Ants & the Ecosystem: Dominants in the Environment

Overview

Ants are ecosystem engineers, shaping the landscape and performing many functions that are directly or indirectly beneficial to humans. The true extent of these benefits is extremely difficult to quantify, though spans all the categories covered by the Millennium Ecosystem Framework, which defines the benefits to humans of ecosystem services by type.

With expanding populations and increasing demand on food production, more sustainable growing methods are required. Ants can be vital components of Integrated Pest Management systems and are effective biocontrol agents under the right conditions. Weaver ant use in agriculture an example of bio-control success, and many species exist with a similar profile. This could be studied further as a potentially significant area of biological control. Ants are a very diverse group of insect species, thought to have originated as long as 120 million years ago during the Cretaceous period.

They often dominate environments and can be found on every continent bar the Antarctic. They are an extremely efficient eusocial species, meaning there is generational overlap, caste systems, and division of labor, and some calculations suggest ants make up on average 15-20% of the biomass of all terrestrial animals. This is even greater in tropical environments, more abundant still at 25% or more of the total animal biomass.

The behavior of ants has a profound enough effect on the wider ecosystem that they are considered ecosystem engineers. Their extreme abundance means that other organisms in the same environment have a very high chance of encountering ants, and as ants are generalist feeders and very territorial, they are very likely to exert control over the local community.

Seed dispersal:

Ants play a key role in the dispersal of many seeds, through an interaction called myrmecochory. This is a mutualistic relationship between plant and ant, the seeds formed with a rich source of nutrients called an elaiosome which is an attractive energy source for ants, which in turn spread and distribute the seeds. This has been recorded for over 11,000 plant species, demonstrating through co-evolution how important ants are to dispersal and the biodiversity of plants.

Ants are a keystone species in many temperate forests, and studies have shown that ants can be more significant dispersers than even rodents, another major group of seed dispersers.

Soil:

Nest construction, maintenance, and the accumulation of organic matter local to the nest all have a big impact on soil structure, aerating the soil and increasing porosity. The areas immediately around ant nests are particularly diverse, with more plant species present due to the nutrient availability. Ants form mutualisms with plants, fungi, and microbes that enhance nutrient cycling, again improving soil quality.

Ants as biological control agents:

Many ant species are very effective and territorial predators, and due to this certain species function very effectively as a biological control against pest species in agricultural systems. The first recorded use of ants as pest control species dates back to 300 AD in China, where weaver ant colonies were established in citrus orchards, as a natural predator against species detrimental to fruit production, such as beetles & caterpillars. This is still used widely today.

Another example is the use of the ant species Dolichoderus thoracicus to control pests of important economic crops such as sapodilla in South East Asia. Maintenance of appropriate ant species with management measures in place can act as a natural form of control against pests and fungus, helping to reduce pesticide use and improving soil health.

How valuable is this to humans?

Ant abundance and behavior clearly play a significant role in the wider ecosystem, through nutrient cycling, impacts on soil structure, and regulating insect and animal communities. However, the actual value to humans of a lot of these benefits is very difficult to quantify, as many are indirect and without convenient measure.

There are still many direct & measurable benefits:

Bioindicators: ants can be used as bioindicator species for diseases in crops or forestry, as well as for assessing the impact of human activities such as mining.

Entomophagy: Ants form a regular part of the diet in many tropical and subtropical regions, as they are abundant and can be an important source of protein. 

Above: red ant larvae, a protein-rich meal.

Weaver ants are a common form of pest bio-control in tropical climates across Asia, Africa & Australia. It is clear to see that they can exert significant control over pest numbers. It was also found that the presence of these ants in turn lead to a higher harvest.

Whilst weaver ants are the more commonly studied ant used in biocontrol, it is not due to particularly unique properties specific to this species. Weaver ants share similar beneficial traits with almost 13,000 other species of ants, many of which could be to some degree suitable agents of control.

Weaver ant colonies can also serve as a good food source, which is easily accessible from nests made in leaves and harvestable in large amounts. It could be a fruitful area of study given the need for more sustainable agricultural practices.

Pest control: Ants are natural enemies to many pest species and can be a very useful biological control agent.

Ecosystem disservices: concerns & threats.

When assessing the ecosystem function of ants, their functions, and the impacts on humans, there are notable pest examples and ecosystem disservices to consider.

Fire ants (Solenopsis invicta) are a big problem in the Southern US, where they respond to electromagnetism and often build nests in electric equipment and machinery. This causes over a billion dollars of damage each year.

The only species as spatially spread across the globe as ants are humans, and this tends to lead to a fair amount of overlap. Ants can be a big domestic pest, invading homes and human structures and potentially transmitting diseases. Hidcote Manor Garden response to L. neglectus

• Stopped selling garden-grown plants
• Ceased transferring plants from the garden anywhere off-site
• Retained all soil/ building waste on site
• Compost and use all green waste on-site
• Changed all processes to ensure not to spread L. neglectus to any other site.

There has been no recording of the species at any other site in the UK, suggesting so far that the mitigation has been effective.

Monomorium pharaonis, or pharaoh ants, are a pest that often builds nests in wall cavities and other human domains, including hospitals. A UK study showed about 10% of hospitals reported some degree of pharaoh ant infestation. This poses a risk of contamination to sterile equipment through the transfer of pathogens the ants can carry, posing a serious health risk.

Invasive species:

The social order & extreme organization of ants also result in them often being highly competitive as invasive species.

The Argentine ant Linepithema humile was inadvertently spread across many other suitable climates around the world, and when left unchecked often outcompetes and ultimately displaces other communities of ants and arthropods. This often results in the removal of the existing natural enemies of other pest species, therefore indirectly serving to protect pests that impact crops & agriculture.  An example of an invasive ant species within the UK is Lasius neglectus, which is thought of by some researchers as having as much damaging potential as the Argentine ant exhibited across Europe. They can form ‘super colonies’, which spread over vast areas with many queens.

The only known colony in the UK was discovered at Hidcote Manor garden in 2010, a colony which covered an area of approximately 12 hectares. Where this L. neglectus colony established, native species were all but entirely displaced from the area, only appearing on the outer edges of the invading species’ range. They are very aggressive towards native species, super colonies of highly territorial and very effective interlopers. These traits that make ants such efficient predators of pests, also make them potentially very effective pests. 

There have been examples of the eradication of invasive ant species on relatively large scales. The Argentine ant was successfully eradicated in New Zealand. This would be a great opportunity for increased citizen science, in terms of the identifying and surveying of ants to monitor the movement of species and to establish where new species colonize sooner, and to keep on top of any ecosystem changes through closer monitoring of a keystone species.