Ants and Plants

Since 2013 Dr McLean has been examining the invasion of a Eurasian hemi-parasitic plant Thesium ramosum into Fish Creek Park (FCP). Hemi-parasitic plants like T. ramosum are green and photosynthesize but get a lot of their energy by sucking carbohydrates out of the roots of host plants. Dr McLean and summer student assistants discovered that the roots of this plant can parasitize upwards of 40 different species of plants, including grasses, weeds, native plants, shrubs and trees in the park. However, it was unknown how the plant was dispersing around the park. The observation of ants carrying the seeds, in addition to the apparent relationship between increased numbers of T. ramosum adjacent to ant mounds, suggested that ants might play a role in T. ramosum dispersal.

In 2018, Dr McLean, in collaboration with one of Alberta’s two ant researchers, Christine Sosiak, were able to to study the role ants play in the distribution of T. ramosum with the help of a $9900 research grant from the Alberta Conservation Association and a $6900 grant from TD Friends of the Environment. Dr McLean spent the summers of 2018 and 2019 conducting extensive fieldwork with her team as they searched for, observed and identified ants. As well several lab experiments were conducted with live ants, to better understand how different species interacted with T. ramosum seeds. The results showed that different ants collected seeds at different rates; F. obscuriventris collected most seeds within the first hour, while F. argentea tended to collect the seeds over longer periods of time.

In addition, depending on the size, some species could carry along these seeds at least 20 meters, and even small species about the same size as the seeds carried them up to 1 metre. The distance that these ants would carry these seeds suggests that they are strongly interested in them and will put considerable resources towards acquiring them.

While ants are considered very territorial animals, Dr McLean was also surprised to observe repeatedly in the field that several ant species commonly shared resource patches and foraging trails with little evidence of conflict. In fact, it was common to find at least three ant species harvesting T. ramosum seeds in any one place.

This research significantly added to the ant species list for FCP, recording 27 species in 7 genera. 11 of these species were observed carrying these seeds, suggesting that that around 40% of the species in the park carry T. ramosum seeds! Dr McLean’s research has shed light on the role of ants in propogating T. ramosum, helping conservationists and ecologists control its spread. Dr McLean is currently in the process of writing-up these fascinating results for publication in a peer-reviewed scientific article.