QUESTIONS
Zooplankton Production
239
Assumptions for the model are
a. Includes the biomass (dry weight) lost as mortality.
b. Assumes a constant temperature of 20°e.
c. Assumes constant mortality and egg production and no emigration of
immigration throughout the period.
e. Uses one-day time intervals.
d. Assumes one-half of eggs found were 0 to 1 day old and one-half were 1 to 2
days old.
f. Assumes that the eggs produced on a given day occurred before mortality
occurred.
Then, from your model, make the following calculations:
a. For each day calculate the egg development in selected females, mortality of
the day class, hatched eggs (i.e., 2 days old), and advance the Daphnia through
each day class.
b. Determine the biomass at t = 14 days. Add the cumulative mortality to the t14
biomass for total production.
c. Determine the net change in biomass t14 - to.
d. Graph biomass (mg) and mortality (mgjday) versus time in days over the 14-day
period.
1. We assume that your population consists only of females. Why? What is the
typical life cycle of Daphnia?
2. Survival rates decrease with increasing age (e.g., Table 16.1). What would you
expect to be dominant causes of mortality in differing age classes?
3. How might survival rates change for a population of Daphnia in the open water
versus one in a littoral zone of dense emergent macrophytes?
4. Using a time interval larger than 1 day would simplify computations in a discrete
model. What would result? How realistic would such production values be?
5. What would be the potential effects of daily vertical migration of Daphnia in a
thermally stratified lake on:
a. Growth rates?
b. Predation?
c. Production values calculated by a discrete time interval model?
6. Was your population expanding or contracting by t = 14 days? Why?
7. Was the rate of increase (or decrease) in production occurring at a constant rate?
Why or why not?
8. What would be the effect of an increase in fecundity on population production?
A decrease in mortality?
9. Is a discrete time interval model more accurate than an instantaneous model?
Why? [See Edmondson and Winberg (1971).]
10. What is the effect of biasing the egg count through faulty sampling or
enumeration? [See Likens and Gilbert (1970).]
11. Among rotifers, production has been calculated by the doubling time method:
p = (N)(w)
Te + p
Zooplankton Production
239
Assumptions for the model are
a. Includes the biomass (dry weight) lost as mortality.
b. Assumes a constant temperature of 20°e.
c. Assumes constant mortality and egg production and no emigration of
immigration throughout the period.
e. Uses one-day time intervals.
d. Assumes one-half of eggs found were 0 to 1 day old and one-half were 1 to 2
days old.
f. Assumes that the eggs produced on a given day occurred before mortality
occurred.
Then, from your model, make the following calculations:
a. For each day calculate the egg development in selected females, mortality of
the day class, hatched eggs (i.e., 2 days old), and advance the Daphnia through
each day class.
b. Determine the biomass at t = 14 days. Add the cumulative mortality to the t14
biomass for total production.
c. Determine the net change in biomass t14 - to.
d. Graph biomass (mg) and mortality (mgjday) versus time in days over the 14-day
period.
1. We assume that your population consists only of females. Why? What is the
typical life cycle of Daphnia?
2. Survival rates decrease with increasing age (e.g., Table 16.1). What would you
expect to be dominant causes of mortality in differing age classes?
3. How might survival rates change for a population of Daphnia in the open water
versus one in a littoral zone of dense emergent macrophytes?
4. Using a time interval larger than 1 day would simplify computations in a discrete
model. What would result? How realistic would such production values be?
5. What would be the potential effects of daily vertical migration of Daphnia in a
thermally stratified lake on:
a. Growth rates?
b. Predation?
c. Production values calculated by a discrete time interval model?
6. Was your population expanding or contracting by t = 14 days? Why?
7. Was the rate of increase (or decrease) in production occurring at a constant rate?
Why or why not?
8. What would be the effect of an increase in fecundity on population production?
A decrease in mortality?
9. Is a discrete time interval model more accurate than an instantaneous model?
Why? [See Edmondson and Winberg (1971).]
10. What is the effect of biasing the egg count through faulty sampling or
enumeration? [See Likens and Gilbert (1970).]
11. Among rotifers, production has been calculated by the doubling time method:
p = (N)(w)
Te + p