Interactions of populations of two different species are termed interspecific interactions. These can be detrimental, beneficial or neutral to the involved species. If symbols are given to denote detrimental effect, beneficial effect and neutral effect as '-', '+' and '0'.

Parasitism is a type of interaction between a parasite and host where only parasite benefits from the relationship but it is detrimental to the host. Thus, parasitism will be' +', '-'

Competition is a type of interaction where the interacting species compete for the same resource and such interaction do not benefit either of the groups involved as resources are limited and it puts a stress on the population. Hence, competition is $\mathrm{‘}–\mathrm{‘}\mathrm{ }\mathrm{’}-\mathrm{‘}.$