Inclusion of the lower ranked prey is independent of its abundance and dependant on the abundance of the highest ranked prey. If it stays too long it will be spending too much time for the amount of energy it is accumulating. Time spent in a patch increases if travel time is long. Reproduction Ecology Reproduction is one of the primary goals of any organisms. In order to keep a species from becoming extinct, its members must reproduce at least enough offspring to replace themselves.
Organisms invest a considerable amount of time and energy into reproducing.
The eggs and sperm they produce are costly cells to make, and their only use is for reproduction. Some organisms also invest a great deal of energy in mate selection and nest preparation. In the case of the higher organisms, parental care may take place, and the organisms will be investing its resources into its offspring for even years to come. If an organism did not have to invest all of this energy into producing and nurturing offspring, they would have more energy available for investing into more complex organs allowing them to possibly be better competitors in its environment. But reproduction is an absolute necessity for organisms that are not immortal, and I do not know any that are.