Chapter 4-HB
Population Ecology
Population growth is a critical factor in specie’s ability to maintain homeostasis within its environment.
Populations of species are described by density, spatial distribution & growth rate.
I. Population dynamics
A. Population characteristics
1. Population density a.
2. b. eg. coyotes in Newark
coyotes in 5 mi. sq. area
Spatial distribution a. defined- b. dispersion-how organisms are placed in an area c. Types p. 93
UNIFORM dispersion -relatively even distribution of a species.
Eg. pine forest
CLUMPED dispersion -
Eg. schools of fish,
eg. mushrooms on a fallen log
RANDOM dispersion -
Eg. deer, large fish, etc.
3. Population ranges - a.
B. b. Distribution ~terminology p. 94
-Science~area where something lives and reproduces
-Common~distribution (passing out) eg. of report cards.
1. Limiting factors-biotic or abiotic factors that keep a population from
increasing forever (indefinitely). a. b. amount of space c.
2. Density-independent factors a. b. independent=doesn’t rely on the number of organisms, would
happen regardless of the number of organisms c. usually abiotic (limit population growth)
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-hurricane
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-drought
-fire (Ponderosa pine needs fire to kill undergrowth which takes all
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the soil nutrients from them. Heat releases seeds). d.
3.
-building dams
-pollution a. dependent= depends on b. factors which depend on density of organisms c.
-parasites
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-predation
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TYPES OF DENSITY DEPENDENT FACTORS d. Predation (Predator/prey populations fluctuate due to the
amount of food available)
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-wolves inc./ moose dec., moose dec./wolves inc. e.
-disease spreads by contact with individual organisms
-the higher the density the higher the disease the higher
the deathrate (limiting factor) f.
-when population numbers increase, so does competition
for available resources
-within same species for a resource and/or
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Eg. cornfield-mice, raccoon, deer all eat corn
High food-pop. Growth increases exponentially
Low food- pop. Growth decreases due to starvation
4. g.
-parasites spread mostly through contact
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-eg. worms-dog less dogs then less worms a. defined-how fast a population grows b. c. d. e.
__________
Mortality
-number of organisms born in a given time period (birthrate)
-number of deaths in a given time period (deathrate)
Immigration -number of organisms moving into an area
______________ -number of organisms moving out of an area f. usually immigration=emigration g. Exponential growth model (J-shaped)
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3 h.
lag phase -at beginning of reproduction when few individuals are
Eg. 2 mice---2 yrs=3 million+
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-all populations grow exponentially until limiting factors slows growth
-Resources become limited with more individuals
-occurs when exponential growth stopped by limiting factors
-growth levels off at carrying capacity i.
-the maximum number of species an area can hold for an
extended period of time
C.
-eg. deer in summer and deer in winter
-resources become limited as population nears carrying capacity
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1. Based on a. number of births per cycle (mice/elephant)
2. b. c. Life span of organism a. short life span b. abiotic & biotic factors fluctuate
-food availability
- c. plan to reproduce as many organisms in shortest time d. normally use little energy to care for their young e. usually controlled by density-independent factors f.
3 a. large organisms b. c. produces few offspring d. e. care for young
-use high energy to get genes to next generation successfully f.
Hypothesize why populations of r-strategists are usually controlled by density-independent factors, whereas populations of k-strategists are usually controlled by density-dependent factors.
Review questions
What are the characteristics of populations and how they are distributed?
What are the differences between density-independent and density-dependent limiting factors?

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What are the similarities between the different models used to quantify the growth of a population?
How does carrying capacity affect reproductive rates?
II.
Would you say that the total population is growing faster today or that it grew faster 50 years ago?
A. Human population growth fig. 11 p.100
1. a. defined-the study of human population size, density,distribution, etc. b. Human population size
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-1999-6 billion
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-2050-9 billion
2. a. Before technology, the environment kept the human population size below
carrying capacity b. Agriculture, technology,medicine reduced the number of deaths &
increased the population size
Explain why an improvement in shelter increased the survival rate of the human population.
3. a. current rate of growth is low~1.2% b. 1940-1950’s-there was a high rate of growth~2.2% c. drops in growth rate may be due to famine, AIDS & birth control
B.
1. Trends influenced by a. b. famine c.
2. Growth rates similar in countries with similar economics.
3. a. high birthrate, high deathrate to low birthrate & low deathrate b. PGR comparison of a developed country & a developing country.
Birthrate-deathrate + migration rate=PGR%
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-Developing country (Hondurus) = 2.02% c. eg. Niger 2010-2050 will have the highest PGR at 2.88%

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4. Zero population growth - birth + immigration=death + emigration
5. a. Number of males & females in pre-reproductive, reproductive
& post-reproductive years . b. affects PGR of a country/county/city
6. a. technology has allowed an increase in humans carrying capacity b. conservation of resources changes carrying capacity c. we must work at keeping humans at or below carrying capacity d. resources used mostly by developed countries
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-land then unable to absorb all the Carbon thus,
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-Global Warming e. developing countries have high PGR & will eventually use more resources
Why will disease and starvation become larger problems if the population continues to increase?
Review questions
What aspects affect human population growth?
What are the trends in human population growth?
What are the age structures of representative nongrowing, slowly growing, and rapidly growing countries?
What might be the consequences of continued population growth?
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