Factors Limiting Distribution: Interrelations With Other Species Chapter 6

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Factors Limiting Distribution Interrelations
With Other Species Chapter 6
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Types of Interactions

• Negative Interactions
• Predation, competition, disease, parasitism
• Positive Interactions
• Mutualism, symbiosis

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Predation

• Prey can be a food plant and the predator a
  herbivore.
• Or prey can be a herbivore and the predator a
  carnivore.

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Predation restriction of prey by predator

• Predators are sometime able to restrict local
  distributions of some prey
• Experiments have shown this to be true when
• Prey individuals will survive when transplanted
  to a site where they do not normally occur if
  they are protected from predators.
• The distribution of prey organisms and suspected
  predator(s) are inversely correlated.
• The suspected predator is able to kill the prey,
  both in the field and laboratory.
• The suspected predator can be shown to be
  responsible for the destruction of the prey in
  transplantation experiments.

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Predation Examples Mussel Transplant
Tidal Open Coast heavy wave action restricts
the size of mussels and prevents predators from
eliminating small mussels Sheltered Waters
Predators eliminate most of the small mussels,
and Mytilus survive only in areas safe from
predators
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Predation on Kelp

• Kelp is a large plant-like brown algae.
• Several herbivores are known to eat kelp.
• There is an inverse correlation between the
  presence of kelp and sea urchins.
• Need to control for other herbivores

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Kelp Predator Controlled Population
It appears that sea urchins are mostly
responsible for controlling kelp
leafy cover From Fletcher 1987
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Rock Wallaby Predator Controlled Population
In Australia, Rock Wallaby populations have been
declining since the introduction of the red
fox. When red foxes are removed, rock wallaby
populations expand.
Extinct Population!
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Rat-kangaroo Predator Controlled Population
Only exists in areas where the red fox is
absent. This case, as well as the others,
demonstrate that predation can control local
distributions of populations.
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Restriction Of Predators By Prey

• If a prey restricts a predators range, then that
  predator must feed only on one or two species of
  that prey.
• Mostly plant/herbivore interactions
• These type of predators are called specialists or
  monophagous.
• One example is Drosphila pachea, a rare fruit fly
  that only breeds in the stems of senita cactus.
• They contain a unique factor needed for growth
  and development by the fly

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Monphagous Insects
Monophagous insects should be limited in their
distribution by their host plant but no species
to date has demonstrated this (Quinn et al. 1998)
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Disease and Parasitism

• Pathogens may eliminate species from areas and
  thereby restrict geographical distribution.
• Chestnut blight

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Hawaiian Bird Populations - disease control
Introduced birds are less susceptible to malaria
than native birds. Mosquitoes much more common in
low elevations. Malaria is most common at
intermediate elevations native birds more
susceptible and species overlap.
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Allelopathy

• Some organisms, plants in particular, may be
  limited in local distributions by poisons or
  antibiotics, also called allelopathic agents.
• Penicillin, toxic secretions from plants

Studies have shown that some plant species
produce a toxin that limits the growth of others.
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Smother Crops
Smother crops act as weed suppressors. It is not
competition for nutrition or water, but rather a
toxic secretion that limits growth.
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Competition

• Competition can occur between any two species
  that use the same type of resource.
• Competition is an important process affecting the
  distribution of plants and animals.
• Species do not need to be closely related
• Birds, rodents, and ants all compete for seeds in
  the desert.

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Competition

• Resource competition when a number of organisms
  utilize common resources that are in short
  supply.
• Interference competition when the organisms
  seeking a resource harm one another in the
  process, even if the resource is not in short
  supply.
• When species A is absent, species B lives in a
  wider range of habitats.
• In extreme cases a habitat will contain either A
  or B, but neither both together.

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Checkerboard Distributions
Two ecologically similar species that have
mutually exclusive but interdigitating
distributions.
Islands may have been colonized by
first-come-first-served basis or slight
competitive advantage.
Two closely related species of fruit pigeons.
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Competition Between Two Salamanders

• Plethodon jordani and P. glutinosus (Hairston
  1980).
• Altitudinal distribution only overlaps 70 120m
  on any one transect up the Black Mountains in
  North Carolina.
• Hairston demonstrated that by removing one
  species, the other expanded its range.
• Superior competitor was excluding the other
  species from preferred habitat of moist soil and
  food.

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Competition

• When two species compete, one always will always
  be better than the other in gathering or
  utilizing the resource that is rare.
• In the long run, the other species either loses
  out and disappears or evolves some adaptation.
• Avoid the superior competitor by selecting a
  different part of habitat.
• Avoid the superior competitor by making a change
  in diet.

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Example - Shift in Diet
These species of the European crossbill have
avoided competition by developing beaks that
allow the use of different food types.