Environmental Problems, Their Causes, and Sustainability 1

8Community EcologyPopulationControlBiodiversityCASE STUDYFlying Foxes: Keystone Speciesin Tropical ForestsThe durian (Figure 8-1, top) is a prized fruit growingin Southeast Asian tropical forests. The odor of thisfootball-sized fruit is so strong, it is illegal to havethem on trains and in many hotel rooms in SoutheastAsia. But its custardlike flesh has been described as“exquisite,” “sensual,” “intoxicating,” and “theworld’s finest fruit.”Durian fruits come from a wild tree that grows inthe tropical rain forest. Various species of nectar-,pollen-, and fruit-eating bats calledflying foxes (Figure 8-1, bottom right)pollinate the flowers that hang highin durian trees (Figure 8-1, left).This pollination by flying foxes is anexample of mutualism: an interactionbetween two species in whichboth species benefit.Many species of flying foxes are listed as endangered,and most populations are much smaller thanhistoric numbers. One reason is deforestation. Anotheris hunting these bat species for their meat, which is soldin China and other parts of Asia. The bats also are killedto keep them from eating commercially grown fruits.Flying foxes are easy to hunt because they tend to congregatein large numbers when they feed or sleep.Some ecologists classify flying foxes as keystonespecies because of the important roles they play insustaining tropical forest communities. In addition topollinating many plant species, the plant seeds theydisperse in their droppings help maintain forest biodiversityand regenerate deforested areas.Thus many other species depend on flyingfox species. This explains why ecologists are concernedthat the decline of flying fox populationscould lead to a cascade of linked extinctions.The story of flying foxes and durians illustratesthe unique role (niche) of interactingspecies in a community. When populations ofdifferent species in a community interact withone another, they influence one another’s abilityto survive and reproduce. In this chapter we willlook at these and other interactions and processesthat occur in biological communities.Figure 8-1 Flying foxes (bottomright) are bats that play key ecologicalroles in tropical rain forests inSoutheast Asia by pollinating (left)and spreading the seeds of duriantrees. Durians (top) are a highlyprized tropical fruit.