The ants go marching …

What do some of our smallest creatures have to tell us about the bigger impacts of climate change? A great deal, it turns out, says Professor Nigel Andrew, from the University of New England’s Insect Ecology Lab.
He believes the common meat ant, found in large numbers across much of Australia, may prove an accurate indicator of environmental health. “Meat ants are dominant and abundant in their habitats; they are also highly responsive to seasonal changes and susceptible to extreme temperatures of the kind already being experienced with a rapidly changing climate,” Professor Andrew says. “When they suffer physiological stress, it also has harmful spin-offs for a range of other species.”
Meat ants are important ecosystem engineers, responsible for dispersing seeds, turning over soil and recycling nutrients. They also provide vital shelter and food for other invertebrates and vertebrates like echidnas.
After studying the charismatic meat ant (Iridomyrmex purpureus) across 300 kilometres of northern NSW – from intact native vegetation to heavily cleared and planted agricultural habitats – Professor Andrew and his UNE team have confirmed that climate change is not all the ant has to worry about. In fact, the way we humans use and manage landscapes might be just as critical to meat ant survival.
“Where land use intensifies for agriculture, the local environment aridifies, and meat ants become less resilient physiologically,” Professor Andrew says. “If they start to struggle, then we can assume that a host of other more sensitive species are already in trouble.
“By understanding the thermal limits these ants can cope with, and what impact climate change is already having on their populations, we can better understand what potentially lies ahead for other species.”
Professor Andrew says land management directly influences how animals respond to extreme weather events, increasing temperatures and temperature extremes. “Changes to land use can have immediate, short- and long-term impacts on soils and vegetation,” he says. “In a diverse, complex landscape, with a mixture of native vegetation types, there are lots of micro-climates that offer animals refuge and the opportunity to escape, adapt or respond to extreme local temperatures and moisture deficits.
“We know that meat ants are highly adaptable – they run faster back to their nest when surface temperatures rise above their critical thermal maximum – but our study found that they are not as tolerant to warming when their habitat is modified. Further exposure to more frequent extreme temperature events will make them even more susceptible to heat stress.”
The findings support an earlier ant biodiversity assessment that Professor Andrew contributed to. It found that the impacts of climate change on insect biodiversity may be mitigated by increasing woody native vegetation cover, reducing land-use intensity and limiting exotic vegetation cover. Benefits of these mitigation methods are likely to be greatest in areas that are currently warmer and drier, or are projected to become so.
“We have long known that land clearing can have dire implications for wildlife, but this confirms the importance of native vegetation even to the smallest of ant communities,” Professor Andrew says. “The findings of both studies have important implications for natural resource management and conservation planning because if we were to reduce or remove ant populations completely, then that threatens a host of other species up and down the food chain.
“We need to consider how land use and climate change are interacting. Land managers and policy makers have an opportunity to mitigate against the negative impacts of climate change on our native species by increasing native vegetation cover and addressing land-use intensity. Such management actions can reduce the annual mean temperatures in an environment by up to 3.8 degrees C, and change the local microclimate temperatures by up to 40 degrees C!”
Professor Andrew’s findings come just days after the release of the United Nation’s Global Assessment Report on Biodiversity and Ecosystem Services, the first such report since 2005, which has highlighted the importance of diversity within species, between species and ecosystems. It identified land-use changes and climate change as two of the five main drivers of “unprecedented” biodiversity and ecosystem change, which has left 25% of species in all plant and animal groups vulnerable.

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