Ecosystems & Populations
Chapters 4 & 5
Levels of Organization in Ecology
• Ecologists study
individual organisms,
but this only provides
part of the story of its
life cycle.
• An individual organism
interacts with others of
its species; it is also
dependant on other
organisms for food,
shelter, reproduction
and protection.
Levels of Organization in Ecology cont.
• Population – a group of
organisms of one species
that interbreed and live in
the same place at the same
time
• Members of the same
population may compete
with each other for food,
water, and other resources.
• How organisms share the
resources determines how
far apart organisms live and
the size of the population.
Levels of Organization in Ecology cont.
• Community – a
collection of
interacting
populations
• A change in one
population in a
community will cause
changes in the other
populations.
Levels of Organization in Ecology cont.
• Ecosystem – made up of
the interactions among
the populations in a
community and the
community’s physical
surroundings
• Terrestrial, freshwater
and saltwater (marine)
ecosystems are the three
major kinds.
Levels of Organization in Ecology cont.
• Biome – a large region
characterized by a
specific climate and
certain plants and
animals
• Biosphere – the portion
of Earth that supports
life
• The biosphere extends
from high in the
atmosphere to the
bottom of the ocean.
Organisms in Ecosystems
• Habitat – the place where
an organism lives out its
life
• Niche – the role and
position a species has in its
environment – how it
meets its needs for food
and shelter, how it
survives and how it
reproduces.
Niche
• Several species may
share a habitat, but the
food, shelter, and other
resources of that habitat
are used in different
ways.
• These differences lead to
reduced competition.
• It is an advantage for a
species to occupy a niche
different from those of
other species.
Living Relationships
• Predator-Prey
Relationship –
beneficial for one
species and harmful to
another, involves a
fight for survival.
• However, some species
enhance their chances
of survival by forming
close, permanent
relationships with
other species symbiosis.
Symbiotic Relationships
• Commensalism –relationship
in which one species benefits
and the other species is
neither harmed nor benefited
• The clownfish lives among
the stinging tentacles of an
anemone and is protected
from potential predators not
immune to the sting of the
anemone.
Symbiotic Relationships cont.
• Mutualism –
relationship in which
both species benefit
• Some fish and shrimp
clean the bodies and
mouths of large fish
and turtles.
• The cleaner fish get a
meal while the large
fish have parasites
removed.
Symbiotic Relationships cont.
• Parasitism – relationship
in which one organism
derives benefit at the
expense of the other.
• Ticks are parasites of
animals like dogs,
obtaining nutrients from
the blood of their host.
• Parasites harm, but
usually do not kill, the
host.