Abstract:
Abiotic factors, biotic factors and dispersal ability affect distribution and abundance. Due to
their intimate host association, pollinating fig wasps are expected to occupy the entire
distribution of their host fig. However, Ceratosolen galili (non-pollinator) has been suggested
to be rarer than the pollinating Ceratosolen arabicus in drier areas due to different desiccation
tolerance. Both species are closely related and utilise the same oviposition sites on Ficus
sycomorus. We question what form of rarity (distribution, abundance or both) is present and
the potential mechanism(s) for this. We used ecological niche modelling to determine whether
C. galili covers the range of F. sycomorus and whether it is consistently rarer than C. arabicus.
We examined emergence times, critical thermal limits, desiccation and starvation tolerances of
the wasps to determine the potential behavioural and physiological underpinning of rarity. The
suggested rarity of C. galili relates 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). Competitive interactions between the species means that the wasp
species with highest abundance at a specific time will ‘close’ the figs to entry by the other
species, lowering the abundance of the second species. In contrast to C. galili, C. arabicus has
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 to C. galili during flight and location of
receptive figs. These factors enable C. arabicus to survive for longer than C. 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.
