Answers to Analyzing Data 19.1 Questions
1. The predation treatments all caused a decline in species richness compared with the control ponds without predation. Thus, it appears that predation caused the local extinction of zooplankton species.
The two species of predators (fish and insect), either alone or together, did not differ in their effects on zooplankton richness.2. Dispersal of zooplankton increased local species richness in the ponds but only if predation was present. If predators were not present, local species richness was similar with or without dispersal. The results suggest that dispersal can have a positive effect on local species richness but presumably only if resources are freed up by predation, thus increasing species coexistence.
3. The results suggest that the effect of predation on local species richness can be so intense that the process of dispersal is inadequate to “rescue” the community from species loss. Yes, the results fit the intermediate disturbance hypothesis but only if dispersal is incorporated into the model.