Food selection by avian floral visitors: an important aspect of plant-flower visitor interactions in West Africa

Abstract

Community‐level studies have shown that plant–pollinator interactions are much more generalized than previously expected. Consequently, many authors have questioned the significance of phenotypic complementarity between plants and pollinators and abundance effects in pollination interactions. Here, we compare the behaviour of three sunbird species feeding on the nectar of five plant species in afromontane vegetation. We studied the feeding behaviour with and without consideration of plant abundance (i.e. diet selectivity and diet composition, respectively). The aims of the study were to estimate: (1) how relative resource abundance influences flower selectivity; (2) the degree of phenotypic matching; and (3) whether different plant resource assessment methods give different answers to this question. The results showed that, although sunbirds frequently feed on both morphologically adapted and nonadapted plants, food selectivity data are consistent with the hypothesis of phenotypic complementarity. Moreover, we found that the type of plant abundance measurement can change conclusions in some cases, as individual plants differ in their growth habits and nectar production. This effect was most obvious for the assessment of selectivity of the northern double‐collared sunbird (Cinnyris reichenowi) and for Hypoestes aristata, a plant producing inflorescences composed of a large number of small flowers possessing small amounts of nectar per flower (a high abundance of flowers, but a low abundance of nectar relative to the remaining plant community). © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, ••, ••–••.

Generalization versus Specialization in Pollination Systems: Visitors, Thieves, and Pollinators of Hypoestes aristata (Acanthaceae)

“…However, according to previous studies it is visited by a much broader spectrum of potential pollinators, including long-proboscid flies in South Africa [40], [41] and various sunbirds, bees, flies, butterflies, and moths in our study area in the Bamenda Highlands, Cameroon [42], [43]. In this area, H. aristata is the most favoured food plant of the sunbird Cinnyris reichenowi [44]. Although the H. aristata morphology suggests pollinator specialization, it is apparently visited by a variety of birds and insects.…”

Species interactions in an Andean bird–flowering plant network: phenology is more important than abundance or morphology

“…In contrast, in a hummingbird–flowering plant network, forbidden interactions from phenological or morphological mismatches were found to drive frequencies of observed interactions (Maglianesi et al, 2014; Maruyama et al, 2014; Vizentin-Bugoni, Maruyama & Sazima, 2014), although they were not important predictors of network structure (e.g., nestedness, connectance, specialization, evenness and asymmetry; see Maglianesi et al, 2014; Vizentin-Bugoni, Maruyama & Sazima, 2014). Similarly, phenological mismatches, in combination with relative abundances of network members, played a role in explaining interaction frequencies between nectarivorous sunbirds and flowering plants (Janecek et al, 2012). …”

Does a Species’ Extinction–Proneness Predict Its Contribution to Nestedness? A Test Using a Sunbird-Tree Visitation Network

“…Moreover, despite their small flowers most obviously adapted for insect pollination, the links between the tree species Nuxia congesta and Albizia gummifera and the orange tufted sunbird may well reflect pollination because the orange tufted sunbird carried significant pollen loads of both species at NNFR [36]. Moreover African sunbirds are known to be relatively unspecialised in terms of morphological adaptations to nectar feeding [29, 30]. To what extent all links (flower visitations) in our network represent pollination rather than nectar robbing, catching visiting insects or even florivory [44, 45] is under investigation.…”

“…Just how the ecology of the sunbirds in the network influences this NODF value needs investigation. Many sunbirds feed on herbs as well as trees [30], while many of the trees in the network are likely pollinated by insects, so that there may well be considerable redundancy in the system. The only confirmed specialization is between A .…”

“…Our network is not closed in that sunbirds visit herbs as well as trees [29, 30] and the trees in our network are occasionally visited by other bird species [31]. At least one tree species ( Anthanotha noldea ) in our network is totally dependent on sunbirds for seed set [32].…”