Non-native plants aren’t staying invisible to enemies anymore

For decades, ecologists have assumed that non-native plants thrive because local insects and fungi barely touch them. Yet new research across Europe challenges that view.

By examining more than 127,000 feeding records, scientists found that many long-established newcomers are no longer invisible to enemies.

Some invasive plants now host herbivore communities that look surprisingly similar to those on native plants.

Non-native plants and local insects

Ecologists call these newcomers non-native species, organisms moved by people beyond their historical range. Local insects and fungi often overlook newcomers, allowing the plants to spread with minimal harm.

According to the enemy release hypothesis – the idea that escaping natural enemies helps invaders succeed – non-native plants can grow faster and reach high densities. 

Many textbooks say these plants stay lightly used because local herbivores never evolved the right adaptations.

The work was led by Ingmar Staude, an ecologist at Leipzig University and the German Center for Integrative Biodiversity Research (iDiv). His research focuses on how plant communities and their consumers respond to global environmental change.

The new findings reveal that this story is incomplete because ecological networks change over time.

With enough time and a large enough range, natural enemies eventually catch up to many non-native plants.

Tracking Europe’s plant enemies

The team focused on microherbivores, small insects and fungi that feed inside living plant tissues. These include leaf miners, gall-forming insects, mites, and disease-causing fungi such as powdery mildews.

To study these interactions, the researchers used a continent-wide dataset with more than 127,000 documented links between European plants and their microherbivores.

The data was combined with information on where each plant grows, when it first arrived in Europe, and whether it is woody or herb-like.

The team counted how many microherbivore species were recorded feeding on each plant in the database. This number gives a snapshot of how each plant is woven into the trophic network, the web of who eats whom in an ecosystem.

A global analysis has shown that many insect herbivores use only a narrow set of host plants rather than sampling everything available.

Specialized natives stand out when they begin feeding on plants absent from their evolutionary past.

Insights into non-native plants

Across the full dataset, non-native plants hosted fewer microherbivore species than native plants, especially when those natives were trees or shrubs.

This means that the usual expectation that newcomers initially escape many enemies still holds when thousands of species are analyzed at once.

The difference fades for plants that have been in Europe for centuries and have spread across wide swaths of the continent.

Some species arrived roughly 200 or more years ago. They now span about 400,000 square miles and support microherbivore counts similar to native plants.

The consumers of invasive plants

Statistical models showed that European range size and time since arrival were the strongest predictors of how many microherbivores a plant hosted.

By contrast, once the main effects were accounted for, geographic origin and close relatedness contributed very little.

Even when non-native plants reached native levels of richness, their enemies included more generalist species, consumers that can use many host plants.

Native plants still host highly specialized feeders that use only a few hosts, a role newcomers never replaced.

Changing pressures on newcomers

The results fit awkwardly with the classic view that escape from natural enemies keeps giving invaders an advantage over natives. Here, widespread non-native plants that have been around for a long time actually host many enemies, not few.

Earlier research on plant pathogens found that species introduced to new continents have fewer fungal and viral diseases than in their original range.

This pattern supported the idea that reduced disease pressure helps some species become successful invaders.

Newer research shows enemy release is often temporary, with enemy-host balances shifting over time. In the new work, long established non-native plants face many generalists, while specialists – species with narrow host ranges – remain concentrated on native plants.

The pattern resembles pollination studies showing that invasive plant species often receive many visits and do not consistently reduce pollination of native plants.

Both lines of evidence point to flexible ecological networks that can absorb new players. They still leave unique roles for long-established native species.

Impacts on conservation work

For managers deciding how to react to new arrivals, questions become how long a plant has been present and how widely it grows. Species that have recently arrived may need different management than long-established plants.

Some naturalized plants that have been present for centuries now support rich enemy communities and help weave local food webs.

This does not mean that all non-native plants are harmless, but it does demonstrate the importance of looking carefully at their actual roles.

“This knowledge can help assess the risks posed by non-native species in a more nuanced way,” said Staude. “In this way, the study will contribute to adapting conservation and management strategies to a changing species composition.”

The study is published in the journal Ecology Letters.

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