Plant–pollinator interactions in ultramafic and non-ultramafic environments in New Caledonia

ABSTRACT Edaphic conditions operate major environmental filtering on plant assemblages and their community structure. Soils derived from ultramafic outcrops (i.e. ultramafic substrates) are characterized by high concentrations of metal and metalloid and nutrient deficiencies constraining plant growth. Due to the coupled effects of edaphic conditions and climate, tropical ultramafic substrates harbour a very particular flora. New Caledonia, one of the main plant biodiversity hotspots worldwide, owes much of its exceptional biodiversity to ultramafic substrates. While the flora of the New Caledonian ultramafic substrates is well known, its pollinating fauna remains to be described. Here, we describe plant–pollinator interactions in some ultramafic and non-ultramafic environments in New Caledonia, with a particular focus on wild alien, native and domestic bees. Wild alien bees were less diverse and less present in ultramafic environments than in non-ultramafic ones; we only recorded six interactions realised by wild alien bee species in ultramafic environments. Apis mellifera was also less present in ultramafic environments. Regarding native bees, they were equally present in both environments but less diverse in non-ultramafic environments. Our results suggest that ultramafic environments may filter alien pollinators. Due to beekeeping, Apis mellifera thrived and was the most active species in both environments. Further studies are needed to explore the diversity of interactions in ultramafic environments and to test whether metal and metalloid found in ultramafic substrates such as nickel may transfer to pollinators through plant rewards.