In nature, some species sometimes form unexpected bonds, working in mutual interest, which provide benefits for both parties. This is called mutualism. There are two types of mutualism. Obligate mutualism in which species are entirely dependent on each other. And optional mutualism in which they benefit from the relationship but could survive without each other. For example, the woolly bat and the plant Nepenthes hemsleyana, a tropical plant from Borneo (Indonesia), have a mutualistic relationship. While the bat is resting in the plant, it takes the opportunity to catch the guano (excrement) produced by the small mammal. This provides the plant with the nutrients it needs to survive. Photo credit: WN Lam