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Tiny ants may pose a big threat for diversity in Laikipia

In the shadow of Mt. Kenya, everyone has a story about a small, shiny ant that steals their cooking oil and sugar. When the seasonal rains come, they retreat into their underground nests, but they strike with full force during the dry months. The “big-headed ants” (Pheidole megacephala, which literally means “big head”) don’t bite or sting humans, but it’s hard to ignore the innocuous little insects picking over every unattended scrap of food.

Big-headed ants are a new resident in Laikipia. They are an invasive species, introduced in the last 2 decades to Mpala Research Centre, and to neighbors at Ol Pejeta Conservancy, Ol Jogi Conservancy, El Karama Ranch, and beyond. When we build a house, dig a well, or drop a few crumbs on the ground during teatime, the ants aren’t far behind. They make the most of any nest or food that we (unwittingly) provide, and are exceedingly good colonists.

I might use similar words to describe heroic explorers, but these ants are problematic for diversity and conservation in Laikipia. Big-headed ants are notorious killers of insects in other ecosystems, especially native ants, and can seriously alter the diversity of the local insect community. What do these ants mean for our beloved Laikipia landscape?

My research seeks to answer some small part of this question. My ‘working relationship’ with big-headed ants began in 2014: as a research assistant to Dr. Todd Palmer, I spearheaded an experiment in invaded and pristine areas of the Mpala conservation grounds, testing the influence of big-headed ants on native dung beetles and termites. Dung beetles and termites might live in lowly holes and eat nature’s refuse, but we can’t ignore their importance: these little critters are crucial parts of the natural recycling of dead and discarded materials. I can try to make this project sound fancy, but it involved a lot of cow dung. As in, “multiple-trips-in-a-LandCruiser-with-an-extended-bed” lot of dung.

How do you measure the effect of ant invasion on dung breakdown? One dung pile at a time…
How do you measure the effect of ant invasion on dung breakdown? One dung pile at a time… Pat wasn’t allowed in the dining room because of “flies”, according to lab-mate Travis Guy.

Sometimes you just have to suck it up and do the work: the project revealed large losses in insect diversity after big-headed ant invasion, and opened the door to new research ideas. If these ants can disrupt an entire insect community, how will they affect other crucial parts of this savanna? My current research project focuses on another iconic part of the Laikipia landscape: a natural partnership between the whistling-thorn acacia and 4 native ants. These native ants receive sugar-rich nectar and shelter, and in return protect the whistling-thorn acacia from hungry elephants. This ant-plant combo can cover massive swathes of the “black-cotton” savanna, and supports many key savanna processes. But it is not impervious to the spread of big-headed ants.

When big-headed ants invade, they kill the beneficial ants and leave entire tree communities unprotected. Acacias have a few backup plans for dealing with herbivores, such as thorns or chemicals in leaves to disrupt digestion. Branches and leaves that are eaten can regrow, chock-full of new chloroplasts — the parts of a leaf cell that turn light, water and carbon dioxide into sugar — as the trees do their best to bounce back. All of these responses require an investment, and the question now arises:

 

Without their ant defenders, can the acacias still make it in their harsh environment? Are the costs of defense too great in a landscape full of elephants, giraffe, and other massive herbivores?

 

I returned to Mpala in May 2016 to tackle this problem with new tools to answer a complicated question. First up, the LiCor LI-6400: this complicated machine can control humidity, temperature, light, and other conditions in a tiny leaf-sized chamber, and can measure the photosynthesis going on inside of the new leaves growing on invaded acacias. And it all fits in a backpack. University of Florida undergraduate Gabby Mizell accompanied me into the field, making sure that our measurements were stable, that we didn’t fall into any aardvark holes, and didn’t complain once about the pre-dawn wakeup times. Some people can’t cut it in the bush — Gabby handled it like she was born in the savanna.

Is it stable yet? Gabby and Pat clamp the LiCor sensor head onto a whistling-thorn acacia, growing strong in an area still untouched by the invasive big-headed ant.
Is it stable yet? Gabby and Pat clamp the LiCor sensor head onto a whistling-thorn acacia, growing strong in an area still untouched by the invasive big-headed ant.

Our other tools are lower-tech. A new mealworm/beetle farm provides a constant supply of test subjects to study the aggression of big-headed ants. Tubs of sticky insect glue — a natural pest deterrant for gardeners — help us to keep the invaders off of some acacia trees. We use shovels, plastic cups and some soapy water to make hundreds of low-cost ant traps, which we use to survey landscape-scale changes in invasive ant numbers. These are just a few tools for a biologist at Mpala, though many more can be carried in the bed of our trusty LandCruiser.

We tinker with nature in small ways: remove some ants here, water some trees there, add fertilizer at times, wait for changes to occur, and measure those changes. The big-headed ant could mean big trouble for Laikipia, which has become my nyumba mbili (“second home”) in the last few years. My PhD work aims to understand this invasion at multiple levels: how it affects important insects, plants, and the crucial parts that make an entire ecosystem work.

About Pat:

I am a 2nd-year PhD student at the University of Florida. I grew up on the coast of the Gulf of Mexico, and have been traveling to Kenya on a yearly basis since 2013. My research focuses on ant-plant interactions and invasive species. As a grad student and future ecologist, I want to use my research to create unique natural learning experiences for students, scientists and the general public, because I believe that everyone can come to appreciate nature if it is presented in the correct way. I post blogs, podcasts, pictures and more at my personal website, www.savannaecology.com, and I am happy to discuss my work on social media @savannaecology, or on Facebook at www.FB.com/UFinKenya