The World Wildlife Fund has placed a certain amount of rare elephants in a conservation
area in Borneo. The number of elephants is given by P(t) = 1900/(1+0.9e^(-0.14t)), where t is the time in
years.
a) What is the carrying capacity?
b) What is the growth rate?
c) What is the initial population?
d) How long will take to reach 1250 elephants?
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a) The carrying capacity is the maximum number of elephants that the conservation area can support. In this case, we can find the carrying capacity by taking the limit of the population function as t approaches infinity.
Taking the limit as t approaches infinity, we have:
lim(t->∞) P(t) = lim(t->∞) 1900/(1+0.9e^(-0.14t))
Since the exponent -0.14t approaches negative infinity as t approaches infinity, the e^(-0.14t) term approaches 0. Therefore, the limiting value of the population function is:
lim(t->∞) P(t) = 1900/(1+0.9(0)) = 1900
So, the carrying capacity is 1900 elephants.
b) The growth rate is the rate at which the population is increasing per unit of time. In this case, we can find the growth rate by taking the derivative of the population function with respect to t.
P'(t) = dP/dt = (1900(0.9)(-0.14)e^(-0.14t))/((1+0.9e^(-0.14t))^2)
Simplifying, we have:
P'(t) = -0.2394e^(-0.14t)/(1+0.9e^(-0.14t))^2
At any given time t, the growth rate is given by P'(t).
c) The initial population is the population at t=0. Plugging in t=0 into the population function, we have:
P(0) = 1900/(1+0.9e^(-0.14(0)))
= 1900/(1+0.9e^0)
= 1900/(1+0.9(1))
= 1900/(1+0.9)
= 1900/1.9
= 1000
So, the initial population is 1000 elephants.
d) To find how long it will take to reach 1250 elephants, we can set the population function equal to 1250 and solve for t.
1250 = 1900/(1+0.9e^(-0.14t))
Multiply both sides by (1+0.9e^(-0.14t)):
1250(1+0.9e^(-0.14t)) = 1900
1250 + 1125e^(-0.14t) = 1900
1125e^(-0.14t) = 650
Divide both sides by 1125:
e^(-0.14t) = 650/1125
Take the natural logarithm of both sides:
-0.14t = ln(650/1125)
Solve for t:
t = (ln(650/1125)) / -0.14
Using a calculator, we find:
t ≈ 5 years
So, it will take approximately 5 years to reach 1250 elephants.