Carrying Capacity

1
Carrying Capacity

• How do limiting factors effect a population?

2
Limiting Factors

• Those factors which are in low supply and
  therefore have the effect of keeping down
  limiting the growth of a population
• Ex availability of food, water, shelter, and
  space competition for resources, predation, and
  disease

3
Carrying Capacity

• The maximum number of individuals of a population
  that can be supported in a given environment
  sustainably.

4
Density Independent Factors

• Drought
• Freezes
• Hurricanes
• Floods
• Forest Fires

5
Darwins Finches

• This graph (from P. T. Boag and P.R. Grant in
  Science, 21482, 1981) shows the decline in the
  population of one of Darwin's finches brought on
  by severe drought that reduced the quantity of
  seeds on which this species feeds. As drought
  ended in 1978, the population recovered but not
  to the pre 1975 numbers due to change in the
  carrying capacity.

6
Checks on populations growth

• Island populations are particularly sensitive to
• population decline brought about by catastrophic
• events

7
Density Dependent Factors

• Intraspecific Competition
• Between members of the same species
• Ex Gypsy Moth
• 1980 infestation in New England
• Resulted in larger infestation in 1981
• Offspring of 1980 parents
• Caterpillars defoliated 50 foot trees in 72 hours
• Mass die out

8
Density Dependent Factors

• Interspecific Competition
• When two species share overlapping niches, they
  may be forced into competition for the resources
  of that niche
• Ex - Paramecia

9
Paramecia

• This graph (based on the work of G. F. Gause)
  shows the effect of interspecific competition on
  the population size of two species of paramecia,
  Paramecium aurelia and Paramecium caudatum.
• When the two species were cultured together, P.
  aurelia is the better competitor of the two
  species.
• Notice initial growth followed by decline in the
  P.caudatum.
• The population of P. aurelia is always greater
  than that of P.caudatum.

10
Density Dependent Factors

• Reproductive Competition
• Declining birth rates lead to reduced population
• Ex Fruit Flies, Lab rats, Honeybees
• Living under crowded conditions have fewer
  offspring

11
Density Dependent Factors

• Migration
• As population increases, many of its members
  emigrate

12
Density Dependent Factors

• Predation
• As population increases, its predators are able
  to harvest more easily
• Ex Flour Beetle

13
Flour Beetle

• In graph1, 2 species of flour beetle were started
  with equal numbers. Tribolium population
  increases while Oryzaephilus is driven to
  extinction.
• Graph 2 shows both species again but glass tubes
  have been added to the medium. Notice how the
  difference in population in population growth of
  Oryzaephilus.

14
Density Dependent Factors

• Parasitism
• Parasite are able to pass from host to host more
  easily as the population density of the hosts
  increases
• Ex Black Death
• Epidemics are more severe in cities than rural
  areas

15
Population Cycles

• Some populations go through regular periods of
  boom and bust
• Driven by predation, or infestation of parasites
• Ex voles, red grouse, and lemmings