Elephants & Ants Help Acacia Trees
Study Shows link Between Large Herbivores, Ants and Healthy Trees
Not only do they help germinate plants, elephants and other African animals ensure the balance of ants on acacia trees, stressing the importance of ecosystem preservation
The relationships between plants, large animals and insects are often more complex than they appear to the casual observer. The case of the ant, the acacia and the elephant is one of them. A carefully balanced mutualism between the trees and the ants is aided by the browsing of elephants and other large herbivores.
Pros and Cons of Elephant Presence in Savanna Ecosystems
No one would argue that herds of elephants can cause massive damage in areas where they are no longer able to migrate. Footage of torn up trees and trampled earth, as well as stories of crops being completely destroyed in one night, are graphic reminders of the potential problems caused by elephants.
What is less often discussed is the role that the elephants play in germinating many of the savannah tree species. When the elephants browse on the trees, seeds are ingested and pass through the digestive tract, preparing them for germination, often in a new area.
Browsing by elephants also creates openings in forest canopies, allowing a greater variety of plant species to survive, which also helps many smaller animal species.
The Study of Ant, Acacia and Large Herbivore Interdependence
By fencing off sections of savanna and comparing the health of the whistling-thorn tree (Acacia drepanolobium) with and without large herbivore browsing, researchers have learned that the acacia trees have a mutualistic relationship with two species of ant, Cregaster mimosae and C. sjostedti, which protect the tree by swarming and biting browsing animals. In exchange, the ants get housing in swollen thorns and nectar to feed on.
Over the course of the 5-10 years of the study the fenced off trees, no longer being browsed by the elephants and other herbivores, produced fewer swollen thorns and less nectar, as they needed less protection. The beneficial ant colonies decreased and two other species of ant, C. nigriceps and Tetraponera penzigi, took over. These detrimental ants help a wood-boring beetle to tunnel through the tree resulting in slower growth and a higher death rate for the acacia trees.
This result reinforces the words of Aldo Leopold:
“The first rule of intelligent tinkering is to save all the parts.”
It was assumed that removal of elephants and other large herbivores would result in a healthier acacia population. The opposite actually happened, serving as a reminder that there are many aspects of balanced ecosystems that are poorly, if at all, understood.
And, as Leopold made clear, it will be necessary to protect ecosystems in their entirety, ants and other insects included, if we are to ensure survival of those species we know well and care the most about.
