Yellow meadow ants influence aboveground plant growth with their excavation work and aphid farms, claims biologist Ciska Veen. Meadow ants cause a change in the local makeup of the ground thus enabling other plant species to grow. Large grazers such as cattle cancel out these effects on plant growth, however. Veen will be awarded a PhD by the University of Groningen on 29 April 2011.
The yellow meadow ant, Lasius flavus, is an ant species that creates large nest mounds and lives in them in symbiosis with root aphids. Although the ants live underground, they have a major effect on plant growth. Veen investigated this effect on biodiversity in meadows in Junner Koeland alongside the river Vecht and on the island of Schiermonnikoog.
The ants turn up soil from deeper layers, with a different composition and pH. This digging work also gives the ground a looser structure. Twigs, leaves and other organic material are more quickly converted to nutrients as a result. ‘The ground is also cleaner’, says Veen. ‘It contains fewer pathogens such as nematodes.’ The beneficial circumstances on top of the nest mounds are reflected in the plant growth. Veen found more red fescue (Festuca rubra) and less sea couch (Elytrigia atherica) on the mounds than around them.
Another of the ant’s habits, farming aphids, appears to influence the aboveground flora. ‘Most of the ants’ diet consists of honeydew, produced by root aphids’, explains Veen. To make things easy for themselves, the ants farm these aphids in the nest mounds, where the root aphids are carefully nurtured. ‘The ants milk the aphids, as it were, just as we farm cows. And they breed the aphid eggs out themselves.’ ‘The presence of root aphids also has an effect on the vegetation’, says Veen, ‘because certain species of plant can cope with them much better than another. So you get species growing on the nest mounds that can cope with root aphids.’
Aboveground grazers, like cows and hares, can both strengthen and cancel out the effect of the yellow meadow ant on plant growth, Veen discovered. Which of the two situations occurs depends on the type of grazer. ‘They are very particular when choosing their food’, Veen explains. ‘Hares are particularly fond of the nutritious red fescue on the nest mounds. Fescues are able to cope with this grazing and even grow more strongly. Cows, on the other hand, need a lot more food than hares and also have larger mouths, which means they are not so selective. They also stimulate the growth of fescue, but over a much wider area. So they cancel out the effects of the nest mounds built by the meadow ants.’
Yellow meadow ants also appear in ordinary gardens, but without the noticeable nest mounds. Veen: ‘You’ll encounter them if you move a container, for example. They are not able to cope with the sun, unlike the black ant or the wood ant. They are actually albino ants.’ In a garden the meadow ants don’t usually have to build nest mounds. ‘They build nest mounds to rise above the vegetation in order to catch sunlight. The heat of the sun is needed to incubate their eggs. In our closely mown lawns they can get enough sunlight without having to build a mound.
Ciska F. Veen (Apeldoorn, 1981) studied ecology at the University of Groningen. She conducted her PhD research at the Center for Ecological and Evolutionary Studies (CEES) and the Community and Conservation Ecology Group (COCON) of the same university. The research was partly financed by an NWO pioneer grant. Veen currently works for the Netherlands Institute for Ecology (NIOO-KNAW). The title of her thesis is ‘Living apart together – interactions between aboveground grazers, plants and soil biota’.
Ciska Veen, e-mail ciska.veen gmail.com
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