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Community Interactions
Chapter 47
Community Interactions
Habitat is a place where an organism lives and it is
characterized by distinctive physical and chemical
features, as well as the array of species living in it.
Community is an association of the populations of
all species that occupy the same habitat
Niche - the sum of all activities and relationships in
which its individuals engage as they secure and use
the resources required for their survival and
reproduction.
The fundamental (potential) niche is the one that could
prevail in the absence of competition
The realized niche result from shifts in large and small
ways over time, as individuals of the species respond to
changes
Categories of Species Interactions
Interactions can occur b/w any two species in a community
Several types of species interactions -
(1) Commensalism - one species benefits and the other
is not affected (ex. Bird’s nest in a tree)
(2) Mutualism - a symbiotic relationship where both
species benefit (plants and their pollinators)
(3) Parasitism - one species (parasite) benefits while the
other (host) is harmed.
(4) Competition - both species are harmed by the
interaction
(5) Predation
Competitive Exclusion
Competitive Exclusion suggests that complete competitors
cannot coexist indefinitely.
- When competitor’s niches do not overlap as much, the
coexistence is more probable
- Differences in adaptive traits will give certain species the
competitive edge.
Resource Partitioning
Resource Partitioning - similar
species share the same resources
in different ways.
Arises in 2 ways:
Bristly
foxtail
(1) Ecological differences b/w
established & competing
populations may increase
through natural selection
(2) only species that are
dissimilar from established
ones can succeed in joining an
existing community
Indian
mallow
Smartweed
Predation
Predation
Predation vs. Parasitism :
Predators get their food from prey, but they do not
take up residence on or in the prey, typically their
prey are killed outright or mutilated.
Parasites get their food from host, and they live on
or in the host for a good part of their life cycle;
they may or may not kill the host.
Many of the adaptations of predators and their victims arose
through coevolution - the joint evolution of two or more
species that exert selection pressure on each other as an
outcome of close ecological interaction.
Adaptations that arise as a result of
Predator-Prey Interactions …
Coevolution
Camouflage
- any adaptation in form, color,
patterning, or behavior that
allows a prey or predator to
blend with its surroundings
Warning Coloration Toxic prey offer bright
colors or bold patterns that
serve as a warning to
predators
Mimicry - Prey not
equipped with defenses
may escape predation by
resembling toxic prey
Yellow Jacket
Mimic
Monarch butterfly
Mimic
Mimic
Moment-of-truth Defense allow prey animals to defend
themselves by startling or
intimidating the predator
with display behavior
Predator Response to Prey
— adaptations used by
predators to counter prey
defenses
Forces Contributing to Community Stability
Succession model
Ecological succession - is the predictable developmental sequence
of species in a community
Pioneer species - first to colonize an area
Climax community - most persistent array of species that results
after some lapse of time
Primary succession - happens in an area that was devoid of life
and begins with a pioneer species (ex. new volcanic island or land exposed
when a glacier retreats)
Secondary succession - is when a community re-establishes itself
to a climax state after a disturbance (abandoned fields, burned forest)
Community Instability
Keystone species - a dominant species that
can dictate community structure
Exotic species - Australia & Rabbits / Kudzu
Caulerpa taxifolia suffocating
a marine ecosystem
Mainland and Marine Patterns
Tropics - Greatest number of
coexisting species
• Resource availability is greatest b/c
more rainfall & sunlight
• Species diversity might be selfreinforcing
• Rates of speciation in the tropics
have exceeded those of background
extinction
Island Patterns
Island Patterns
Distance Effect
islands distant from source
areas receive fewer
colonizing species
Area Effect
Larger island supports more species