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 population 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

3. Growth Rate A population will grow if: Birth Rate > Death Rate (# of individuals born) (# of individuals who die) A population will stay the same if: Birth Rate = Death Rate A population will decline if: Birth Rate < Death Rate

Emigration – Exit (out) 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) Remember…. Immigration – Into Emigration – Exit (out)

Population Growth Initial growth- birth (natality) is high 1 2 3 4 5 Initial growth- birth (natality) is high Exponential growth Carrying capacity- steady state Decline- increase in death rate Extinction

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 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

Exponential Growth = J-curve At first, the number of individuals increases slowly, over time the population becomes larger and larger until it approaches an infinitely large size. 1 million Exponential Growth = J-curve Population size 500,000 100 One year Under ideal conditions with unlimited resources, a population will grow exponentially

Exponential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 (the size has not dropped, but the population is growing slower).

Logistic Growth Logistic Growth = S-curve As resources become less available, the growth of a population slows or stops forming an S-shaped curve- logistic growth Birth rate decreases and death rate increases Logistic Growth = S-curve

Carrying Capacity When growth levels off 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 Logistic Exponential growth Limits on S-shaped curve can be represented by characterized by which cause a Exponential growth Logistic Falling growth rate S-shaped curve Limits on No limits on J-shaped Constant Unlimited resources

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

Characteristics of Population Growth J curve S curve Carrying capacity Exponential growth Time Population DISEASE SPACE PREDA-TORS FOOD

Density-Dependent Limiting Factors A limiting factor that depends on population size is a density-dependent limiting factor. Density-dependent factors include competition predation parasitism disease Disease, for example, can spread more quickly in a population with members that live close together. Density dependent factors create an S-shaped curve Population sizes are limited not only by abiotic factors, but also are controlled by various interactions among organisms that share a community.

Competition 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 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

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

Parasitism and Disease

Density-Independent Limiting Factors Density-independent factors can affect all populations, regardless of their size Most density-independent 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 Time Population Density

Limitations on Population Growth

Human Population Growth Industrial Revolution begins Agriculture begins Bubonic plague Plowing and 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

Human Impact on the Environment Environmental resources can be classified into two types: Renewable Can regenerate (replaceable) Nonrenewable Cannot be replenished by natural processes Example: Fossils fuels (formed over hundreds of millions of years) Sustainable Use Way of using natural resources at a rate that does not deplete them. Renewable resources affected: Land, air, and water

Human Impact: Land Deforestation The loss of forests which leading to severe erosion and changes in soil properties 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 erosion water pollution and desertification

Human Impact: Air Greenhouse effect Acid Rain 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 Chemical Transformation Nitric acid Sulfuric acid Condensation Emissions to Atmosphere Nitrogen oxides Sulfur dioxide Dry Fallout Precipitation Acid rain, fog, snow, and mist particulates, gases Industry Transportation Ore smelting Power generation

Human Impact: Water 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 Although water is a renewable resource, the total supply of fresh water is limited

Humans need to learn to be a part of nature not apart from nature! 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!

Biodiversity is one of the world’s greatest resources Biological Diversity Biodiversity: the sum total of the genetically based variety of all organisms in the biosphere 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

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: Biological Magnification Fish-Eating Birds Threats to Biodiversity: Biological Magnification Magnification of DDT Concentration 10,000,000 Increasing concentrations of a harmful substance in organisms at higher trophic levels in a food chain or web Example: DDT Large Fish 1,000,000 Small Fish 100,000 Zooplankton 10,000 1000 Producers 1 Water

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 density-dependent 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 the US. These furry rodents eat water plants that protect fragile shorelines from erosion. This destroys the habitats of species native to those ecosystems.