Ecosystems Review
Biotic factors: living parts of the ecosystem (ex: trees, birds, etc.)
Abiotic factors: non-living parts of the ecosystem (ex: rocks, water, etc.)
Population  Community  Ecosystem
Population: group of organisms of the same species living together
Community: groups of populations living in the same area
Ecosystems: community + all the non-living surroundings
Predator-Prey:
Predators feed on other organisms.
Prey are the organisms that get eaten.
The prey population needs to be larger than the predator population. As the prey
population increases, the predator population increases. If the prey population
decreases, the predator population decreases.
Predation keeps population size within the limits of available resources.
Symbiosis: means “living together”; there are 3 types of symbiotic relationships
1. Parasitism: the host is harmed and the parasite benefits (ex: human and a
tapeworm)
Host
Parasite
2. Commensalism: one organism is not harmed nor benefited and the other
organism benefits (ex: tree and a bird)
Organism
Organism
Unaffected
Benefitted
______
3. Mutualism: both organisms benefit (ex: clown fish and an anemone)
Organism
Organism
Benefitted
Benefitted
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Food Chain: represents the flow of energy in an ecosystem; the arrows represent the direction
of energy flow and are called trophic levels, there are usually 3-4 trophic levels in a food chain,
but no more than 5 levels
Grass  Insect  Bird  Hawk
Producer: organisms that undergo photosynthesis (grass); these are also called
autotrophs
Consumer: organisms that must eat producers/consumers; these are also called
Heterotrophs
Primary consumer: these organisms eat the producers (insect)
Secondary consumer: these organisms eat the primary consumers (bird)
Tertiary consumer: these organisms eat the secondary consumers (hawk)
Scavengers: organisms that feed on dead animals (ex: vultures)
Decomposers: organisms that break down dead organic material (ex: fungi)
Herbivores: eat only producers
Carnivores: eat only consumers
Omnivores: eat producers and consumers
Food Webs: interconnected food chains
`
Food chain 1: seeds  chipmunk  grizzly bear
Food chain 2: berries  chipmunk  goshawk
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Pyramids:
Energy Pyramid
Fox
0.1%
Birds
1%
Grasshoppers
10%
Only 10% of the energy
from one trophic level
is used by the next level.
The rest of the energy
is lost as heat.
Grasses
100%
Number Pyramid
Biomass Pyramid
Fox
1 kg
Birds
10 kg
Grasshoppers
100 kg
Grasses
1000 kg
There must always be more prey than predators because the predators can not use all the energy that is
consumed from the prey. The lower an organism is on the food chain, the higher the numbers of these
organisms. The more organisms there are at a trophic level, the more mass the group of organisms has.
Biological Magnification:
If a chemical or toxin (ex: DDT) enters the food chain at a low level (ex: grass) the amount of
that chemical increases as you move up the food chain.
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