Transcript 14.4 Interactions within Communities

INTERACTIONS
WITHIN COMMUNITIES
 Community: Populations of different species
living in the same area.
INTERACTIONS
WITHIN COMMUNITIES
 Ecological niche: The role an organism fills
within a community (what it does, eats, its
pattern of living)
INTERACTIONS
WITHIN COMMUNITIES
 Interspecific competition: competition for
resources among members of two or more
different species.
Hyenas battle with a lioness and win the day. Photo by Brittany Gunther, 2008
Types of Niches:
 Fundamental niche: the role the
organism would fill under ideal
enviromental conditions (if there was no
interspecific competition).
 Realized niche: the portion of the
fundamental niche the organism actually
fills (due to competition).
A. Symbiosis
 Interactions in which members of two (or
more) species maintain a close
association.
 There are 3 main types:
1. Parasitism
 The interaction is
beneficial to one
species and harmful
(but not fatal) to the
other species.
 Parasites can be both
micro- and
macroscopic as well as
ecto- and
endoparasites.
 Social parasites
mimic the behaviour
of another species in
order to complete
their lifecycle (i.e.
cowbirds).
2. Mutualism
 The interaction is beneficial
to both species. Ex. Bees
and flowers
 Obligatory mutualism is
when neither species can
survive without the other
(gut bacteria in herbivores,
oxpecker birds).
3. Commensalism
 The interaction is beneficial to one species
while the other is unaffected.
 Remoras and sharks are a possible
example.
B. Types of Interspecific Competition:
1. Interference
Competition: two
species are actually
fighting over the
resources (birds
over birdhouses,
lion vs. hyena).
B. Types of Interspecific Competition:
2. Exploitative
Competition: two
species are using a
common resource and
one species is more
efficient at obtaining it
ex. arctic foxes and
snowy owls eating
arctic hares, canopy
trees in rainforest.
Gause's Principle/ Principle of
Competitive Exclusion:
 if the resources are
limited, no two species
can remain in
competition for exactly
the same niche
indefinitely.
 One species will
always out compete
the other.
Resource Partitioning
 The avoidance of, or
reduction in,
competition for similar
resources by
individuals of different
species that do not
occupy the same niche
Resource Partitioning
 i.e. Plant root systems, lizards/insects/birds in
different parts of the tree.
C. Predation
 Predator-prey relationships
are an important interaction
in a community.
C. Predation
 When the prey population increases, the
predator population will increase shortly
thereafter. Predator-prey populations follow a
cyclical pattern.
C. Predation
 Predator-prey interactions have caused
prey to evolve diverse defence
mechanisms in order not to be eaten.
 Predators are evolving to bypass these
defences (Evolutionary Arms Race).
D. Defense Mechanisms
 Plants use morphological defenses such
as thorns, hooks, needles, spines and
chemical defenses such as toxins,
hormones, and other chemicals to deter
herbivores from eating them.
D. Defense Mechanisms
 Animals use passive defences such as
hiding / being poisonous or active
defences such as fleeing/ fighting/
producing venom.
D. Defense Mechanisms
 Some animals use mimicry, which is one
species appearing very similar to another
species.
D. Defense Mechanisms
 Batesian mimicry: a harmless species
mimics a harmful one (ie. An edible
butterfly mimics a toxic species so it won't
get eaten)
D. Defense Mechanisms
 Mullerian mimicry: dangerous species all
appear similar which causes predators to
learn quickly to avoid them.