1_populationdynamics - Intro & Part 1 Page 1 Population...

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Unformatted text preview: Intro & Part 1 Page 1 Population Dynamics Introduction: Overfishing, habitat degradation, and a m yriad of other factors have driven many m arine species that were once comm on 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 an d abundance patterns of organisms. There are five species of sea turtles in U.S. wa ters, 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. Prim ary 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-sca le m anipulative experiments with massive organism s such as sea turtles, managers often utilize m odels to explore the impacts of potential conserva tion 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 sim ple population growth m odels using EXCEL. Part 1 - Closed Population Growth W hat pieces of information are n eeded to determine the number of sea turtles in a population, N, at a particular time? Four factors can influence population size: birth, death, im migration, and emigration rates. For this exercise, we consider sea turtles in Hawaii. Due to the extrem e isolation of the Hawaiian islands (Hawaii is the m ost isola ted land m ass in the world, separated by >1000 km from the nearest neighboring islands), we assume that im migration and emigration rates are negligible. Therefore, population dynamics will be influenced solel y by rates of birth and death. Populations in which imm igration and em igration rates are near zero are called “closed populations”. In such populations, birth and death rates im pact directly the number of in dividuals in subsequent generations. Sea turtles generally spawn once per year, laying eggs on sandy beaches. Therefore, population size will equal the num ber of turtles in the population last year plus the num ber of births in a year m inus the num ber of turtles from last year’s population that died. Sim ply: population size (N t+1 ) = last year’s population (N t ) + births - deaths. Generally, calculating births and deaths involves taking the population size an d m ultiplying it by a per capita birth rate, b (which represents th e n umber of offspring produced per individual in the population) and by a per capita death rate, d....
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This note was uploaded on 08/06/2008 for the course ESM 260 taught by Professor Lenihan during the Spring '08 term at UCSB.

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1_populationdynamics - Intro & Part 1 Page 1 Population...

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