acids.
• Nitrogen is returned to the atmosphere through
denitrification, which occurs when anaerobic
bacteria break down nitrates and release
nitrogen gas back into the atmosphere.
• Plants can absorb nitrates from the soil,
but animals cannot.
• How can animals get nitrogen?
• Animals get nitrogen the same way they
get energy – by eating plants and other
organisms and then digesting the
proteins and amino acids to get
nitrogen.
The Phosphorus Cycle
Phosphorus Cycle
• Unlike carbon, oxygen, and nitrogen,
phosphorus does not enter the atmosphere.
• Phosphorus remains mostly on land in rock
and soil minerals, and in ocean sediments.
• Phosphorus exists in the form of inorganic
phosphate
• As the rocks and sediments gradually wear
down, phosphate is released.
Any Questions ???