Imagine running a shop where you must hire both a guard and a salesperson. The guard keeps thieves away but may sometimes scare customers. The salesperson brings revenue but dislikes being interrupted. Balancing both roles can be tricky.

Plants face a similar dilemma when they attract ants for protection while also needing pollinators for reproduction.

Sweet deals with ant allies

Plants rarely survive in isolation. They form alliances with many creatures, gaining protection, pollination, and nutrients.

One of the most fascinating examples involves extrafloral nectaries – small glands on leaves, stems, or branches of around 4,000 plant species.

These glands release sugary nectar not to attract pollinators but to lure protective ants and insects. In exchange for this reward, ants chase away herbivores. This partnership benefits plants, but it can complicate relationships with pollinators.

Ant guards disrupt pollinators

A new study published in the Journal of Ecology shows that ants can interfere with pollination when nectaries are located near flowers.

Bees, which need close contact with flowers, are disrupted. Their visits shorten or stop altogether when ants patrol nearby.

Yet the story shifts when extrafloral nectaries are found on leaves or stems farther away. In such cases, plants gain the protection of ants without losing pollination benefits, often achieving greater reproductive success.

Different plant visitors, different risks

Not all flower visitors respond the same way. Butterflies, with their long feeding tubes, remain largely unaffected. They can sip nectar from a distance, safe from ant encounters.

Bees, however, must get close and linger, making them prime targets for interference. This contrast shows how visitor behavior shapes the outcome of plant–ant interactions.

“Bees, on the other hand, need to get very close to the flower to collect pollen and floral nectar, but ants don’t allow them to stay for long,” said Amanda Vieira da Silva, the lead author of the study.

“Not surprisingly, our analysis showed that the presence of ants is detrimental to pollination when extrafloral nectaries are close to flowers but has a positive effect on plant reproduction when they’re located farther away.”

Trade-offs shape plant survival

The study examined data from 27 experiments across 25 plant species. Overall, the average impact of ants on pollination was low but highly variable.

Ants consistently reduced floral visitation, especially by bees, but this did not always reduce reproductive success. In fact, plants with nectaries on vegetative tissues often benefited, producing more fruits and seeds.

Researchers suggest several reasons for the low costs. Protective benefits against herbivores may offset pollination losses. Some plants with reproductive nectaries gain more defense from florivores, balancing reduced pollinator visits.

Others reduce dependence on pollinators through self-pollination, making ant interference less harmful. Even reduced visits may not matter if short or fewer visits still transfer enough pollen.

Ant guards change plant futures

Ant interference may have influenced the evolution of plant traits. Species with high reliance on bee pollination may lose nectaries over time.

Others may evolve seasonal separation, producing leaves with active nectaries at one time and flowers at another, preventing conflict.

“We know that in some groups of plants with extrafloral nectaries and flowers pollinated by the vibration of bees, new leaves with active extrafloral nectaries and flowers are produced in different seasons throughout the year, which would avoid conflict between the two,” said Anselmo Nogueira, co-author of the study.

Sweetness fuels bigger networks

Additional partnerships add complexity. Nitrogen-fixing bacteria in roots can boost plant productivity, supporting both pollinators and protective ants.

Resource quality also shapes interactions: plants with richer nectar attract more aggressive ants, which can either improve defense or worsen pollinator deterrence. Context, environment, and species traits all decide the balance.

Plant protection and pollination intertwined

Studies have typically focused on the effect of only one isolated interaction on plants. For example, they quantify how much ants favor the defense of plants against herbivores or how much pollinators favor plant reproduction.

“But these interactions can occur at the same time,” said Laura Carolina Leal, co-author of the paper. “So, to understand how these interactions influence plant growth and reproduction, we need to look at them in an integrated way.”

The findings highlight how delicate balances shape ecosystems. Ants reduce visits but can still help plants thrive, depending on where nectaries sit and which visitors dominate. Long term, these dynamics may influence the evolution of floral traits and mating systems.

The study is published in the Journal of Ecology.

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