Intraspecific Population Regulation

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Chapter 11

• Intraspecific Population Regulation

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I. Population growth curves

• No population grows indefinitely
• Will confront the limits of environment
• Most do not grow exponentially
• Interactions tend to regulate populations size

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II. Regulation by growth mechanisms

1. Density-dependence regulation by mechanisms
   controlled by size of population
2. Density-independence effects of influence do
   not change with population density

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1. Density-dependent

• Effect increases as population size increases
• No influence at low density
• Larger population / more individuals affected
• Largely through competition for resources

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2. Density-independent

• Effects do not change with population density
• Proportion of individuals affected same at any
  density
• Can have significant impact on populations
• Can mask or eliminate density-dependent regulation

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III. Competition

• Among same species individuals for resources
• One aspect of population regulation
• 2 kinds of competition
• Scramble competitionno onereceives enough of
  the resource
• Contest competitionsome claim enough and deny
  others a share

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• Limited resource will cause species to exhibit
  only one type of competition
• Scramble competitionproduces chaotic
  oscillations in populations
• Wastes resourceslimits average density to below
  carrying capacity of habitat
• Contest competitioncauses a fraction to suffer
  (unsuccessful individuals)
• Eliminates waste of resources
• Permits maintenance of high density

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• As populations increase toward insufficient
  resources, scrambling competition reduces food
  intake.
• this slows growth and limits reproduction
• seen in overstocking of fish
• vertebrates fecundity affected
• Biomassa function of accumulated living tissue
• can be few large or many smaller individuals

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IV. Aggression

• High density causes stress
• Aggressive contacts increases
• Stress triggers hyperactivation endocrine glands
• Suppresses growth, reproduction and immune
  system

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V. Coping with stress

• Pheromones encourage or inhibit reproduction
• Seeking new vacant habitatdispersal
• Success rate low
• Few arrive at suitable habitat and flourish
• Dispersal before resource depletion is important
  with low density

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VI. Dispersal

• Individuals dispersed are normally in good
  condition, either sex, any agegood chance of
  survival
• Relocation habitats have increased resources
  breeding sites, decreased competition
• Distance relative to availability of habitat
• Requires a source and sink

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VII. Social issues of populations

• Social behavior limits populations
• Surplus animals, not breeding, or attempting and
  failing
• Prevented from breeding
• Removal of dominant animals results in breeding
  of surplus animals
• Breeding animals not using all space or food

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Social organization

• Common in populations
• Based on aggressiveness, intolerance and
  dominance of one over another
• 2 opposing forces at work
• Mutual attraction
• Negative reaction against crowding and need for
  personal space

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Simple social organization

• Alpha individualdominant over all
• Betadominant over all except alpha
• Omegasubordinate to all
• Rankings established by fighting, bluffing,
  threatening
• Ranking maintained by habitual subordination and
  punishment
• Important for populationsstabilizes
  intraspecific competition
• Resolves disputes with minimal energy

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IX. Movement and distribution

• The space occupied during a year home range
• May differ with sex
• Not defended
• Range defended territory
• Varies with availability of food
• Size of territory
• Carnivores gt herbivores/omnivores
• Dominant gt subordinate
• Males gt females
• Adults gt subadults

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Territoriality

• Animal defends exclusive area no shared with
  rivals
• Occurs in regular patterns of distribution
• Costly in energy and time
• May interfere with breeding, feeding and rearing
  of young
• Quality territory dominant male
• Floating reserveevicted individuals

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X. Territory vs home ranges

• Indicates the carrying capacity
• Management becomes ecological/economical problem
• Plants can be territorial
• Shading and competition for nutrients
• Release of organic toxins

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XI. Review

• Density dependent influences? population growth
  and fecundity
• Density independent factors may be more important
• May eliminate density dependent factors
• May go beyond a limit of tolerance