Chapter 4-B1 Population Ecology Population growth is a critical factor in specie’s ability to maintain homeostasis within its environment. Main themes ~Scientists study population characteristics to better understand growth and distribution of organisms. ~Populations have different distributions and densities depending on the species represented in the population ~Organisms in a population compete for energy sources, such as food and sunlight ~Homeostasis within a population is controlled by density-dependent and density-independent limiting factors ~Human population varies little overall, but can change greatly within small populations. I. Population dynamics A. 1. Population density a. defined- b. eg. deer in Newark deer in 5 mi. sq. area 2. a. defined-organism pattern in area (eg. more deer on Londondale than on Green Wave Drive) b. c. Types p. 93 -UNIFORM dispersion-relatively even distribution of a species. Eg. pine forest -CLUMPED dispersion-organism are clumped near food. Eg. schools of fish, eg. mushrooms on a fallen log -_________________-unpredictable & changing. Eg. deer, large fish, etc. 3. a. area where organisms CAN/ARE living b. Meaning of Distribution -in Science~it is area where something lives and reproduces -in everyday language ~it means distribution (passing out) eg. of report cards. B. 1. Limiting factors-biotic or abiotic factors that keep a population from increasing forever (indefinitely). a. b. amount of space=abiotic c. 2. Density-independent factors a. b. independent=doesn’t rely on the number of organisms, would happen regardless of the number of organisms c. it is usually abiotic (limits population growth) -flood (eg. no matter how many deer in an area) - -blizzard - -fire (Ponderosa pine needs fire to kill undergrowth which takes all the soil nutrients from them. Heat releases seeds). d. -building dams - 3. Density-dependent factors a. dependent= depends on b. factors which depend on density of organisms (eg. more deer means more predation, disease and parasites) c. -parasites - -predation - TYPES OF DENSITY DEPENDENT FACTORS d. Predation (Predator/prey populations fluctuate due to the amount of food available - -wolves inc. then moose dec./ moose dec./wolves inc. e. -disease spreads by contact with individual organisms -the higher the density of an organism, then the higher the disease, then the higher the deathrate (limiting factor) f. -when population numbers increase, so does competition for available resources (eg. food) -within same species for a resource and/or - Eg. cornfield- mice, raccoon, deer all eat corn High food-then population growth increases exponentially (very quickly) Low food-then population growth decreases due to starvation g. -parasites spread mostly through contact - -eg. worms&dog ~less dogs then less worms 4. a. defined-how fast a population grows b. Natality-number of organisms born in a given time period (birthrate) ~eg. c. Mortality-number of deaths in a given time period (deathrate) d. Immigration-number of organisms moving into an area ~eg. e. Emigration-number of organisms moving out of an area f. usually immigration=emigration g. -growth with no limiting factors -lag phase-at beginning of reproduction when few individuals are Eg. 2 mice---2 yrs=3 million+ - -all populations grow exponentially until limiting factors slows growth (eg. run out of food) -Resources become limited with more individuals h. -occurs when exponential growth stopped by limiting factors - -limiting factors (lack of food, predators, space, etc. causes exponential growth to stop and level off) i. -the maximum number of species an area can hold for an extended period of time -eg. how many deer in the summer in Newark and how many deer in the winter in Newark -resources become limited (run out of food, etc) as population nears carrying capacity - C. 1. Based on a. number of births per ______________(compare mice/elephant) b. What age reproduction begins c. Life span of organism 2. a. short life span b. -food availability -temp. change (seasons) c. d. normally use little energy to care for their young e. usually controlled by density-independent factors f. 3. a. large organisms b. long life span c. d. population reaches carrying capacity e. -use high energy to get genes to next generation successfully f. Review questions What are the characteristics of populations and how they are distributed? What are the differences between density-independent and density-dependent limiting factors? What are the similarities between the different models used to quantify the growth of a population? How does carrying capacity affect reproductive rates? II. Would you say that the total population is growing faster today or that it grew faster 50 years ago? A. Human population growth fig. 11 p.100 1. a. defined- b. Human population size -1805-1 billion -1999- -2012-7 billion -2050- 2. a. Before technology, the environment kept the human population size below carrying capacity (eg. we ran out of food, space, disease because no medicine, etc) b. Agriculture, technology, medicine reduced the number of deaths & increased the population size Explain why an improvement in shelter increased the survival rate of the human population. 3. a. current rate of growth is slow~1.2% b. 1940-1950’s-there was a high rate of growth~2.2% c. drops in growth rate may be due to famine, AIDS & birth control B. 1. Trends influenced by a. war b. c. disease etc. 2. Growth rates similar in countries with similar economics. 3. a. high birthrate, high deathrate to low birthrate & low deathrate b. PGR comparison of a developed country & a developing country. Birthrate-deathrate + migration rate=PGR% 10 -developed country (USA) = -Developing country (Hondurus) = c. eg. Niger 2010-2050 -this means 13 million people to 53 million! 4. birth + immigration=death + emigration 5. a. Number of males & females in b. affects PGR of country/county/city 6. a. technology has allowed an increase in humans carrying capacity b. conservation of resources changes carrying capacity c. we must work at keeping humans at or below carrying capacity. Why? d. -burning fossil fuels causes too much CO2 in atmosphere -land then unable to absorb all the Carbon thus, - -Global Warming e. developing countries have high PGR & will eventually use more resources (more food, more energy needs, etc.) Why will disease and starvation become larger problems if the population continues to increase? Review questions What aspects affect human population growth? What are the trends in human population growth? What are the age structures of representative nongrowing, slowly growing, and rapidly growing countries? What might be the consequences of continued population growth? .