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CHAPTER 52 POPULATION ECOLOGY Characteristics Density Distribution Size Age Structure Density Direct Counts– Larger, less numerous organisms Plankton Population Sampling – Time x velocity x diameter = M3 – Total # of plankton/ M3 = # plankton per M3 – 75 plankton/0.5 M3 = 150/M3 Mark & Recapture- many animals Aerial Surveys – – Line transects etc. – observe large areas, large animals by sight Mist nets for migrating birds Mark & Recapture # marked in 1st catch = # recaptures in 2nd catch Population total total # in 2nd catch OR: N = # marked in 1st catch x total # in 2nd catch # of recaptures in 2nd catch # marked = 50 recaptures = 10 N = 50 x 100/10 Total in 2nd catch = 100 # N = 500 Dispersion How the individuals are arranged in the landscape. Uniform – – all parts of the habitat suitable, but has intraspecific competition Random – all parts of habitat suitable Clumped– Habitat is patchy or – Social behaviors Dispersion Population Size Starting size of population Add: Births and immigration Subtract: Deaths and emigration Gives the New population size, Population Growth Time # Females Eggs/Female # Flies 1 1 100 100 2 50 100 5,000 3 2,500 100 250,000 4 125,000 100 12,500,000 5 6,250,000 100 625,000,000 6 312,000,000 100 31,250.000,000 7 15,625,000,000 100 1,563,500,000,000 Exponential Growth Growth curve for field Mice in a cornfield Exponential Growth Biotic Potential – Pop. Grows as fast as physiology allows. Unlimited resources No pollution build up Ideal conditions Short lived period Often quickly die out, colonize new areas Fig. 9.4, p. 201 R selected species Population size (N) Time (t) Exponential Growth Logistic Growth Logistic Growth Slower initial growth Long –term stable pop. At carrying capacity (K). K is size of pop. Area can sustain. Growth slowed by limiting factors Population size (N) K Time (t) Logistic Growth Fig. 32.2 Population Limiting Factors Density dependent factors – – – – – – – Competition Predation Stress/crowding Waste accumulation Disease Space Resources Density independent factors – Weather/climate – Periodic disturbances Population Life History Strategies K R Type I vs Type III Type III (R selected) – Short maturation & lifespan – Many offspring – No parental care – High death rate Type I (K selected) – Long maturation & lifespan – Few offspring – Extensive parental care – Low death rate K-Selected Species elephant saguaro Fewer, larger offspring High parental care and protection of offspring Later reproductive age Most offspring survive to reproductive age Larger adults Adapted to stable climate and environmental conditions Lower population growth rate (r) Population size fairly stable and usually close to carrying capacity (K) Specialist niche High ability to compete Late successional species r-Selected Species cockroach dandelion Many small offspring Little or no parental care and protection of offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Adapted to unstable climate and environmental conditions High population growth rate (r) Population size fluctuates wildly above and below carrying capacity (K) Generalist niche Low ability to compete Early successional species European Kestrals r selected – Population grows at biotic max – Lots of offspring – Little parental care – Reproduce early, often K selected – Population adapted to being at carrying capacity – Few offspring – Lots of parental care – Reproduce late, infrequently Testing a hypothesis Human Population Growth or Go Forth and Multiply Human Population growth For most of our history a logistic curve. Currently exponential growth – Not uniform around the globe – Developing nations growing fastest What has made the change possible? – Drop in death rate. Birth rate has fallen, not increased. How long will this be sustainable? Future predictions for growth? Human Population Growth World – Wide Trend?? Growth rates differ within and between countries: Births per woman Births per woman <2 4-4.9 2-2.9 5+ 3-3.9 Data not available Infant deaths per 1,000 live births <10 10-35 36-70 71-100 100+ Data not available Infant deaths Population Growth Annual world population growth <1% 1-1.9% 2-2.9% 3+% Data not available Fig. 11.3, p. 240 Income and country GNP per capita, 1998 Low income (Under $1,000) Middle income ($1,000–$10,000) High income (Above $10,000) Fig. 1.5, p. 9 General age structure diagrams Rapid Growth Slow Growth Zero Growth Negative Growth Males Females Males Females Canada United States India Australia Mexico China USA age structure Diagrams Age Females Males 20 Millions 20 Millions 24 1955 Millions 24 1985 24 24 24 Millions 24 2015 Yellow= Baby Boomers 2035 NOW WHAT? Where we are: 1930, 2 billion September 1999, 6 billion – 3 people every second – 250,000 every day – 87 million every year –12 billion by 2050 –8 Billion- if slower rate Influence on environment More land for agriculture, resource exploitation More land for cities, roadways, suburbs Less fish in the sea for the food chain Deforestation Oil, gas won’t last forever Pollution builds up Better “green” technologies? Heightened awareness, concern? Better understanding of ecosystems? Human domination of landscape Arctic Circle Tropic of Cancer Equator Tropic of Capricorn Human disturbance Antarctic Circle Predominantly natural Partially disturbed Human dominated Every second… 5 people are born and 2 people die, a net gain of 3 people. Improved medical care has dramatically reduced infant mortality and mortality of women during labor. Demographic transition Larger urban families cost more, birth rate drops Population now much larger, slows its growth rate Influence of other (cultural, religious) pressures can slow birth rate decline Women often lack freedom to determine family size, education employment opportunities Demographic transition Death rate (infant mortality) drops first Birth rate remains constant Population increases quickly Economy transitions from agriculture to urban Stage 1 Preindustrial Stage 2 Transitional Stage 3 Industrial Stage 4 Postindustrial relative population size births deaths low increasing very high decreasing low zero negative Births per thousand population USA demographic transition & population size 32 30 28 26 24 22 20 18 16 14 0 1910 World War II Demographic transition 1920 Depression 1930 1940 Baby boom 1950 1960 Year Baby bust 1970 Echo baby boom 1980 1990 2000 2010 Total fertility rates in USA 1917-2000 4.0 Births per woman 3.5 3.0 2.5 2.1 2.0 1.5 Baby Boom (1946-64) 1.0 0.5 0 1920 1930 1940 1950 1960 1970 1980 1990 2000 1975 on ….Below native replacement rateimmigration keeps population growing 2010 Legal immigration to the United States between 1820 and 1997 1907 1914 New laws restrict immigration Great Depression
