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Biology 1001A - lecture 22.docx

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Western University
Biology 1001A
Tom Haffie

Biology 1001A Lecture 22: Community Biology I November 28, 2011 Recap: Human Population Growth  Most K-selected species show logistic growth… what about us? o K-selected species grow in a logistic pattern of growth  i.e. Exponential growth o Humans can modify their environment for suitable growth o No competitors, to compete for resources CLCIKER QUESTIONS: Why is human population size (worldwide) still increasing? ANS: Increased carry capacity, K; decrease death rate due to improvement in medicine; increased birth rates. Human Populations Vary in r  Population will generally increase by 2025 o Due to higher birth rates o Lower death rates r Reflects Age Structure  (Mexico) Large base range o Big younger population  Higher birth rates in future  Increase in Population  (United States) …. Increasing N, but Decreasing r  Globally, r=0.012 or 1.2% (per person per year) o All-time high was 2.2% in the 1960’s Demographic Transition Model  Over time, human societies get wealthier… o Pre-industrial era, r was relatively low o Transitional era, decrease in death rate (d). Value of r is at max o Industrial era, death rates decrease, birth rates decrease, r decreases o Postindustrial era, (i.e. Europe), birth rates reach to zero, death rates decrease/ level off. r decreases Population size isn’t everything… Community Ecology I  Community has multiple species o Population includes only one specie Why are populations distributed the way they are?  Some species limited by a single critical factor  Many species have multidimensional tolerance limits Imagine this in n-dimensional Space o Too hot on right, cold on left o Middle is optimum (tolerance limit)
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