African Acacia
An acacia on a plain looks so innocent, the classic (23)_____ of the African savannah. I think I saw it on The Lion King. Well, the tree is a mass murderer. If an African Acacia tree is (24)_____ attack by a grazing animal, say a kudu, it (25)_____ a cloud of ethylene gas, thus warning trees up to 50 yards downwind to produce extra tannin in their leaves, making them toxic.
Zoologist Wouter Van Hoven figured this out when he was asked to (26)_____ the sudden death of some 3000 kudu antelope on game ranches in the Transvaal. (27)_____ the grazing activity of animals in the area, he concluded that the giraffes, who were free to roam and (28)_____ the trees they ate, ate only certain acacia trees, about one out of ten, and avoided acacia trees that were downwind of others. The kudu, on the other hand, who were (29)_____ in on game ranches, had little to eat in the winter but acacia leaves, and thus ate toxic leaves until they died. The trees killed the kudu by (30)_____ with each other.
(31)_____ using gas, toxins, and thorns to defend themselves, acacias often hire an army of ant bodyguards. The trees (32)_____ housing and nectar for the ant, and the biting ants attack whatever comes near the tree. The plant does need herbivores to help propagate it, however, so the ants can’t be too efficient in chasing away all grazers and pollinators. Thus acacias have some complicated three-way relationships.
