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Lecture 15

ZOL 355 Lecture Notes - Lecture 15: Doubling Time, Exponential GrowthPremium

6 pages98 viewsSpring 2018

Department
Zoology
Course Code
ZOL 355
Professor
P.Ostrom
Lecture
15

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Lecture 15: Population Structure & Growth
Introduction
o Why study populations
Key to saving endangered species
Helps us control pests
Managing fish and game
populations
Study Diseases/Parasites
Population response to humans
o Characteristics of populations
Size or abundance (number of
individuals)
Growth
Reproductive rate
Age distribution
Immigration/emigration
Spacing
Population Growth
o Factors that influence population growth:
factors leading to Increases in pop size
number of births in the entire population (B)
number of immigrants in the entire population (I)
factors leading to decrease in pop size
number of deaths in the entire population (D)
number of emigrants in the entire population (E)
Population size is N = B + I - D - E
o Equation to estimate population size (N) at time t+1
Nt+1 = Nt + B + I - D - E
o If the population size in 2012 = 1000 what will the population size be in 2013 if there
are 20 births, 5 deaths and there is no immigration or emigration.
Nt = N2012 = 1000
B = 20
D= 5
Nt+1 = 1000 + 20 5 =1015
From this point forward we assume I = 0 and E = 0, a closed population
(WILL HAVE A PROBLEM LIKE THIS ON THE EXAM - AND MANY OTHERS)
o Equation to estimate change in population size (population growth) over a specific time
period
Nt+1-Nt = B - D
ΔN = B – D
o Now we want to understand how N changes over time and to estimate N at any point
in time.
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Models of population growth
o Exponential growth - continuous addition of new
individuals
o Exponential growth equation
Nt = Noert
Nt = number individuals at time t (size at time t)
No = initial number of individuals
r = per capita growth rate
e = base of natural log (2.72)
o Understanding r
r = per capita (per individual) growth rate
r = b d
b = per capita birth rate (average births per individual) number of births per
individual per unit time units are births/(individual * time)
d = per capita death rate number of deaths per individual per unit time units are
deaths/(individual * time)
r = births/(individual *time) deaths/(individual *time)
o Average number of births (b) = 2 births per person per year,
o Average number of deaths (d) = 0.5 deaths per person per year
o r = 2 births/(person* year) 0.5 deaths/(person*year) = 1.5 individuals added per
person per year
o Can r be less than 0?
Yes, the case would be; population growth rate is declining.
o Now that we understand r we can find Nt, the population size at any point in time
Nt = Noert (KNOW EQUATIONS)
Nt = number individuals at time t (size at time t)
No = initial number of individuals
r = per capita growth rate
e = base of natural log (2.72)
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