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Lecture 9 BIOL 3500 Chapter 11: Intraspecific Population Regulation Learning Objectives Contrast: Density dependance vs. independence Scramble vs. contest competition Home range vs. territory Define: “Self thinning” Philopatry Discuss: Effects of crowding Density Dependence

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lecture 9

Lecture 9

BIOL 3500

Chapter 11: Intraspecific Population Regulation

learning objectives
Learning Objectives
  • Contrast:
    • Density dependance vs. independence
    • Scramble vs. contest competition
    • Home range vs. territory
  • Define:
    • “Self thinning”
    • Philopatry
  • Discuss:
    • Effects of crowding
density dependence
Density Dependence
  • Refers to factors regulating population, effect is proportional to pop size.
  • Number of indiv affected depends upon intensity.
    • Ex: food limitation, communicable disease
birthrate mortality rate
Birthrate & Mortality Rate
  • Density dependent factors can affect either or both
density independence
Density Independence
  • Refers to pop-infuencing factors not influenced by pop size.
  • Typically what we call “natural disasters”
    • Ex: hurricanes, fire
competition
Competition
  • Will occur any time there are more individuals than a resource can support
    • One resource will limit
    • If it becomes plentiful, another resource will become limiting
two types of competition
Two Types of Competition
  • Intraspecific
    • Between individuals of the same species (Chapter 11)
  • Interspecific
    • Between individuals of different species (Chapter 14)
two more types of competition
Two More Types of Competition
  • Scramble competition
    • All individuals are depressed equally
      • Too many pine trees planted in a forest (all will be small)
  • Contest competition
    • Some individuals are better at getting limited resources
      • Baby birds in a nest (big one gets most of food)
crowding and tadpoles
Crowding and Tadpoles
  • Tadpoles grown in higher density population have lower mean body mass
  • Slower to reach maturity
  • Presumably compete for food
crowding and clover
Crowding and Clover
  • White clovers grown at high density have decreased mean weight
bluegills and crowding
Bluegills and Crowding
  • When stocked at high density, only small fish result
    • May never reach breeding size
  • Careful monitoring of size, control of stocking rates important
    • MSU website
    • NC State website
question
Question
  • We already knew that limited resources cause reduced growth
  • We saw that competition causes limitation in resources, and affects growth
    • Is the response of an organism in competition different in intensity than just resource limitation?
competition and limitation
Competition and Limitation

Two types of pots: 1 plant vs. 16 plants

Broadleaf Peppermint

Note: water is per pot

Limitation + competition interact! (shape of curves is different)

horseweed
Horseweed
  • Unlike pine trees, tadpoles, or bluegills, horseweed is “self thinning”
    • If too crowded, competition will kill some
reproduction interspecific competition
Reproduction & Interspecific Competition

Fecundity of females can change under competition

Most notable in large mammals

Bison have sharp drop

Grizzly bears affected linearly

harp seals
Harp Seals
  • Age of sexual maturity depends upon population density
fecundity and plants
Fecundity and Plants

Corn and salt marsh plants

quick review
Quick Review:
  • List all the ways that intraspecific competition can regulate a population.
stress and competition in animals
Stress and Competition in Animals
  • Crowding may cause increased aggression
  • Stress causes hormone changes, resulting in:
    • Retarded growth rate
    • Delayed onset of reproducton
    • Reproductive failure (miscarriage, low birth weight)
    • Immune system compromise
social dominance
Social Dominance
  • Among wolves, usually only alpha male and alpha female mate
    • All others are prevented from doing so
  • When food becomes limiting, subordinates are chased out of the pack
    • Lone wolves have harder time hunting (mortality increases)
home range
Home Range
  • Home range = area used by one individual over a year
    • Size often depends upon food needs
      • Type of food
      • Amount (ie: body size of individual)
    • Sex matters too. Males’ ranges generally bigger. Why?
territoriality
Territoriality
  • Territory = part of the home range, actively defended
    • Birds might sing, display, fight for an area
    • Grasshopper sparrows return to same territory yearly (philopatry)