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A population’s size is the number of individuals it contains. Population density measures how crowded a population is. (Expressed as the # of individuals per unit of area) Dispersion is the spatial distribution of individuals within the population.(clumped, even, or random) Growth Rate = Change in # of individuals ÷ Time Four factors determine whether the population grows, shrinks, or stays the same: 1. 2. 3. 4. Birth Rate Death Rate (mortality rate) Immigration Emigration Exponential Growth: Population increases rapidly after only a few generations Forms a J-Shaped growth curve Logistic Growth: Builds on the exponential model, but accounts for the influence of limiting factors. Limiting Factor = Restrains the growth of a population Includes carrying capacity: The maximum # of individuals that can be supported with the available environmental resources. Forms an S-shaped curve At Carrying Capacity (K) – Birth Rate = Death Rate Density-Dependent Limiting Factor: Limits a population only when the population reaches a certain density. Examples: Resource Limitations (shortages of food or nesting sites) Competition, Predation, Parasitism, Disease Regulates population size Moose Wolves Density-Independent Limiting Factor: Affect all populations in the same way regardless of density Examples: Natural disasters (floods, fires, hurricanes, tornadoes) Many human activities Causes a growing or stable population to collapse suddenly Forms a Boom-and-Bust Curve Shows the likelihood of survival at different ages throughout the lifetime of the organism. 3 TYPES Type I: Likelihood of dying is small, until late in life (humans) Type II: Probability of dying does not change throughout life (linear) – some species of birds Type III: Organisms that are very likely to die when young (Oysters, salmon, many insects) Hydra is a genus of simple, fresh-water animals possessing radial symmetry. Hydras are predatory animals belonging to the phylum Cnidaria and the class Hydrozoa. They can be found in most unpolluted freshwater ponds, lakes and streams in the temperate and tropical regions by gently sweeping a collecting net through weedy areas. They are usually a few millimeters long and are best studied with a microscope. Hydras mainly feed on small aquatic invertebrates such as Daphnia and Cyclops. All species of Hydra exist in a mutual relationship with various types of unicellular algae. The Hydra affords the algae protection from predators and in return, photosynthetic products from the algae are beneficial as a food source to the Hydra. Age Structure: The distribution of individuals among different ages in a population. Presented in graphs U.S. Population Rwandan Population Hunter-Gatherer Society Agricultural Society Industrial Society (1700’s) Led to severe environmental damage What major event caused an increase in the human population? Development of the Germ Theory of Disease Identified bacteria and other microorganisms as the agents responsible for many diseases Improved hygiene Sterile surgery Better methods of waste disposal Water treatment Louis Pasteur (1822-1895) Agriculture begins Industrial Revolution begins Plowing and irrigation Bubonic plague In 1798 the English economist, Thomas Malthus, observed that babies were being born faster than people were dying. ___________________________________ Malthus reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone.