Landscape effects on pollination networks in Mediterranean gypsum islands

Abstract

ABSTRACT• Habitat fragmentation is a major driver of global change that has operated historically on Mediterranean ecosystems. However, more needs to be understood about how fragmentation influences ecological interactions, particularly pollination. Gypsum outcrops are historically fragmented Mediterranean habitats and settings for the evolution of many endangered soil-specialist plants with narrow ranges.• In this study, we aimed to determine how fragmentation (area and connectivity) affects: (i) pollinator community composition and (ii) structural properties of pollination networks; and whether there are differences in the effects of fragmentation on: (iii) the number of interactions and visits among pollinator functional groups; and (iv) the number of interactions and specialisation degree between soil-specialist and soil-generalist plants. We characterised the degree of fragmentation and the pollination network structures in 12 gypsum habitat fragments embedded in a cropland matrix during two consecutive years.• We found significant relationships between fragmentation and network structure. The effects of fragmentation differed among pollinator functional groups, but not between soil-specialist and soil-generalist plants, in terms of number of interactions. However, the relatively higher pollinator specialisation of soil-specialist plants suggested greater dependence on pollinators.• Inter-annual variations in the network structures demonstrated the importance of temporal replication. The observed patterns related to the landscape structure and pollination at both the network and species levels provide insights into the key ecological processes in gypsum islands. These findings may help to identify the potential drivers of species persistence, especially for endangered soil-specialist plants with narrow ranges in a changing scenario with exacerbated habitat fragmentation.

Agricultural intensification drives changes in hybrid network robustness by modifying network structure

“…Even though we combined two bipartite network types with archetypically different network structures into a single hybrid network, our findings align with previous studies on the response of bipartite networks to anthropogenic disturbance. Namely, that as disturbance increases, mutualistic bipartite networks become more nested (Grass et al ), both mutualistic and antagonistic networks become less modular (Ximenes Pinho et al ; Grass et al ; Santamaría et al ), and reciprocally specialised interactions are most vulnerable to disturbance (Aizen et al ; Weiner et al ). However, prior studies have identified a range of relationships between disturbance and antagonistic and mutualistic network structure (Burkle et al ; Spiesman & Inouye ; Vanbergen et al , ; Bordes et al ; Santamaría et al ; Traveset et al ), suggesting that effects of disturbance may depend on interaction or disturbance type.…”

“…Namely, that as disturbance increases, mutualistic bipartite networks become more nested (Grass et al ), both mutualistic and antagonistic networks become less modular (Ximenes Pinho et al ; Grass et al ; Santamaría et al ), and reciprocally specialised interactions are most vulnerable to disturbance (Aizen et al ; Weiner et al ). However, prior studies have identified a range of relationships between disturbance and antagonistic and mutualistic network structure (Burkle et al ; Spiesman & Inouye ; Vanbergen et al , ; Bordes et al ; Santamaría et al ; Traveset et al ), suggesting that effects of disturbance may depend on interaction or disturbance type. Overall, changes in network structure can impact the outcome of direct interactions (Burkle et al ) and intra‐guild and inter‐specific competition (Bastolla et al ; Bascompte & Jordano ; Brosi & Briggs ; Goldstein & Zych ), potentially altering ecological and evolutionary trajectories of species within communities (Guimarães et al ; Pires & Guimaraes ).…”

Habitat fragmentation and population features differently affect fruit predation, fecundity and offspring performance in a non‐specialist gypsum plant

“…Flowering occurs in late spring, usually in May or June. No study has specifically assessed the pollinator guild of this study species, but according to Santamaría et al (2018), the main pollinators of large-flowered legumes in our study site are Hymenoptera, particularly bees such as Apis melifera and Anthophora atroalba, and several species from the genera Colletes, Osmia, Amegilla and Bombus. Nevertheless, a certain rate of autogamy is commonly found in similar legumes (Galloni et al, 2007;Sánchez et al, 2017) and cannot be discarded for our species.…”

Plant reproductive ecology and evolution in a changing Mediterranean climate

“…In a study of how pollinator–plant networks are affected by landscape structure for species on gypsum outcrops, Santamaría et al . () illustrate how high degrees of fragmentation in the landscape causes randomness in such networks, and identify a link between plant specialisation on soil characteristics and pollinator specialisation. Pollinators are more sensitive to fragmentation than plants (although this may be a temporal difference), and something very common in the Mediterranean region, inter‐annual variation in meteorological factors, has a marked effect on plant–pollinator interactions.…”