Adaptive extent and seed yield predictions for Microula sikkimensis grown in the Qinghai-Tibet Plateau, China

Microula sikkimensis (Family Boraginaceae) is a species with multiple potential applications in medicine, food and fodder. From 1994 to 2004, field surveys and transplanting trials were conducted in eleven counties of three provinces in China in order to collect information about the habitat of this species. Extending Hutchinson's concept of a niche as an n-dimensional super-volume, the habitat niche-fitness (HNF) of M. sikkimensis is defined as the degree of similarity between the supply of an actual habitat and the requirement for the habitat to be optimum, in which the supply of the actual habitat and the requirement for the optimum habitat represent realistic habitat conditions and species attributes, respectively. A new model of HNF is constructed to evaluate the adaptive extent of M. sikkimensi with the main habitat factors as independent variables and factor weights as parameters. The calculation results show that the model of HNF notably outperforms the proportional similarity index and the geometric parallelism formula both in mathematical justification and biological principle testing. With HNF as a surrogate for composite environmental factors, a seed yield prediction model was selected from all probable regression models by cross validation method. The apparent prediction error and 45° line test showed that there was no significant difference between the observed seed yield from the test set and the corresponding expected seed yield values from the selected model, confirming the validity of the selected model in predicting seed yield across a wide-spread area. The seed yield prediction model and its uses are recommended within the limitations of the data used in the study area. Beyond this range, validation of the seed yield prediction model will be necessary.