The long and the short of it: a global analysis of hawkmoth pollination niches and interaction networks.
The long and the short of it: a global analysis of hawkmoth pollination niches and interaction networks.
复制标题
DOI：
10.1111/1365-2435.12753
复制
发表时间：
2017-01
影响因子：
5.2
通讯作者：
Raguso RA
中科院分区：
文献类型：
--
作者：
Johnson SD;Moré M;Amorim FW;Haber WA;Frankie GW;Stanley DA;Coccuci AA;Raguso RA
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. A global perspective on hawkmoth pollination niches Steven Johnson, Marcela Moré, Felipe Amorim, William Haber, Gordon Frankie, Dara Stanley, Andrea Coccuci and Robert A. Raguso Niches are ecological opportunities for organisms and determine where they can survive and reproduce. To occupy a particular niche, species must either evolve or already possess certain functional traits. Some of the major challenges in the field of ecology are to identify niches in nature, to uncover the various environmental variables that define niches, and to discover which traits are important for niche occupancy. Because pollination is usually required for seed production in plants, animal pollinators represent niches that plants adapt to in order to reproduce successfully. In this study we sought to determine whether proboscis length is a key dimension of the pollination niche. We used hawkmoths as a study system since these insects are important pollinators of night-flowering plants, particularly in the species-rich tropics, and vary greatly in the length of their proboscides. The analyses were based on studies conducted in nine regions spread across the Old and New Worlds. In many of these studies, relationships between plants and hawkmoths were inferred from analysis of the pollen loads carried by the hawkmoths. The proboscis lengths of hawkmoths can vary between 2 cm and 25 cm, even within a single community, and tend to exhibit a frequency distributions characterized by several peaks (multimodality). These peaks can be considered to be pollination niches, and this proposition is supported by a good match between peaks in the frequencies of hawkmoth proboscis length and tube lengths of night-opening flowers. Analysis of the networks of interactions between hawkmoths and flowers reveals that hawkmoths are even more generalist in their foraging habits than are bees and hummingbirds. Long-proboscid hawkmoths have a particularly wide niche breadth in terms of the diversity of flowers that they visit, although they tend to concentrate their foraging activity on longer-tubed flowers that have greater nectar rewards. By contrast, the hawkmoth pollination niche for plants becomes narrower and more specialized as their floral tube length increases. This is the first study that has explored morphological niche axes for a pollination system at both regional and global scales. The approach could be extended to other pollination systems and could ultimately help to explain species distributions as well as co-diversification of insects and angiosperm flowers. By incorporating traits into analyses of species interaction networks, biologists may finally be able to identify some of the key principles underlying pollination niches. Flowers of the African shrub Gardenia thunbergia are pollinated exclusively by the convolvulus hawkmoth Agrius convolvuli. The 10 cm floral tube of this shrub matches the length of proboscis of this hawkmoth species. Photograph by Steven Johnson.
