Download Population Interactions

Community Interactions
Vocabulary:
A community consists of all the interacting populations
within an ecosystem
An ecosystem is all the organisms and their nonliving
environment within a defined area.
A niche is an organisms habitat, way of life, and
physical environment.
An organisms habitat is were it lives.
Interactions
When populations interact with one another, they
influence each other ability to survive and reproduce.
They are agents of Natural Selection.
Competition between different species is called
inter-specific competition.
Competition between the same species is called
intra-specific competition.
No two species occupy the exact same niche.
The competitive exclusion principle states if you put
two species with the same niche together then one will
out compete the other and kill it off.
Predator - Prey
Prey and predator populations both follow cyclical trends
When predators get too numerous, prey population drops and
predator resources are thus depleted
When prey get too numerous, disease and other densitydependent factors decrease the population
During the population
drops only the least fit
individuals will die.
A change in the prey
population illicit evolution
in the predator population
and vice versa.
This Process is
Co-Evolution
Predator-Prey population trends
Prey and predator populations both follow cyclical
trends. Note that the predator lags behind the prey then
overshoots, causing its population to crash.
Niche
This encompasses all the aspects of an organism way
of life., it including:
• the physical home or habitat
•all the physical factors like temperature, pH,
type of soil, etc.
•how the organism gets its supply of energy
•its predators, prey and interactions with other
organisms.
Same Niche: Competitive
Exclusion
Gause (1934): “If two organisms are competing for
the same resources, one will be better at acquiring
those resources.”
One organism will therefore win out over another if
they are in the same niche. This is called competitive
exclusion.
Seashore Gastropod Competition
Snails of the intertidal zone will
eat algae. Niches overlap but they
are never the same. Rough
periwinkles are able to live high in
the “splash zone” avoiding direct
competition with common
periwinkles and predation by
crabs.
Both periwinkles can be observed
in the same location --------------->
Common periwinkles prefer the
lower portions of the seashore.
Barnacle Competition
Other Interactions
Symbiosis is a close relationship between different
species over an extended period of time.
• Symbiosis (“living together”)
– Parasitism (still predator and prey)
• Predator much smaller than prey
– Mutualism (everybody wins)
• Partnerships with other species
– Commensalism (at least somebody wins…)
• One species gains, the other loses nothing
Parasitism
Parasitism is a symbiotic relationship in which one
organism benefits by feeding on the other.
•
•
•
•
Nematodes in cod fish
tape worms on salmonids
tapeworm larvae in snails
But what about evolution? Are parasites
who damage or kill their host the parasites
that are always selected for? Can you
anticipate evolutionary change with the
above parasites?
Newfoundland Example:
Tapeworm from salmonid gut.
Parasite under trout skin.
Mutualism
Mutualism is a symbiotic relationship
in which both species benefit.
And...
Bacteria in our gut
Mitochondria
Nitrogen fixing bacteria
& legumes
Domesticated plants
and animals
In fact, almost every known organism has some mutualistic
relationship with at least one other organism...
Commensalism
Commensalism is a symbiotic relationship
in which one organism benefits while the
other is not harmed.
Newfoundland Example:
Barnacles on Whale Skin
Keystone Species
In some communities a certain species, called a keystone
species plays a major role in determining community
structure.
Removing a keystone species dramatically alters the
community.
Eg. The predatory Star fish
It eats the mollusks that feed on
plankton
Community Interactions
Have a look at the movies that
detail interactions on the seashore
and intertidal organisms.