6. Population Density and
Spatial Distribution
Population density is the number of individuals
per unit area.
• High population density
– injures all individuals within the population
– because they compete for resources
7. 7.2 A Population Growth Curve
Biotic potential is the inherent reproductive
capacity of a species
• (biological ability to produce offspring).
biotic potential is much above replacement level.
• natural tendency for increase
11. Population growth curve
Lag Phase:
first portion of the curve
slow population growth
Few births
12. Population growth curve
Exponential Growth Phase (Log Phase):
More organisms reproducing
causing accelerated growth
continues if birth rate exceeds death rate
13. 7.2 Population Growth Curve
• Deceleration Phase:
– The population growth rate slows
– death rate and birthrate equal one another
14. 7.2 Population Growth Curve
Stable Equilibrium Phase:
The death rate and birth rate become equal
the population stops growing
15. 7.3 Factors That Limit Population Size
Limiting Factors--prevent unlimited population
growth
• Extrinsic limiting factors
• Intrinsic limiting factors
• Density-dependent factors
• Density-independent factors
16. 7.3 Factors That Limit Population Size
Extrinsic limiting factors
Come from outside the population
•
•
•
•
Predators
Loss of food source
Lack of sunlight
Accidents of nature
17. 7.3 Factors That Limit Population Size
Intrinsic limiting factors
• factors that originate within the population
• exercise control over it
• Behavioral changes amongst the population cause
lower birthrates and higher death rates.
18. Other limiting factors
Density-dependent limiting factors
• become more effective as the density of the
population increases.
• Denser population
– Predators more effective
19. Other limiting factors
Density-independent limiting factors
• population-controlling influences not related to the
density of the population.
• Accidental
• Extrinsic factors
20. Density dependent or independent?
Mutualism between two species.
A wolf eating rabbits.
A large fire burns down many of the trees in a
forest.
A disease kills all the mice in a local radius and
the foxes have nothing to eat.
21. 7.4 Categories of Limiting Factors
For most populations, limiting factors recognized
as components of environmental resistance
•
•
•
•
Raw material availability
Energy availability
Accumulation of waste products
Interactions among organisms
24. 7.5 Carrying Capacity
Carrying capacity is the maximum sustainable
population for an area.
It is not an inflexible number; it can be
influenced by environmental differences
27. 7.6 Reproductive Strategies
and Population Fluctuations
Species divided into two broad categories based
on their reproductive strategies:
• K-strategists
• r-strategists
28. 7.6 Reproductive Strategies
K-strategists: Organisms that typically reach a stable
population as the population reaches the carrying
capacity.
K-strategist characteristics:
Usually occupy relatively stable environments
• Large organisms
• Long-lived
• Produce few offspring
29. 7.6 Reproductive Strategies
and Population Fluctuations
K-strategist characteristics:
• Provide substantial parental care
• Reproductive strategy
– invest a great deal of energy in producing a few offspring
that have a good chance of living to reproduce.
K-strategists
• controlled by density-dependent limiting factors.
31. 7.6 Reproductive Strategies
r-strategist characteristics include:
•
•
•
•
•
Small, short-lived organisms
Produce many offspring
Little if any parental care
Exploit unstable environments
Usually do not reach carrying capacity (boom-bust
cycles)
35. Summary
The birthrate (natality) is the number of individuals
entering the population by reproduction during a
certain period.
The death rate is the number of deaths in a
population in a certain period.
A typical population growth curve shows a lag
phase followed by an exponential growth phase, a
deceleration phase, and a stable equilibrium
phase at the carrying capacity.
37. 11.3 Invasive Species
Impact populations (affect population size)
Some introductions of exotic species are
purposeful, while others are accidental.
Globalization is responsible for spreading
thousands of invasive alien species around the
world.
38. 11.3 Invasive species
The IUCN estimates about
• 30% of birds and 15% of plants are threatened
• because they are unable to successfully compete against
invasive exotic species.
Various insects have had an effect on ecosystem
structure.
• Asian long horned beetle
Freshwater ecosystems have been greatly affected.
• Zebra mussel