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BIOLOGY UNIT 3 Vocab for unit 3: populations ◦Population Density ◦Age Structure ◦Immigration ◦Emigration ◦Exponential growth ◦Logistic Growth ◦ Carrying capacity ◦ Limiting Factor ◦ Density-dependent limiting factor ◦ Density-independent limiting factor ◦ Demography ◦ Demographic transition Describing Populations ◦We describe populations by looking at: ◦Geographic range ◦Population density ◦Growth rate ◦Age structure Geographic Range ◦The area inhabited by a population Example: the range of the emperor penguin is the coast of Antarctica Population density ◦The number of individuals per unit area ◦ Example: if you have 375 dogs in 15 square kilometers the population density of dogs would be 25 dogs per 1 square kilometer Growth rate ◦The population growth rate is the rate at which the number of individuals in a population increases in a given time period as a fraction of the initial population. ◦ Example: Global human population growth amounts to around 75 million annually, or 1.1% per year. ◦Determines if a population increases, decreases, or stays the same ◦ Factors: Birthrate, death rate, immigration, emigration Age Structure ◦The numbers of males and females in each age group How do populations increase? ◦Birth ◦Immigration How do populations decrease? ◦Death ◦Emigration Populations ◦Populations stay the same when growth factors (birthrate & immigration) equal decrease factors (death rate & emigration) Plicker Questions (multiple choice) ◦The movement of individuals into an area is called… ◦All other things being equal, the size of a population will decrease if… 2 Types of Growth ◦Exponential ◦Logistic Exponential Growth ◦ Population growth where the size of each generation is larger than the generation before it ◦ With exponential growth the larger a population gets, the faster it grows ◦ Under ideal conditions with unlimited resources, a population will grow exponentially Logistic Growth ◦ The various growth phases that most populations go through ◦ Phase 1: exponential growth ◦ Phase 2: growth slows down ◦ Phase 3: growth stops (at the carrying capacity) Carrying Capacity ◦The maximum number of individuals of a particular species that a particular environment can support. ◦Once a population reaches the carrying capacity of its environment the size of the population starts to stabilize. Plicker Questions ◦ In the presence of unlimited resources and in the absence of disease and predation, what would probably happen to a bacterial population? ◦ Which of the following refers to when a population’s birthrate equals its death rate? Limiting Factors ◦ A limiting factor is something that controls the growth of a population ◦ Limiting factors determine the carrying capacity of an environment for a species Population Size Can be limited by Two Types of Limiting Factors Density Dependent Limiting Factors ◦Happen only when population density reaches certain levels ◦Does not typically impact small scattered populations Density Independent Limiting Factors ◦Affect all populations in similar ways, regardless of population size and density. Density Dependent Limiting Factors ◦ Competition: when populations are crowded individuals compete for resources ◦ Predation: predator prey relationships ◦ Herbivory: herbivores are PREDATORS to plants. ◦ Parasitism / Disease: the denser the population, the easier it is for parasites and disease to spread ◦ Stress from overcrowding: Some species fight amongst themselves if they’re overcrowded – fighting can lead to high levels of stress which weakens the individuals ability to fight disease Density Independent Limiting Factors ◦Unusual weather: hurricanes, droughts, floods, … ◦Natural Disasters: wildfire, earthquakes, …. Remember that not all limiting factors will limit all populations. For example, a wildfire might not be a limiting factor for fish in the ocean Plicker Questions ◦ Which of the following is not an example of a density-dependent limiting factor ◦ Which of the following is not an example of a density-independent limiting factor ◦ What could cause a population to sharply decline? ◦ What would increase competition in a population?