Download AP Biology, Chapter 53 Population Ecology Counting Sheep 53.1

AP Biology, Chapter 53
Population Ecology
Counting Sheep
53.1 Dynamic biological processes influence population density, dispersion, and demographics
Intro
Density and Dispersion
Intro
1. Define and distinguish between density and dispersion.
Density
= number per unit of area
Not static; birth, death, immigration, and emigration
Dispersion
= pattern of spacing between individuals
Dispersion shows finer detail
Density: A Dynamic Perspective
2. How are animal population sizes estimated by the mark-recapture
method?
Some(s) are marked, released, and allowed time to mix in
Second sample: # marked (x) and total (n) are counted
Pop. Size (N) = sn/x
Patterns of Dispersion
3. Describe conditions that may result in the clumped, uniform, and
random dispersion of populations.
Clumped
From heterogeneous resources
Most common
Uniform
From interactions among individuals like territoriality
For example, plants avoiding one another's shade
Random
From lack of interaction and homogeneous
environment
For example, trees in a rainforest
Demographics
Intro
Life Tables
Survivorship Curves
4. Describe the characteristics of populations that exhibit Type I, Type II,
and Type III survivorship curves.
Type I
High survivorship until late in lifespan (elephants)
Large size, few offspring, good care
Type II: constant proportion dies at each age gray squirrel)
Type III
Very high death rates for the young (invertebrates)
Small size, many offspring, little or no care
Reproductive Rates
53.2 The exponential model describes population growth in an idealized, unlimited
environment
Intro
Per Capita Rate of Increase
5. How are the most basic demographic statistics combined to calculate the
change in population size?
In a fixed interval
Change = Births + Immigrants – Deaths - Emigrants
Exponential Growth
6. Describe the exponential model of population growth.
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
Ever steeper; not sustainable
53.3 The logistic model describes how a population grows more slowly ast it nears its carrying
capacity
Intro
The Logistic Growth Model
7. Describe the exponential model of population growth.
dN/dt = rmaxN((K-N)/K)
K is the carrying capacity
As N approaches K, dN/dt approaches zero
S-shaped curve; levels off at the carrying capacity
The Logistic Model and Real Populations
8. Explain how an environment's carrying capacity affects the intrinsic rate of
increase of a population.
Real populations rarely have infinite resources
The closer to the carrying capacity, the slower the growth
There may be overshoot and fluctuation at K
9. How does the Allee effect counter an assumption built into the logistic
model?
Assumption each new individual has a negative effect on growth
Allee effect: populations can be too small
Sparse populations may make finding a mate difficult
Smaller groups may not be able to defend
53.4 Life history traits are products of natural selection
Intro
10. What main traits make up an organism’s life history?
Age at first reproduction
Frequency of reproduction
# of offspring per episode
Evolution and Life History Diversity
11. Define and distinguish between semelparity and iteroparity.
Semelparous species breed once in their lifetimes
Called "big-bang"
Salmon and agave
Iteroparous species breed repeatedly
12. How may resource availability affect the evolution of life histories.
Variable, unpredictable environments
Large numbers of offspring
Ex.: desert plants germinate, produce many seeds, and die in a
rainy month
Dependable environments
More intense competition; fewer, larger young
Ex.: tropical species like Brazil nut trees
“Trade-offs” and Life Histories
13. Give examples of the trade-off between reproduction and survival.
Fecundity is inversely proportional to probability of death in birds
Restriction of reproduction in beetles lengthens life
Flycatchers burdened with many eggs produce fewer the following year
14. Distinguish between r-selected populations and K-selected populations.
r-selected: adapted for high growth when possible
Early mauturation, short life, small size, high death rate, many
offspring, no parental care
Ex.: bacteria, insects, weeds
K-selected: adapted for equilibrium at carrying capacity
Late mauturation, long life, large size, low death rate, few
offspring, much parental care
Humans, elephants
53.5 Many factors that regulate population growth are density dependent
Intro
Population Change and Population Density
15. Explain how density-dependent factors affect population growth.
Usually more intense when populations are more dense
Competition, predation, disease, stress, waste accumulation
16. Explain how density-independent factors affect population growth.
Not affected by density
Natural disasters and habitat destruction by humans
Mechanisms of Density-Dependent Population Regulation
Intro
17. How may feedback mediate density-dependent population
regulation?
Competition for Resources
Predation
Denser population uses up resources faster
Fewer resources means less reproduction, greater mortality
Lower density allows resources to recover
Toxic Wastes
Intrinsic factors
As population density increases, stress increases, fertility drops
As population growth slows density drops
Lower density eases stress and increases fertility
Territoriality
Disease
Denser populations allow easier transmission
Easier transmission means more disease/mortality
Lowered density lowers the incidence of disease
Population Dynamics
Intro
Stability and Fluctuation
18. Describe several boom-and-bust population cycles, noting possible
causes and consequences of the fluctuations.
Cicada 13 and 17 year life cycles: evade predation
Snowshoe hare and lynx: carrying capacity overshoot
Population Cycles: Scientific Inquiry
Immigration, Emigration, and Metapopulations
19. How are immigration and emigration affected by changing densities
in metapopulations?
Metapopulation= linked local populations
Higher density in one part increases emigration
53.6 The human population is no longer growing exponentially but is still increasing rapidly
Intro
The Global Human Population
Intro
20. Describe the history of human population growth.
Exponential growth since the Industrial Revolution
Birth rate steady, death rate down from medicine, sanitation, etc.
Greatest pressure on the global environment
Regional patterns of Population Change
21. Define the demographic transition.
Transition from high birth and death rates to low
First death rates drop
There is a period of rapid growth
Then birth rates drop and population size stabilizes
Age Structure
22. Compare the age structures of Italy, Kenya, and the United States.
Describe the possible consequences for each country.
Italy has a smaller fraction of pre-reproductive and
reproductive; no growth
Kenya has a high fraction of pre-reproductive and reproductive;
high growth
Us is in between, moderate growth
Infant Mortality and Life Expectancy
Global carrying Capacity
Intro
23. When is the global human population projected to reach ZPG and
what is the projected peak size?
2075?
8-12 billion?
Estimates of Carrying Capacity
24. What methods have been used to estimate our carrying capacity?
Logistic growth curves
“Maximum” population density time habitable area
Combine amount of farmland, yield, diet
Limits on Human Population Size
25. How is the ecological footprint concept applied to the calculation of
Earth’s carrying capacity?
Ecological footprint
All of the land and water area required per person
Includes production of resources and absorption of
wastes
Application
1.7 hectares/person = sustainability
U.S. uses 10 ha/person