Transcript Carrying Capacity

Carrying Capacity
How do limiting factors effect a
population?
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
Carrying Capacity
The maximum number of individuals of a
population that can be supported in a given
environment sustainably.
Density – Independent Factors
Drought
Freezes
Hurricanes
Floods
Forest Fires
Darwin’s Finches
This graph (from P. T. Boag
and P.R. Grant in Science,
214:82, 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.
Checks on populations growth
Island populations are particularly sensitive to
population decline brought about by catastrophic
events
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
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
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.
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
Density – Dependent Factors
Migration
– As population increases, many of its members
emigrate
Density – Dependent Factors
Predation
– As population increases, its predators are able to
harvest more easily
Ex – Flour Beetle
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.
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
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