DETERMINING POPULATION GROWTH ASSIGNMENT
In one year, biologists tracking a bear population counted 33 new baby bear cubs in a population of 546 bears.
A. Calculate the birth rate (b) of this population.
The per capita birth rate is: b =
!!
!"#
= 0.06044 or (0.06044 x 100%) = 6.044%
B. In the same year, the biologists counted 28 black bear deaths. Calculate the death rate for this population.
The per capita death rate is: m =
!"
!"#
= 0.05128 or (0.05128 x 100%) = 5.128%
C. What is the per capita rate of increase for this black bear population?
The per capita rate of increase is: r = b – m à r = 0.06044 - 0.05128 à r = 0.00916 or (0.00916 x 100%) =
0.916%
D. What would you estimate the change in black bear population size would be for the following year? Be sure to
adjust the N to reflect the new births and deaths. When you get your answer, round to the "nearest bear" and
answer the question - is this population increasing or decreasing in size?
The value of N is adjusted: N = total population + (births - deaths) à 546 + (33-28) = 551
Change in black bear population size for the following year:
∆N = unknown
N = 551
∆t = time interval of 1 year
r = per capita rate of increase of 0.00916
Hence:
∆!
∆!
= rN à
∆!
!
= (0.00916)(551) à ∆N = (1)(0.00916)(551) à ∆N = 5.04716 = 5 black bears
The total population would be:
551 + 5 = 556
Thus, the change in black bear population size would be 5 and the total population would be 556.
As well, the population is clearly increasing in size, we know this not only by the increase to 556 black bears but
also because r > 0 à 0.00916>0
E. Determine the number of births and deaths you would expect the following year. Round to the "nearest bear".
Expected number of births: B = b x N à B = 0.06044 x 556 = 33.6 = 34 births
Expected number of deaths: M = m x N à M = 0.05128 x 556 = 28.5 = 29 deaths