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Objectives How are changes in population size determined by immigration, births, emigration and deaths? How is population growth based on available resources? Compare exponential growth and logistic population growth. What are the ecological factors that limit population growth? Changes In Population The size of the population is supported by the amount of resources Abundant resources = population growth Few resources = population decreases Therefore, population change as the supply of resources changes Four Factors Of Population Change Immigration: Movement of individuals into a population from another population Births: Births increase the number of individuals in a population. Emigration: Movement of individuals out of a population and into another population. Deaths: Size of a population decreases when individuals die. Population & Resources Population growth is a response to the environment Amount of growth is directly related to the amount of resources available. Two type of population growth: Exponential Growth Logistic Growth Exponential Growth When a population increases in size in a short period of time Occurs when resources are abundant Example: Introduction of an animal into a previously uninhabited area Logistic Growth Period of slow and quick growth, making an S shaped curve Due to limited resources Abundance creates growth, then as resources deplete growth slows, finally population growth stops as the environment cannot support the population size. Exponential vs. Logistic Carrying Capacity Environment determines how many individuals of the species can be supported based on natural cycles and species diversity. Carrying Capacity: the maximum number of individuals of a particular species that the environment can normally and consistently support Carrying capacity can change when an environment changes Population size can rise and fall depending on the natural changes in the supply of resources Population Crash Population crash is a dramatic decline in the size of a population over a short period of time. Occurs when the carrying capacity for a population suddenly drops Heavy snow or rain decreases expected food stores Not enough precipitation means not enough food for existing population Factors Affecting Carrying Capacity There are many factors that affect the carrying capacity of an environment The factor that has the greatest effect is called the limiting factor Two Categories of Limiting Factors: Density-Dependent Density Independent Density Dependent Limiting Factors Limiting factors that are affected by the number of individuals in a given area Include many different species interactions Competition Predation Parasitism & Disease Density Dependent Limiting Factors Competition Members of populations compete with one another for resources As the population becomes denser the resources are used up, limiting how large a population can grow Density Dependent Limiting Factors Predation: Population of a predator can be limited by the number of available prey Prey numbers can be limited by the fact that they are being used as food Density Dependent Limiting Factors Density Dependent Limiting Factors Parasitism & Disease: Parasites and disease spread quickly through dense populations The parasite or disease can then cause the size of the population to decrease Density Independent Limiting Factors Aspects of the environment that limit a population’s growth regardless of the density of the population Unusual Weather Natural Disasters Human Activities Density Independent Limiting Factors Unusual Weather Changes in normal weather patterns can affect the size of a population independent of its density Example: Change in water flow of the ocean can cause a change in the food chain of the ocean This can affect small populations, but can also be felt all the way up the food chain Density Independent Limiting Factors Natural Disasters: Volcanoes, tsunamis, tornados, hurricanes, and earthquakes can all cause a population to be wiped out no matter its density Example Earthquake in Nepal has caused large loss of life no matter where, or how dense, the population was Density Independent Limiting Factors Human Activities: Humans drastically change any ecosystem or habitat that they move into in a variety of ways Destruction of habitat (loss of wetlands due to developments) Introduction of nonnative species causes population crashes in many parts of the world, especially where biodiversity is part of the ecosystem’s function Pollution of land, water, and air can cause population crash in populations that support other populations Output Use the Frayer model to outline the concepts densitydependent limiting factors and density-independent limiting factors. List and briefly describe the four factors that determine the growth rate of a population. Draw and label graphs showing exponential growth and logistic growth.