Plant-parasites niches

Crotalaria species are used as preplant cover crops, intercrops, or soil amendments. When used as cover crops, Crotalaria spp. reduces plant-parasitic nematode populations by i) acting as a nonhost or a poor host, ii) producing allelochemicals that are toxic or inhibitory, iii) providing a niche for antagonistic flora and fauna, and iv) trapping the nematode. 

Plants that defend themselves effectively constitute an ecological niche almost devoid of herbivores and pathogens. It is not surprising that during evolution a number of organisms evolved which have specialized on a particular host plant species and found ways to tolerate, or even to exploit, the defense chemistry of their hosts 4,10-22). As compared to the huge number of potential enemies, the number of adapted specialists is usually small, and in general a status quo or equilibrium can be observed between the specialists (or parasites) and their hosts. A specialist is not well advised to kill its host, since this would destroy its own resources a mutualism is more productive for survival. 

Humans have also expanded the dimensions of their realized niche by managing the intensity of their interactions with other species. Humans control their own competitors, predators, parasites, and diseases, thereby reducing the constraints that these biological stressors exert on the realized, human niche. Humans also manage the ecological constraints of their mutualistic plants and animals such as agricultural cows, pigs, chickens, and plant crops. 

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