Name _______________________________________
Period ______
Date ____________
Ecology Practice Problems
1. In the simplest population growth model (dN/dt = rN).
a. What do each of the terms stand for?
Term
Stands for……
Change in population size
dN
Change in time
dt
Rate of increase
r
Population size
N
b. What type of population growth does this equation describe?
Exponential
c. What assumptions are made to develop this equation?
Organisms have access to unlimited resources
2. Population growth may also be represented by the model, dN/dt = rmaxN[(K – N)/K].
a. What is K? Explain.
K = the carrying capacity or the number of individuals that the environment can
reasonably support
b. If N = K, then what is dN/dt?
This would mean population size is equal to the carrying capacity and growth should be
zero.
c. Describe in words how dN/dt changes from when N is very small to when N is large
relative to K.
When N is small dN/dt changes slowly as there are few individuals that are of
reproductive age and the population is small.
dN/dt will change most rapidly when the population size is intermediate, there are many
individuals of reproductive age and resources are still plentiful.
When N is very large (near K) the rate of increase slows due to competition for resources
(approaching carrying capacity).
This growth pattern of slow, fast and slow is what gives us the “S” curve we see in
logistic growth.
d. What assumptions are made to develop this equation?
Resources are limited and a carrying capacity exists (amt. of food, shelter, habitat, water,
mates, etc. are limited)
3. You and your friends have monitored two populations of wild lupine for one entire
reproductive cycle (June year 1 to June year 2). By carefully mapping, tagging, and censusing
the plants throughout this period, you obtain the data listed in the chart.
Parameter
Population A
Population B
Initial number of plants
Number of new seedlings
established
Number of the initial plants
that died
500
300
100
30
20
100
a. Calculate the following parameters for each population.
Parameter
Population A
100
Population B
30
20
100
0.2
0.1
0.04
0.33
B (births during time interval)
D (deaths during time interval)
b (per capita birth rate)
m (per capita death rate)
0.16
-0.23
r (per capita rate of increase)
Remember that per capita birth rate is the number of births divided by the total population. Per
capita death rate is the # of deaths divided by the total population.
The rate of increase will be B(irths)-D(eaths) = r
4. The net annual productivity of a particular wetland ecosystem
is found to be 8000 kcal/m2. If respiration by the aquatic
producers is 12,000 kcal/m2 per year, what is the gross annual
primary productivity for this ecosystem in kcal/m2 per year?
Round to the nearest whole number.
GPP = light energy converted to chemical energy per unit
time
R- Respiration
NPP = Chemical energy from GPP – respiration (remember
plants do both photosynthesis and respiration so some energy
is used to respire)
NPP = GPP – R
8,000kcal/m2 = GPP – 12,000 kcal/m2
GPP = 20,000 kcal/m2
5. A scientist recorded the amount of dissolved oxygen produced
by elodea, an underwater plant, as 52 mg O2/L. How much
carbon (in mg/L) was fixed by this plant? Round your answer to
the nearest tenth.
52mgO2/L X 0.698 ml/mg = 36.296 ml O2/L
36.296 mlO2/L X 0.536mgC/mlO2 = 19.5 mg C fixed
Had to use both formulas from AP formula sheet.
6. The diagram below shows the movement of carbon through a simplified food web. How
much carbon (g/m2) is released into the atmosphere as a result of metabolic activity by
herbivores? Round your answer to the nearest whole number.
We’re only focused on herbivores so 100g/m2(input) – 50g/m2(output)- 8g/m2(output) = 42
g/m2 (left for emission through respiration to atm.)
7. What percent of the biomass in the forest community represented below is tied up in the shrub
layer? Give your answer to the nearest whole number.
1.9e4-1.3e4-1.1e3 = 4,900 (shrub)
As a percent = 4,900/1.9e4 = 0.257 or rounded 26%