Development of spines. Production of cyanogenic glycosides. A mimic feeds on the same food plant as the target species. Mimics are not rare. Aposematic colouration is a warning cue to predators.
Commensalism involves a positive gain for both partners.
Different species cannot occupy the same niche. The niche is multidimensional. The niche includes both biotic and abiotic components. The realized niche is usually less in dimension than the fundamental niche. Reduced exposure to pathogens in the countryside recruits.