Ch. 2: Principles of Ecology
I.
Organisms and their Relationships
Main Idea: Biotic and abiotic factors interact in complex ways in
communities and ecosystems.
A. Ecology: the scientific study of the relationships among living
organisms and the interaction the organisms have with their
environment.
1.ecologists: scientists who study ecology
a. may study how organisms survive in their
environment or how to make long term
observations and analyses (longitudinal analysis)
b. ecologists frequently use models to simulate a
process or system to control variables
B. Biosphere: the part of Earth that supports life
 forms a thin layer around the Earth from several miles
above the surface to several miles below the ocean’s
surface to the deep-ocean vents.
 includes landmasses, bodies of freshwater and
saltwater, and all locations below Earth’s surface that
supports life.
 b/c most organisms depend on green plants or algae for
survival, green plants are a good indicator of the
distribution of living organisms in an area.
 biosphere also includes frozen polar regions, deserts,
oceans and rain forests b/c each contains organisms
specialized to survive in these regions.
1.Biotic factors: the living factors in an organism’s
environment
a. interaction of organisms are necessary for the
health of all species in the same geographic
location.
b. ex: the biotic factors in a salmon’s habitat might
include all the organisms that live in the water
(other fish, algae, frogs, microscopic organisms),
organisms that live on land adjacent to the water,
and migratory animals like birds.
c. Salmon need other members of their species to
reproduce, depend on other organisms for food and
are food sources for other organisms.
2.abiotic factors: the nonliving factors in an organism’s
environment
a. these factors vary across the biosphere but are shared
by organisms in the same area
b. ex: temperature, air or water currents, sunlight, soil
type, rainfall, or available nutrients.
c. organisms are adapted to surviving in the abiotic
factors that are present in their natural environments
and might die if moved to a new area and can’t adapt
quickly enough.
C. Levels of Organization
1. b/c the biosphere is too large and complex to study as a whole,
ecologists look at smaller pieces and relationships. These
levels of increasing complexity are:
Increasing
complexity
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organism
population
biological community
ecosystem
biome
biosphere
2. organisms, populations, biological communities
a. organism: the individual of a species
b. population: individuals of a species that share the
same geographic location
i. size of population depends on the
availability of resources
c.biological community: a group of interacting
populations that occupy the same geographic area at the
same time.
i.organisms may or may not compete for the same
resources in a biological community
3.Ecosystems, biomes, and the biosphere
a. ecosystem: a biological community and
all of the abiotic factors that affect it
i.can be large or small with flexible
boundaries
b.biome: a large group of ecosystems that
share the same climate and have similar types of
communities (ex: marine, desert, forest biomes)
c.biosphere: combination of all the biomes
on Earth.
D. Ecosystem Interactions: a community of organisms
increases the chances for survival of any one species by
using the available resources in different ways.
1. habitat: an area where an organism
lives
2. niche: the role or position that an
organism has in its environment.
 Determines how an organism
meets its needs for food,
shelter, and reproduction
 Also determines requirements
for living space, temperature,
moisture, or appropriate mating
or reproduction conditions
E. Community Interactions
1. competition: occurs when more than
one organism uses a resource at the
same time.
a. ex: food, water, space, light
b. strong usually compete
directly with the weak
2.predation: the act of one organism
consuming another organism (predator-prey
interaction)
 mostly animals but some plants
are predators
F. Symbiotic relationships: close relationships that exist
when two or more species live together. 3 types:
1. mutualism: relationship b/w two or
more organisms that is beneficial to
both organisms
a. ex: lichens are a combination of
fungi and algae (fungi provides
habitat for the algae, and algae
provide food)
2. commensalism: relationship where one
organism benefits and the other organism is
neither helped or harmed (ex: sea anemones
and clown fish)
3. parasitism: relationship where one organism
benefits at the expense of another organism
(ex: ticks, fleas, bacteria, tapeworms,
roundworms, brown-headed cowbirds)
II.
Flow of Energy in an Ecosystem
Main Idea: Autotrophs capture energy, making it available
for all members of a food web.
A. Energy in an Ecosystem
1. autotrophs (primary producers): an organism that
collects energy from sunlight or inorganic substances
to produce food.
 Organisms that have chlorophyll absorb energy
during photosynthesis and use it to convert the
inorganic substances carbon dioxide and water to
organic molecules.
 In places with no sun, bacteria use hydrogen
sulfide and carbon dioxide to make organic
molecules
2. heterotroph (consumers): an organism that gets its
energy by consuming other organisms.
 Herbivore: heterotroph that consumes only
plants (ex: cow, rabbit, grasshopper)
 Carnivore: heterotrophs that prey on other
heterotrophs (ex. Wolves, lions, lynxes)
 Omnivore: heterotrophs that consume both
plants and animals (ex: bears, humans,
mockingbirds)
 Detritivores: heterotrophs that eat fragments
of dead matter in an ecosystem and return
nutrients to the soil, air, and water to be
reused by living organisms (ex: worms and
aquatic insects)
o Decomposers: break down dead
organisms by releasing digestive
enzymes (ex: fungi and bacteria); most
responsible for breaking down organic
molecules and making the nutrients
available to producers again.
B. Models of Energy Flow
1. food chains: simple model that shows how energy
flows through an ecosystem.
Grass ---->
Grasshopper -->
Toad ---->
Snake ---->
Hawk
2.food webs: more complex model that describes the feeding
relationships in an ecosystem.
Alaskan Coastal Food Web
3. Ecological pyramids: diagram that shows the relative
amounts of energy, biomass, or numbers of organisms at
each trophic level in an ecosystem.
a. Biomass: the total mass of living matter at each
trophic level; biomass decreases at each level
Trophic Levels Pyramid:
Numbers Pyramid:
Energy Pyramid
Energy Pyramid 2:
b. in the energy pyramid, about 90% of all energy is not
transferred to the level above it due to the energy
being used for cellular processes or released as heat
c. energy, biomass and number of organisms all
decrease at each trophic level b/c there is less
energy available to support organisms
III.
Cycling of Matter
Main idea: essential nutrients are cycled through biogeochemical
processes
A. Cycles in the Biosphere
 a constant supply of usable energy is necessary for the
biosphere to function, but this is not true of matter.
 the law of conservation of mass = matter is neither
created nor destroyed
 natural processes cycle matter through the biosphere
 nutrient: a chemical substance that an organism must
obtain from the environment to sustain life and undergo
life processes (ex: carbon, nitrogen, phosphorus)
 biogeochemical cycle: the exchange of matter through
the biosphere
a. involves both matter in living
organisms and physical processes
found in the environment
1.
water cycle
 90 % of water vapor evaporates from oceans,
lakes, and rivers; 10% evaporates from plants
through transpiration
 3% of all water is freshwater; 69% of this is
located in ice caps and glaciers leaving living
organisms depending on 31% of all freshwater
2.
carbon cycle: all living things are composed of molecules that
contain carbon.
 Photosynthesis by green plants turns atmospheric carbon
dioxide into carbohydrates and release oxygen
 Carbon dioxide is recycled back into the air during
cellular respiration.
 Long-term storage of carbon occurs when organic matter
is buried and converted to peat, coal, oil or gas deposits
and is released when burned
 Carbon is released when fossil fuels are burned
 Carbon and oxygen can also be stored long-term in the
form of calcium carbonate: found in shells of plankton,
and animals such as coral, clams and oysters and when
algae fall to ocean floor---- released by weathering and
erosion
3. nitrogen cycle: needed for proteins
 largest concentration found in atmosphere (78%) but plants
and animals can’t use it directly from atmosphere
 nitrogen fixation: certain bacteria in water, soil or in roots
of some plants capture and covert free nitrogen to usable
form (nitrates)
 nitrogen enters the food web when plants absorb nitrogen
compounds from the soil and convert them into proteins
 consumers get nitrogen by eating plants or animals that
contain nitrogen
 nitrogen is returned to the soil when animals urinate, when
organisms die and decomposers transform the nitrogen in
proteins into ammonia
 supply of nitrogen in food web depends on the amount that
is fixed so nitrogen limits the growth of producers.
 denitrification: some bacteria convert fixed nitrogen
compounds back into nitrogen gas when returns to the
atmosphere
4. phosphorus cycle: essential for growth and development of
organisms
 short-term cycle: phosphates are cycled from the soil to
producers and then to consumers; return to soil in waste
products or by decomposers
 long term cycle: rock formation takes phosphorus away
from the short-term cycle and is only returned through
weathering and erosion
 limiting factor for growth of producers: only present in
small amounts in the soil.