A comparative approach to understanding factors limiting abundance patterns and distributions in a fig tree–fig wasp mutualism

Abstract

Numerous factors affect distribution and abundance. Due to their intimate host association, pollinating fig wasps are expected to occupy the entire distribution of their host fig. An understanding of the physiology of fig wasp species and the factors affecting adult survival are important for understanding and explaining wasp abundance and distribution patterns. We examine distribution and abundance patterns of a fig tree–fig wasp system in which the non‐pollinator (Ceratosolen galili) has been reported to be rarer than the pollinator (Ceratosolenarabicus) in drier areas due to lower desiccation tolerance. Both species are closely related and utilise the same oviposition sites onFicus sycomorus.We used ecological niche modelling to determine whetherC. galilicovers the range ofF. sycomorusand whether it is consistently rarer thanC. arabicus.We examined emergence times, critical thermal limits, desiccation and starvation tolerances of the wasps. The suggested rarity ofC. galilirelates to lower abundance in certain months and at certain localities but a similar number of occurrence records within the distributional range (except in arid regions, e.g. Namibia). In contrast toC. galili,C. arabicushas a wider thermal range, lives longer under hydrating and dehydrating conditions and is a nocturnal flier. The synergistic effect of physiological tolerances and flight time differences exacerbate the less favourable conditions available toC. galiliduring flight and location of receptive figs. These factors enableC. arabicusto survive for longer thanC. galili, meaning that they are more likely to disperse to trees that are flowering further away in space and time. Combining correlative and mechanistic approaches has aided us in understanding the ecological niches of these species.