<p> Population Biology  Population: all members of a single species that live together in a specific area  Population size: produces baseline description of population, then used to describe changes over time  Compare changes Populations  Change in size (total number of individuals)  Change in density (number of individuals in a certain space)  Change in age distribution (proportion of individuals in each age group)  Change in habitat distribution</p><p>Distribution  Dispersion  Clumps  Uniform  Random  Most species live in clumps or groups Clumps  Resources may vary greatly from place to place  Better protection against predators  Some predator species increase chances of securing a meal—wolf pack  Temporary clumps for mating and care for young Population Measurement  Count directly  Mark the presence of individuals in a representative area and extrapolate to a larger area  Estimated based on sign of presence such as droppings, birdcalls, etc. Change in Population Size  Increases are exponential, not arithmetic  Increase is proportional to number of individuals already present</p><p>J-shaped growth  Exponential growth: slow at first, followed by increasingly faster rates of growth, also called  Geometric growth: growth follows a geometric pattern of increase (2,4,8,16)  Rule of 70: divide 70 by annual percentage yields approximate doubling time in years S-shaped Growth  Growth model starts off like J-shaped form, but rate of growth slows and ceases altogether  Stabilizes at certain level, denoted as K  Environmental resistance limits growth in S-shaped growth  Logistic growth S-shaped Growth  Growth model starts off like J-shaped form, but rate of growth slows and ceases altogether  Stabilizes at certain level, denoted as K  Environmental resistance limits growth in S-shaped growth  Logistic growth Biotic Potential  Capacity for growth  “r”=intrinsic rate of increase if the population has unlimited resources  Most populations grow at rate less than this</p><p>Real World  Population growth varies in complex ways</p><p> May show J- or S-shaped growth at various times</p><p> Growth rates may hover around K</p><p>K  Carrying capacity not fixed  Stable in stable environments, population can hover above K or below K depending on environmental variables Patterns  Rate of population decrease is faster than increase=population crash or dieback  Population explosion followed by dieback is called irruptive of Malthusian growth</p><p>Growth Rate  Difference between birth and death rate over a period of time  birthrate=# of individuals born in a given time expressed as a proportion of the total population=r</p><p>Growth Rate  Death rate=# of individuals who die in a given time  Growth rate (r)=birth rate-death rate  r<0: population shrinks  r>0: population grows  r=0: population at zero population growth Reproductive Strategies  r-selected or Malthusian:  Opportunistic species in highly variable environments  High growth rates—take advantage of infrequent favorable conditions  Reproduction is rapid, with little care of offspring</p><p> r-selected  High growth rates—take advantage of infrequent favorable conditions  Pressures are density-independent: physical (abiotic) forces and predation limitlimit growthgrowth  Smaller size r-selected  Reproduction is rapid, with little care of offspring, many offspring  Sheer numbers and effective dispersal</p><p>Reproductive Strategies  K-selected or Logistic: relatively stable environment, numbers fluctuate within narrow range around K  Population size limited by carrying capacity  Reproduction slower, considerable care of offspring K-selected</p><p> Larger size  Pressures are density-dependent: as population increases, food and living space limit growth  Live longer, mature slowly, fewer offspring/generation</p><p>Examples  r-selected: rodents, many insects, marine invertebrates, weedy annual plants  K-selected: whales, wolves, elephants, primates</p><p> What about humans? Factors that Increase or Decrease Population Size  Natality—production of new individuals, by whatever means, main source of addition  Sensitive to environment  Wide variation among species  Variation within species depending on conditions</p><p>+/- Population Size  Fecundity—physical ability to reproduce  Fertility—measure of actual number of offspring produced</p><p> Not all fecund individuals find mate or successfully produce offspring +/- Population Size  Immigration—movement into new ecosystem  Fly or float  Hitchhike  Rafts  Fly, swim, walk +/- Population Size  Emigration  Movement out of ecosystem +/- Population Size  Mortality—death rate  Number of organisms that die in a period÷number alive at the beginning of the period  Survivorship—percentage that survives to certain age  Life expectancy—probable # of years survival for individual at given age +/- Population Size  Life span—longestlongest periodperiod ofof lifelife reachedreached byby organismorganism  Wide variation—minutes (bacteria) to thousands of years (bristle cone pines in CA White Mountains) Survivorship  Survivorship curves—depict time in lifespan when death occurs  Late loss—(K-selected), most lives lost late in life because most survive intointo oldold ageage  Constant loss—nearly constant death rate throughout potential life span: birds  Early loss—highest death rates in early life, insects, marine inverts., trees</p><p>+/- Population Size  Emigration—movement of individuals out of population  Dispersal  Take genes with them—protect species in case of catastrophe Factors that Regulate Growth  Intrinsic—within organism  Extrinsic—outside the population  Biotic  Abiotic  Density-dependent  Density-independent</p><p>Density-independent  Abiotic-weather, climate  Extremes at wrong time of year  Without regard to the number of organisms present Density-dependent  Decrease natality, increase mortality  Interactions between populations  Some within population  Interspecific—predator-prey population levels, peaks and valleys slightly offset  Cyclical</p><p>Density-dependent  Intraspecific—compete for resources  As carrying capacity is reached, resources are limited  First, quickest, clever, lucky  Territoriality  Fighting equipment  Attractiveness-song and dance Density-dependent  Stress—”stress shock” causes physical and psychological and behavioral changes  Combinations—OK food and water, space is lacking, lab animals, humans, chickens  Humane livestock practices—not crowding chickens, livestock, “slow food” movement Human Populations  We don’’t have a separate set of rules  We play within them, with variation  Over 6 billion, with a b, humans  Concentrated population centers  Environmental impacts  Goal: sustain, or improve, conditions </p><p>U. S. Population  11:30 a. m., Feb. 18, 08: 303,462,880  1 birth every 7 seconds  1 death every 13 seconds  1 international migrant net every 26 seconds  Net gain of 1 person every 10 seconds World Populations  As of 11:30 a.m.: 6,651,418,102  18 February 2008 Human Population  Focus only on numbers?  Focus on wealth distribution?  Focus on power?  Focus on type of government?  Focus on women’’s role?  ?????—no easy approach or answer results in solving dilemma</p><p>Human Population  Resource depletion and degradation?  Human talents—deal with it  Grow more food  Pollution control  Energy sources</p><p>Most Populous Countries 2007  Rank Country Population  1.China 1,321,851,888  2.India 1,129,866,154  3.United States 301,139,947  4.Indonesia 234,693,997  5.Brazil 190,010,647  6.Pakistan 169,270,617  7.Bangladesh 150,448,339  8.Russia 141,377,752  9.Nigeria 135,031,164  10.Japan 127,467,972  11.Mexico 108,700,891  12.Philippines 91,077,287  13.Vietnam 85,262,3561  14.Germany 82,400,996  15.Egypt 80,264,543 Most populous country in 50 years Uneven Distribution of Population Human Population Trends  J-shaped curve  300 million at beginning of common era  Disease and starvation major controls  Black Death—plague, periodically reduced number  1700—600 million</p><p>Human Population Trends  1 billion—1804  3 billion—1960  6,651,418,102: 2/28/08  Pre-industrial humans: 90% of time  Today: 90% of all humans are alive today  Not just numbers, but the rate  Overall—global annual growth=1.25% (2004) (2.25% in 1963)</p><p>Doubling Time  Rule of 70: 70 divided by the percentage growth rate  As percentage increases, doubling time decreases  Resources delivered and consumed at faster and faster rates</p><p>Fertility rates in U.S. Demography  Study of size, composition, distribution of human population and causes and consequences of characteristics</p><p> Changes in size, composition and distribution have social, economic, health effects Demographic Transition  Change in patterns of growth and death rates  High birth and death rates to lower birth and death rates Demographic Transition Demographic Transition  Used to link economic development and population growth</p><p>Growth Rates  Developed countries—0.1%  Developing—1.5%  Developed—1.2 billion—littlelittle changechange  Developing—5.2 billion (2004) to 8 billion in 2050</p><p>Birth Rates  Fertility--# births per individual woman (or in population)  Three types:  Crude --# of births/1000 persons  Replacement-level--# of children/couple to replace themselves (2.1-2.5)  Total fertility—average # of children a woman has during reproductive years BR and FR Factors  Importance of children as members of workforce  Cost of raising and educating children  Availability of private and public pension systems  Educational and employment opportunities for women Total Fertility Rate  Dropped since 1950  Global: 2.8 children/women  Developed: 1.5  Developing: 3.1  Highest: 5.2 parts of Africa</p><p>BR and DR Factors  Infant mortality rate  Average age at marriage  Availability of legal abortions  Religious beliefs, traditions and cultural norms  Availability of reliable birth control methods Fertility Control  Traditional—breast feeding, sex avoidance  Modern:  Hormonal—pills, patches, rings, injections  Physical—IUD, diaphragm, condoms  Chemical—foams, films, creams  Abortions Fertility Rates  Vary  US—Depression, World War II, baby boom, echo baby boom  Also: famine, epidemics, war, genocide </p><p>Zero Population Growth  Births + immigration=deaths + emigration  Several generations of replacement-level</p><p>Poorest and Least Developed  Life expectancy = ≤ 49  AIDS, genocide, war  Infant mortality=excellent indicator of quality of life  Level of nutrition  Level of health care  Level of infrastructure (water delivery and sewage treatment) Infant Mortality  Undernutrition  Malnutrition  Infectious disease  AIDS Age Structure  Number of people in young, middle and older age groups determine growth rate (+ or -)  % males, females in 3 categories  Prereproductive (0-14)  Reproductive (15-44)  Postreproductive (45 +)</p><p>Age Structure  #of individuals under 15—major factor  “built in” momentum to increase  More reproducers, even if 1-2 children/female</p><p>Age Structure Age Structure  Important social implications  Providing services  Education-which types  Medical care-pediatric, middle age, geriatric  Younger members supporting older  Older supporting “young” concerns  Education  recreation Age Structure  Political implications—right of return for Palestinians  Loss of older members  Genocide, AIDS  Loss of collective identity  No experience in new generations  No babysitters Poorest and Least Developed  Life expectancy = ≤ 49  AIDS, genocide, war  Infant mortality=excellent indicator of quality of life  Level of nutrition  Level of health care  Level of infrastructure (water delivery and sewage treatment) Infant Mortality  Undernutrition  Malnutrition  Infectious disease  AIDS Age Structure  #of individuals under 15—major factor  “built in” momentum to increase  More reproducers, even if 1-2 children/female</p><p>Old Populations  Are there enough young to support old  Old people can be expensive  Not forward looking</p><p> www.iiasa.ac.at/Research/LUC/ChinaFood/data/anim/pop_ani.htm 3 Major Impacts of Humans on Environment  Hunter-gatherers had little impact  Some changes have allowed us to live with J-shaped curve  3 major cultural changes  Agricultural revolution (10,000 to 12,000 years ago)  Industrial and medical revolution (275 yeas ago)  Information and globalization revolution (began 50 years ago) Controversies  State mandated controls  1 child policies  Subsidizing additional children  Forced birth control  Abortion control Controversies  Which group has more negative impact?  Developed countries with high consumption and pollution rates  Developing countries with high growth rates and environmental demands  Both present problems with deveolping sustainability Controversies  Lifeboat ethics  Social justice—fair share for all  Emigration control—Sierra Club</p>