Seeds in farmland food-webs: resource importance, distribution and the impacts of farm management

Whilst considerable research effort in Europe has linked agricultural intensification with dramatic declines of seed-feeding birds, surprisingly little is known about the wider importance of seeds in animal food-webs. Moreover, understanding the dynamics of farmland seed food resources for species of conservation concern is of considerable research interest.

We examined the distribution of berries and soil-surface seeds in the managed and unmanaged habitats of a 125 ha organic farm. We took soil suction-samples over a year, counted and identified all seeds, and compared abundances and species-richness between habitats. We constructed ecological networks from literature records and by rearing insects to investigate the importance of these seeds for insects, birds and mammals. We predicted the impacts of management on seed biomass, energy and the ecosystem service of pest control across the whole farm.

We estimated seed and berry food resources of up to 33 metric tons of biomass and 560 GJ of energy on the farm. Potentially, more than 330 species use the seeds as a food resource, the overwhelming majority of which are invertebrates (82%) relying predominantly on non-crop and weed species. Generally, uncultivated semi-natural habitats such as woodland and mature hedgerows were more species-rich and had higher seed biomass and energy than crop habitats throughout the year, but fallow land was disproportionately important for seeds during the summer. Models of increased management intensity revealed declines of up to 19% in seed biomass and energy and cascades through the network that resulted in a substantial decrease in potentially pest-controlling parasitoids.

Highlights
► We estimate seed and berry animal food resources on a whole farm.
► We examine farm management impacts on seed biomass, energy and a tripartite food-web.
► Animal food resources of up to 33 tons of biomass and 560 GJ of energy are available.
► Management intensity affects the food-web and can lead to a 19% decline in resources.