BIOL 4120: Principles of Ecology Lecture 12: Interspecfic competition

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BIOL 4120 Principles of Ecology Lecture 12
Interspecfic competition

• Dafeng Hui
• Room Harned Hall 320
• Phone [phone]
• Email dhui_at_tnstate.edu

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Outline (chapter 13)
13.1 Interspcific competition 13.2 Lotka-Volterra
model 13.3 Laboratory experiments support L-V
model 13.4 Competitive exclusion principle 13.5
Competition is influenced by nonresource
factos 13.6 Temporal variation in environmental
factors 13.7 Multiple resources 13.8 Competition
change along environmental gradients 13.9 Niches
of species 13.10 Resource partitioning 13.11
Competition influence national selection 13.12
Competition involves biotic and abiotic factors
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13.1 Interspecific competition

• A relationship in which the populations of two or
  more species are affected adversely (--)
• Seek a common resource in short supply
• Food Living space etc
• An example squirrels, mice, deer, various birds
  competing for acorns
• Model One. Two forms
• Exploitation
• Interference
• Model Two. Six forms
• Consumption
• preemption
• Overgrowth
• Chemical interaction
• Territorial
• encounter

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• Consumption
• Utilization of a shared resource by 2 species
• Preemption
• Occupation of a site by 1st organism stops
  occupation by 2nd organism
• Usually sessile organisms
• Overgrowth
• Where organism covers another preventing access
  to a resource. Trees shade other plants
• Chemical interaction
• Release of toxin to inhibit or kill competing
  organisms
• Allelopathy in plants
• Territorial
• Behavioral exclusion of 1st organism by 2nd
  organism defending territory
• Encounter
• Non-territorial encounters cause a negative
  effect on one or both species
• Lion and wild dogs over a antelope kill

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12.2 Possible outcomes of Interspecific
competition

• When two species compete, how many outcomes?
• Species 1 wins, species 2 loses
• Species 1 loses, species 2 wins
• Coexistence (stable equilibrium)
• Competition can go wither way (unstable
  equilibrium)
• These competition results can be described by
  Lotka-Volterra model.

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Lokta-Volterra Model
Derived from logistic equation Add influence
of another species (a competition component)
alpha(2,1)alpha Alpha(1,2)beta
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Lokta-Volterra Model

• aN2 and ßN1 effect of interspecific competition,
  namely, where a and ß per capita effects of
  competition
• In term of resource use, an individual of species
  2 is equal to a individuals of species 1
• No interspecific competition, then a and ß are 0
  and normal growth to carrying capacity
• Interspecific competition is density dependent

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(a) Species 1 alone or no competition
Diagonal line is zero growth isocline
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(b) Species 2 alone or no competition
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(c) Species 1 inhibits growth of species 2 and
latter goes extinct
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(d) Species 2 inhibits growth of species 1 and
latter goes extinct
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(e) Unstable situation, both inhibit in a density
dependent manner. Depending on initial density,
either can make other extinct
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(f) Each species inhibits its own population
growth more than competitor. Neither can
eliminate competitor
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(No Transcript)
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13.3 Laboratory experiments support the
Lotka-Volterra Equations
Russian biologist G.F. Gause Competition between
two species P. aurelia has a high growth rate
and can tolerate a higher population density
Two Paramecium (unicellular ciliated
protozoan) One with higher rate of growth
Extinction of slower grower With different food
supplies Coexistence
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Diatom experiment
David Tilman, University of Minnesota Asterinella
formosa (Af) and Synedra ulna(Su) compete for
silica for the formation of cell walls. Adequate
silica, coexist Insufficient silica, Su drove Af
to extinction
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13. 4 Competitive exclusion principle

• Complete competitors can not coexist. One species
  must go extinct
• Complete competitions two species that live in
  the same place and possess exactly the same
  ecological requirements.
• Assumptions
• Exactly the same resource requirement (no more,
  no less)
• Environmental conditions remain constant
• Most of the time species can coexist

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13.5 Competition is influenced by non-resource
factors

• Many non-resource factors would influence the
  outcomes of the competition. For example, space,
  light.
• Favor species with high photosynthetic rate,
  allocate C to height growth and leaves production
  (fast-grow species)

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Patterns of seed germination along T gradient
Fakhri Bazzaz, Harvard University (Retired) Five
annual species T influences the germination, thus
seedling establishment, resource competition and
structure of community.
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13.6 Temporal variation in environment influences
competition interactions

• As environmental conditions vary, the competition
  advantages change
• No one species can reach sufficient density to
  displace its competitors
• Thus lead to co-exist.

Shift in dominant grass species caused by moisture
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13.7 Competition occurs for multiple resources

• Systems are not simple one resource situations
• Usually competition for more than one resource
• Territorial defense against wide range of other
  species
• Plants
• Monoculture
• Root competition
• Skeleton weed reduce by 35
• Shoot competition
• Skeleton weed reduced by 53
• Root and shoot competition
• Skeleton weed reduced by 69
• Thus clover superior to skeleton weed for all
  resources

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13.8 Relative competition abilities change along
environmental gradients

• Effect of interspecific competition across an
  environmental gradient
• Note changes in response when in mixture

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• Similar effect for summer annuals and moisture
  gradient
• Also happens in nature with water, anoxia and
  salt stress in a salt marsh

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Chipmunks Alpine Cold tolerant Lodgepole Most
aggressive Needs shade Yellow Pine aggressive Leas
t Heat tolerant
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13.9 Niche of a species

• Concepts of niche
• describes how an organism or population responds
  to the distribution of resources and competitors
  (e. g., by growing when resources are abundant,
  and predators, parasites and pathogens are
  scarce) and how it in turn alters those same
  factors.
• dimensions of a niche represent different biotic
  and abiotic variables.
• These factors may include descriptions of the
  organism's life history, habitat, trophic
  position (place in the food chain), and
  geographic range.
• According to the competitive exclusion principle,
  no two species can occupy the same niche in the
  same environment for a long time.

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• Concepts of niche
• Fundamental niche range of conditions and
  resources a species can use to survive and
  reproduce under no interference by other species
• Realized niche portion of fundamental niches
  that a species actually exploits as a result of
  interactions with other species (e.g.,
  competition).

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Examples
Distribution of twp species of cattail (Typha
latifolia and T. angustifolia) Fundamental
Niche Tl water depth -20 70 cm Ta
-20110 cm Realized Niche Tl -20 70
cm Ta 20 110 cm (Changes) Niche overlap
20-70 cm
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Fundamental and realized niches
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Competition release

• A species expands its niche in response to the
  removal of a competitor
• Two examples
• Response of Stipa neomexicana plants
• Commercial whaling in Antarctic Ocean

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Response of Stipa neomexicana plants
Jessica Gurevitch University of New York at Stony
Brook Stipa C3 perennial grass Semi-arid
grassland in Arizona
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Commercial whaling in Antarctic Ocean

• Baleen whales 1 million a century ago
• eat Antarctic krill (4 of body weight)
• Now, less than 200,000
• Other krill-dependent predators such as seals and
  penguins have been found greatly increased in
  abundance

Competition release due to the dramatic decrease
in baleen whale population
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13.10 Resource partitioning

• Complete competitors can not co-exist
• Why did not the best competitor force others out?
• Co-existing species must be different in the use
  of resources
• Niche differentiation differences in the range
  of resources used or environmental tolerance
• Examples
• Plants grow together
• Animals share the same habitat

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Resource partitioning
Use water and nutrients at different
depths Spatial differentiation.
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Resource partitioning
Size (diameter) of canine teeth for small cat
that co-occur in Israel. Size is correlated with
size of prey selected by different species.
Morphological differentiation.
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Another example

• Seven Anolis lizards in tropical rainforest
• Share common food needs mainly insects.
• They avoid competition by occupying different
  sections of the rainforest
• the leaf litter floor
• shady branches
• All resources are subject to partitioning, such
  as space, food, nesting sites.
• This minimizes competition between similar
  species.
• (Temporal differentiation.)

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Niche dimensions
Rarely do two or more species possess exactly the
same combination of requirement. Species may
overlap on one D of the niche, but not on another.
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13.11 Competition can influence natural selection

• Competition is at the heart of Darwins theory of
  natural selection. Characteristics that enable an
  organisms to reduce competition will function to
  increase fitness.

Character displacement
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Character displacement

• The outcome of the competition was a shift in
  feeding niches. When the shift involves features
  of the species morphology, behavior, or
  physiology
• The process of evolution toward niche divergence
  in the face of competition

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13.12 Competition involves both biotic and
abiotic factors

• Removal experiment is an effective method to
  study competition
• Hidden treatment effects removal changes space,
  light, soil temperature, and moisture,
  evaporation.
• Competition is a complex interaction involving a
  variety of environmental factors that directly
  influence survival, growth, and reproduction.
• Outcome of competition may differ markedly under
  different set of environmental conditions.

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End
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FACILITIES MANAGEMENT DEPARTMENTDEPARTMENTAL
NOTIFICATION

• LOCATION
• CAMPUS-WIDE
•  
• PROJECT
• IN RESPONSE TO THE DROUGHT AND HEAT THIS SUMMER,
  ALL TREES THAT HAVE EXCEEDED THEIR PERMANENT
  WILTING POINTS WILL BE REMOVED
•  
• DURATION  
• TWO DAYS, OCTOBER 15-16, 2007 (FALL BREAK)

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• Science 12 October 2007Vol. 318. no. 5848, pp.
  268 271
• Reports
• Functional Divergence of Former Alleles in an
  Ancient Asexual Invertebrate
• Natalia N. Pouchkina-Stantcheva, et al.
• Theory suggests it should be difficult for
  asexual organisms to adapt to a changing
  environment because genetic diversity can only
  arise from mutations accumulating within direct
  antecedents and not through sexual exchange.

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• Science Reports (cont.)
• Functional Divergence of Former Alleles in an
  Ancient Asexual Invertebrate
• Natalia N. Pouchkina-Stantcheva, et al.
• In an asexual microinvertebrate, the bdelloid
  rotifer, we have observed a mechanism by which
  such organisms could acquire the diversity needed
  for adaptation. Gene copies most likely
  representing former alleles have diverged in
  function so that the proteins they encode play
  complementary roles in survival of dry
  conditions.

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• Science Reports (cont.)
• Functional Divergence of Former Alleles in an
  Ancient Asexual Invertebrate
• Natalia N. Pouchkina-Stantcheva, et al.
• One protein prevents desiccation-sensitive
  enzymes from aggregating during drying, whereas
  its counterpart does not have this activity, but
  is able to associate with phospholipid bilayers
  and is potentially involved in maintenance of
  membrane integrity. The functional divergence of
  former alleles observed here suggests that
  adoption of asexual reproduction could itself be
  an evolutionary mechanism for the generation of
  diversity.

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Al Gore, UN panel share Nobel for Peace

• Al Gore
• U.N.'s IPCC (Intergovernmental Panel on Climate
  Change)
• For Global warming