Ecology

1
Ecology

• Lecture 9
• Ralph Kirby

2
The struggle for Existence

• Remember Population Interactions
• Neutral 0 0
• Mutualism
• Competition - -
• Note interspecies competition
• Seek a common resource in short supply
• Food Living space etc
• See 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

3

• 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
• Light in rain forest
• Chemical interaction
• Release of toxin to kill competing organisms
• Antibiotics in soil by Streptomyces
• 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

4
Mathematical approach

• N population size
• t time
• K carrying capacity
• r rate of increase
• aN1 and ßN2 effect of interspecific competition,
  namely, where a and ß per capita effects of
  competition
• Species 1
• dN1/dt r1N1((K1-N1-aN2)/K1)
• Species 2
• dN2/dt r2N2((K2-N2-ßN1)/K2)
• No interspecific competition, then a and ß are 0
  and normal growth to carrying capacity
• Interspecific competition is density dependent

5

• (a) Species 1 alone or no competition
• (b) Species 2 alone or no competition
• (c) Species 1 inhibits growth of species 2 and
  latter goes extinct
• (d) Species 2 inhibits growth of species 1 and
  latter goes extinct
• (e) Unstable situation, both inhibit in a density
  dependent manner. Depending on initial density,
  either can make other extinct
• (f) Each species inhibits its own population
  growth more than competitor. Neither can
  eliminate competitor
• Diagonal lines are zero growth isoclines

6
Laboratory experiments to verify Lotka-Volterra
Equations

• Two Paramecium
• One with higher rate of growth
• Extinction of slower grower
• With different food supplies
• Coexistence
• Two Diatoms
• Require silica in water for growth
• Adequate silica
• Coexistence
• Inadequate silica
• One goes extinct

7
Competitive exclusion principle

• Two species possessing exactly the same
  ecological requirements cannot coexist
• One species must go extinct
• Not normal situation
• Immigration
• Use of other resources
• No selection
• No changes in the environment
• Thus most of the time species can coexist

8

• Thus if environment varies
• Then competition varies
• See secondary succession success in graph
• Also moisture
• Grass species southern African savanna
• Species change
• 1971 to 1981
• Low rainfall in 1971-1973
• This is the norm

9

• 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

10

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

11

• Similar effect for summer annuals and moisture
  gradient
• Also happens in nature with water, anoxia and
  salt stress in a salt marsh
• Chipmunks
• Alpine
• Cold tolerant
• Lodgepole
• Most aggressive
• Needs shade
• Yellow Pine
• aggressive
• Least
• Heat tolerant

12
(No Transcript)
13

• For competing species to all survive
• Partitioning of resources
• Cat species in Israel
• Cats with larger canines can kill bigger prey
• Note regular spacing of sizes
• Therefore distinct prey groups

14
Evolution is thus affected by competitionSelectio
n causes changes in resource utilization
15
See finches on Galapogos islandsBeaks of same
species are different when they compete
16

• Fundamental Niche
• Where species can exist with no competion
• Realized Niche
• Niche utilized under competition
• See cattail in water depth experiment
• See two models for species competition
• Compression
• Splitting to suboptimum periphery

17

• See effect of environmental gradients
• Note effect of competitive release

18
(No Transcript)