definitions population ecology - linn–benton...
TRANSCRIPT
1
Population ecology
Definitions
• Habitat
• Population
• Community
• Ecosystem
• Biotic Factors
• Abiotic Factors
Characteristics of Populations
• Size
• Age Structure
• Density
• Distribution
45.1
Age Structure Diagrams
Shows age distribution of a population
Rapid Growth
Slow Growth
Zero Growth
Negative Growth
• Different species occupying the same
area compete…
– These interactions influence the density and dispersion of individuals and
populations.
Distribution
45.1
Distribution
clumped • Clumped populations:
– Suitable physical, chemical, and biological conditions are patchy, not uniform.
– Social groups
– Offspring not mobile
45.1
2
Distribution
• Rare in nature
• Result of fierce
competition for very
limited resources
uniform
45.1
Distribution
• Uniform environmental
conditions
• Members are neither
attracting nor repelling each other
random
45.1
Determining population size
• Direct counts are most accurate but
seldom feasible
• Sample an area, then extrapolate
• Capture-recapture method is used for mobile species
45.2
Capture-Recapture Method
Total captured in sampling 2
Marked individuals in sampling at time 2
Total population size
Marked individuals in sampling at time 1
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.
45.5Fig. 45-10a, p.805
3
Fig. 45-10b, p.805 Fig. 45-10c, p.805
Life History Patterns
• Patterns of timing of reproduction and
survivorship
• Vary among species
• Summarized in survivorship curves and
life tables
Reproductive Strategies
• Different environments and population densities can favor different reproductive strategies
• r-selection favors traits that maximize number of offspring
• K-selection favors traits that improve offspring quality
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
4
Population Growth
45.3
r
• Net reproduction per individual per
unit time
• Can be used to calculate rate of
growth of a population
45.3
r = b - d
Exponential Growth
45.3
Population growth per unit time
(G)
Per capita growth rate
(r)
Total population
(N)
x=
G=r x N
Exponential Growth: Any quantity that is growing at a rate proportional to its size.
TIME
PO
PU
LATI
ON
SIZ
E
45.3
Biotic Potential
• Biotic potential: Maximum rate of increase
per individual (r) under ideal conditions
• Varies between species
• In nature, biotic potential is rarely reached
45.3
Limits on Growth of
Populations
Limiting factor: any essential
resource that is in short supply
5
Actual rate of increase is influenced by
environmental conditions:
• nutrient supply
• competition for space
• Pollution
• floods
• etc.
45.4
Carrying Capacity (K)
• Maximum number of individuals that
can be sustained in a particular
habitat
• Logistic growth occurs when
population size is limited by carrying
capacity45.4
Logistic Growth
45.4
Logistic Growth
Population
growth per unit time
(G)
Net
reproduction per indiv. per
unit time
(r)
#
Individuals
(N)
x=Proportion
of resources not yet used
x
45.4
TIME
PO
PU
LATI
ON
SIZ
E
Fastest growth of pop.
Births > Deaths
Resources
abundant
Resources
become limiting Births = Deaths
Carrying capacity
45.4
Overshooting Capacity
• Population may
temporarily increase
above carrying
capacity
• Overshoot is usually
followed by a crash;
dramatic increase in
deaths
Reindeer on St. Matthew’s Island
Fig. 45-9, p.803
6
Density-Dependent Factors
• Logistic growth equation
deals with density-
dependent controls
• Limiting factors become
more intense as
population size increases
45.4
• Factors unaffected by population
density.
• Natural disasters, climate changes, etc.
Density-Independent factors
Human Populations World population density
Human Population Problems
• 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
Side-Stepping Growth Controls
• Expanded into new habitats
• Agriculture increased carrying
capacity; use of fossil fuels aided
increase
• Hygiene and medicine lessened
effects of density-dependent controls
7
Human Population Growth Future 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