Plant–pollinator networks: adding the pollinator’s perspective

Abstract

Pollination network studies are based on pollinator surveys conducted on focal plants. This plant-centred approach provides insufficient information on flower visitation habits of rare pollinator species, which are the majority in pollinator communities. As a result, pollination networks contain very high proportions of pollinator species linked to a single plant species (extreme specialists), a pattern that contrasts with the widely accepted view that plant-pollinator interactions are mostly generalized. In this study of a Mediterranean scrubland community in NE Spain we supplement data from an intensive field survey with the analysis of pollen loads carried by pollinators. We observed 4265 contacts corresponding to 19 plant and 122 pollinator species. The addition of pollen data unveiled a very significant number of interactions, resulting in important network structural changes. Connectance increased 1.43-fold, mean plant connectivity went from 18.5 to 26.4, and mean pollinator connectivity from 2.9 to 4.1. Extreme specialist pollinator species decreased 0.6-fold, suggesting that ecological specialization is often overestimated in plant-pollinator networks. We expected a greater connectivity increase in rare species, and consequently a decrease in the level of asymmetric specialization. However, new links preferentially attached to already highly connected nodes and, as a result, both nestedness and centralization increased. The addition of pollen data revealed the existence of four clearly defined modules that were not apparent when only field survey data were used. Three of these modules had a strong phenological component. In comparison to other pollination webs, our network had a high proportion of connector links and species. That is, although significant, the four modules were far from isolated.

Missing and forbidden links in mutualistic networks

“…Number of missing links was reduced by (i) extending sampling time to a full season and (ii) using both a phytocentric and a zoo-centric approach to monitor links, i.e. flower-/fruit-visit data and data on pollen on the body surface of flower visitors and seeds in faeces of frugivores, respectively ( [22]; the 'smoking gun' method sensu [23]). As in any biodiversity monitoring, accounting for sampling effects when monitoring interactions has long been recognized as a fundamental aspect [6], and this two-sided approach was recommended by Blü thgen [24]; also see [22,25] to reduce effects of observation bias.…”

Foraging ofScaptotrigonaaff.depilis(Hymenoptera, Apidae) in an Urbanized Area: Seasonality in Resource Availability and Visited Plants

“…The food sources exploited by bees can be identified by direct observation of the visiting bee at the flower [23,24] or by pollen analysis [14,25,26]. Pollen analysis enables quantification of the diversity and frequency of pollen grains found on the bodies of the bees [14,27], the nest [28,29], and/or feces of adult and immature bees [13].…”

Pollination: Impact, role-players, interactions and study – A South African perspective

“…10,11 The same can be applied from the pollinator's perspective -that is, the range of plants a pollinator prefers relates to it being generalised or specialised, as discussed below. 10,12 In some extreme cases, both parties could co-evolve morphologically and behaviourally to allow only one-on-one plant-pollinator interactions, whereby the plant protects access to rewards for its specific pollinator -a feature of, amongst others, many genera in the Orchidaceae. 13 It has been argued that the formation of specific floral structures in plants is largely driven by means of natural selection from their respective pollinators.…”

“…27 Oligolectic bees still visit flowers from plant taxa other than those from which pollen are collected for other resources, such as nectar and oils. 12 Floral choices of bee pollinators play an important role in the sustainability of a plant community. According to food web theory, the more complex http://www.sajs.co.za…”