Article: Complex Systems—How One Little Ant Species Changed a Whole Savannah

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A recent study of the effects of an invasive ant species on an ecosystem in Africa serves to remind us of the immense challenge humans face when trying to understand complex systems and how subtle changes to the system can have significant effects. A biological ecosystem with the entirety of its animals, plants, and microorganisms interacting with each other, a city with millions of people living in close quarters, and an economy with trillions of transactions all represent complex systems.  Complex systems involve many interactions and forces.  For example, a city requires materials so people can build homes, businesses, and infrastructure such as water and sewer systems.  Additionally, cities need energy such as electricity and natural gas to warm and cool people’s homes and offices as well as help them cook food for survival.  Moreover, people have laws and regulations to help them live peacefully and productively together in crowded urban settings.  The constant interactions among all the people and their environment in a city comprise a very complex system that defies total comprehension.  We can predict the outcome of major changes such as how the removal of traffic signals would impact traffic patterns in a city. The same holds for ecosystems, but subtle changes can have large, unpredictable effects.

In a study published in the journal Science titled “Disruption of an ant-plant mutualism shapes interactions between lions and their primary prey” the authors detail changes to the African savannah that started with the invasion of an ant species new to the ecosystem. (science.com) Over recent decades, the big-headed ant originally found on the island of Mauritius off the coast of East Africa, has moved into parts of the African savannah.  Big-headed ants have pushed out another local ant species that has developed a symbiotic relationship with acacia trees—ant-plant mutualism. The native ants known as Crematogaster spp. live on the branches of the whistling thorn tree. The ants protect the trees from foraging elephants by crawling up the elephants’ trunks and inflicting painful bites.  The elephants tend to avoid the whistling thorn trees because of the biting ants, while the ants benefit from the nutritious nectar from the trees.  However, the big-headed ants have moved in to take advantage of the nectar on the trees and overpowered the local ants.  But the big-headed ants do not bite the elephants, opening up the trees to over grazing. The elephants would eat all the leaves off the trees and then destroy the trees by knocking them down.  The result of the deforestation by elephants changed the hunting pattern of the local lions. 

For the lions, the whistling thorn trees provided the necessary cover for them to sneak up on their favorite prey—zebras.  With the trees knocked down, the lions could not effectively stalk and catch the speedy zebras because the zebras could see the lions coming from far away.  The lions have since pivoted from zebras to the African buffalo as their main food source, which will help grow the zebra population.  Clearly, a change in the ant species population has significantly altered very observable elements of the savannah ecosystem.  Other elements may have changed as well such as the bird populations that depend on the trees and other more subtle elements of the ecosystem, but these were not included in the study.

The lesson of the big-headed ants and the savannah serves to emphasize the unpredictable nature of seemingly small changes that can reverberate through a complex system.  Moreover, people generally cannot comprehend complex systems because complex systems have too many unpredictable dependencies.  The human brain likes to reduce problems into individual components and study each component in isolation, but such an approach cannot respect the unpredictable interdependencies of complex systems.  Such a known limitation of the human brain should remind people to seriously question any project that suggests that simply changing one element of a complex system will clearly have the predicted and desired outcome. 

Dr. Smith’s career in scientific and information research spans the areas of bioinformatics, artificial intelligence, toxicology, and chemistry. He has published a number of peer-reviewed scientific papers. He has worked over the past seventeen years developing advanced analytics, machine learning, and knowledge management tools to enable research and support high-level decision making. Tim completed his Ph.D. in Toxicology at Cornell University and a Bachelor of Science in chemistry from the University of Washington.

You can buy his book on Amazon in paperback and in kindle format here.