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)/N)
					.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