why does a decline in predators sometimes spell disaster for a other species?

[porphyro]

i.e. the animals they prey on?

[jno]

I guess if the prey are free to live without being hunted they may rapidly expand and outstrip the available food supply?

[Noweia]

I thought it was more the other way round? That if the number of prey species drops, the predators will drop accordingly. So the number of predators can be used to gauge the health of the ecosystem?

[LoftyLottie]

Basically I agree with Noweia.

However, as predators generally take the weakest of a species leaving only the fit to breed, without those predators a species might decline due to more outbreaks of fatal diseases and general health problems. - Just a thought.