1. the reduction in the average probability that any one individual animal will be preyed on when many animals carry out the same activity at the same time. For example, young birds may leave a nesting colony en masse, or insects may emerge synchronously; as a result, predators are able to take proportionally fewer prey. See also antipredator behavior; confusion effect.

2. the protection against disease transmission that may occur when the presence of incompetent reservoirs (i.e., organisms that do not efficiently transmit a particular pathogen) dilutes the effect of competent reservoirs; in this situation, a decrease in biodiversity may lead to an increase in the transmission of a pathogen. In contrast, the amplification effect occurs when an increase in biodiversity leads to an increase in disease transmission.