Invasive Northern Red Oaks benefit Temnothorax crassispinus ant colonies
In the paper “Invasive Northern Red Oaks benefit Temnothorax crassispinus (Hymenoptera: Formicidae) ant colonies” by Łukasz Myczko, Łukasz Dylewski, Sławomir Mitrus, and Tim H. Sparks published 2018 in Myrmecol. News, the authors reveal that Temnothorax crassispinus is more abundantly found and that colony condition was significantly better under Northern Red Oaks canopies. In this review, Suzanne Koptur highlights their main points.
A Review compiled by Suzanne Koptur
Many studies focus on the problems that invasive species bring for native plants and animals, but that is not always the case. Myczko and colleagues observed that the common wood ants were abundant under the canopies of exotic red oaks – perhaps more so than under native oaks. The ants of this species nest in acorns or sticks, using entrance holes provided by previous insect herbivores. The investigators first demonstrated this preference by comparing the natural occurrence of ant nests in acorns of red oak and two native oak species (with acorns very similar to each other) in areas under 50 red oaks and 50 native oaks of comparable age. In 2 x 2 m study plots, they searched the whole plot and collected all potential nest sites for the ant (acorns with holes, newer acorns, and sticks). They kept the collections cold until they were examined in the lab to prevent movement of ants, and then recorded the presence of ant colonies, the number of workers, and presence of queens. They found many more acorns with colonies under exotic red oak canopies than under native oaks. The majority of the occupied acorns were those of red oaks, and there were many more workers in exotic red oak acorns, and more larvae as well.
Using colonies collected from the acorns, they conducted experiments to test the preference of the ants for acorns. Simulating insect damage by drilling holes into acorns, they presented the different species in choice tests with the captive colonies. After 24 hours, the acorns were inspected for presence of workers and queen. Ants preferred the exotic red oak acorns over the native acorns.
The researchers also used an in-vitro choice test using cotyledons of the acorns to see if one might be preferred due to nutritional considerations. There was no difference in these choices, with both cotyledons being equally desirable.
The key to the preference may be simply one of fruit morphology: The red oak acorns have a thicker pericarp, more than twice as thick as the native oak acorns; consequently, they may provide sturdier accommodations for the wood ant colonies. It appears that the wood ants are not unlike the Three Little Pigs, choosing stronger, longer-lasting homes to protect them from the Big Bad Wolf of environmental challenges.
This is quite interesting. It would be of further interest to know to what extent this oak invasion has favored other native organisms, perhaps in particular, oak folivores.
I would note that the term “wood ants” is normally used to refer to members of the Formica rufa and Formica integra groups of species. In North America at least, the term “acorn ants” is an accepted vernacular name for members of the genus Temnothorax.