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Plants grow in communities where they interact with other plants and with other living organisms such as pollinators. On the one hand, studies of plant–plant interactions rarely consider how plants interact with other trophic levels such as pollinators. On the other, studies of plant–animal interactions rarely deal with interactions within trophic levels such as plant–plant competition and facilitation. Thus, to what degree plant interactions affect biodiversity and ecological networks across trophic levels is poorly understood. We manipulated plant communities driven by foundation species facilitation and sampled plant–pollinator networks at fine spatial scale in a field experiment in Sierra Nevada, Spain. We found that plant–plant facilitation shaped pollinator diversity and structured pollination networks. Nonadditive effects of plant interactions on pollinator diversity and interaction diversity were synergistic in one foundation species networks while they were additive in another foundation species. Nonadditive effects of plant interactions were due to rewiring of pollination interactions. In addition, plant facilitation had negative effects on the structure of pollination networks likely due to increase in plant competition for pollination. Our results empirically demonstrate how different network types are coupled, revealing pervasive consequences of interaction chains in diverse communities.

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Plants acting as ecosystem engineers create habitats and facilitate biodiversity maintenance within plant communities. Furthermore, biodiversity research has demonstrated that plant diversity enhances the productivity and functioning of ecosystems. However, these two fields of research developed in parallel and independent from one another, with the consequence that little is known about the role of ecosystem engineers in the relationship between biodiversity and ecosystem functioning across trophic levels. Here, we present an experimental framework to study this relationship. We combine facilitation by plants acting as ecosystem engineers with plant–insect interaction analysis and variance partitioning of biodiversity effects. We present a case‐study experiment in which facilitation by a cushion‐plant species and a dwarf‐shrub species as ecosystem engineers increases positive effects of plant functional diversity (ecosystem engineers and associated plants) on ecosystem functioning (flower visitation rate). The experiment, conducted in the field during a single alpine flowering season, included the following treatments: (1) removal of plant species associated with ecosystem engineers, (2) exclusion (covering) of ecosystem engineer flowers, and (3) control, i.e., natural patches of ecosystem engineers and associated plant species. We found both positive and negative associational effects between plants depending on ecosystem engineer identity, indicating both pollination facilitation and interference. In both cases, patches supported by ecosystem engineers increased phylogenetic and functional diversity of flower visitors. Furthermore, complementarity effects between engineers and associated plants were positive for flower visitation rates. Our study reveals that plant facilitation can enhance the strength of biodiversity–ecosystem functioning relationships, with complementarity between plants for attracting more and diverse flower visitors being the likely driver. A potential mechanism is that synergy and complementarity between engineers and associated plants increase attractiveness for shared visitors and widen pollination niches. In synthesis, facilitation among plants can scale up to a full network, supporting ecosystem functioning both directly via microhabitat amelioration and indirectly via diversity effects.

RESUMENEl catálogo objeto de este trabajo es una primera entrega de una serie de tres que los autores han realizado sobre la familia Megachilidae en el área mediterránea occidental, como base de la revisión que se está llevando a cabo sobre los megaquílidos ibéricos. En esta ocasión, se trata de los componentes de la tribu Osmiini, formada por 10 géneros, 33 subgéneros y 243 especies, muchas de ellas diferenciadas en varias poblaciones subespecíficas, que hacen un total de 278 y asimismo se incluyen. De todos los taxones, además de la correspondiente discusión, si procede, se incluye su lista sinonímica y la distribución geográfica. Palabras clave: Hymenoptera, Apoidea, Megachilidae, Osmiini, catálogo, Mediterráneo occidental. ABSTRACT A catalogue of the western Mediterranean Megachilidae (Hymenoptera, Apoidea). I. OsmiiniThe present work is the first of three by the authors that make up a catalogue of the family Megachilidae in the western Mediterranean region, based on the revision currently undertaken on Iberian Megachilidae. It includes taxa of the tribe Osmiini, their synonymies, discussion, when necessary, as well as their geographic distribution. The results of our study indicate that the fauna of this tribe in the western Mediterranean is composed of 10 genera, 33 subgenera, 243 species and 278 subspecies, all of which are included.