1) A population of 200 organisms experiences 25 births and 30 deaths in a month’s time. Calculate r for
a one year period.
r = (births – deaths) / population
Births – deaths per month: 25 – 30 = -5
Births – deaths for a total year = -5 X 12 = -60
r = (-60) / 200
r = -0.3
2) A population of bacteria exhibits exponential growth. The r max, the maximum per capita growth
rate, of the population is 0.5 bacteria/(bacteria • month). Calculate the maximum population growth
rate for the population when the population is at 500 organisms.
dN / dt = r max X N
= 0.5 X 500
= 250
3) A population of ants exhibits logistic growth. The carrying capacity of the population is 500 ants, and r
max, the maximum per capita growth rate, of the population is 0.20 ants/(ants • month). Calculate the
maximum population growth rate for the population if the maximum growth occurs when N = k/2.
N = k / 2 (500 / 2)
= 250
dN / dt = rmax X N (K-N / K)
= 0.2 X 250 (500 - 250 / 500)
= 25
4) Population size is being estimated using the mark and recapture method. Twenty individuals are
captured at random and marked with a dye or tag and then are released back into the environment. At
a later time a second group of animals is captured at random from the population. 10 individuals were
marked out of 35 that were captured the second time. Calculate the estimated population size.
𝒔 𝒙
=
𝑵 𝒏
rearranged to 𝑵 =
N = 20 (35) / 10
= 70
𝒔𝒏
𝒙
5) Calculate the mean rate of change in the population from August 2001 to April 2006.
dN / dt
dN = 60,000 (Apr. 2006) – 35,000 (Aug. 2001)
= 25,000
dt = This would depend on the unit of time you’re looking at. I should have specified more here. I will
go by months. Including Aug. 2001 and Apr. 2006, this would 57 months.
dN / dt = 25,000 / 57
= 438.6
6) A community has a total of 594,000 producers. How many organisms would be expected to be found
at the secondary consumer level?
You would expect to have 10% of the number of organisms as the previous trophic level. That would
mean that there would be 59,400 primary consumers then 5,940 secondary consumers.