From Petri dishes to plants: scaling up the functional response of a whitefly predator

Much of the information used to understand ecosystem function is based on laboratory bioassays. While useful, extrapolation to the field often results in misleading estimates of ecological variables. This is often the case for functional responses, which are mathematical functions that describe the number of prey eaten by a predator as a function of prey density, and are important components of predator-prey models. We hypothesize that information on prey distribution and predator foraging patterns obtained at the plant level can be used to scale up functional responses from the laboratory to whole plants. We developed a spatially explicit individual-based model that estimates predation rates within plants, and is based on a functional response model estimated in the laboratory. The model is parametrized and validated with data from a predator-prey system consisting of the coccinellid predator Delphastus catalinae preying on the sweetpotato whitefly, Bemisia tabaci biotype B (Hemiptera: Aleyrodidae), inhabiting tomato plants. From our results, we found the model is useful in scaling up from laboratory functional responses to predation in whole tomato plants of varying sizes. Furthermore, the model shows that the observed reduction in predation rates and the shift in the shape of the functional response across spatial scales is associated with imperfect alignment between intra-plant predator and prey distribution and predator foraging habits. We demonstrate that simple measures of prey distribution and predator foraging patterns can be used to scale up functional responses estimated through small experimental settings.