• Definition: the scientific study of
interactions among organisms and
their environment
– Branch of biology that was developed from
natural history
– Study reveals the relationships between
living and non-living parts of the world
The environment is divided into living and non living parts:
• Abiotic
– Physical factor such
as: air, temperature,
moisture, soil, light
– These factors make up
an organism’s habitat
• Habitat: the area
where an organism
• Biotic:
– All living or once living
components of an
– Includes dead
organisms and the
waste of organisms
Levels of Organization
in Ecology
To help ecologists understand the interactions of
the biotic and abiotic parts of the world, scientists
have organized the living world into levels:
Levels of Organization
• Biosphere
– The part of the Earth’s covering where life is
• Goes from the top of the atmosphere to the
bottom of the ocean; about 12 miles high!
• Supports a wide variety of organisms
• If the earth were shrunk to apple size, the
biosphere would be thinner than the apple skin
Levels of Organization
• Ecosystem
– A community of organisms and their living
and non living surrounds
• Living components of an ecosystem are the
biotic factors
• Non living components of an ecosystem are
the abiotic factors
Levels of Organization
• Community
– A group of various species that live in the same
habitat and interact with each other
• Population
– group of organisms of one species that interbreed
and live in the same place at the same time
• Organism
– living member of species
Levels of Organization
In a desert…..
• Organism: coyote
• Population: pack of coyotes
• Community: pack of coyotes, hawks, owls,
snakes, scorpions, & reptiles
• Ecosystem: populations of animals listed
above, cacti, shrubs, sand dunes, climate,
rocks, temperature
• Biosphere: the earth
• Includes:
– The variety of organisms within a given area
– The genetic variation within a population
– The variety of species in a community
– The variety of communities in an ecosystem
– Both abiotic and biotic factors help to
determine the biodiversity of an area
In an Ecosystem
• Habitat: a place where an organism
lives out its life
• Niche: the specific role and position a
species has in its environment.
– Organisms may share parts of their niche,
but never the whole thing!
In an Ecosystem
• Fundamental Niche: the entire range of
conditions where a species can survive
– Shaped by competition for resources between species
• Realized Niche: the actual niche that an
organism occupies within an ecosystem
The establishment of a niche allows for several
organisms to live in the same habitat while
reducing competition for resources!!
Changes in an Ecosystem
• Succession: the replacement of one community by
another at a single location over a period of time
• First organisms to appear are pioneer organisms
– Primary Succession occurs after natural disasters
• Volcanic eruptions, fires, hurricanes, tornadoes, etc
– Secondary Succession occurs after HUMAN
• Clearing of land for development, clear cutting the
forest, etc
Relationships in an Ecosystem
• Symbiosis
– Two species live in close association with each other.
Can be positive or negative
• Mutualism: both species benefit
– Ex: cleaner shrimp/fish
• Commensalism: one species benefits, the other
does not, but is not harmed
– Ex: orchids growing on trees
• Parasitism: one species is helped while the other is
– Ex: Ticks on a dog.
– The tick is the parasite and the dog is the host

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