1. How do limiting factors effect a population?
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. 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.

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