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These different species live in different ecologies and are reproductively isolated by their characteristic songs . Everybody believed that because animals such as sea urchins and abalone and some kinds of clams and scallops produced literally millions of gametes , they figured there was no chance that the animals could ever be reproductively limited . It is defined as a potentially interbreeding group comprising various populations that are reproductively isolated from other such groups . The concept defines species as " groups of interbreeding natural populations that are reproductively isolated from other such groups . It might be that the adult females of the newly formed group were reproductively suppressed due to that social stress , and therefore were not advertising reproductive cycles ( Dunbar , 1980 ) . Trial plants must also be reproductively isolated from weedy relatives by a minimum of 50 metres , unless other methods of reproductive isolation has been successfully used . Ernst Mayr 's Biological Species Concept , the most widely accepted definition for species , defines species as " groups of interbreeding natural populations that are reproductively isolated from other such groups " . The most useful definition of species ( which does not assume evolution ) for sexual metazoans is the Biological Species Concept : species are groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups ( Mayr 1942 ) . Species are usually defined as populations of animals that are reproductively isolated from other populations ( i.e ., they can not breed beyond their own population ) , though there are enough exceptions that one might adopt a less formal definition such as " a species is a group that someone who studies systematics has said is different from other groups .