In case a species (x) becomes extinct, the plant and animal species (M, N, O, Z) associated within an obligatory way also become extinct.

For example:

(i) When a fish species which is a host for a number of parasites becomes extinct the parasite species which are uniquely dependent on the host fish will also become extinct.

(ii) The insects may be polyphagous (feed on more than one plant species) or monophagous (feed on only one particular plant species) in nature. The monophagous insect species are valuable and may become extinct if the plant species upon which it feeds becomes extinct.