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Ecology
The study of interactions
between organisms & their
environment.
Ecosystems
An ecosystem is an interaction
among populations of all the
organisms in a community with
the non-living parts of their
environment.
Species, Population, &
Community
 A species is a group of organisms
that interbreed & produce fertile
offspring.
 A population is a group of
organisms all of the same species,
which interbreed and live in the
same place at the same time.
 A biological community is all the
organisms in a given area.
Limiting Factors
Anything that limits the
number of individuals that can
live in an ecosystem is a
limiting factor.
Examples of
Limiting Factors:
 Food
 Water
 Climate
 Disease
 Shelter
 Predators
Population Density
 Population density is measured by the # of
organisms that can live & be supported in a
defined space.
 Density-dependent factors are triggered by
overcrowding. Examples are: competition
(food, water, shelter, space), predation,
parasitism, & disease.
 Density-independent factors occur regardless
of how large the population & it reduces the
size of the population in the area in which they
occur. Examples are: weather changes, human
activity (pollution), & natural disasters (fire).
Biotic Factors
The living components of an
ecosystem are called biotic
factors.
Examples of
Biotic Factors:
 Animals
 Plants
 Fungi
 Bacteria
 Protists
Abiotic Factors
The non-living components of an
ecosystem are called abiotic
factors.
Examples of
Abiotic Factors:
Water
Nitrogen
Oxygen
Salinity
pH
Soil nutrients & composition
Temperature
Sunlight
Precipitation
Stable Ecosystem
 A stable ecosystem is one where
the population numbers, supply
of resources, & energy
fluctuates at a predictable rate.
What keeps an ecosystem stable?
 Competition is the relationship that occurs
when two or more organisms need the same
resource at the same time.
 Predation is an interaction between species.
– Predator – the animal that preys on others
– Prey – the animal hunted and killed for food
 Symbiotic Relationships exists between
organisms of two different species that live
together in direct contact.
Examples of Symbiotic
Relationships
 Parasitism – one organism (parasite)
benefits at the expense of the other
organism (host)
 Mutualism – Both organisms benefit.
 Commensalism – one species benefits
and the other is neither harmed nor
benefited
Remember:
 The Sun is the ultimate energy source.
 The flow of energy can be described in food chains,
food webs, & pyramids.
 Each level in the transfer of energy through an
ecosystem is called a trophic level.
 1st level – producers (green plants or autotrophs)
 2nd level – primary consumers (herbivores or
heterotrophs)
 3rd or higher – consumers (carnivores or omnivores)
 Decomposer – returns nutrients to soil, water, or air for
1st level