Biology 1B Ecology Lecture 3 Page 1 Assigned readings 8th Edition pp 1174 1181 7th Edition pp 1136 1139 Dynamics of Populations Outline of Lecture 3 A Density B Dispersion 1 Random 2 Uniform 3 Clumped contagious and aggregated C Sampling effort to estimate population size D Density dispersion and statistical precision Three principles used in sampling effort E Demography A Density the number of individuals per unit area or volume densities are determined using direct counts quadrats or indirect methods e g mark recapture N Number marked initially X total catch on second trapping Number recaptured in second trapping B Dispersion degree of aggregation spatial distribution etc the pattern of spacing of individuals within the boundaries of a population see Fig 52 3 on p 1138 7th Edit or Fig 52 2 on p 1153 6th Edit Random Regular or Uniform Contagious or Clumped Professor Resh Spring 2009 Biology 1B Ecology Lecture 3 Page 2 Assigned readings 8th Edition pp 1174 1181 7th Edition pp 1136 1139 Dynamics of Populations 1 Random spacing varies in an unpredictable way the distribution of one individual doesn t affect the distribution of others absence of repulsion and attractions 2 Uniform spacing is even antagonistic behavior 3 Clumped contagious aggregated individuals are aggregated in patches habitat heterogeneity Which type occurs most often C Sampling effort sample size requirements number of required samples needed to estimate population size is a function of 1 Size of density mean 2 Dispersion pattern spacing of individuals 3 Desired precision allowable error D Density dispersion and statistical precision are related and can each be manipulated to solve for any of these population characteristics N s2t2 x2D2 x mean s2 variance D precision expressed as a decimal t constant Professor Resh Spring 2009 Biology 1B Ecology Lecture 3 Page 3 Assigned readings 8th Edition pp 1174 1181 7th Edition pp 1136 1139 Dynamics of Populations 1 As density increases sampling effort decreases assuming dispersion and precision are unchanged 2 As dispersion becomes more clumped i e departs from random the value of s2 x2 in the above formula increases assuming density and precision are unchanged sampling effort increases as clumping increases 3 As the desired precision say expressed as a percentage 20 error but used as a decimal 0 2 increases which would be a 20 allowable error compared to 40 error sampling effort increases Why is it important to understand sampling effort and statistics Professor Resh Spring 2009 Biology 1B Ecology Lecture 3 Page 4 Assigned readings 8th Edition pp 1174 1181 7th Edition pp 1136 1139 Dynamics of Populations B Demography 1 Population size increases from reproduction and immigration and decreases from death and emigration 2 Overlapping generations result when the average life span of an individual in a population is greater than the time it takes for that individual to mature and reproduce i Co existence of generations results in a specific age structure e g Sweden Mexico and US differ in age structure Japan s has changed over time ii Generation time average span between the birth of an individual and the birth of its offspring shorter generation time faster population growth because of compounding iii Sex ratios iv Mortality and survivorship Professor Resh Spring 2009
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