Jack Sprat could eat no fat
his wife could eat no lean,
and so, you see, between them both
They licked the platter clean.
Jack and his wife had different preferences for the food they ate, so never took food from each other’s plate.
Similarly, some birds eat nuts, others fruit, others flying insects, and others worms and grubs.
So they can happily forage and feed together without having to chase each other away from the food supply.
Similar ideas work in economics where some companies specialise in niche markets, and leave others to make products for the mainstream consumers.