* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project
Chapter 5 & 6- Populations Chapter 5 Outline 5–1 How Populations Grow A. Characteristics of Populations B. Population Growth C. Exponential Growth D. Logistic Growth 5–2 Limits to Growth A. Limiting Factors B. Density-Dependent Factors 1. Competition 2. Predation 3. Parasitism and Disease C. Density-Independent Factors 5–3 Human Population Growth A. Historical Overview B. Patterns of Population Growth 1. The Demographic Transition 2. Age Structure C. Future Population Growth What Affects Population Size? A population is a group of organisms belonging to a single species that lives in a given area. Characteristics of a Population 1- Geographical Distribution 2- Density 3- Growth Rate 1- Geographical Distribution -area inhabited by a population -could be as small as a few cubic centimeters like a bacteria or as large as millions of kilometers like killer whales 2- Population Density the number of individuals per unit How organisms are dispersed can be important Three patterns of dispersal are random, clumped, and uniform 3- Growth Rate - 3 factors that affect a populations size - number of births - number of deaths - number of individuals entering and leaving a population -A population will increase or decrease in size depending on the number added or removed from it -A population will grow if: Birth Rate > Death Rate -A population will stay the same if: Birth Rate = Death Rate -A population will decline if: Birth Rate < Death Rate 3 – Growth Rate Individuals entering and leaving the population will also increase or decrease a population’s size Immigration- movement of individuals into an area (increase population) Emigration- movement of individuals out of an area (decrease population) Peaks of Otter Salamander Exponential Growth If a population has abundant space and food, protection from predators and disease then the organisms in the population will multiply and the population will increase Under ideal conditions with plenty of nutrients, heat, moisture, & light a bacteria can reproduce by splitting in half within 20 minutes producing 2 bacteria In 20 minutes the population is 2 In 40 minutes the population is 4 In 1 hour: the population is 8 In 2 hours: 64 In 3 hours: 512 In one day: 4,720,000,000,000,000,000,000 Population size 1 million 500,000 One year •The pattern of growth is a J-shaped curve and the population is undergoing exponential growth •Exponential growth occurs when the individuals in a population reproduce at a constant rate •If there are unlimited resources and no predators, exponential growth will continue Logistic Growth Exponential growth doesn’t continue in natural populations for very long If a new species of organism is introduced into a new environment, at first the population grows slowly, then exponentially, eventually the population growth slows down As resources become less available, the growth of a population slows or stops forming an S-shaped curvelogistic growth Logistic Growth occurs when a population’s growth slows or stops following a period of exponential growth Birth rate decreases and death rate increases Carrying Capacity When growth levels off and the population is not growing Carrying capacity- the largest number of individuals that an environment can support When a population overshoots the carrying capacity, then limiting factors may come into effect A balance between environmental factors must exist for a population to survive For example: Producers & consumers Water use & rainfall Population Growth 3 2 1 1. 2. 3. 4. 5. 4 5 Initial growth- birth (natality) is high Exponential growth Carrying capacity- steady state Decline- increase in death rate Extinction Population Growth can be Logistic growth Exponential growth characterized by No limits on growth Unlimited resources represented by Constant growth rate J-shaped curve characterized by Limits on growth which cause a Falling growth rate represented by S-shaped curve 5–2 Limits to Growth A. Limiting Factors B. Density-Dependent Factors 1. Competition 2. Predation 3. Parasitism and Disease C. Density-Independent Factors What can limit growth? Limiting Factors Any factor that causes population growth to decrease Limiting factors, such as availability of food, disease, predators, or lack of space, will cause population growth to slow Under these pressures, the population may stabilize in an S-shaped growth curve Population Carrying capacity 0 J curve S curve Time FOOD PREDATORS SPACE Exponential growth DISEASE Characteristics of Population Growth Bacteria Growth Carrying Capacity Decline Prolonged Decline Exponential Initial Density-Dependent Limiting Factors A limiting factor that depends on population size is a Density-dependent limiting factor Density-dependent factors include disease, competition, predators, parasites, and food. Disease, for example, can spread more quickly in a population with members that live close together. Density dependent factors create an S-shaped curve Organism Interactions Limit Population Size Population sizes are limited not only by abiotic factors, but also are controlled by various interactions among organisms that share a community. Competition within a population Competition is a density-dependent factor When only a few individuals compete for resources, no problem arises When a population increases to the point at which demand for resources exceeds the supply, the population size decreases Competition can also occur between members of different species- this creates evolutionary change The two species competing are under stress to change in way that decrease competition- eventually evolving to occupy separate niches Predation affects population size Predation is a density-dependent factor When a predator consumes prey on a large enough scale, it can have a drastic effect on the size of the prey population Populations of predators and their prey are known to experience cycles or changes in their numbers over periods of time Predation affects population size The data in this graph reflect the number of hare and lynx pelts sold to the Hudson’s Bay Company in northern Canada from 1845 through 1935. Lynx and Hare Pelts Sold to the Hudson’s Bay Company Number of organisms in thousands) Lynx Hare Times (in years) Moose Wolves • The periodic increase in the moose population is quickly followed by a rise in the number of wolves. • This increase in the number of wolves increases the number of moose captured by their predator and the moose population drops. • The wolf population will then decrease after the moose numbers drop because the wolves are less able to find food. • The predator prey cycle can be repeated indefinitely. Parasitism and Disease Parasites can also limit a population’s size-density-dependent As the # of individuals , parasites which then causes the # of individuals to Parasites are similar to a predator in that they take nourishment at the expense of their host As a population increases in size, disease is more common because individuals are in closer contact with one another Density-independent limiting factors and population growth Density-independent factors can affect all populations, regardless of their size Most densityindependent factors are abiotic factors, such as temperature, storms, floods, drought, and major habitat disruption Density-Independent Factors Density-independent factors create a boom-and bust curve (exponential growth followed by a sudden collapse) Examples: Weather- a drought kills grass Human activity: deforestation- destroys habitat Seasons: a severe winter regulates insect population Boom-and-Bust Curve Population Density Time Limitations on Population Growth Reproduction Patterns In nature, animal and plant populations change in size. Biologists study the factor that determines population growth—an organism’s reproductive pattern, also called its life-history pattern A variety of population growth patterns are possible in nature- R strategists and K-strategists Rapid life-history patterns- R Strategists rapid life-history patterns are common among organisms from changeable or unpredictable environments rapid life-history organisms have a small body size, mature rapidly, reproduce early, and have a short life span Slow life-history patterns – K-strategists large species that live in more stable environments usually have slow life-history patterns. reproduce and mature slowly, and are long-lived. They maintain population sizes at or near carrying capacity 5–3 Human Population Growth A. Historical Overview B. Patterns of Population Growth 1. The Demographic Transition 2. Age Structure C. Future Population Growth Demography Demography, the study of human population size, density and distribution, movement, and its birth and death rates Demography examines the characteristics of human populations and attempts to explain how those populations will change over time Demographic transition- a change in a population from high birth and death rates to low birth and death rates; Examples- United States and Japan Human Population Growth Industrial Revolution IndustrialBegins Agriculture begins Agriculture begins Revolution begins Bubonic Plowing and Plowing irrigation and plague Bubonic plague irrigation Until about 500 years ago, the population grew slowly. Agriculture and industry made life easier and safer. Human Population We are growing exponentially Due to technological advances: medicines, a dependable food supply, and sanitation The death rate is decreasing and the life expectancy is increasing The human population will eventually reach its carrying capacity Age Structure Population Distribution Per Age Range for Several Countries Stable growth Rapid growth Male Slow growth Reproductive years Age Female Population (percent of total for each country) Population growth depends on how many people of different ages make up a given population Demographers can predict future growth using age-structure diagrams Age-structure diagrams graph the number of people in each age group Age Structure U.S. Population Rwandan Population Ch.6-2: Human Impact on the Environment Air Greenhouse effect Trapping of heat by gases in the Earth’s atmosphere (carbon dioxide) This may lead to global warming- increase in the Earth’s temperature from the rapid buildup of carbon dioxide and other greenhouse gases Acid Rain Burning of fossil fuels release nitrogen and sulfur into the atmosphere which combined with water form nitric and sulfuric acid Acid Rain kills plants Smog Mix of chemicals in the air from automobile exhaust Affects the respiratory system especially those with asthma The Formation of Acid Rain Section 6-2 Emissions to Atmosphere Nitrogen oxides Sulfur dioxide Chemical Transformation Nitric acid Sulfuric acid Dry Fallout particulates, gases Industry Transportation Ore smelting Power generation Condensation Precipitation Acid rain, fog, snow, and mist Human Impact of the Environment Water Excessive nutrients can cause an increase in algae growth and depletion of oxygen for other organisms Over harvesting of fish has reduced the number of fish Human Impact of the Environment Land Erosion The wearing away of surface soil by water and wind Desertification The combination of farming, overgrazing, and drought in dry climates which turn productive areas into deserts Deforestation The loss of forests which leading to severe erosion and changes in soil properties Deforestation erosion water pollution and desertification Consequences If humans continue to alter the environment, they will have to deal with the results Examples: fossil fuels combustion, habitat destruction, deforestation, ozone layer destruction, global warming Human Overpopulation results in: Worldwide malnutrition Increased disease Increased pollution Humans need to learn to be a part of nature not apart from nature! Ch. 6-3: Biological Diversity Ecosystem diversity- variety of habitats, communities, and ecological processes in the living world Species diversity- the number of different species Genetic diversity- sum total of all the different forms of genetic information carried by all organisms living on Earth today Biodiversity increases as you move toward the equator. Areas around the world differ in biodiversity Biodiversity can bring stability to an ecosystem. Biodiversity is one of the world’s greatest resources Variations within a species also helps protect against disease or parasite Genetically different individuals within a species have a better chance of resisting disease Example: world cheetah population reduced by a single virus Tree plantation has same type of trees (single species) vulnerable to disease, etc..- spread easily Diversity among individuals in a population is important to resistance of population as a whole (genetically different) Biological diversity causes ecological stability Adaptations- changes in response to factors in the environment (physical and behavioral changes) Slow process that takes place over many generations Organisms can be specialized to occupy a specific niche Advantages The more specialized an organism’s method of obtaining food and life requirements are (NICHE), the less competition they will have with other species (they have a better chance of surviving) Example: anteater with long snout can reach into ant hills Disadvantages If there are changes in the environment, organisms may not be able to adapt fast enough in response Example: Koala bears eat only Eucalyptus trees Species Diversity Insects 54.4% Protists 4.2% Other Animals 19.7% Plants 18% Fungi Bacteria 0.3% 3.4% Loss of Biodiversity Extinction is the disappearance of a species when the last of its members dies Extinction is a natural process and Earth has experienced several mass extinctions during its history A species is considered to be an endangered species when its numbers become so low that extinction is possible Threats to Biodiversity Complex interactions among species make each ecosystem unique Changes to habitats can therefore threaten organisms with extinction Human activity can reduce biodiversity by altering habitats, hunting species to extinction, introducing toxic substances into food webs, and introducing invasive species Habitat loss-One of the biggest reasons for decline in biodiversity Threats to Biodiversity: Habitat fragmentation Habitat fragmentation is the separation of wilderness areas from other wilderness areas Habitat fragmentation creates “islands” of habitat that are isolated from each other Threats to Biodiversity: Demand for wildlife products Hunting has caused many animals to go extinct For example: passenger pigeon and Stellar sea cow Humans hunt for food, fur, hides, and body parts thought to have medicinal properties In the United States animals are protected from hunting if they are endangered Fish-Eating Birds Threats to Biodiversity: Biological Magnification Increasing concentrations of a harmful substance in organisms at higher trophic levels in a food chain or web Example: DDT Magnification of DDT Concentration 10,000,000 Large Fish 1,000,000 Small Fish 100,000 Zooplankton 10,000 Producers Water 1000 1 Threats to Biodiversity: Introduced Species Introduced species threaten biodiversity Introduced species are organisms that have been introduced into new habitats and often become invasive, reproduce rapidly Invasive species lack densitydependent limiting factors to keep their populations in check and take over areas and out compete existing species Native to South America, nutrias have become pests in coastal areas of se US. These furry rodents eat water plants that protect fragile shorelines from erosion. This destroys the habitats of species native to those ecosystems.