Plant growth functions and possible spatial and temporal scaling errors inmodels of herbivory

Recent studies have provided detail of the mechanisms by which plants and a nimals interact, but attempts to apply this knowledge to understand functio n at the scale of whole fields or grazed ecosystems can be fraught with dif ficulties. Faced with a plethora of detail, and yet demands to make models more comprehensive, modellers face pressure to revert to simplified account s for what are assumed to be well-established biological phenomena, for exa mple, for describing plant growth and intake, but this raises the risk; tha t important insights may be lost, or that the analyses may face errors of s caling. The predictions of a previously described spatial model are compared with t hose of a non-spatial rendition of the same model to identify the differenc es in predictions and the sources of these differences. In particular, the use of the conventional empirical growth functions and their interaction wi th temporal and spatial scaling errors are examined. The comparison exposed how substantial Errors could be made in predicting yield and stability und er grazing. It is proposed that such errors might be avoided by ensuring th at the functional responses used capture the insights of more detailed stud ies, and by recognizing the difficulties of scaling-up from the level of pr ocesses to the field scale and beyond.