Bio1b Summer 2008 Eric Harris Ecology Lecture 3 Page 1 of 2 ECOLOGY LECTURE 3 POPULATION BIOLOGY I DEMOGRAPHY LIFE HISTORY Reading 7th ed 1136 1143 8th ed 1174 1181 A population a group of species of the same species in the same general area recall population genetics A Population Structure i Density number of individuals area or volume Difficulty of measuring directly Estimation e g mark recapture method assumes the proportion of marks in the second sample is equal to the proportion of marks in the population as a whole Knowing the number marked x and recaptured n in the second sample and the number initially marked m we can calculate the population size N x n m N therefore N mn x Density is the result of births deaths immigration emigration ii Distribution or dispersion Random rare in nature Regular or overdispersed frequently caused by competition Clumped or patchy many possible causes distribution of resources for example iii Age Structure organisms may change in many ways as they age e g food source predators and competitors may all change Comparison of human populations Graphical presentations B Demography the study of the factors that influence population growth and decline i Life tables Cohort follows a group of individuals born at the same time hard to do but accurate Static looks at all the individuals present during one time period easier but harder to interpret Updated on 06 30 08 Bio1b Summer 2008 Eric Harris Ecology Lecture 3 Page 2 of 2 ii Survivorship curves Type I e g humans mortality is low until most individuals die late in their lifespan Type II e g some bird species a constant proportional mortality Type III e g many insect and fish species most individuals die young the few that survive may then live for much longer C Life History Traits i Life history components Semelparity vs iteroparity reproduce once or repeatedly Age at first reproduction precocity vs delay Clutch size Size as an adult and growth rates to reach that size ii Life history trade offs All life history variables cannot all be maximized at the same time e g current reproduction may reduce future growth or survivorship Updated on 06 30 08
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