1) Predator-prey relationships involve one species (the predator) capturing and feeding on another (the prey). This acts as a mechanism of population control, with predator and prey populations fluctuating inversely. 2) Mutualistic relationships benefit both species, such as bees collecting nectar from flowers in exchange for pollination. 3) Commensalism involves one species benefiting without affecting the other, like birds following cattle to feed on insects disturbed by the cattle.