December 5, 2021

I, Science

The science magazine of Imperial College

Madeleine Hurry on what makes ants fight or give way, in the rainforests of Borneo

View through Borneo rainforest_Doug Wheller_2768374584_4179607402_oAnts are more likely to fight with colonies similar in body size than with colonies of larger or smaller body size. This rule alone appears sufficient to explain the observed pattern of ant diversity in tropical fern-dwelling ants.

When two species inhabit the same area, they may compete for resources. This idea of competitive exclusion is prevalent in ecology, yet it is difficult to find empirical evidence to demonstrate the link between individual competition and overall community structure. Researchers from Imperial in collaboration with the Natural History Museum, University of Cambridge and Universiti Malaysia Sabah have explored this concept using ant species.

The study looked at species composition of tropical ants inhabiting ferns in the forest canopy in Malaysian Borneo. With up to 12 ant species coexisting on a single plant, researchers tested whether size-based competition drove overall community structure. It was predicted that ants of a similar size have similar niches and therefore have greater competition for resources, and so will fight to out-compete each other.

Birds Nest ferns by Pinke_3617922025_dd92f18408_zThe first part of the study involved observing and recording the ant communities on 86 bird’s nest ferns in the Danum Valley Conservation Area in Sabah, Malaysia. They found that species whose body size differed by less than 13% were significantly less likely to live in close proximity.

Secondly, to see whether size-based competition was really driving this pattern, lab experiments in which resident colonies were threatened with invaders of either similar or dissimilar body size were carried out. They found that invaders were less likely to successfully occupy a fern when their body size was similar to the resident, due to increased aggressive defence by the resident colony.

Finally, a computer-based model was applied to test whether these size-based rules drive diversity. Simulations where ecologically similar species fought with invaders gave a final diversity outcome similar to the observed diversity in the natural environment. Thus, using the size-based rules allowed the model to successfully converge on a community similar to the natural one.

Therefore, simple rule-based interactions between individuals can have far-reaching consequences in the higher levels of community structure, potentially explaining the huge diversity of ants in the tropical forest canopy.

Fayle et al (2015) Experimentally testing and assessing the predictive power of species assembly rules for tropical canopy ants. Ecology Letters 18: 254–262 (full text)

Madeleine Hurry is an MRes student studying experimental neuroscience.

Images: View through Borneo rainforest by Doug Wheller (Flickr); Bird’s Nest Fern by Pinke (Flickr); Featured image: Sunrise in Danum Valley, Borneo, Wikimedia Commons