Ecology Notes outline: Interactions between organisms, population, cycles and food webs
Ecosystem= all the biotic and abiotic factors in a given area.
Abiotic factors=non-living factors such as soil, rock, air, temperature and sunlight
Biotic factors=all the living factors in an area.
Habitat=area where an organism lives and its basic needs are met.
Population=group of organisms of the same species that live in the same area
Community=all the populations living together in a given area, includes all the plants and animals
Population density=the number of individuals of a population in a given area.
How to determine population size-direct observations=count all the organisms and indirect
observations=sampling and mark and recapture techniques
Changes in a population’s size are due to=birth and death rates, immigration and emigration and limiting
factors.
Limiting factors=any factor that prevents a population from becoming any larger. Examples are food, space,
weather, predation, sunlight
Carrying capacity=the maximum number of individuals in a population that an ecosystem can support
Interactions between organisms and between populations in a community
II. Interactions between organisms of the same population
A. Competition =
For what: basic resources such as food, water, shelter, space
Why do they compete? To get their basic needs that are in limited supply
Why do they establish territories? To ensure they will be able to get their needs
How do plants compete? Vines grow up trees to reach sunlight, seeds release chemicals to
prevent germination of other seeds
Examples: wolves using urine to mark territory, birds singing, monkeys screaming,
B. Cooperation- Definition= working together for the benefit of all
Social Hierarchy/Dominance=populations will establish a social hierarchy where members are
ranked in dominance. Seen in wolf populations
Castes= members of a population are put into groups or castes with specific jobs. Working bees
are an example
Examples of how organisms cooperate for:
Food: hunt in packs
Protection: musk ox form circle around young
Shelter: termites, bees, wasps
Rearing young: elephants and meerkats take turns babysitting.
III. Interactions between populations in a community
A. Interact=act in such a way as to have an effect on each other
B. Niche= the role an organism has in the environment
Often an organism’s physical characteristics are clues to the niche it fills in a
community.
Example: keen eyes of a hawk=predator
C. Three ways populations interact
1. Competition
Example of Animal competition=antelope and bison competing for plants to eat. Red
tailed hawk and Red shouldered hawk competing for food
Hyena and vultures competing for a carcass
Example of Plant competition=vines climbing trees, broader leaves to get more sunlight,
2. Predation=one organism hunts another for food
Predator=does the hunting
Prey=is hunted
Examples: Lynx and hare
3. Symbiosis
Definition= a close and permanent relationship between two different species
Mutualism=Relationship where both species benefit
Examples-bees and flowers, oxpecker bird and rhino, leopard shark and remora
Commensalism=One organism is benefited and the other one is neither harmed or
helped
Examples-clown fish and sea anemone, cattle and cattle egrets, barnacle and
scallop
Parasitism=One species is benefited and the other is harmed
Examples-tick and humans, lice and humans, tapeworms and humans
IV. Cycles in Ecosystems
A. Water cycle-Precipitation, evaporation/transpiration, condensation
B. Carbon Cycle-CO2 in air is taken in by plants who turn it into sugar during photosynthesis.
Consumers eat the plants and release the CO2 and energy back into the environment. Carbon in
plants/ and animals can be stored in the soil for millions of years and released during the burning of
fossil fuels.
C. Nitrogen cycle-Nitrogen in the air is fixed into a usable form by bacteria in the roots of plants.
Plants take this nitrogen and make proteins. Consumers eat the plants and consume the nitrogen in
them. When the consumer dies the nitrogen inside it is broken down by bacteria who either release it
as N2 gas back into the atmosphere or as NH4 that is taken up by plants.
V. Energy flow-Food chains
Food chain-shows how energy moves from one organism to another.
Food web- consists of many overlapping food chains.
Producer=autotroph=organism that can make its own food
Consumer=Heterotroph=organism that obtains energy by eating other organisms. Depending where
they are found in a food chain, consumer can be a first order, second order or third order consumer.
First order consumers are either herbivores or omnivores.
Decomposers-breakdown dead and decaying matter and recycle nutrients.
Energy pyramid-show how much energy is passed on to each trophic level or feeding level in a food
chain.
Grass-------------Grasshopper----------------Frog---------------------Snake--------------------Hawk
Producer
first order consumer
second order
Third order
fourth order
st
nd
rd
th
1 trophic
2 trophic level
3 trophic level
4 trophic level
5th trophic
1000 units
100units
10 units
one unit
.10 unit
90% of all energy is used for life functions and only 10% is passed on to the next consumer.