Ecological network complexity scales with area.

Larger geographical areas contain more species-an observation raised to a law in ecology. Less explored is whether biodiversity changes are accompanied by a modification of interaction networks. We use data from 32 spatial interaction networks from different ecosystems to analyse how network structure changes with area. We find that basic community structure descriptors (number of species, links and links per species) increase with area following a power law. Yet, the distribution of links per species varies little with area, indicating that the fundamental organization of interactions within networks is conserved. Our null model analyses suggest that the spatial scaling of network structure is determined by factors beyond species richness and the number of links. We demonstrate that biodiversity-area relationships can be extended from species counts to higher levels of network complexity. Therefore, the consequences of anthropogenic habitat destruction may extend from species loss to wider simplification of natural communities.

A new native plant in the neighborhood: effects on plant-pollinator networks, pollination, and plant reproductive success.

Ecological communities are dynamic entities subjected to extinction/colonization events. Because species are connected through complex interaction networks, the arrival of a new species is likely to affect various species across the community, as observed in plant biological invasions. However, plant invasions usually represent extreme scenarios in which the community is strongly dominated by the alien species, confounding the effects of a change in species composition with a massive increase in floral resource availability. Our study addresses changes in plant community composition involving native species, a common phenomenon under the current climate change scenario in which plants are modifying their distribution ranges. We experimentally manipulated patches of a natural scrubland community by introducing a native plant (henceforth colonizing plant). To avoid introducing a disproportionate amount of floral resources we adjusted the number of flowers of the colonizing plant to the amount of floral resources locally available in each patch. We had two objectives: (1) to analyse the effects of the arrival of a new plant on the pollinator community, the rearrangement of plant-pollinator interactions and the structure of the plant-pollinator network; (2) to evaluate potential consequences for pollination and the reproductive success of resident plant species. The colonizing plant acted as a magnet species, attracting bumble bees and facilitating interactions to other plants through spill-over. The introduction of the colonizing plant also affected the structure of plant-pollinator networks (colonized networks were more generalized and more nested than control networks) and modified the arrangement of plant and pollinator species into modules. Ultimately, these changes resulted in higher heterospecific (but not conspecific) pollen deposition and had contrasting effects on the reproductive success of two resident plant species (higher fruit set and lower seed set, respectively). Our study shows that relationships between plants and pollinators are rapidly rearranged in response to novel situations (even when the new plant is not overly dominant), with important functional consequences on pollination and plant reproductive success. Our study establishes a link between network structure and pollination and plant reproductive success, which may be mediated by differences among pollinator species in foraging behavior.

Pollinators show flower colour preferences but flowers with similar colours do not attract similar pollinators.

BACKGROUND AND AIMS: Colour is one of the main floral traits used by pollinators to locate flowers. Although pollinators show innate colour preferences, the view that the colour of a flower may be considered an important predictor of its main pollinators is highly controversial because flower choice is highly context-dependent, and initial innate preferences may be overridden by subsequent associative learning. Our objective is to establish whether there is a relationship between flower colour and pollinator composition in natural communities. METHODS: We measured the flower reflectance spectrum and pollinator composition in four plant communities (85 plant species represented by 109 populations, and 32 305 plant-pollinator interactions in total). Pollinators were divided into six taxonomic groups: bees, ants, wasps, coleopterans, dipterans and lepidopterans. KEY RESULTS: We found consistent associations between pollinator groups and certain colours. These associations matched innate preferences experimentally established for several pollinators and predictions of the pollination syndrome theory. However, flowers with similar colours did not attract similar pollinator assemblages. CONCLUSIONS: The explanation for this paradoxical result is that most flower species are pollination generalists. We conclude that although pollinator colour preferences seem to condition plant-pollinator interactions, the selective force behind these preferences has not been strong enough to mediate the appearance and maintenance of tight colour-based plant-pollinator associations.