Goldilocks’ quarter-hectare urban farm: An agent-based model for improved pollination of community gardens and small-holder farms

Abstract

Industrial agriculture’s expansive monocultures contrast against community farms of diverse crops in small allotments constrained by urban regulations. These human-controlled differences in scale, arrangement and crop diversity, may differently impact insect foraging and pollination. The relationship between human management and insect pollination is under-explored, especially regarding the implications of insect flower constancy–the tendency of insects to favour visits to a single rewarding flower species during a foraging bout. Although high flower-constancy is associated with reliable pollen transport, its impact on pollination depends also on planting regimes, the vicinity of neighbouring crops, weeds and wildflowers. This study explores the potential pollination impacts of insect flower constancy, heterospecific pollen transfer, and human-dictated crop patch size, using an agent-based model of insect pollinators foraging from two flowering plant species. Highly constant pollinators were most effective in the smallest patches when heterospecific pollen transfer was an issue. As patch size increased, pollination rates improved overall, but less constant insects produced better pollination rates for intermediate sized areas because they rapidly switched preferences between flower species. As patch size increased further, the influence of flower constancy on pollination rates was reduced. Study results suggest that typical community farms containing small single-crop patches operated by independent growers within an allotment, may be better pollinated if operated collaboratively to increase single-crop patch size. Crop patches needn’t be large homogeneous agricultural monocultures, but neither should they be so small and heterogeneous as to inhibit pollination. We found a “Goldilocks zone” around 11m x 11m to be a good compromise for pollination, regardless of the level of flower constancy in local insects. As climate and human land use increasingly impact insect populations, the relationships between pollination systems, growers and policy makers must be continually examined to safeguard food supplies and native ecosystems.