Better many small than a few large: how landscape configuration affects arthropod communities in rice agroecosystems

Can splitting agricultural ecosystems help reduce yield losses for rice farmers? Associate Editor, Juan Corley highlights the importance of Dominik et al.’s recent research, Landscape composition, configuration, and trophic interactions shape arthropod communities in rice agroecosystems.

A Spanish version of this post is available here.

For many of us city dwellers, rice is common in much modern cuisine, from Sushi to Spanish paella. However more significantly, rice is known to be the most important human food crop in the world, directly feeding more people and over a longer time than has any other crop. More than 3.5 billion people (half the world population) depend on rice for a significant proportion of their daily calories. Rice is also enormously diverse, both in the way it is grown and how it is used by humans who consume nearly 80% of what is produced. In fact, the domestication of rice is likely one of the most important developments in human history. Still, a significant part -nearly 40%- of what we grow is lost to pests and diseases. How to manage such damaging species in rice fields in a sustainable way, remains a world challenge for this key staple food crop.

Banaue rice terraces
Banaue rice terraces (N. Luzon, Philippines) taken from observation point at beginning of road to Bontoc (via Wikimedia Commons)

Ecologists have known for quite some time, that appropriate agricultural landscape configuration can help lessen the impact of herbivorous insects on crops by facilitating natural control by organisms living in adjacent non-crop habitat patches. Across Asia, where nearly 90% of rice is produced and yield losses are the highest, farmers typically own small areas of land. There are more than 200 million rice farms; many smaller than 1 ha and interconnected by bunds (terrestrial levees surrounding the fields), leading to highly fragmented landscapes with varying degrees of connectivity. Such habitat fragmentation in rice agroecosystems can negatively affect natural enemies, although most evidence in this respect comes from studies conducted at field and plot scales. The functional role bunds and their connectivity play on the arthropod community of rice agroecosystems in the Philippines at landscape scales, is the main question tackled by Dominik and colleagues.

By combining intensive arthropod sampling at 3 sites in Luzon (Philippines) with a quantification of landscape configuration using GIS methods, the international team, led by Christophe Dominik from Germany and with researchers from the Czech Republic, Australia and the Philippines, was able to show that both trophic interactions and landscape configuration affect the arthropod community in the rice fields. They note that landscape diversity reduced the number of herbivores but did not affect their natural enemies. For highly mobile parasitoids- key regulators of many insect herbivores- the connectivity of the rice bunds best explained their abundance.

Mature rice panicles
Mature rice panicles. Image collection of IRRI, International Rice Research Institute (via Wikimedia Commons)

Their findings provide a strong, if unexpected, suggestion that a mosaic of increasing number of rice fields and a diverse surrounding landscape of connected bunds may lower herbivore abundance and provide natural enemies with food availability. Increased fragmentation of rice agroecosystems at the appropriate scales may potentially help reduce the use of pesticides and minimize harvest losses.  Given that rice is grown by more people than any other crop and is cultivated in wide range of climates and terrains, investigation such as this one, that provide ecologically robust methods to reduce yield losses is critical to world food security – and to ensure tasty meals are still out there for us!

Read the full article, Landscape composition, configuration, and trophic interactions shape arthropod communities in rice agroecosystems in Journal of Applied Ecology.

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