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1_populationdynamics

1_populationdynamics - Intro Part 1 Population Dynamics...

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Intro & Part 1 Page 1 Population Dynamics Introduction: Overfishing, habitat degradation, and a myriad of other factors have driven many marine species that were once common to the brink of extinction. In response to this global environmental catastrophe, managers are faced with the formidable task of staving off the tide of population decline. In order to conserve endangered species, it is crucial that managers have a thorough understanding of which factors affect distribution and abundance patterns of organisms. There are five species of sea turtles in U.S. waters, and the Environmental Protection Agency lists all as either threatened or endangered. Consequently, intensive efforts have been directed towards sea turtle conservation since the 1970’s. Primary causes for sea turtle decline are habitat degradation, intentional harvest, by-catch related mortality, marine pollution, and boat strikes. Because it is often impossible to conduct large-scale manipulative experiments with massive organisms such as sea turtles, managers often utilize models to explore the impacts of potential conservation strategies on population dynamics. The aim of this lab is to enable you to understand how changing per capita birth and death rates affect population growth. You will get practice working with simple population growth models using EXCEL. Part 1 - Closed Population Growth What pieces of information are needed to determine the number of sea turtles in a population, N, at a particular time? Four factors can influence population size: birth, death, immigration, and emigration rates. For this exercise, we consider sea turtles in Hawaii. Due to the extreme isolation of the Hawaiian islands (Hawaii is the most isolated land mass in the world, separated by >1000 km from the nearest neighboring islands), we assume that immigration and emigration rates are negligible. Therefore, population dynamics will be influenced solely by rates of birth and death. Populations in which immigration and emigration rates are near zero are called “closed populations”. In such populations, birth and death rates impact directly the number of individuals in subsequent generations. Sea turtles generally spawn once per year, laying eggs on sandy beaches. Therefore, population size will equal the number of turtles in the population last year plus the number of births in a year minus the number of turtles from last year’s population that died. Simply: population size (N t+1 ) = last year’s population (N t ) + births - deaths. Generally, calculating births and deaths involves taking the population size and multiplying it by a per capita birth rate, b (which represents the number of offspring produced per individual in the population) and by a per capita death rate, d.
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