Quantifying the global environmental niche of an underutilised tropical fruit tree species using herbarium records

Bowe, C. and Haq, N. (2010) Quantifying the global environmental niche of an underutilised tropical fruit tree species using herbarium records. Agriculture, Ecosystems & Environment. (doi:10.1016/j.agee.2010.06.016). (In Press)

Abstract

The importance of identifying the environmental adaptation of underutilised species such as tamarind (Tamarindus indica) and their ecogeographic distribution is widely recognised. Lack of physiological or quantitative yield/growth data does not permit the use of more traditional methods of crop modelling. In this study a representative dataset of tamarind’s global distribution appropriate for modelling the species distribution is produced mainly from herbarium records; while minimising the effects of error and bias inherent with such data.
Techniques were used to address bias and to flag erroneous data points. Most erroneous points were identified through the process of geographical validation. Groups of outliers were found isolated both environmental and geographical space. The exploratory analysis of the clean dataset also showed that both at the bioregional and sub regional scale tamarind experiencing different conditions in different regions. This indicates the existence of spatial nonstationarity, which due to the semi domesticated nature of the species, could be caused by evolution of the niche. Spatial niche variation in tamarind indicates that its range may have been expanded east from Africa into regions with a less pronounced dry period and with lower maximum temperatures. Difference in environmental niche between East African and West African populations is assumed to be due to the role of the Rift Valley preventing gene flow between the two regions of the continent. The implication of spatial nonstationarity and spatial variation within the niche, when considering using global or regional/multi-scale models to predict the world distribution of such species under current and future climate scenarios are discussed.

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