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
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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.