N Population: All Members of a Single Species That Live Together in a Specific Area
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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
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
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
Real World Population growth varies in complex ways
May show J- or S-shaped growth at various times
Growth rates may hover around K
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
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
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
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
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
Larger size Pressures are density-dependent: as population increases, food and living space limit growth Live longer, mature slowly, fewer offspring/generation
Examples r-selected: rodents, many insects, marine invertebrates, weedy annual plants K-selected: whales, wolves, elephants, primates
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
+/- Population Size Fecundity—physical ability to reproduce Fertility—measure of actual number of offspring produced
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
+/- 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
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
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
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
Human Population Resource depletion and degradation? Human talents—deal with it Grow more food Pollution control Energy sources
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
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)
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
Fertility rates in U.S. Demography Study of size, composition, distribution of human population and causes and consequences of characteristics
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
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
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
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
Zero Population Growth Births + immigration=deaths + emigration Several generations of replacement-level
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 +)
Age Structure #of individuals under 15—major factor “built in” momentum to increase More reproducers, even if 1-2 children/female
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
Old Populations Are there enough young to support old Old people can be expensive Not forward looking
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