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Chapter 14 “Populations” 14.1 “Populations and How They Grow” Objective: – Describe the different ways that populations may change. Populations A group of organisms of a single species that live in a given area. Changes in Population Size In nature populations will stay relatively the same in number. HOWEVER, sometimes those numbers will change dramatically. Growth Rate A change in population size. (+ or -) Depends on how many organisms are added and removed (immigration & emigration). AND interaction between organisms. Why do Populations Grow? Ideal conditions (adequate food supply, shelter, protection from predators) = growth. Birth rates are higher than death rates. Mexican Population Growth Baby Boom If ideal conditions continue, the larger the population gets, the faster it grows. Exponential Growth = constant growth that takes place under ideal conditions. Exponential Growth in Bacteria Growth with Limits In nature, exponential growth does not continue forever. Growth slows down because resources are limited. Growth with Limits Carrying Capacity Growth Limits continued... Zero Population Growth – birth rate and death rate are the same – population stays the same = steady-state Carrying Capacity – the largest # of individuals of a population that a given environment can support Boom & Bust In nature species increase in # until they reach their carrying capacity. Some however reach a “boom” and then crash in size “the bust”. Boom and Bust 14.2 “Why Populations Stop Growing” Objective: –Identify the factors that control population growth in nature. Population Growth Limited by the size and density of a population. Population Density = the # of organisms in a given area. Limiting Factor = a factor that causes a population to decrease. Density-Dependent Limiting Factors Depends on population size, affects large & dense pops more. Include: – Competition – Predation – Parasitism – Disease – Crowding & Stress Competition When populations become too crowded, organisms will compete for resources. Can occur between different species = evolutionary change. Increases death rates. Predation Predator-Prey relationship controls populations. Defenses for both predator & prey. Predator Prey Graph Parasitism Range in size from microscopic (bacteria) to tapeworms (30+ cm). Like predators, parasites take nourishment at the expense of their hosts. Host-specific. Parasites – tapeworm Crowding and Stress Most organisms need a certain amount of space. Overcrowding causes disturbances among organisms leading to weakening. Density-Independent Limiting Factors Affects populations regardless of size. Some examples include: unusual weather seasonal cycles human activities: –damming rivers –clear-cutting forests Clear Cut Forest