Download Define the scope of population ecology

AP Biology, Chapter 52
Population Ecology
SUMMARY
INTRODUCTION
CHARACTERISTICS OF POPULATIONS
Introduction
Two important characteristics of any population are density and the spacing of
individuals
1. Define and distinguish between density and dispersion.
a. Definitions
i. Density = number per unit of area
ii. Dispersion is the pattern of spacing between individuals
b. Distinction: dispersion shows finer detail
2. Describe conditions that may result in the clumped dispersion, uniform
dispersion, and random dispersion of populations.
a. Clumped
i. From heterogeneous resources
ii. Most common
b. Uniform
i. From interactions among individuals
ii. For example, plants avoiding one another's shade
c. Random
i. From lack of interaction and homogeneous environment
ii. For example, trees in a rainforest
Demography is the study of factors that affect the growth and decline of
populations
3. Describe the characteristics of populations that exhibit Type I, Type II, and
Type III survivorship curves.
a. Type I
a. High survivorship until late in lifespan
b. Large size, few offspring, good care
c. Humans, elephants, condors
b. Type II
a. Constant proportion dies at each age
b. Annual plants, Hydra, gray squirrel
c. Type III
a. Very high death rates for the young
b. Small size, many offspring, little or no care
c. Invertebrates, salmon
LIFE HISTORY OF TRAITS
Introduction
Life histories are highly diverse but exhibit patterns in their variability
Limited resources mandate trade-offs between investments in reproduction
and in survival
4. Explain how limited resources affect life histories.
a. Life history = schedule of reproduction and death
b. Desert plants germinate, produce many seeds, and die in a rainy
month
c. Tropical species, subject to greater competition, have fewer offspring
5. Give examples of the trade-off between reproduction and survival.
a. Fecundity is inversely proportional to probability of death in birds
b. Restriction of reproduction in beetles lengthens life
c. Flycatchers burdened with many eggs produce fewer the following
year
6. Define and distinguish between semelparity and iteroparity.
a. Semelparous species breed once in their lifetimes
i. Called "big-bang"
ii. Salmon and agave
b. Iteroparous species breed repeatedly
POPULATION GROWTH MODELS
Introduction
An exponential model of population growth describes an ideal population in an
unlimited environment
7. Compare the geometric model of population growth with the logistic model.
a. Geometric = exponential
i. dN/dt = rmaxN
.dN/dt is the instantaneous growth rate
. rmax is the intrinsic rate of increase, = birth rate - death
rate
.N is the population size
ii. Ever steeper curve
iii. Not sustainable
A logistic model of population growth incorporates the concept of carrying
capacity
b. Logistic
i. dN/dt = rmaxN((K-N)/K)
.dN/dt is the instantaneous growth rate
. rmax is the intrinsic rate of increase
.N is the population size
.K is the carrying capacity
ii. S-shaped curve
iii. Levels off at the carrying capacity
8. Explain how an environment's carrying capacity affects the intrinsic rate of
increase of a population.
a. Real populations rarely have infinite resources
b. The closer to the carrying capacity, the slower the growth
c. There may be overshoot and fluctuation at K
9. Distinguish between r-selected populations and K-selected populations.
a. r-selected: adapted for high growth when possible
i. Early mauturation, short life, small size, high death rate, many
offspring, no parental care
ii. Bacteria, insects, weeds
b. K-selected: adapted for equilibrium at carrying capacity
i. Late mauturation, long life, large size, low death rate, few
offspring, much parental care
ii. Humans, elephants
POPULATION LIMITING FACTORS
Introduction
Density-dependent factors regulate population growth by varying with density
10. Explain how density-dependent factors affect population growth.
a. Usually more intense when populations are more dense
b. Competition, predation, disease, stress, waste accumulation
The occurrence and severity of density-independent factors are unrelated to
population density
11. Explain how density-independent factors affect population growth.
a. Not affected by density
b. Natural disasters and habitat destruction by humans
A mix of density-dependent and density-independent factors probably limits
the growth of most populations
Some populations have regular boom and bust cycles
12. Describe several boom-and-bust population cycles, noting possible causes
and consequences of the fluctuations.
a. Examples
i. Cicada 13 and 17 year life cycles
ii. Lemmings
iii. Snowshoe hare and lynx
b. Causes
i. Cicadas evade predation
ii. Crowding may affect endocrine systems
iii. Lagging response to density-dependent factors
HUMAN POPULATION GROWTH
Introduction
The human population has been growing almost exponentially for centuries
but cannot do so indefinitely
12. Describe the history of human population growth.
a. Exponential growth since the Industrial Revolution
b. Birth rate steady, death rate down from medicine, sanitation, etc.
c. Greatest pressure on the global environment
13. Define the demographic transition.
a. Transition from high birth and death rates to low
b. First death rates drop
c. There is a period of rapid growth
d. Then birth rates drop and population size stabilizes
14. Compare the age structures of Italy, Kenya, and the United States. Describe
the possible consequences for each country.
a. Italy has a smaller fraction of pre-reproductive and reproductive; no
growth
b. Kenya has a high fraction of pre-reproductive and reproductive; high
growth
c. Us is in between, moderate growth