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Chapter 13
13-1 Ecology – scientific study of the interactions among living things and between
Living things and their surroundings.
Biosphere – part of the earth in which life exists including land, water and air or
atmosphere.
Ecological Levels of Organization – smallest to largest
- individual organism – species – group of similar organisms that can breed and
produce fertile offspring.
- population – group of individuals of the same species that live in the same area
- community – different populations that live together in defined area
- ecosystem – collection of all the organisms that live in a particular place, together with
their non-living environment
- biome – group of ecosystems that have the same climate and similar dominant
communities
- biosphere – highest level
3 Ecological methods ecologists use:
1. observing – using the 5 senses (ex. visual – counting)
2. experimenting – testing hypotheses (ex. testing a water sample)
3. modeling – ecological models are made when the subject is too large to study by a
controlled experiment (ex. computer generated models – weather, global warming)
13-2
An ecosystem includes both biotic and abiotic factors.
Biotic factors are living things; plants, animals, fungi, bacteria
Abiotic factors are nonliving things; water, rocks, atmosphere, temperature
Changing one factor in an ecosystem can affect many other factors.
o Biodiversity is the assortment, or variety, of living things in an ecosystem.
o Rain forests have more biodiversity than other locations in the world, but are
threatened by human activities.
o A keystone species is a species that has an unusually large effect on its ecosystem.
o Keystone species form and maintain a complex web of life.
13-3 Producers provide energy for other organisms in an ecosystem.
o Producers get their energy from non-living resources.
o Producers are also called autotrophs because they make their own food.
o Producers provide energy for other organisms in an ecosystem.
o Consumers are organisms that get their energy by eating other living or once-living
resources.
o Almost all producers obtain energy from sunlight.
o Photosynthesis in most producers uses sunlight as an energy source.
plants, algae, cyanobacteria use sunlight, carbon dioxide and water to make glucose
and oxygen
CO2 + H2O → C6H12O6 + 6O2
o Chemosynthesis in prokaryote producers uses chemicals as an energy source.
Consumers – Heterotrophs
o organisms that cannot make their own food
o types of heterotrophs:
a. herbivores – plant eaters
b. carnivores – meat eaters
c. omnivores – meat and plant eaters
d. detritivores – feeds on plant and animal remains and other dead material
e. decomposers – break down and obtain energy from dead organic matter
13-4
A food chain is a model that shows a sequence of feeding relationships.
o A food chain links species by their feeding relationships.
o A food chain follows the connection between one producer and a single chain of
consumers within an ecosystem.
o Consumers are not all alike.
o Specialists are consumers that primarily eat one specific organism or a very small
number of organisms.
o Trophic levels are the nourishment levels in a food chain. Trophic level is
each step in a food chain or food web (sometime referred to as feeding
level) Can be illustrated by showing the relative number of organisms at
each level.
o Only 10% of the energy stored in an organism can be passed to the next
trophic level.
o Energy is used by organisms for respiration, movement, and
reproduction. The rest is lost as HEAT.
Energy flows in one direction (not recycled)
sun → producers → consumers
Food chain – series of steps in an ecosystem in which organisms transfer energy by
eating and being eaten
Ex. Grass → grasshopper → frog → snake → hawk
A food web shows a complex network of feeding relationships.
o An organism may have multiple feeding relationships in an ecosystem.
A food web emphasizes complicated feeding relationships and energy flow in an
ecosystem. (several food chains together)
13-5 Recycling in the biosphere
Biogeochemical cycle – A biogeochemical cycle is the movement of a particular chemical
through the biological and geological parts of an ecosystem.
Matter (nutrients) – can be recycled; biological systems do not use up matter, they
transform it. * Organisms need nutrients in order to carry out essential life functions
(respiration, movement, reproduction)
Water cycle – The hydrologic, or water, cycle is the circular pathway of water on Earth.
Evaporation – process by which water changes from liquid to atmospheric gas
Transpiration – when water evaporates from the leaves of plants
Oxygen cycle - The main processes involved in the oxygen cycle are photosynthesis and
respiration. Oxygen cycles indirectly through an ecosystem by the cycling of other nutrients.
Carbon cycle – Carbon is the building block of life:
1. photosynthesis – biological process
2. burning fossil fuels – human process
3. decomposition of plants and animals
Carbon is stored:
1. in the atmosphere as carbon dioxide
2. underground as fossil fuels
3. in the oceans as dissolved carbon dioxide
Nitrogen cycle – atmospheric nitrogen, as well as animal wastes/decay, fuel the nitrogen
cycle. The nitrogen cycle mostly takes place underground. Animals would have the least
affect on the nitrogen cycle. Bacteria are important parts of the cycle.
•Bacteria are responsible for:
Nitrogen fixation – process of converting nitrogen gas into ammonia
Denitrification – conversion of nitrates into nitrogen gas
Limiting nutrient – single nutrient that either is scarce or cycles slowly, limiting the
growth of organisms in an ecosystem. (ex. Phosphorus in freshwater pond)
Algal bloom – event that can occur after a lake receives a large input of limiting nutrient
13-6 Pyramid models
An energy pyramid shows the distribution of energy among trophic levels.
o Energy pyramids compare energy used by producers and other organisms on trophic
levels.
Other pyramid models illustrate an ecosystem’s biomass and distribution of
organisms.
o Biomass is a measure of the total dry mass of organisms in a given area.
o A pyramid of numbers shows the numbers of individual organisms at each trophic
level in an ecosystem.
1) Tertiary consumers – top
2) Secondary consumers
3) Primary consumer
4) Producers - bottom