Biology 1B, Ecology Lecture 3, Page 1 Professor Resh • Spring 2009*Assigned readings, 8th Edition pp. 1174-11817th Edition pp. 1136-1139Dynamics of PopulationsOutline of Lecture 3A. DensityB. Dispersion1. Random2. Uniform3. Clumped, contagious, and aggregatedC. Sampling effort to estimate population sizeD. Density, dispersion, and statistical precision* Three principles used in sampling effortE. DemographyA. Density: the number of individuals perunit area or volume; densities aredetermined using direct counts, quadrats,or indirect methods (e.g. mark-recapture)N = Number marked initially X total catch on second trappingNumber recaptured in second trappingB. Dispersion (degree of aggregation; spatialdistribution, etc.): the pattern of spacing ofindividuals within the boundaries of a popula-tion (see Fig. 52.3 on p. 1138, 7th Edit. or Fig.52.2 on p. 1153, 6th Edit.).Random Regular or Uniform Contagious or ClumpedBiology 1B, Ecology Lecture 3, Page 2 Professor Resh • Spring 2009*Assigned readings, 8th Edition pp. 1174-11817th Edition pp. 1136-1139Dynamics of Populations1. Random: spacing varies in anunpredictable way; the distributionof one individual doesn’t affect thedistribution of others; absence ofrepulsion and attractions.2. Uniform: spacing is even;antagonistic behavior3. Clumped, contagious, aggregated:individuals are aggregated inpatches; habitat heterogeneityWhich type occurs most often?C. Sampling effort (sample sizerequirements, number of requiredsamples) needed to estimate populationsize is a function of(1) Size of density mean(2) Dispersion pattern (spacing ofindividuals)(3) Desired precision (allowable error)D. Density, dispersion, and statisticalprecision are related and can each bemanipulated to solve for any of thesepopulation characteristics.N = s2t2x2D2x = means2 = varianceD = precision (expressed as a decimal)t = constantBiology 1B, Ecology Lecture 3, Page 3 Professor Resh • Spring 2009*Assigned readings, 8th Edition pp. 1174-11817th Edition pp. 1136-1139Dynamics of Populations1. As density increases, sampling effortdecreases (assuming dispersion andprecision are unchanged).2. As dispersion becomes moreclumped (i.e. departs from random),the value of s2/x2 in the aboveformula increases; assuming densityand precision are unchanged,sampling effort increases asclumping increases.3. As the desired precision [say, ex-pressed as a percentage (20% error)but used as a decimal (0.2)] increases(which would be a 20% allowableerror compared to 40% error) sam-pling effort increases.Why is it important to understand samplingeffort and statistics?Biology 1B, Ecology Lecture 3, Page 4 Professor Resh • Spring 2009*Assigned readings, 8th Edition pp. 1174-11817th Edition pp. 1136-1139Dynamics of PopulationsB. Demography1. Population size increases fromreproduction and immigration, anddecreases from death and emigration.2. Overlapping generations result whenthe average life span of an individualin a population is greater than thetime it takes for that individual tomature and reproduce.i. Co-existence of generationsresults in a specific age structure(e.g. Sweden, Mexico, and USdiffer in age structure; Japan’shas changed over time).ii. Generation time: average spanbetween the birth of an individualand the birth of its offspring;shorter generation time, fasterpopulation growth because ofcompounding.iii. Sex ratiosiv. Mortality and
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