We know less about other factors that probably contribute to the decline of biological diversity. We know little about how changes in our atmosphere, such as global warming or ozone depletion, is affecting other life forms.
Disease and insect infestations, which are natural and nonthreatening phenomena in many ecosystems, can deal a death blow to populations weakened or depleted by other pressures.
We know very little about how all these factors interact to affect plant and animal populations. We do know, however, that these "natural" changes are becoming proportionately less significant as human impacts increase in magnitude, intensity, and duration.
Note: Emphasized words can be found in the glossary.