A Bug’s Life: Climate Change Edition

How Ants Predict the Planet’s Future

Ants make up 15–20% of the biomass of all land animals and have been around since the mid-Cretaceous period. And while mighty Triceratops and the giant woolly mammoth have disappeared from this earth, the ant has persisted to become one of the most successful organisms to have existed.

For millions of years, ants have thrived in a variety of ecosystems from Mediterranean woodlands to manmade concrete jungles to the Australian outback, occupying key roles in the web of life. We can observe trends in ant populations and behavior to better understand macro-level changes in ecology, especially with respect to global climate change.

The introduction of invasive ant species in particular serves as an interesting field study. How do ants adapt to their new environment? How will native ant species defend their territory, given human-introduced changes in temperature and habitat?

Queensland

The Great Barrier Reef, which sits along the coastline of Queensland

Queensland is a northeast state in Australia and home to a rich array of biodiversity. The Great Barrier Reef extends along most of Queensland’s coastline and hosts a vast encyclopedia of tropical fish and other sea creatures. Considered a biodiversity hotspot of the world, Queensland also contains 70% of Australia’s mammals, 80% of its native birds, and more than 50% of native reptiles and plant species ranging from koalas to sea turtles. Unsurprisingly, the state also hosts up to a hundred different genera of ants.

Data sourced from the Bureau of Meteorology, Australian Government

Based on data from 1950 to the present day, we see increased occurrence of abnormally high annual temperatures, with the past six years being six of the hottest years on record.

The risks of accelerating climate change are magnified in the Queensland region. Rising temperatures make hotter, arid days more frequent. The ocean will become warmer and more acidic, endangering reef ecosystems depending on a stable pH level. Invasive species arriving in this delicate ecological balance could thus find easy prey for expansion.

In recent years, the introduction of the invasive Pheidole ant weakened local populations. Known as the “big-headed ant,” Pheidole is a highly successful invasive ant and was seen in Australia as early as 1942. In this article, I explore the growth and decay of ant populations in Queensland through a global database on abundance counts of ants provided by Gibb et al. The database gathers records from studies over the past three decades, including both published and unpublished data. Specifically, abundance counts record the number of individuals from a species found in a particular sector.

Available data on ant counts in Queensland. Source: Gibb et al

As evident from the figure above, abundance counts are an imperfect way to estimate ant population health. Data is dependent on how many researchers decide to sample the ant population in this region that year and only sample a minuscule fraction of the overall population. However, they serve as a useful heuristic for relative abundance of each species.

To visualize trends in the rise and fall of ant populations, I selected the top four ant species by fraction of the total ant count. I graphed their population proportional to the total abundance count of all ants in that year.

In 2008, we see a drastic plummet in the population of Iridomyrmex, an aggressive genus of ant native to Australia. Though perhaps due to the sparsity of data in 2008 and 2011, we cannot discount a rise in the biodiversity of dominant ant genera. We see a steady growth in Pheidole ants’ abundance at the expense of Iridomyrmex and Rhytidoponera, suggesting an ecological force on Pheidole’s side in Queensland’s ant war.

Interestingly, the decline in Iridomyrmex ants mirrors coverage loss in the Great Barrier Reef from 2005 to 2012. Perhaps the same factors of climate change that are acidifying the barrier reef are also playing a role in the battles between Queensland’s ant genera. Though some research argues that climate change weakens invasive Pheidole ants, the Queensland data is worth investigating further.

Conclusion

Climate change in Queensland endangers a variety of nature’s treasures, including the manta rays of the barrier reef, koalas perched in eucalyptus trees, and the delicate balance struck in the Australian ecosystem. Though Queensland is simply one hotspot among many globally, ants may offer a window into the complex and massive ecological mechanisms behind biomes around the world.

Ants will likely outlast most of the species currently extant on the planet, though climate change will fundamentally alter how they interact with each other as well as other organisms in the ecosystem. We can’t say for sure whether the new patterns in ant behavior are truly harmful, or simply a shift in the natural hierarchy of ants. Nevertheless, ants are fascinating creatures that may signal approaching changes in our environment. More likely than not, Pheidole will be around to witness them.