Biogeography of a multifunctional trait: Spiny plant species in the flora of Israel and the Palestinian Authority

Functional biogeography is the discipline that studies the geographic distribution of organismal traits and their relationships with environmental conditions and ecosystem functioning. Trait multifunctionality can be a major challenge in such analyses, so deciphering trait geographic distributions from functions is not always straightforward. We studied spinescence in the flora of Israel and the Palestinian Authority as a case of a multifunctional trait, associated mainly with antiherbivory defence, aridity alleviation, and propagule and seed dispersal. We studied how the proportion of spiny species in the flora of Israel and the Palestinian Authority and the distribution of different spine locations within the plants vary along a very strong bioclimatic (especially rainfall) gradient in Israel and the Palestinian Authority. We found that plant spinescence, as expressed in species proportion, is more frequently positively associated with increasing aridity and summer heat, and more generally with resource limitations. However, spinescence of reproductive plant parts, which in many species aids seed dispersal, presents opposite trends. These patterns reflect the differing importance of each of the three major roles attributed to plant spinescence, and point to the relative importance of each in driving overall spinescence geographic distribution. Thus, the traits' geographic distribution patterns can elucidate these traits' multifunctionality and improve our understanding of the evolution and spatial variation among these functions.