AP Environmental Science Unit 3 Populations

Unit 3: Populations ● Population Ecology ○ Population - a group of organisms of the same species ■ Population Density - the number of individuals of a population that inhabit a certain unit of land or water area ■ Population Dispersion - how individuals of a population are spaced within a region ● Clumped Dispersion ○ The most common dispersion pattern for populations ○ Adheres to the “those of a feather flock together” idea ○ Eg: Plants & fish ● Uniform Dispersion ○ Members of a population are uniformly spaced throughout their geographic region; usually a result of competition for an ecosystem’s resources ○ Eg: Trees ● Random Dispersion ○ A relatively uncommon pattern of dispersion ○ Occurs when the position of each member of a population is not determined or influenced by other members of the population ○ Population Growth & Carrying Capacity ■ Biotic Potential ● How much a population would grow if there were unlimited resources in the environment ● Not a practical model for population growth because resources in an environment are limited ■ Carrying Capacity ● The maximum population size that can be supported by the available resources in the region ● Differ by species, as different species have different requirements for life ■ Graphing Population Growth ● J-Curve Model - Exponential Growth ○ ● Logistic Population Growth (S-Curve) - Initial burst then growth rate drops ○ ■ Rule of 70 - the time it takes for a population to double can be approximated by dividing 70 by the current growth rate of the population 70 ● Eg: = 2.8 years 25% ○ Reproductive Strategies ■ R-selected Organisms ● Reproduces early in life ○ ○ ○ ● ○ ● Usually have a high capacity for reproductive growth ● Little to no care given to offspring ○ Eg; Bacteria, algae, protozoa ■ K-selected Organisms ● Reproduces later in life ● Produces fewer organisms ● Devote significant time and energy to nurturing of offspring ● Parents are invested in each individual offspring ○ Eg: Humans, lions, cows Survivorship and Population Cycles ■ Boom-and-Bust Cycle ● Very common among r-strategists ● Rapid increase→Equally rapid drop-off ■ Predator-Prey Cycle Factors Influencing Population Growth ■ Density-dependent Factors ● Increased predation ● Competition for food or living space ● Disease ● Buildup of toxic materials ■ Density-independent Factors ● Fires ● Storms ● Earthquakes Survivorship Curve ■ Type I ● The majority of offspring will live for a long period of time; eventually they will start to die off ■ Type II ● Offspring have a 50-50 chance of surviving to old age ■ Type III ● Most offspring die young, but if they live to a certain age, they will live a longer life ○ Human Population World Population ■ Birth rate = the number of live births per 1,000 members of the population in a year ■ Death rate = the number of deaths per 1,000 members (𝐵𝑖𝑟𝑡ℎ 𝑟𝑎𝑡𝑒+𝑖𝑚𝑚𝑖𝑔𝑟𝑎𝑡𝑖𝑜𝑛)−(𝑑𝑒𝑎𝑡ℎ 𝑟𝑎𝑡𝑒+𝑒𝑚𝑖𝑔𝑟𝑎𝑡𝑖𝑜𝑛) ■ Growth Rate = 1,000 ○ Population Changes ■ Emigration - the movement of people out of a population ■ Immigration - the movement of people into a population ■ Total Fertility Rate ● The number of children a woman in a given population will bear during her lifetime ● Based on an analysis of data from preceding years ● TFRs cannot be depended on because they assume the conditions of the past will be the conditions of the future ■ Replacement Birth Rate ● The number of children a couple must have in order to replace themselves in a population ● Worldwide, the replacement birth rate is slightly higher than 2 ● In developing countries, this number is as high as 3.4 due to higher mortality rates ■ Factors that Affect TFRs of a Population ● Availability of birth control ● Demand for children in the labor force ● Base level of education for women ● Existence of public and/or private retirement systems ● The population’s religious beliefs, culture, and traditions ■ Factors that Affect the Growth Rate of a Population ● Base level of education for women ● Dominant religion ● Existence of public and/or private retirement systems ● The population’s religious beliefs, culture, and traditions ● Human Impact on Earth ○ Ecological Footprint ● Used to describe the environmental impact of a population ■ IPAT Model ● I=P*A*T ○ I - The total impact ○ P - Population size ○ A - Affluence ○ T - Level of technology ○ Environmental Problems ■ Overgrazing & Desertification ● Green Revolution - the technological innovation and an increased use of pesticides and fertilizers, which allowed farmer to increase crop production throughout the world ● Extensive Pastoralism - the shifting of animal herds between grazing pastures has remained popular in several arid parts of the world ● Population Pressure - too many people and too many animals on too little lands ● Overgrazing - led to significant amounts of dry grassland being denuded, eroded, and desertified ● Desertification - any human process that turns a vegetated environment into a desert-like landscape ● Soil Salinization - the salt content in soil increasing due to nonanthropogenic and/or anthropogenic influences ■ Irrigation Agriculture ● Irrigation - the application of controlled amounts of water to plants at needed intervals ● Aquifers - underground water tables ○ Aquifer supplies are being depleted at a rapid rate in largescale countries such as India, China and the United States ■ Deforestation ● Deforestation - the act of clearing a forested area of trees and other vegetation without the intention of replanting ● Threatened & Endangered Species ○ Vulnerable Species ■ The species is likely to become endangered if no action is taken ○ Endangered Species ■ The species is likely to become extinct ○ Critically Endangered ■ The species is at a very high risk of extinction ○ Background Extinction Rate ■ Species that are the most endangered have several factors in common ● They: ○ Require large ranges of habitat to survive ○ Have low reproductive rates ○ Have specialized feeding habits ○ Have some sort of value for humans ○ Have low population numbers ■ Fragmentation - habitats are broken into smaller pieces by, for example, building of roads and cities ■ Degradation - pollutants are added to the environment ■ Overexploitation - contribution to extinction ■ Biodiversity Hotspot ● HIPPCO - an acronym to memorize the cause of extinction ○ H - Habitat Destruction/Fragmentation ○ I - Invasives ○ P - Population ○ P - Pollution ○ C - Climate Change ○ O - Overharvesting/Overexploitation