Download Community Ecology - Liberty High School

Community Ecology
Communities

A community is a
group of organisms
of different species
that live in a
particular area
Individualistic Hypothesis vs.
Interactive Hypothesis

Individualistic Hypothesis:


A community is a chance group of species
found in the same area because they have
similar abiotic requirements
Interactive Hypothesis:

A community is a group of closely linked
species locked together in mandatory biotic
interactions that cause the community to
function as an integrated unit
Interspecific Interactions


Interspecific interactions are interactions
that occur between populations of different
species living together in a community
There are 4 major interspecific interactions:




Predation (and parasitism)
Competition
Commensalism
Mutualism
Predation (and Parasitism)

(+ -)


The interaction is
beneficial to one
species and
detrimental to the
other
Predation:


When a predator
eats its prey
Example in
picture:
Predation (and Parasitism)

Parasitism:

Predators that live
on or in their
hosts, usually
feeding off their
body tissues or
fluids
• Usually do not kill
their hosts

Examples:
Plant Defenses Against
Herbivores


“Plants Fight Back!”
Plants have 2
major mechanisms
by which they
defend themselves
against being eaten

Mechanical
Defenses
• Thorns, hooks,
etc.
Plant Defenses Against
Herbivores

Chemical Defenses



Produce
chemicals that are
distasteful or
harmful to an
herbivore
Morphine (opium
poppy)
Nicotine (tobacco)
Animal Defenses Against
Predators



Animals defend
themselves against
predators passively
(hiding) or actively
(fleeing)
Cryptic coloration
(camouflage) makes
prey difficult to spot
Aposematic
coloration (warning
coloration)warns
predators not to each
animals that may be
toxic or may sting.
Animal Defenses Against
Predation

Mimicry


When one species “imitates” or “mimics” another
Batesian mimicry
• When one edible or harmless species mimics an badtasting (unpalatable) or harmful species
• Example: hawkmoth mimics a snake
Animal Defenses Against
Predation

Mimicry

Mullerian mimicry
• Two species, both of which are unpalatable (taste
bad) or harmful, resemble each other
• Example: monarch butterfly (unpalatable) and queen
butterfly (unpalatable) resemble each other
Symbiosis- close relationship
between two organisms.
Parasitism (+,-)
 Commensalism (+,neutral)
 Mutualism (+,+)

Parasitism


One organism (the
parasite) gets its
nourishment from
another organism (the
host), which is harmed
in the process
Endoparasites:


Live within host
tissues (tapeworms)
Ectoparasites:

Feed on external
surfaces (mosquitoes)
Interspecific Competition
Competition between organisms of
different species
 The Competitive Exclusion Principle:

Two species with similar needs for the
same limiting resources cannot
coexist in the same place
 Niches may overlap but they may not
be identical.

Ecological Niches

An organism’s niche is the
specific role it plays in its
environment


All of its uses of biotic and
abiotic resources in its
environment
Example: oak tree in a deciduous
forest
• Provides oxygen to plants,
animals, etc.
• Home for squirrels
• Nesting ground for blue jays
• Takes water out of the soil
• Etc., etc.
Fundamental v. Realized
Niche


Fundamental Niche
includes resources an
organism could
theoretically use (if no
competition)
Realized Niche
includes resources it
actually does use
given competition
from other species.
Resource Partitioning

Similar species develop ways to
partition/divide resources in order to
coexist.
Commensalism



(+0) relationship
One partner benefits, the
other is not affected
Examples:


Cattle and cattle egret
(birds)
Sea anemone and
clownfish
• Clownfish gets a place to live,
sea anemone is not affected
Mutualism
(++) relationship
Both partners benefit from the
relationship
“You scratch my back, I’ll
scratch yours”
Examples:
Ants & acacia tree
tree provides high protein
food in beltian bodies & habitat for
nests inside thorns; ant protects
against predators
Mycorrhizae-fungal extentions
on plant roots
Plant gets increased
water/nutrition, fungi gets
food
Hummingbirds & flowers
Hummingbirds get food,
flowers can reproduce
Dominant & Keystone
Species

Dominant Species:



Species in a community that have the
highest abundance or highest biomass
Sugar maple in eastern North America
Keystone Species:



Important to a community because of their
ecological roles (niches), not by numbers
Sea otters control sea urchin population,
which controls kelp population
Sea stars are keystone predators in many
aquatic environments.
Ecological Succession

Ecological succession is a change in the
species that live in a given area over a
period of time



One community replaces another
Primary succession = occurs in places
where soil is not yet formed (bare bedrock)
Secondary succession = occurs in places
where there is soil, but where some
disturbance has eliminated the previous
community
Ecological Succession
Ecological Succession

The first organisms to inhabit an area
undergoing succession are known as
pioneer organisms



These are usually small organisms (bacteria,
lichens, algae, etc.)
The ecosystem goes through a number of
stages, with each new stage usually
consisting of larger organisms than the last
one
Once a community has become stable and
is not changing much, it is known as a
climax community
Causes of Ecological Succession

There are 3 major causes of ecological succession:
1.
Human Activities
- logging, mining, development, etc.
2.
Natural Disasters/Disturbances
- fires, volcanic eruptions, etc.
3. Natural Competition Among Species
- Fictitious example:
- turtles and frogs both eat crickets
- frogs are faster, turtles are slower
- frogs eat more crickets, turtles starve
- turtle population dies out, frog population
gets bigger