Competition - PowerPoint PPT Presentation

Loading...

PPT – Competition PowerPoint presentation | free to view - id: 44a7-MjAyM



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Competition

Description:

Now let's focus on the effects of other individuals and other species. ... Terns on Christmas Island (Ashmole 1968) ... Islands & extinction ... – PowerPoint PPT presentation

Number of Views:64
Avg rating:3.0/5.0
Slides: 77
Provided by: hartne
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Competition


1
Competition Coexistence
  • Chapter 8

2
Competition Coexistence
  • Weve seen how abiotic factors affect
    populations.
  • Now lets focus on the effects of other
    individuals and other species.

3
Species Interactions
  • Biotic interactions include
  • Herbivory
  • Predation
  • Parasitism
  • Competition
  • Mutualism
  • Commensalism

4
Species Interactions
  • Herbivory, predation, parasitism
  • Positive for one population.
  • Negative for the other population.
  • Batesian mimicry
  • Mimicry of a non-palatable species by a palatable
    one.
  • Positive for one population.
  • Negative for the other population.

5
Species Interactions
  • Amensalism
  • One-sided competition.
  • One species has a negative effect on another, but
    the reverse is not true.
  • Neutralism
  • Coexistence of non-interacting species.
  • Probably rare.

6
Species Interactions
  • Mutualism and commensalisms
  • Symbiotic relationships.
  • Species are intimately associated with one
    another.
  • Mutualism both benefit.
  • Commensalism beneficial for one neutral for
    the other.
  • Not harmful, as is the case with parasitism.

7
Species Interactions
  • Competition
  • Negative effect for both species.
  • Interspecific competition between species.
  • Intraspecific competition among members of a
    single species.

8
(No Transcript)
9
Characterizing Competition
  • Resource competition
  • Organisms compete for a limiting resource.
  • Common in invertebrates.
  • Interference competition
  • Individuals harm one another directly by physical
    force.
  • Most common in vertebrates.

10
(No Transcript)
11
Intraspecific Competition
  • Quantifying competition in plants vs. animals.
  • For plants, expressed as change in biomass.
  • For animals, expressed as change in numbers.
  • Plants can not escape competition.
  • Animals can move away from competition.

12
Intraspecific Competition
  • Yoda (1963)
  • Quantify competition between plants.
  • Yoda's Law or self-thinning rule 3/2 power
    rule.
  • Describes the increase in biomass of individual
    plants as the number of plant competitors
    decrease.

13
(No Transcript)
14
Interspecific Competition
  • Field experiments
  • Organisms can interact with all other organisms.
  • Natural variations in the abiotic environment is
    factored in.
  • Laboratory experiments
  • All important factors can be controlled.
  • Vary important factors systematically.

15
Interspecific Competition
  • Laboratory experiments show how the outcome of
    interspecific competition can vary with changes
    in the abiotic and biotic environment.

16
Interspecific Competition
  • Thomas Park competition experiments.
  • Tribolium castaneum and T. confusum flour
    beetles.
  • Large colonies of beetles can be grown in small
    containers with dry food-medium.
  • Large number of replications.

17
Interspecific Competition
  • Observed changes in population sizes over
    two-three years.
  • Waited until one species became extinct.
  • Cultures were infested with a parasite.
  • T. confusum won 89 of the time.
  • Without the parasite, T. castaneum won 67 of the
    time.
  • Either way no 100 winner.

18
Interspecific Competition
  • Microclimate effects
  • T. confusum did better in dry environments.
  • T. castaneum did better in moist environments.

19
Interspecific Competition
  • Mechanism of competition - predation of eggs.
  • Predatory tendencies varied with different
    strains.

20
Interspecific Competition
  • Parks experiments showed that the results of
    competition could vary as a function of at least
    four factors temperature, moisture, parasites,
    genetic strains.
  • Stochasticity occurred even under laboratory
    conditions.
  • Results in nature probably even more variable.

21
Interspecific Competition
  • In nature, interspecific competition may vary
    among habitats and areas.

22
Interspecific Competition
  • Assessing the importance of competition in
    natural systems.
  • Remove species A and measure the response of
    species B.
  • Difficult to do outside of laboratory.
  • Migration problems.
  • Krebs or cage effect numbers are artificially
    high.

23
  • Examples in nature
  • Parasitic wasps used to control scale pest.
  • Climate can alter competitive outcome.

24
Interspecific Competition
  • Well documented case of competition.
  • All species introduced perhaps it should be
    expected that they would be more competitive than
    if they had evolved together.
  • Study of competition important in real world
    situations.

25
Interspecific Competition
  • Is the release of multiple species of biological
    control agents beneficial?
  • Control of pests in agriculture is of paramount
    importance.
  • Biological control is seen as a preferable
    alternative to chemical control.

26
Interspecific Competition
  • Should multiple species of biological control
    agents be released?
  • Observe which enemy does the best job.
  • Is this the best strategy?
  • Intensive competition for the prey leads to lower
    effectiveness of the biological agents.
  • Greater population establishment rate with fewer
    enemy species.
  • Establishment rate of single-species releases
    were significantly greater than the simultaneous
    release of two or more species (76 vs. 50).

27
(No Transcript)
28
Frequency of Competition
  • Joe Connell (1983)
  • Competition was found in 55 of 215 species
    surveyed.
  • Effects of number of competing species
  • Single pairs competition was almost always
    reported (90).
  • Multiple species, competition was reported in 50
    of the studies.
  • Differing opinions - Schoener (1983).

29
(No Transcript)
30
Frequency of Competition
  • Common flaws of Connells Shoeners studies
  • Positive results tend to be more readily accepted
    into the literature.
  • Scientists do not study systems at random - may
    work in systems where competition is more likely
    to occur.

31
Frequency of Competition
  • Failure to reveal the true importance of
    competition in evolution and ecological time
  • Most organisms have evolved to escape competition
    and lack of fitness it may confer.
  • Competition may only occur infrequently and in
    years where resources are scarce.

32
  • Patterns of competition

33
Mechanisms of Competition
  • Consumptive or exploitative using resources
    most common.
  • Preemptive using space.
  • Overgrowth one species growing over another
    limiting light or some other resource.

34
Mechanisms of Competition
  • Chemical production of toxins.
  • Territorial defense of space.
  • Encounter transient interactions directly over
    specific resources.

35
Mechanisms of Competition
  • Consumptive most common.
  • Preemptive overgrowth primarily sessile
    organisms.
  • Territorial and encounter primarily actively
    moving animals.
  • Chemical terrestrial plants (and some sponges
    corals).

36
Frequency of Competition
  • Often, only one member of a pair of species
    responded to experimental manipulations.
  • Asymmetric competition should be expected
    superior competitor may be limited by some other
    factor.
  • Amensalism

37
Frequency of Competition
  • Differing views of competition
  • Gurevitch et al. 1992
  • Found no differences in competition between
    different habitat types but did find filter
    feeders and herbivores competed more than
    carnivores or plants.

38
Frequency of Competition
  • Grime 1979
  • Competition unimportant for plants in
    unproductive environments.
  • Tilman 1988
  • Competition occurs across all productivity
    gradients resources involved may differ.
  • Supported by Gurevitchs results.

39
Modeling Competition
  • The effect of competition on the growth of a
    population can be predicted by mathematical
    models.

40
Modeling Competition
  • Lotka-Volterra competition models are based on
    the logistic equation of population growth the
    s-shaped curve from chapter 6.

41
Modeling Competition
  • Four possible outcomes of the Lotka-Volterra
    competition equations
  • Species 2 eliminated.
  • Species 1 eliminated.
  • Either species 1 or species 2 eliminated,
    depending on starting conditions.
  • Both species coexist.

42
Modeling Competition
  • Test of Lotka-Volterra equations
  • Populations of yeast are greater in pure cultures
    than in mixed cultures, although logistic growth
    curve is still followed.
  • Carrying capacity is set by alcohol concentration
    a by-product that increases as the colonies
    grow.

43
Modeling Competition
  • The values obtained from the Lotka-Volterra
    equations were in general agreement with
    experimental results.

44
Modeling Competition
  • Deficiencies
  • The maximal rate of increase, the competition
    coefficients, and the carrying capacity are all
    assumed to be constant.
  • There are no time lags.
  • Field tests of these equations have rarely been
    performed.
  • Laboratory tests have shown divergence.

45
Modeling Competition
  • Mechanisms that drive competition are not
    specified in the Lotka-Volterra model.
  • R - Tilman (1982, 1987) alternative.
  • Need to know the dependence of an organism's
    growth on the availability of resources.

46
Modeling Competition
  • Theoretically, the species with the lowest R
    will outcompete all others.
  • Sometimes there are several limiting factors,
    allowing coexistence.

47
Modeling Competition
  • Coexistence may occur in a spatially variable
    habitat, where if a species is out-competed in
    one area, it may win in another.
  • Or, herbivores may graze vigorous competitors
    preventing them from taking over.

48
Coexistence of Species
  • Niche
  • Grinnell (1918) a subdivision of a habitat that
    contains an organism's' dietary needs, its
    temperature, moisture, pH, and other
    requirements.
  • Elton (1927) and Hutchinson (1958) an organism's
    role within the community.

49
Coexistence of Species
  • Gause two species with similar requirements
    could not live together in the same place.
  • Gause's principle, known as competitive exclusion
    principle, where direct competitors cannot
    coexist.

50
Coexistence of Species
  • David Lack Competition and coexistence in about
    40 pairs of birds was mediated by habitat
    segregation.

51
Coexistence of Species
  • Examples of coexistence
  • Darwin's finches on the Galapagos.
  • Terns on Christmas Island (Ashmole 1968).

52
Coexistence of Species
  • Ranks for resource partitioning (Schoener 1974)
  • Macrohabitat (55).
  • Food type (40).
  • Time of day or year (5).

53
Coexistence of Species
  • Hutchinson (1959)
  • Seminal paper, "Homage to Santa Rosalia, or why
    are there so many kinds of animals?"
  • Examined size differences for
  • Sympatric species (species occurring together).
  • Allopatric species (occurring alone).
  • Hutchinson's ratio, 11.3.

54
Coexistence of Species
  • Criticism of Hutchinson
  • Further tests showed no differences between
    species than would occur by chance alone.
  • Size-ratio differences could have evolved for
    other reasons.
  • Biological significance cannot always be attached
    to ratios, particularly to structures not used to
    gather food.

55
Coexistence of Species
  • Support of Hutchinson
  • d/w analysis for separation on continuous
    resource sets.
  • d distance between maxima.
  • w measure of spread.

Resource partitioning Three species with
similar, normal resource utilization curves
utilize a resource supply K. Variables d
distance between means, w standard deviation of
resource utilization, and d/w resource
separation ratio.
56
Division of resources along two niche dimensions.
57
Coexistence of Species
  • Resources can have a discontinuous distribution
    or occur in distinct units, like leaves on a
    shrub.

58
Coexistence of Species
  • Two insect species one feeds toward the top of
    the plant, the other feeds all over except at
    very top bottom.
  • Overlap only on 2nd 3rd pairs of leaves.

59
Coexistence of Species
  • The niche overlap between the two insect species
    can be measured by the proportional similarity
    (PS).

60
Coexistence of Species
  • PS resource.
  • PS 0.70 indicates competitive exclusion for
    single resource.

61
Coexistence of Species
  • Proportional similarity indices for two or more
    resources can be combined.
  • Multiply separate PS values to determine overall
    PS value.
  • Coexistence for two resources
  • 0.70 x 0.70 0.49 or less.

62
Summary
  • Competition may be interspecific or
    intraspecific.
  • Competition may be viewed as resource competition
    or interference competition.
  • Intraspecific competition between plants may be
    described by the 3/2 self-thinning rule.

63
Summary
  • Outcome of competition can be influenced by
  • Environmental conditions.
  • The presence or absence of natural enemies.
  • The genetic strain of the competitors involved.

64
Summary
  • Experimental studies show that in nature
    competition occurs between different types of
    organisms over a broad scale.
  • Such studies focused on exotics and
    generalizations to natural ecosystems are
    questionable.

65
Summary
  • Competition between exotics and native species
  • Serious consequences for natural ecosystems.
  • Frequency of competition.
  • 55 to 75 of species involved.
  • Competition is often asymmetric.

66
Summary
  • Six mechanisms of competition
  • Consumptive
  • Preemptive
  • Overgrowth
  • Chemical
  • Territorial
  • Encounter

67
Summary
  • Lotka-Volterra model early competition model.
  • Two species interaction.
  • Four possible outcomes
  • Species 1 becomes extinct.
  • Species 2 becomes extinct.
  • Either species 1 or species 2 becomes extinct
    based on starting conditions.
  • Coexistence.

68
Summary
  • Competition is minimized and species can coexist
    if they use different resources.
  • How much can they overlap?
  • Hutchinson's 11.3 ratio.
  • d/w values greater than unity.
  • Proportional similarity (PS) values no greater
    than 70 (0.70).

69
Review
  • Chapter 1 Why How to Study Ecology
  • What is ecology?
  • Four main areas of ecology
  • Factors limiting population size
  • Ecosystem functions
  • Biodiversity
  • Four hypotheses concerning diversity
  • What are statistical tests?
  • Correlation
  • Types of experiments
  • Spatial and Temporal Scales

70
Review
  • Chapter 2 Genetics Ecology
  • How are new species formed?
  • What is a mutation?
  • Types of mutations
  • Importance of genetic variation
  • Inbreeding
  • Genetic drift
  • Neighborhoods
  • 50/500 rule
  • Effect of immigration

71
Review
  • Chapter 3 Extinction
  • Definition
  • What does fossil record show regarding
    extinction?
  • Large scale extinctions 11-13 thousand years ago
    causes
  • How do humans cause extinctions?
  • Islands extinction
  • Introduced species
  • Characteristics of organisms that may contribute
    to likelihood of extinction
  • Endangered species

72
Review
  • Chapter 4 Group/Individual Selection
  • What is group selection?
  • What is individual selection?
  • Which is the favored theory?
  • Altruism
  • Kin selection including case study
  • Many-eyes hypothesis
  • Selfish herd theory

73
Review
  • Chapter 5 Life History Strategies
  • Semelparous vs. Iteroparous
  • Reproductive strategy and population age
    structure
  • What happens when an age class is removed?
    (overfishing removes older, over browsing removes
    younger age class)
  • Sex ratio what is it and how is it maintained
  • Monogamy/polygyny/polyandry
  • Resource based polygyny
  • r-selected vs. K-selected species -
    characteristics

74
  • Chapter 6 Population Growth
  • Life tables what are they what do they show
  • Time-specific vs. age specific life tables
  • Survivorship curves Types I, II, III
  • Net reproductive rate what is it
  • What happens if net reproductive rate is equal to
    one, greater than or less than 1?
  • Geometric growth (what is it, shape of curve)
  • Logistic growth (what is it, shape of curve)
  • Assumptions problems
  • Deterministic vs. stochastic models
  • What are stochastic models based on, what do they
    introduce that was not present in deterministic
    models and why is this valuable?

75
  • Chapter 7 Physical Environment
  • Distribution and abundance of many species are
    limited by abiotic factors what are they and
    how do they affect distribution and abundance?
  • Liebigs law of the minimum
  • Optimum range
  • Ectotherms vs. endotherms
  • Degree-days
  • Fire before after arrival of Europeans
  • Global warming
  • Greenhouse effect
  • Human influences on greenhouse effect
  • Positive negative feedback
  • Effect of climate change on natural communities

76
  • Chapter 8 Competition Coexistence
  • Competition Interspecific vs. Intraspecific
  • Types of biotic interactions
  • Herbivory
  • Predation
  • Parasitism
  • Competition
  • Mutualism
  • Commensalism
  • Resource vs. interference competition
  • 3/2 thinning rule
  • What influences the outcome of competition?
  • Competition between exotics natives
  • Frequency of competition
  • What are the 6 mechanisms of competition?
  • Lotka-Volterra model outcomes
  • Hutchinsons 11.3 ratio
  • Proportional Similarity
About PowerShow.com