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Lecture 7

BIOB50Winter2012 Lecture 7 and 8.docx - notes from text and lecture slides (includes pictures)

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Department
Biological Sciences
Course
BIOB50H3
Professor
Marc Cadotte
Semester
Summer

Description
BIOB50Winter2012 Lecture 7 and 8 Population Growth and Regulation Chapter 9 and Chapter 10 Chapter 9 Population growth and regulationCase Study Human Population Growth o In 1975 the population was growing at an annual rate of nearly 2meaning that population would double every 35 years o If this growth rate was sustained we would reach 32 billion people by 2080growth rate has recently slowed down to 121 per yearresulting in 16 billion people by 2080o Could Earth support 16 billion people Introduction o One of the ecological maims is No population can increase in size forever o Earth cannot support everincreasing numbers of ANY species o Challenge for ecologists is to figure out what factors promote population growth and what factors limit the population growth Life Tableso Life tables show how survival and reproductive rates vary with age size or life cycle stage o Information about births and death is essential to predict trends or future population sizeLife Table ExamplePoa annuao Life table providews a summer of how survival o Fc fecundityaverage number of offspring and reproductive rates vary with the age of an produced by a female while she is of age x organism o Data for a life table for the grass Poa annua were collected by marking 843 naturally germinating seedlings and then following their fates over time o Nxthe number of individuals alive at age x where x in this case is measure in increments of 3 months o Sx age specific survival ratechance that an individual of age x will survive to age x1 o Ix survivorshipproportion of individuals that survive from birth age 0 to age x oo For example 856 of individuals will survive from 0 to 3 months o The table shown above is an example of a cohort tableo A cohort life table follows the fate of a group of individuals all born at the same time a cohortusually used for plants and other sessile organisms because individuals can be marked and followed over time relatively easily 1o In some cases a static life table can be usedsurvival and reproduction of individuals of different ages during a single time period are recordedused when the organism lives over a long period of time example trees or is highly mobile example fish o When birth and death rates correlate poorly with age for example a plant will not reproduce until conditions are favourable no matter its age or when age is difficult to measure life tables based on the sizes or the life cycle stages newborn juvenile adult of individuals in a population can be constructedo Extensive life data tables exist for humans tooexample is Table 92 Survivorship Fecundity and Life expectancy by Age of US Females in 2005 o Figure 94 Survivorship Varies among Human Populationsplot of Sx of US and Gambians showing that the survivorship of females does not drop below 95 until after they are 50 years old while Gambians have a much lower survival rate 4762 reach age 45Gambians born in the hungry season which is July to October when food is sparse have an even lower survival rate than those born between November and June Survivorship Curves o A survivorship curve is a plot of the number of individuals from a hypothetical cohort that will survive to reach different ages o Survivorship curves can be classified into 3 general types o Type Ideath rates do not begin to increase greatly until old age o Type II equal chance of dying and surviving at all ageso Type III mortality is very high at young ages oand very low at older agesmost common in o Example mountain sheep have type I birds are species that produce high number of offspring of type II and desert shrub is of type III example corals mostinsects many plants etcAge Structure o Life table data can be used to project the future age structure size and growth rate of a population o A population can be characterized by its age structurethe proportion of the population in each age class o Age structure influences whether a population will increase or decrease in sizeif one population has many people in the elderly age group then it will increase at a much lower rate than a population with many people as young adults2
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