Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
CHP. 52 - POPULATIONS Introduction Population: group of individuals of a single species in an area. SIZE DENSITY DISPERSION SIZE Vs DENSITY Size = # of individuals in an area Density = # of individuals area Size =4 Density = 4/sq.inch Measuring density: Mark-recapture method. Fig. 52.1 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Mark-recapture method. Satellite Tracking Mark-recapture method.: a way to estimate population size 10 crocodiles captured & marked 5 captured in next attempt; Out of 5, 2 marked or recaptured # Captured = # Marked/ recaptured Total (N) Total recaptured TOTAL (N) = (10 X 5) = 25 2 3) Dispersion = pattern of spacing Patterns of dispersion -Depends on resource/food distribution, mating opportunities, predator avoidance, strong attractions/repulsions Clumped dispersion - individuals aggregate in patches - MOST COMMON (why?) Protection, gathering food (swarms), ‘housing” may be limited (pill bugs), mating, Fig. 52.2a Uniform dispersion - individuals are evenly spaced - not as common -very territorial species - ‘me casa ‘not your’ casa!’ Fig. 52.2b Random dispersion - the position of each individual is independent of the others. Very rare - like the dandelions in your yard - depends on where the seed landed Fig. 52.2c Recap: What factors can change pop. Size/density? 1)Birth rate 2)Death rate 3)Immigration - into 4)Emigration - out of 5)Survivorship - how long you live 6)Repoductive output - when you start makin’ babies ad how many? (last two together is 7) life history!) Evolution influences life history (K and r selection) What affects population size? Demography -study of factors that affect the growth and decline of populations 1) Birth Rate = # Births/ Time (1/8 sec) 2) Death Rate = #Deaths/Time (1/13 sec) BIRTH AND DEATH RATES IN USA: FYI Birth Rate = # Births/ Time (1/8 sec) Death Rate = #Deaths/Time (1/13 sec) Per Capita Birth Rate = # Births/Person ( 13.9 /1000 people) Per Capita Death Rate = # Deaths/Person (8.1 /1000 people) 5) Life Table: Age Specific Summary Of Survival Pattern In A Population This life table is important to ‘population size’ and ‘density’ because the longer a population lives, larger/denser it gets Table 52.1 (humans) Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings 5) Life Table - *Cohort (grp of individuals of the same age) x-Age nx dx 0 1000 200 1.00 2.7 1 800 100 0.80 2.25 2 700 200 0.70 1.50 3 500 300 0.50 0.90 Deaths 4 200 200 0.20 0.50 5 0 0 0.00 -- ex = Life TOTAL 1000 1000 Ix ex x=Age Category nx = # living dx = # of Expectancy 2.7 Ix=Survivorship – Proportion of offspring that survive to a particular age Years in retirement How long can you expect to live past your retirement? ex = Life Expectancy – How long a Person Can Expect To Live Your Current Age 5) Life Table - *Cohort (grp of individuals of the same age) x-Age nx dx 0 1000 200 1.00 2.7 1 800 100 0.80 2.25 2 700 200 0.70 1.50 3 500 300 0.50 0.90 Deaths 4 200 200 0.20 0.50 5 0 0 0.00 -- ex = Life 1000 2.7 TOTAL Ix ex x=Age Category nx = # living dx = # of Expectancy Ix=Survivorship – Proportion of offspring that survive to a particular age 5)Survivorship Curve (these are drawn based on life tables) 1000 100 nx = # living 10 20 40 60 % of nx life lived 0% 1000 20% 800 30% 700 50% 500 80% 200 80 100 100% 0 Survivorship (%) 5) X axis shows how much life is left to live •A Type I curve shows a low death rate early in life (humans) with most individuals living upto old age. (few babies compared to type 3) •The Type II curve shows constant mortality (squirrels). •Type III curve shows a high death rate early in life (oysters). Species lay a LOT of eggs in this type….why? 6) Okay so apart from how long population lives, how many babies they make affects population size/densiy: Reproductive table: age-specific summary of the reproductive output in a population. 6) Reproductive table – age specific summary of reproductive rates in a mx = average # of population offspring produced x 0 nx Ix 1000 1.00 mx Ix mx 0.0 0.0 1 800 0.80 0.5 0.4 2 700 0.70 0.8 0.56 3 500 0.50 0.9 0.45 4 200 0.20 0.0 0.0 5 0 0.00 0.0 0.0 7) Life History: when you can start making babies, how many babies your population usually makes, when do you typically DIE (Survivorship)! All of these affect pop. Size/density! •2 types: BIG BANG - invest in one massive reproductive effort - huge number of seeds/eggs once in many years (Semelparity); why? Big Bang /Semelparity – once - reproduce Iteroparity – several reproductions 7) Life History: when you can start making babies, how many babies your population usually makes, when do you typically DIE (Survivorship)! All of these affect pop. Size/density! •2 types: Iteroparity- invest in several, regular reproductive efforts - few seeds/eggs once in a year or so - more dependable environment/resources Big Bang /Semelparity – once - reproduce Iteroparity – several reproductions Can you have high reproduction and survivorship to increase pop. size? Red deer show a higher mortality rate in winters following reproductive episodes. What does this mean? There is usually a trade off Fig. 52.5 Recap: What factors can change pop. Size/density? Birth rate Death rate Immigration - move into an area Emigration - move out of an area Survivorship - how long you live Repoductive output - when you start makin’ babies ad how many? (last two together is life history!) Evolution influences life history (K and r selection) Population Growth -what is it? Population Growth Rate ‘r’ = Per Capita Birth Rate – Per Capita Death Rate Zero population growth rate (r= 0): Birth rate = Death rate 1) Type: Exponential Population Growth Example of exponential growth 1) Exponential Population Growth 1) Exponential Population Growth Ideal conditions, LOTS of resources The number of individuals in each generation is a multiple of the previous generation Change in number over time dN rN dt Number of individuals Population growth rate 1) Exponential Population Growth 1) Exponential Population Growth Two stages in Exponential Pop. Growth: First it starts out slow (why?); then it escalates rapidly (why?) Answer: -not enough mating parters in first case, then as pop. Grows to a critical mass, there are plaenty of “happy” people! J Shaped Curve Density Independent Population Growth can be negative! Example for a population of algae r=0 r<0 (-) r>0 (+) 6 offspring in a lifetime - elephants , within 750 years - 19million! Bacteria - doubling every 20 min. 1 foot of bacteria around the globe in 36 hrs! 2) Logistic Population Growth •Carrying capacity (K) – maximum stable population size a particular environment can support. 2)Logistic Population Growth S Shaped Curve Density Dependent dN N rN 1 •4 phases: a) slow start dt (same reasonKfrom before); b) rapid exponential growth (lots of resources still around…); c)slowing down (why?); d) population stabilizes - that means Density Dependent Checks - these are limitations/checks imposed on growing populations to keep their growth down 1)Intraspecific Competition: within one species Food is limited Density Dependent Checks 2)Interspecific Competition: competition between species. Food and space are limited. If they are by themslves, they show higher pop. growth Density Dependent Checks 3) Decrease in Reproductive Output: less babies! Density Dependent Checks 4) Accumulation of wastes: living in your own poop is not healthy! Density Dependent Checks 5)Predation: Boom Bust 10 year cycle – snowshow hare and lynx show a cycling rise and fll in population that are correlated (why?) Density Dependent Checks Boccaccio said that the victims of plague, "ate lunch with their friend and dinner with their ancestors in paradise." 6) Disease:has to serious enough to wipe out populations or sections of it: plague/black death 2) Logistic Population Growth •Carrying capacity (K) – maximum stable population size a particular environment can support. Density-dependent factors increase their affect on a population as population density increases. This is a type of negative feedback. Density-independent factors are unrelated to population density, and there is no feedback from the population Both keep populations at Fig. 52.13 equilibrium Density Independent Population Checks: can act anytime! Natural Disasters •drought •freezes •hurricane •floods •forest fires K and r selection - based on logistic growth evolution favors different traits dependng on how close a popultion is to carrying capacity K selection: Near carrying capacity; few-but-large-young r selection: Low population density; small-andunprotected young (close to carrying capacity; r = 0). K Selection for K strategies: (elephants, tortoise, endangered species) 1.They mature slowly 2.They have long life spans. 3.They begin breeding later in life. 4.They usually have long generation times. 5.Most produce small numbers of offspring. 6.They take good care of their young (parental investment) 7. They are usually found in stable habitats 8. Very good at exploiting their minimal habitat (far away from carrying capacity; r > 0). R Selection for R strategies: (mice (pests), oysters; r is ‘rapid’) 1.They mature rapidly. 2.They have short life spans. 3.They begin breeding early in life. 4.They usually have short generation times 5.They produce large numbers of offspring. 6.They take little care of their offspring, and infant mortality is huge. 7.They have efficient means of dispersal to new habitats. 8. They are usually found in disturbed and/or transitory habitats DEMOGRAPHIC TRANSITION has 5 stages •The movement from the first toward the second Human Population state is called the demographic transition. Age structure changes simultaneously •Zero population growth = high birth rates – high death rates. •Zero population growth = low birth rates – low death rates. Age Structure Defined Share of people younger than 30 in a population compared to share of people age 60+ Each country is one of 4 major types of age structures: 1. Very Young (>67% under 30) 2. Youthful (60-67% under 30) 3. Transitional (45-60% under 30) 4. Mature (<45% under 30) Very Young Age Structures 62 countries: most of subSaharan Africa, Syria, Iraq, Afghanistan, 3 countries in Central America, Haiti, Laos High mortality and fertility rates (stage 2) Youthful Age Structures 27 countries: Bangladesh, Bolivia, Jordan, Morocco, Nepal, Peru, Philippines, Saudi Arabia Fertility rates declining, but still above replacement level (stage 2) Transitional Age Structures 40 countries: Brazil, China, India, Israel, Indonesia, Lebanon, Malaysia, Mexico, Sri Lanka, Thailand, Vietnam Middle of demographic transition (stage 3) Mature Age Structures 47 countries: Nearly all of Europe, Canada, Cuba, Russia, South Korea, Australia, U.S. Low mortality and fertility rates (stages 4/5) Age Structure and Conflict 80% of all new conflicts occurred in countries in which at least 60% of the population was under age 30. Age Structure and Governance Nearly 90% of countries with very young structures had autocratic or weakly democratic governments. More than 80% of countries with mature age structures were fully democratic. Mexico 1975 - 2005 Very Young Transitional 73% under 30 59% under 30 World Age Structures 2005 Human Population – Age Structure •Age structure is the relative number of individuals of each age changes with each stage of demographic transition. •can reveal a population’s growth trends, future social conditions.