Delayed compensation for missing keystone species by colonization

Because individual species can play key roles, the Loss of species through extinction OF their gain through colonization can cause major changes in ec osystems. For almost 20 years after kangaroo rats were experimentally remov ed from a Chihuahuan desert ecosystem in the United States, other rodent sp ecies were unable to compensate and use the available resources. This chang ed abruptly in 1995, when an alien species of pocket mouse colonized the ec osystem, used most of the available resources, and compensated almost compl etely for the missing kangaroo rats. These results demonstrate the importan ce of individual species and of colonization and extinction events in the s tructure and dynamics of ecosystems.