Niches and Community
Interactions
Unit 5 Section 2
Why do organisms live where they do?
• Each species has a range of conditions under
which it can grow and reproduce
• These conditions help define where and how
an organism lives
Habitat and Niche
• Habitat – place where an organism lives
– Example: Habitat of a bullfrog is a pond
– Think of it like an organism’s address
• Niche – Occupation of an organism
– Includes: how it gets its food, reproduces, avoids
predators, etc.
– Niche determines its habitat
• Example: woodpeckers can’t live in grasslands because
their niche is to find insects in tree trunks!!
Competition
• Organisms often try to use a limited resource in
the same place at the same time as other
organisms
– This is called Competition
– Can occur between the same species or different
species
– Compete for things like: food, space and mates
– Competition results in natural selection. Only those
with the best traits for that environment will survive
and reproduce
– No two species can have the same niche in the same
environment at the same time this is called the
competitive exclusion principle
Predator-Prey Relationships
• Predation:
– Members of one population are the food source for
members of another population
– Predator – organism doing the eating
– Prey – organism that is being eaten
– Predator keeps the prey population from getting
too big
Herbivore-Plant Relationships
• Herbivory – when herbivore feeds on a
producer
– Keeps the plant population from getting too large
Keystone Species
• A population change in one species can cause
dramatic changes in a community
– This is called a keystone species
Symbioses
• Symbiosis – any relationship in which two
species live closely together
– Three main types of symbiotic relationships
• Mutualism
• Parasitism
• Commensalism
Mutualism
• Mutualism – both organisms benefit
• Clownfish is immune to sea anemone stings and gets
protected from predators
• Sea anemone gets protection from clownfish who chases
away bigger fish that try to eat it
Parasitism
– Parasite – lives on or in another organism that it
uses for food and sometimes for shelter
• Host – organism the parasite uses
• One organism is helped while the other is harmed
• Host organism continues to live and is not killed right
away just harmed
• Examples: tapeworms, flukes, ticks
Commensalism
• One organism benefits and the other is
neither helped nor harmed
– Barnacles attach themselves to whales and
benefit from constant movement of water and
food particles past the swimming whale
– Whale is neither harmed nor helped by the
barnacle