Chapters 5 & 6 Populations & Humans in the Biosphere 5-1 How Populations Grow Characteristics of Populations: 1. Geographic Distribution- describes The area inhabited by a population 2. Density- the number of individuals per Unit area 3. Growth Rate- rate in which a population changes (+, 0, or -) 4. Age-Structure Population Growth: 3 Factors IF: 1. Number of births 2. Number of deaths 3. Number of individuals that enter or leave the population Birthrate > Death rate = increase in pop. Size 1 Birthrate = Death rate = Pop. stays about the same Birthrate < Death rate = Decrease in pop. size Immigration- The movement of individuals into an area Emigration- The movement of individuals out of an area Exponential Growth: (J-shaped)(Fig. 5-3) -It occurs when the individuals in a population reproduce at a constant rate. (No limits) Logistic Growth: (S-shaped)(Fig. 5-4) - It occurs when a population’s growth slows or stops following a period of exponential growth. (Growth with limits) Carrying Capacity- the largest number of individuals that a given environment can support over time. 5-2 Limits to Growth Limiting Factors- is a factor that causes population growth to decrease. 2 Density-Dependent Factors: -Factors that depend on population size Examples: 1. Competition- When populations become crowded, organisms compete with each other for food, water, space, sunlight, etc. 2. Predation- The regulation of a population takes place within a predator-prey relationship. 3. Parasitism and Disease- Parasites can also limit the growth of a population. Density-Independent Factors: -Factors that affect all populations in similar ways, regardless of the population size. Examples: 1. Unusual weather-drought, heavy rains. 2. Natural Disasters- hurricanes, tornados 3. Certain human activities- clear cutting forests 3 5-3 Human Population Growth Historical Overview: -For most of human existence, the population grew slowly. (Food was scarce, diseases.) -Not long ago, only ½ the children in the world survived to adulthood. -About 500 years ago, the human population began growing more rapidly. Agriculture and industry made this possible. Patterns of Population Growth: Demography – the scientific study of human populations. Birthrates, death rates and the age-structure of a population help predict why some countries have high growth rates while others grow more slowly. Demographic Transition- a dramatic change in birth and death rates. Stage I= both birth rate and death rate are high 4 Stage II= the death rate drops but the birth rate remains high. Stage III= both birth and death rates drop. Age Structure Diagrams- Show the population of a country broken down by gender and age group. (Fig. 5-13) Future Population Growth: -Current projections suggest that by 2050, the world population may reach 9 billion people. -By 2050 the growth may level off or even decrease. 5 Chapter 6 Humans in the Biosphere 6-3 Biodiversity Biodiversity- Is the sum total of the genetically based variety of all organisms in the biosphere. Ecosystem Diversity- Includes the variety of habitats, communities and ecological processes in the living world. Species Diversity- Refers to the number of different species in the biosphere. Genetic Diversity- Refers to the sum total of all the different forms of genetic information carried by all organisms living on Earth today. Threats to Biodiversity: -Human activities like; altering habitat, overhunting, introducing toxic compounds into food webs and introducing foreign species to new environments can reduce biodiversity. 6 Biological Magnification- Concentrations of a harmful substance increase in organisms at higher trophic levels in a food chain or web. (Fig. 6-16) Conserving Biodiversity: Conservation- Is used to describe the wise management of natural resources, including the preservation of habitats and wildlife. 6-4 Charting a Course for the Future Ozone Depletion: Ozone Layer- between 20-50 kilometers above Earth’s surface, the atmosphere contains a relatively high concentration of ozone gas. Ozone consists of 3 O2 atoms. -Ozone layer functions as an absorbent of harmful ultraviolet (UV) radiation from sunlight before it reaches the Earth’s surface. 7 -Think of it as a global sunscreen. Early Evidence: -In the 1970’s a scientist found evidence from satellite data that a hole in the ozone layer over Antarctic exited during the winter. -Since then it has grown larger and a similar ozone hole also appeared over the Arctic. The Cause: -In the mid 1970’s scientists published that CFC’s could damage the ozone Solution: -Reduce CFC usage!!! Today, most uses of CFC’s are banned **Current data shows that the ozone holes should shrink and disappear within 50 years. Global Climate Change: -Scientists are concerned about the strong evidence that the climate is changing. 8 -Since the late nineteenth century, the average atmospheric temperature’s on Earth’s surface have risen about 0.6 degrees C. (About 0.2-0.3 since 1980!!!) Global Warming- The term used to describe this increase in the average temperature of the biosphere. **New Term: Global Change- Is the new term because not all places are actually warming. Evidence of Global Warming: -The most widely accepted hypothesis is that current warming is related to human activities that are adding CO2 other greenhouse gases to the atmosphere, thus causing the atmosphere to retain more heat. Possible Effects of Global Warming: -Sea levels may rise enough to flood some coastal areas. Social and economic consequences. 9 -Some parts of North America may experience more droughts during the growing season. -New organisms may live where they once could not. -Other organisms may become threatened or extinct in area where they once lived. 10