Download Population ecology Definitions Characteristics of Populations Age

Definitions
Population
ecology
• Habitat
• Population
• Community
• Ecosystem
• Biotic Factors
• Abiotic Factors
Characteristics of Populations
Age Structure Diagrams
• Size
Shows age distribution of a population
• Age Structure
• Density
• Distribution
45.1
Rapid
Growth
Slow
Growth
Zero
Growth
Negative
Growth
Distribution
Distribution
clumped
• Different species occupying the same
area compete…
• Clumped populations:
– Suitable physical, chemical,
and biological conditions
are patchy, not uniform.
– These interactions influence the density
and dispersion of individuals and
populations.
– Social groups
– Offspring not mobile
45.1
45.1
1
Distribution
Distribution
• Rare in nature
uniform
random
• Result of fierce
competition for very
limited resources
• Uniform environmental
conditions
• Members are neither
attracting nor repelling
each other
45.1
45.1
Capture-Recapture Method
Determining population size
• Direct counts are most accurate but
seldom feasible
Total population size
Total captured in
sampling 2
Marked individuals in
sampling at time 1
Marked individuals in
sampling at time 2
• Sample an area, then extrapolate
• Capture-recapture method is used for
mobile species
45.2
45.2
Survivorship Curves
• represent age-specific patterns of death for a
given pop in a given environment
• Each species has a characteristic curve.
• Three types of curves are common in nature.
45.5
Fig. 45-10a, p.805
2
Fig. 45-10c, p.805
Fig. 45-10b, p.805
Reproductive Strategies
Life History Patterns
• Patterns of timing of reproduction and
survivorship
• Vary among species
• Different environments and population
densities can favor different reproductive
strategies
• r-selection favors traits that maximize
number of offspring
• Summarized in survivorship curves and
• K-selection favors traits that improve
offspring quality
life tables
Life History and Reproductive Strategies-Certain combinations of traits tend to occur
together:
Trait
r-selected
K-selected
Lifespan
Short
Long
Growth rate
Fast
Slow
1st Reproduction
Early
Late
Reproductive effort
High
Low
Parental care
Less
More
Offspring
Many, small
Few, large
Reproductive
episodes
all at once
more than once
Kind of environment
Variable
Stable
r- or K- selected?
•
•
•
•
•
•
Mouse
Mushroom
Oak tree
Human
Elephant
Dandelion
3
r
• Net reproduction per individual per
unit time
Population Growth
r =
b
-
d
• Can be used to calculate rate of
growth of a population
45.3
45.3
Exponential Growth
(G)
Per capita
growth rate
x
Total
population
(r)
(N)
POPULATION SIZE
Population
growth per =
unit time
G=r x N
Exponential Growth: Any quantity that is growing at
a rate proportional to its size.
TIME
45.3
45.3
Biotic Potential
• Biotic potential: Maximum rate of increase
Limits on Growth of
Populations
per individual (r) under ideal conditions
• Varies between species
• In nature, biotic potential is rarely reached
Limiting factor: any essential
resource that is in short supply
45.3
4
Carrying Capacity (K)
Actual rate of increase is influenced by
environmental conditions:
• nutrient supply
• competition for space
• Pollution
• floods
• etc.
• Maximum number of individuals that
can be sustained in a particular
habitat
• Logistic growth occurs when
population size is limited by carrying
capacity
45.4
45.4
Logistic Growth
Logistic Growth
Population
growth per unit =
time
(G)
Net
reproduction
per indiv. per
unit time
x
#
Individuals
(N)
x
Proportion
of resources
not yet used
(r)
45.4
45.4
Overshooting Capacity
• Population may
temporarily increase
above carrying
capacity
POPULATION SIZE
Carrying capacity
Resources
become limiting
Births = Deaths
• Overshoot is usually
followed by a crash;
dramatic increase in
deaths
Fastest growth of pop.
Resources
abundant
Births > Deaths
Reindeer on St. Matthew’s Island
TIME
45.4
Fig. 45-9, p.803
5
Density-Dependent Factors
Density-Independent factors
• Logistic growth equation
• Factors unaffected by population
density.
deals with densitydependent controls
• Natural disasters, climate changes, etc.
• Limiting factors become
more intense as
population size increases
45.4
Human Populations
World population density
Human Population Problems
Side-Stepping Growth Controls
• World pop reached 6 billion in
1999
current population
• About 2 billion live in poverty
• Most resources are consumed by
the relatively few people in
developed countries
• Expanded into new habitats
• Agriculture increased carrying
capacity; use of fossil fuels aided
increase
• Hygiene and medicine lessened
effects of density-dependent controls
6
Future Growth
Human Population Growth
• Exponential growth cannot continue
forever
• Breakthroughs in technology may
further increase carrying capacity
• Eventually, density-dependent factors
will slow growth
Fertility Rates
• Worldwide, average annual rate of
increase is 2.6%
• Total fertility rate (TFR) is average
number of children born
• Highest in developing countries, lowest
in developed countries
Fig. 45-17b, p.815
7