How to manage sustainable agriculture in the face of threats such as global climate change and invasive alien species? In climate and biodiversity hot spots, such as the Mediterranean Basin, it is a question that farmers need to answer.

When modelling the effects on invasive pest species of a changing environment, researchers tend to use “ecological niche models”, says Luigi Ponti, Marie Curie research fellow in the EU-funded GlobalChangeBiology project, coordinated by Ente per le Nuove Tecnologie, l’Energia e l’Ambiente (ENEA), Italy. “In the field, you see where a certain species is present, and the environmental conditions – usually temperature and precipitation – that characterise the ‘ecological niche’ where it is comfortable.”

Unfortunately, projecting geographic distribution of this ecological niche into the future – using data from climate simulations – cannot take account of inter-species interactions or responses to conditions which do not yet exist within the species’ current geographical range.

“But if you start from the biological mechanisms,” says Ponti, “you can project for climates that are currently not found where the species and natural or agricultural ecosystems exist.”

The crop, the pest and its predator

His project has pioneered a ‘physiologically-based demographic model’ that captures the climate-driven biology of the species and its food chain or web.

“The idea is to describe each organism regardless of its trophic level – whether it is a plant, herbivore or carnivore – and to regard it as a consumer,” says Ponti. The model describes species based on their demand for resources and how they allocate them. All organisms do this in a similar way, so they can be described using the same analogous scheme.

“We are able to tackle a much higher level of complexity, which is the main constraint when you simulate an ecological system,” he says. The same underlying mathematical functions can model this resource acquisition and allocation using relatively few parameters.

“We mainly describe the thermal biology – what the organism does at different temperatures,” explains Ponti, including the minimum and maximum thresholds between which it thrives.

“We focus on the key species in an agricultural-ecological system – the crop, a herbivorous pest and, if appropriate, the carnivore that feeds on the pest,” he says. This leads to a more complete picture because they may have different tolerances, and this is especially relevant when a new species enters a new environment like invasive alien species.

Winners and losers

The model has already assessed the ecological and economic impact of projected 1.8°C climate warming on olive crops and their infestations by the olive fly Bactrocera oleae – resulting in economic winners and losers. These findings are reported in the Proceedings of the National Academy of Sciences (PNAS), USA.

“The paper tries to give a more detailed picture of what happens under climate change, and including species interactions significantly influences the results you obtain,” says Ponti. Olive trees have a wider tolerance in terms of temperature than the olive fly, so while oil quality may fall, yields may rise as the average temperature rises.

If the temperature is outside the range of tolerance of the fly, such as in North Africa and the Middle East, he explains, “it’s like someone spraying insecticide over your field”.

These positives may minimise ecological and economic impacts for the Basin as a whole, but they mask the damage that will occur in some areas.

“We showed for Mediterranean olives – where this crop is important ecologically, economically and socially – even small negative effects would impact smaller farms,” says Ponti. Small farms play a valuable role in environmental stewardship, maintaining soil quality and biodiversity and reducing fire risk. Abandoned farms would start a cascade of events negatively affecting the overall environment, Ponti suggests.

As lead author of the PNAS paper, Ponti has received significant attention from the media and invitations to present to major organisations, including the European Food Safety Agency and the European Plant Protection Organisation. He hopes the model can be integrated into their risk analysis and contribute to future reviews of the EU’s Common Agricultural Policy.

Having worked with a pioneer in the field, Andrew Gutierrez, at the University of California at Berkeley, USA, Ponti carried out his research at the ENEA with the support of an EU Marie Curie International Reintegration Grant. One of the goals of the grant is to transfer knowledge back to Europe, and at the time, there was no one on the continent taking this kind of approach, Ponti explains.

He is now working on making the software more adaptable to new species and situations. “We’re using the same kind of approach to address an invasive insect-transmitted bacteria called Xylella fastidiosa which is attacking very ancient olive groves in Southern Italy,” he says.