Population Ecology Notes PDF

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Population Ecology Notes I. Characteristics of populations : Each population has its own group of individuals of the same species in a given area : 1. Population size: number of individuals in the gene pool 2. Population density: number of individuals in a given area 3. Population distribution: pattern of distribution (uniform, random, clumped)

4. Age structure: pre-reproductive, reproductive, post-reproductive 5. Reproductive base: those individuals in the pre-reproductive or reproductive stage

II. Population Size and Exponential Growth   

Births and immigration increase population size, Deaths and emigration decrease population size Zero Population Growth (ZPG) = no net increase or decrease

Growth of populations over time: For a small population, as long as the birth rate is slightly above the death rate, a population grows exponentially with a characteristic J-curve: Example: population of 2000 mice; 200 die each month, but 1000 are born Birth rate: 1000 born / 2000 = 0.5 (50%) Death rate: 200 die / 2000 = 0.1 (10%) Net change: 0.5 - 0.1 = 0.4 (net growth rate) (40%) 

After one month: 2000 x 0.4 = 2000 + 800 = 2800 mice!

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After 2 months: 2800 x 0.4 = 2800 + 1120 = 3920 mice! After 3 months: 3920 x 0.4 = 3920 + 1568 = 5488 mice! After 1 year: 158,726 mice! After 18 months: 1,195,134 mice!...and so on

If you plot number of mice per time: J-curve Why is this exponential (or geometric - a curved line) rather than linear (or arithmetic - a straight line)? Every month, the reproductive base gets larger!

III. Limits to Population Growth Two major themes govern the growth of populations over time: 1. The resources of an environment control the growth and continued existence of populations 2. The resources of an environment are limited Few populations can live up to their biotic potential = where conditions are ideal, every member has food, shelter, no predators or pathogens in the environment, maximum reproduction. Limiting factors in the environment on food, water, minerals, predators, shelter, buildup of waste materials usually prevent organisms from reaching their biotic potential Carrying capacity: maximum number of individuals an environment's resources can sustain

Typically, after a period of exponential growth, growth levels off or even stops when the carrying capacity is reached Density-dependent factors that are related to carrying capacity: Sometimes, populations grow too large and "overshoot" their carrying capacity Overcrowding can cause diseases, pathogens, and parasites to spread quickly Examples: 1910 - Reindeer on St. Matthew Island, Alaska : 1910: 4 male, 22 female deer 1930: 250 deer 1940: 2,000 deer 1950: CRASH ! = 8 deer left! Bubonic plague in Europe, 14th century = 25 million humans died in 5 years, over 100 million died in the decades following....Effects of Yersinia pestis on the human population

A population can also "crash" due to factors like depletion of resources, buildup of wastes and pollutants. Density-independent factors: Natural or man-made disasters can reduce population size, regardless of whether carrying capacity has been reached.

IV. Human Population Growth 1. The history of human population growth: How we began sidestepping controls over our growth rate: FIRST, Humans developed the capacity to expand into new habitats   

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2,000,000 YPB (years before the present): Early humans were vegetarians, but ate meat when they could get it! 200,000 YBP: Humans organized into bands of hunter/gatherers 40,000 YBP: Hunter / gatherers spread throughout the world, using knowledge passed on to generations to live in diverse habitats by building fires, building shelter, making clothing and tools. Knowledge and language development allowed humans to survive in habitats throughout the world.

SECOND, Humans increased our carrying capacity in existing habitats 

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12,000 YBP: Humans shifted to farming - agriculture, domestication of animals and wild grasses (rice, corn, wheat, rye), irrigation, to meet specific human needs. (Human population in 10,000 BC: 5-10 million) Agriculture increased the carrying capacity for the human population.

THIRD, Humans sidestepped limiting factors over our growth rate 

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~200 YBP: (1802) Knowledge of disease processes, increased medical care, improved sanitary conditions, use of fossil fuels for heat, warmth = dropped death rate sharply. (Human population in 1800: 1,000,000,000) ~100 YBP: (1902) Development of antibiotics, surgical procedures, vaccines, machines, allowed support of larger population. (Human population in 1930: 2,000,000,000) Knowledge about disease and treatments allowed humans to sidestep limiting factors to growth.

2. Growth curve for the human population: YIKES!!!!!

3. Human Population Growth Adding a billion new people has taken LESS AND LESS time.... (PS. Fill in the numbers of the left column!!!)

Elapsed time ~2,000,000 years 10,000 years

Year ~10,000 BC 1 A.D.

Human Population 5 - 10 million 170 million

1,800 years

1800

1,000,000,000

1930

2,000,000,000

1960

3,000,000,000

1975

4,000,000,000

1987

5,000,000,000

1999

6,000,000,000

2050

??? 8,500,000,000 ???

On October 12, 1999 the population of the Earth reached 6,000,000,000 - "Y6B"

4. Births and Deaths Per Time Unit: 2004 (year shown below is 1999) Time unit

Births

Deaths

Natural increase

Year

131,468,233

54,147,021

77,321,212

Month Day

10,955,686 360,187

4,512,252 148,348

6,443,434 211,839

Hour Minute

15,008 250

6,181 103

8,827 147

Second

4.2

1.7

2.5

"Someone make it stop!"

5. What is the current world and US population? U.S. Census Bureau: US population World population Friday, April 9th, 1999

272,252,017

5,978,619,205

Monday, April 17, 2000 274,623, 248

6,064,415,203 (85 M more!)

Friday, April 24, 2001 Friday, March 1, 2002 Friday, April 17, 2004

6,142,298,012 (77 M more!) 6,208,604,220 (66 M more!) 6,360,788,963 (152 M more in 2 years)

284,036,458 286,538,112 293,034,631

Check back next year for ~75 million more!

6. Total population and population density for a select few cities: Feeling a little crowded yet? Total population People / sq. mi

City

108,978 6,069,974

276.3 3,221.4

Bloomington, IN Chicago, IL

363,811 1,249,822 96,946 8,063,164 8,546,846

268.4 407.0 175.2 2,183.1 4,847.6

Fort Wayne, IN Indianapolis, IN Kokomo, IN Los Angeles, CA New York, NY

Slightly different values (people / sq. km), worldwide population density of the 20 most populous "urban areas": OK, now we're talking crowded!!!

Top 100 countries ranked by population. Feeling a little less crowded now? You decide: which country is the most overpopulated in terms of resource consumption and creation of environmental damage? See more at Population and the Environment

U.S.A. Production / consumption of goods & services

21%

India 1%

Use of world's non-renewable resources

25%

3%

Creation of world's trash and pollution

25%

3%

5%

16%

Percent of world's population ~280 million ~1.10 billion

7. Sustaining the masses: Our staggering population growth continues even though worldwide 2,000,000,000 people live in abject poverty (malnourished or starving, without clean water, sewage treatment, medical treatment, or shelter) Every day, ~24,000 - 40,000 people die from starvation. WHY? - when there is enough food already on the planet to feed everyone? ...what are some of the real issues behind hunger? [Image]

Oxfam America Feeding a Growing World Population: Toward a "Greener" Revolution America's Second Harvest: Who are the hungry in America?

V. Population Control Many governments are trying to lower birth rates through family planning programs.  

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Average "replacement rate" of ~2 children per couple But, even if each couple on the planet decided TODAY to have only 2 kids, the human population would keep growing for another 60 years because of all the young people around today who will one day reach reproductive age! (Currently, more than 33% of the world's population is in the pre-reproductive state!) Today: total fertility rate in the US - 6.5 in 1950 and 3.1 in 1995

A country's age structure tracks the number of prople in the pre-reproductive, reproductive, and post-reproductive years. Age structures for a few countries:

Slowing the birth rate - some trends:     

Delayed reproduction: until '30s (rather than teens or 20s) Use of natural or artificial means of birth control Nature's most important check on human fertility - breastfeeding! Breastfeeding prolongs the return of menstruation after childbirth, and inhibits ovulation. Note: don't count on it :-) The erosion (in the 1930s - 60s) of breastfeeding and, with it, the early return of fertility has fueled the exponential growth of the human population! (80s and 90s - big comeback!)

VI. Population growth and economics The Demographic Transition - Differences in a country's population growth correlate with economic development    

Pre-industrial: Birth rates high, but death rates high too. Population growth is LOW Transitional: Industrial society begins. More foor, more medical care. Birth rates high, death rates lowered. Population growth is HIGH Industrial: Population is "well off" and realtively wealthy. Birth and death rates are low, but population size grows rapidly! Post-industrial: ZPG: Birth rate very low, even less that death rate, but population size is still high

Objectives:   

1. Distinguish between population size, population density, population distribution, age structure, and reproductive base. 2. Know how to calculate the net growth rate for a population, and how to graph the resulting numbers to produce a J-curve (worksheet) 3. Explain the factors that limit the biotic potential and carrying capacity of a population, including density-dependent, and density-independent limiting factors.

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4. Explain how human population growth went from 1 billion in 1800 to 6 billion in 1999. Have a reasonable estimate of the population of the US and world. 5. Know how to interpret how a country's age structure affects its growth rate. 6.Explain what the demographic transition represents - and where the US falls in this graph...