Interactions Between Populations
Interactions Between Populations
• Traditional approaches to population
interactions have been to consider just the
direct pairwise interactions
• This is simplistic in that the population either
interact, or they do not
Interactions Between Populations
• There are a number of ways in which the
populations my impact one another, if they do
Interactions Between Populations
• Competition ( - , - ) is the most widely
interaction we think of
• Both parties are negatively impacted
• If the resource is in short supply or high
demand, there will be competition
• If that resource is prey, the form of
competition is exploitation competition
Interactions Between Populations
• Other kinds of competition also occur
• It may be direct (agonistic) encounters such as
allelopathy or territorial defense
(interference)
Interactions Between Populations
• Predation, parasitism, and Batesian mimicry
• Predation is usually killing another organism,
although can you think of exceptions?
• Parasitism could be considered a form of
‘weak’ predation
Interactions Between Populations
• Batesian mimicry and herbivory could also be
a form of ‘weak’ predation
Interactions Between Populations
• Mutualism, Müllerian mimicry
Interactions Between Populations
• Commensalism
Interactions Between Populations
• Amensalism
Interactions Between Populations
• The interactions among populations can
become quite intricate and therefore quite
fascinating
• Consider the case of hummingbirds
Interactions Between Populations
• Four nectar feeding birds, two species of mites
and four species of flowers
• Three hummingbirds are
the primary pollinators
• Corollas differ in length
• Strong selection for a bird/
flower relationship
Interactions Between Populations
• One mite lives in Panterpe and Eugenes,
others are specialists
• Even though suitable ‘habitat’ is found in
other flowers, they are not found there..why?
• Male mites will actively
fight/kill other species of
mites within the same flower
Interactions Between Populations
• Within this 10 species community there is
(and please name them)
• exploitative competition, interference
competition, facultative mutualism,
parasitism, and commensalism
Interactions Between Populations
• Symbiosis is a term used for a general
relationship in which organisms live together
without harming one another
• Neutralism: who cares
• Mutualism: Acacia & ants
Interactions Between Populations
• Ants and many species of caterpillars
Interactions Between Populations
• Mesquite and root nodules housing bacteria
that fix nitrogen
• Mycorrhizae (fungal roots)
Interactions Between Populations
• Bioluminescent bacteria and deep sea
creatures
• Photosynthetic algae
Interactions Between Populations
• It has been hypothesized that ‘endosymbiosis’
exists
• The certain of the cell organelles found in
higher organisms, particularly chloroplasts and
mitochondria, are actually the remnants of
symbiotic prokaryotic organisms that have
since been permanently incorporated into the
eukaryotes
Interactions Between Populations
• Cattle egrets & oxpeckers
Interactions Between Populations
• Honey guides and honey badgers
Interactions Between Populations
• Cleaner wrasse
• Saber-toothed
bleeny
Interactions Between Populations
• Think about the plant/pollinator relationships
that exist
• Not just large animals, but many insects (e.g.
euglossine bees and epiphytic orchids)
• Up to 23km
• Outcrossing
Interactions Between Populations
• Producing nectar and pollen (and fruit) has
costs
• Rewards must be sufficient to allow returns to
get them to specialize on a particular species
(why?)
• However, they must be small
enough to the animal will
travel the distance between
plants
Interactions Between Populations
• Obligate mutualisms are much less common
than facultative ones
• Figs and fig wasps (100’s)
Interactions Between Populations
Interactions Between Populations
• Termites and the protozoans they house in
their intestines
• Next generation of endosymbionts are passed
to one another through
shared
intestinal contents
Interactions Between Populations
• Commensalism
Interactions Between Populations
• What about indirect interactions
• Darwin actually accounted for this
• E.g. clover, bees, mice and cats
Interactions Between Populations
Interactions Between Populations
• There is the classical exploitative competition
• But there is also ‘apparent’ competition
(consider
Interactions Between Populations
• There are also ‘food-chain mutualisms’ (aka
cascading effects)
• Aquatic example: plants, minnows,
and bass
• Is it ‘bottom-up’ or ‘top-down’?
Interactions Between Populations
• Consider three species’ populations at the
same trophic level (horizontal interactions)
• P1 and P3 are mutualists because they both
inhibit P2
Interactions Between Populations
• A four-species system that results in an
indirect mutualism is termed facilitation
• Consumers indirectly interact as they eat
similar, but different prey items (but the plants
themselves compete)
Interactions Between Populations
• Conditions that
can lead to CM
• There is a
considerable
time lag in the
indirect effects
of CM
Interactions Between Populations
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Interactions Between Populations