Passage IV

Three studies were conducted to examine the relationship between ants and the acacia trees they inhabit.

Study 1

Table 1 shows the results of a comparison between a species of acacia tree that is inhabited by ants (ant trees) and a species that is not inhabited by ants (non-ant trees).

Study 2

Table 2 shows the results of a comparison between acacia ants and a closely related ant species that does not inhabit acacia trees.

Study 3

Acacia trees were divided into three groups. Acacia ants were removed from the trees in Group A, but were left on the trees in Group B. Group C consisted of a species of non-ant acacia tree. All the trees were initially healthy and of similar size. The number of trees still alive in each group 300 days after the start of the study is shown in Table 3.

Trees in Group A were killed by plant-eating insects and large mammals that ate the leaves on lower branches. There was no evidence that trees in Groups B and C were killed by grazing animals.