Question

In a closed population, the balance between reproduction and mortality determines the population dynamics. A distinction is made between additive and compensatory forms of mortality.

a) Explain the terms additive and compensatory mortality with text and with the help of figures.

b) Under what conditions can we expect a predator to cause compensatory mortality?

c) Under what conditions can we expect a predator to cause additive mortality?

Answer 1

a). In compensatory mortality, at low to intermediate exploitation rates, total mortality of a population remains unchanged. For example- Pomoxis nigromaculatus and P. Annularis, annual exploitation didn't affect annual mortality rate at low to moderate exploitation.

In additive mortality, there is increase in total mortality when exploitation increases. eg- fishing.

b). Increase in predation results in compensatory declines. The degree of predisposition is inversely related to the death of predated individuals. Overall survival rate of population is not decreased.

c). Increase in exploitation at very high rate, leads to additive mortality. It can be compensated because the death of individual by predators is fast to overcome with growth.