31_Population_growth - Population growth Pop lation gro th...

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Unformatted text preview: Population growth Pop lation gro th Today's questions: T d ' ti I. What is population ecology? What is population ecology? II. What are the basic models used to describe p p population growth? g III. Case studies in population growth A. Density dependence A. Density dependence B. Population cycles I. What is population ecology? What is population ecology? Members of the same population live in the same area at the same time Interbreed on a regular basis I t b d l b i Are exposed to a similar environment/selection pressures Interact via intraspecific competition Interact via intraspecific competition II. What are the basic models used to describe h h b d l d d b population growth? 280 240 Data on Whooping Cranes (Wood Buffalo Nat'l ParkAransas NWA) 2010 How fast is the whooping crane population growing? Total population = 22 in early 1940s; now 599 (10/11) 3 wild populations: 2010 2011 3 wild populations: 2010 2011 Wood Buffalo 263 279 Florida resident 25 20 WisconsinFlorida 119 115 Growth rate, over 1 year G th t 1 Wood Buffalo Florida resident Florida resident WisconsinFlorida Generalizing these ideas: Let N0 = population size at start N1 = population size one breeding interval later Then N1 / N0 = is the finite rate of increase In the Wood Buffalo flock, 201011, 1 061 I h W d B ff l fl k 2010 11 = 1.061 What is if N1 = 250? What is if N1 = 290? Rearranging: N1 = N0 In general, Nt = N0 t i is an aggregate growth rate, computed over discrete t th t t d di t intervals How can we express population growth on a per capita (per individual) basis, computed at any time? Use r to symbolize the per capita growth rate r = per capita birth rate per capita death rate = per capita birth rate per capita death rate = er (this is a fundamental relationship between finite rates and instantaneous rates) rates and instantaneous rates) Wood Buffalo = 1.061 r = ? Florida resident = 0.80 r = ? WisconsinFlorida = 0.966 r = ? Note that in general, Nt = N0 ert describes discrete g growth; r describes ; continuous growth Nt = N0 ert Consider whooping cranes again. If 22 individuals were alive in 1942 and 599 in 2011, what is r? Exponential versus densitydependent growth III. Case studies in population growth A. Density dependent growth What densitydependent factor(s) constrain growth? How to test these hypotheses? B. Population cycles e.g. Red grouse in England; 4year cycles in abundance Hypothesis: The population crashes every four years because there is rapid transmission of a parasitic nematode worm at high population density. t d t hi h l ti d it Experiment: In "crash years," catch birds at the roost (at night) and administer an antiworm medication. night) and administer an anti worm medication Interpret these graphs Interpret these graphs ...
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