My name is Patrick Milligan. I'm a PhD student at the University of Florida and I work in
the Lycopia Plateau in Kenya and I study interactions between ants and trees and how they are
affected by an invasive ant species from Ethiopia. The Lycopia Plateau is about a mile high area in
Kenya where the savannas are dominated by a single acacia tree species and this tree is
really dominant because it can partner with native ant species which protect it from large
herbivores and in exchange for that protection the ants receive shelter and nectar from the tree.
There are four species of native ants that live on the acacia trees. Three of them are from the
genus chromatogaster. One is from the genus tetraponera but all of them have the ability to
sting large herbivores that try to attack the tree and they can also release alarm
pheromones into the air when a when an elephant or a giraffe comes along and they try to rip off
a branch or eat some leaves. The ants that are near that spot will spray the pheromone into the air.
The ants then band together and swarm the animal that is attacking the tree. They can even sting
the inside of an elephant's trunk and scare that elephant away. The big headed ant is listed by the
international union for the conservation of nature as one of the 100 worst invasive species in the
world. They're really effective at colonizing tropical and subtropical systems and when they
move into an area they kill many of the native insects there and they especially are good at
preying on native ant species. We noticed in the past 10 or 15 years that this ant has invaded
the Likipia Plateau and they can directly affect the ants that live on those acacia trees. When the
big headed ants invade an area and remove the native ants from that tree they then take up
residence in that canopy but they don't provide the protection that a native acacia ant colony would.
When an acacia loses its ant colony it can try to make up for that in a few different ways.
The response that I actually look at with my research is how the tree changes its photosynthesis.
I use the Lycor Li6400 Portable Photosynthesis Meter which allows me to clamp a sensor onto
an acacia leaf and then it can tell me the rate of photosynthesis that is going on in that leaf
based on the chemical reactants and products involved in photosynthesis. By studying the
photosynthetic rate in invaded acacias and comparing it to areas that have not yet been
invaded I'm able to determine if those trees are altering their physiology to make up for
the negative effects of invasion. The main question that defines my PhD is what are the
functional effects of this biological invasion and how do the changes to the acacia trees cascade
to affect other species in this area? I often call Lycopia my Nyumba and Bili which is Swahili
for second home because I've become really attached to the ecosystem there and the people that live
there. There's this really beautiful harmony between the cattle ranchers and the conservationists
and the scientists that live in this area where everyone is very conscious of how their own welfare
is tied to the environment and so they work together to try to find the best solution to
not only understand those species interactions but how we can preserve them for the future.
