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Biodiversity, Species Interactions,
and Population Control
Chapter 5
5-1 How Do Species Interact?
 Concept 5-1 Five types of species interactions –
competition, predation, parasitism, mutualism,
and commensalism – affect the resource use and
population sizes of the species in an ecosystem.
Species
Interactions
COMPETITION
 Organisms compete for shared or limited resources
such as food, water, space, and habitats.
 Competitive exclusion principle – No two species
can occupy the exact same niche for very long
• More in Section 5-2
COMPETITION
 Interspecific competition is the competition
between member of two different species. The
result is that neither species can obtain as many
resources as they could in the absence of the
other species.
 Intraspecific competition is the competition
between member of the same species.
• This also includes the competition
for mates.
PREDATION
 Species called predators feed on other species
called prey.
 Organisms use their senses to locate objects and
their prey.
 Some predators are fast enough to catch their prey,
some hide and lie in wait, and some inject chemicals
to paralyze their prey.
PREDATION
 Some prey may escape their
predators by:
• Camouflage
• Outer protection
• Chemical warfare
• Warning coloration
• Mimicry
• Deceptive looks
• Deceptive behavior
Predator and Prey Species Can Drive
Each Other’s Evolution
 Intense natural selection pressures exist between
predator and prey populations
 Coevolution – changes in the gene pool of one
species can lead to changes in another species
• Evolution in the predator population – improved abilities to capture prey
• Evolutionary response – the prey improves its abilities to avoid capture
• The evolution of improved escape abilities should result in increased
capture abilities.
 Evolutionary “arms race”
• The levels of defense and counter-defense will continue
to escalate.
Parasitism
 Parasitism occurs when one species feeds on part
of another organism.
 Although parasites can harm their hosts, they can
promote community biodiversity.
• Some parasites live inside the host (micororganisms,
tapeworms).
• Some parasites live outside the host (fleas, ticks,
mistletoe plants, sea lampreys).
• Some have little contact with host (cowbirds – lay eggs in
another’s nest…let them take care of young.)
Parasitism
Mutualism
 In mutualism, two species interact
in a way that benefits both of them.
 Most organisms benefit through
mutualistic interactions by gaining
nutrition or protection.
Commensalism
 Commensalism is an
interaction that benefits
one species but has little,
if any, effect on the other
species.
 Epiphytes
5-2 How Can Natural Selection Reduce
Competition between Species?
 Concept 5-2 Some species develop
adaptations that allow them to reduce or avoid
competition with other species for resources.
5-2 How Can Natural Selection Reduce
Competition between Species?
 Niches (way of life)
become separated to
avoid competition for
resources.
• Reduce niche overlap
 This is also the basis of
natural selection – the
pressure that drives the
evolution of new
species.
• Chapter 4
5-2 How Can Natural Selection Reduce
Competition between Species?
 Some species evolve adaptations that allow them to
reduce or avoid competition for resources with other
species (resource partitioning).
 Each species minimizes competition with the others for food by spending
at least half its feeding time in a distinct portion of the spruce tree and by
consuming somewhat different insect species.
5-2 How Can Natural Selection Reduce
Competition between Species?
 Genetic variation and
specialized feeding niches
can lead to evolutionary
divergence.
 Use shared resources at
different:
• Times
• Places
• Ways
 Each species has a beak
specialized to take
advantage of certain types
of food resource.