Climate drives plant–pollinator interactions even along small‐scale climate gradients: the case of the Aegean

Abstract

Plant-pollinator network structure is the outcome of ecological and evolutionary processes, and although the importance of environmental factors is beyond doubt, our knowledge of how abiotic factors (e.g. climate) shape plant-pollinator networks remains limited. This knowledge gap is critical, as climate change poses a major threat to ecosystems, especially in the Mediterranean. This study focuses on one of the hottest parts of the Mediterranean Basin, the Aegean Archipelago, Greece, and examines how climate affects species richness and network properties (e.g. nestedness, modularity and specialisation) - either directly or indirectly through species richness. We sampled systematically 39 local plant-pollinator networks on eight islands along a north-south climate gradient in the Aegean. All plant-pollinator material used in the analyses was collected in 2012 and identified to species level. Aspects of climate used in the models were expressed as average conditions (mean temperature and annual precipitation) or as seasonal variability (isothermality and temperature seasonality). Structural properties of plant-pollinator networks were found to be strongly associated with species richness, which was in turn affected by climate, implying that pollination network structure is driven indirectly by climate. In addition, climate had a direct effect on network structure, especially on modularity and specialisation. Different aspects of climate affected network properties in different ways. We highlight that even in a relatively narrow latitudinal gradient, such as within the Aegean Sea region, climate constitutes a significant driver of plant-pollinator interactions.

Geography, climate, ecology: What is more important in determining bee diversity in the Aegean Archipelago?

“…We selected seven independent variables potentially affecting species richness, belonging to three categories: (a) geographical, accounting for area and isolation, and known to influence island species richness (Kreft et al., ; Weigelt & Kreft, ): (i) island area (area, in km 2 ), (ii) surrounding land mass proportion (SLMP, in %), (iii) distance to climatically similar largest island/mainland (Dist cl , in km), and (iv) maximum step length from pathway to nearest island/mainland (Dist max , in km); (b) climatic, that is, annual means that have been shown to affect bee richness in the Aegean (Petanidou et al., ): (i) annual mean temperature (Temp, in °C) and (ii) annual precipitation (Prec, in mm); and (c) ecological: (i) floral abundance (FlAb), a factor known to act as key determinant of bee communities (Petanidou & Ellis, ; Potts et al., ).…”

“…Integrating climate into models of global insular species richness has been shown to increase their predictive ability (Cabral, Weigelt, Kissling, & Kreft, ; Kalmar & Currie, ; Kreft, Jetz, Mutke, Kier, & Barthlott, ). Indeed, the effect of climate on species diversity is manifest even within a narrow latitudinal gradient (Petanidou et al., ). Geographical factors, such as geographic distance, are also important in shaping diversity patterns (Diver, ).…”

Specialization of plant–pollinator interactions increases with temperature at Mt. Kilimanjaro

“…So far, climate change was expected to disrupt plant-pollinator interactions by causing spatial and phenological mismatches between interaction partners (Hegland, Nielsen, Lázaro, Bjerknes, & Totland, 2009), or by increased frequency of extreme weather events (Hoiss et al, 2015), with negative consequences for interaction resilience and fitness of plants and pollinators (Forrest, 2015;Schenk, Krauss, & Holzschuh, 2018). The direct impact of temperature on the specialization of species, which has also been reported from smallscale climatic gradients for network specialization (Petanidou et al, 2018), imposes additional challenges to species interactions.…”

“…Frequent interspecific interactions, resulting from, for example, high pollinator richness or high visitation rates, may permanently restrict diet breadth promoting species coexistence in the long term (Goulson, Lye, & Darvill, ). Third, climate shapes plant and pollinator richness, composition and phenology and has been directly linked to network properties, including specialization (Petanidou et al, ). Temperature determines the costs of foraging flights in ectothermic pollinators (Kovac, Stabentheiner, & Brodschneider, ) and may thus modulate resource usage strategies in a way that species broaden their dietary spectrum in energy‐limited habitats (Miller‐Struttmann & Galen, ).…”

“…Frequent interspecific interactions, resulting from, for example, high pollinator richness or high visitation rates, may permanently restrict diet breadth promoting species coexistence in the long term (Goulson, Lye, & Darvill, 2008). Third, climate shapes plant and pollinator richness, composition and phenology and has been directly linked to network properties, including specialization (Petanidou et al, 2018).…”