The long and the short of it: a global analysis of hawkmoth pollination niches and interaction networks

Abstract

Summary 1. Proboscis length has been proposed as a key dimension of plant pollination niches, but this niche space has not previously been explored at regional and global scales for any pollination system. Hawkmoths are ideal organisms for exploring pollinator niches as they are important pollinators in most of the biodiverse regions of the earth and vary greatly in proboscis length, with some species having the longest proboscides of all insects. 2. Using datasets for nine biogeographical regions spanning the Old and New World, we ask whether it is possible to identify distinct hawkmoth pollination niches based on the frequency distribution of proboscis length, and whether these niches are reflected in the depths of flowers that are pollinated by hawkmoths. We also investigate the levels of specialization in hawkmoth pollination systems at the regional and community level using data from interaction network studies. 3. We found that most regional hawkmoth assemblages have bimodal or multimodal distributions of proboscis length, and that these are matched by similar distributions of floral tube lengths. Hawkmoths, particularly those with longer proboscides, are polyphagous and at the network level show foraging specialization equivalent to or less than that of bees and hummingbirds. In the case of plants, shorter-tubed flowers are usually visited by numerous hawkmoth species, while those that are longer-tubed tend to exclude shorter-proboscid hawkmoths and thus become ecologically specialized on longer-proboscid hawkmoth species. Longer-tubed flowers tend to have greater nectar rewards and this promotes short-term constancy by long-proboscid hawkmoths. 4. Our results show that pollinator proboscis length is a key niche axis for plants and can account for patterns of evolution in functional traits such as floral tube length and nectar volume. We also highlight a paradoxical trend for nectar resource niche breadth to increase according to proboscis length of pollinators, while pollinator niche breadth decreases according to the tube length of flowers.

Effective pollinia transfer by settling moths’ legs in an orchid Habenaria aitchisonii

“…The nectar spurs of H. aitchisonii are much shorter than their pollinators’ proboscises, in contrast to previous studies on Habenaria , which indicated that only pollinators with proboscises roughly equal to or slightly shorter than the nectar spurs could ensure efficient pollinia transfer and reproductive success (Singer & Cocucci, ; Singer et al, ; Peter et al, ; Pedron et al, ; Xiong et al, ; Johnson et al, ; Zhang & Gao, ; Tao et al, ). In other words, the mechanical mismatch could result in an opposite situation in which visitors probe flowers without touching the column and removing pollinia.…”

“…Previous investigations indicated that Habenaria species were predominantly pollinated by lepidopterans (Singer & Cocucci, ; Singer, ; Singer et al, ; Peter et al, ; Pedron et al, ; Ikeuchi et al, ; Xiong et al, ; Zhang & Gao, ; Tao et al, ), which usually have long proboscises. The pollinia in Habenaria species were observed to be placed on various sites on moths’ or butterflies’ bodies, such as on their eyes, heads, or at the base of their proboscises, depending on the match between the nectar spur and pollinator proboscis length (Singer & Cocucci, ; Singer et al, ; Peter et al, ; Pedron et al, ; Xiong et al, ; Johnson et al, ; Zhang & Gao, ; Tao et al, ). In Habenaria limprichtii Schltr., pollinia were observed attached to sphingids’ eyes but sometimes attaching to settling noctuid moths’ legs (Tao et al, ).…”

Pollination in Lilium sargentiae (Liliaceae) and the first confirmation of long‐tongued hawkmoths as a pollinator niche in Asia

“…Moth pollination has been considered to be relatively rare in the Asian flora (Corlett, ). However, it is reasonable to doubt this conclusion given that studies of nocturnal pollination by moths have been especially scarce in Asia (see the review by Johnson et al, ). Moreover, a number of moth flowers have been revealed there over the past few years, including some cases involving hawkmoths (Zhang et al, ; Mizusawa et al, ; Yokota & Yahara, ; Liu & Huang, ; Xiong et al, ; Yan et al, ).…”

Plant–pollinator interactions and threats to pollination: perspectives from the flower to the landscape

“…In a global scale morphometrics study, Johnson et al . () have analysed hawkmoth proboscis lengths, flower lengths and the degree of specialisation in nine biogeographical regions spread across the Old and New Worlds. At a regional level, proboscis lengths of hawkmoths show discontinuous frequency distributions which tend to be matched by tube lengths of the night‐opening flowers that they visit.…”

“…The study of Johnson et al . () is particularly valuable for bringing together a large body of data on moth‐flower relationships (including analyses of pollen loads) collected across several species‐rich tropical regions.…”