In this new post, Masayoshi Hiraiwa – postdoctoral researcher at Kindai University – presents his work ‘Loss of functional diversity rather than species diversity of pollinators decreases community‐wide trait matching and pollination function’. He discusses the importance of functional traits on biotic interactions, the challenge of finding proper study sites, and his interest in less studied pollination groups.
A Japanese translation of this blog post is available here!
About the Paper
Large and long-tongued insects such as bumblebees and butterflies are essential pollinators for many flowers with long corolla tubes and spurs. They play an important role in the evolution of complex flowers as well. In the Izu Islands, a group of oceanic islands in Japan, bumblebees and swallowtails are absent or very scarce. The absence of these pollinators is known to promote evolutionary changes in flowers in several plant species in the Izu Islands. One well-known example is the reduced flower size of a Campanula species in the Izu Islands. Campanula punctata is pollinated mainly by bumblebees in the main island whereas C. microdonta has smaller flowers and rely on small bees in the Izu Islands.
While individual cases of flower evolution are relatively well studied, the impacts of the bumblebee absence on entire plant-pollinator networks and their functions remain unraveled. We examined the impacts of long-tongued pollinator loss on pollination communities by comparing the networks between oceanic and main islands.
About the research
This topic is intriguing not only from the perspective of island biogeography but also provides valuable insights into the unknown impacts of global declines in bumblebees and butterflies due to human activities on real plant-pollinator networks and their pollination services. Can the remaining short-tongued bees and flies compensate for the absence of the bumblebees?
To date, the impacts of pollinator loss have been examined using experimental settings with a few to several plant and pollinator species while the impacts on natural systems with diverse species are largely untested. To clarify the impacts on natural communities, we made much effort to search study sites which had similar plants but different pollinator compositions before the study started. Coastal vegetation was chosen because it is composed of many common sea-dispersed plants with a wide distribution range across the study islands. Regarding pollinators, as the Izu Islands are relatively close to the main island, they share many species. The most time-consuming and painstaking part was finding the main island sites with bumblebees or other long-tongued bees. We surveyed many shores and found those where no such bees were observed likely due to various human impacts such as coastal development and surrounding forest loss.
We found that on the main island, networks exhibited efficient interactions between long-tongued pollinators and long-tubed flowers, as well as short-tongued pollinators and short-tubed flowers. This morphological matching ensured effective pollination for plant communities. In contrast, the absence of bumblebees in the Izu Islands disrupted the matching between flowers and pollinators. Long-tubed flowers received visits from short-tongued pollinators, leading to network-level mismatches and reduced overall pollination efficiency.
Our results suggest that the generally observed interactions between well-matched species in many ecosystems are a consequence of competition between pollinators with different tongue lengths. Furthermore, the decline of long-tongued pollinators, including bumblebees and butterflies, may not only affect long-tubed plants but also impact the entire plant community’s pollination function. When addressing ongoing declines in such pollinators, it is important to consider not only the plants directly interacting with them but also the entire community.
About the Author
I am currently a postdoctoral researcher at Kindai University. My interest in hoverflies led me to start researching pollination ecology. This study was conducted during my ph.D. course supervised by Prof. Atushi Ushimaru who is a pollination ecologist in Kobe University. While honeybees and bumblebees tend to get the most attention in pollination ecology, I am also interested in the functional roles of other diverse pollinators, including small bees and hoverflies, which are dominant within plant-pollinator networks. Recently, there have been reports of a decrease in pollinator diversity and the introduction of invasive species due to human activities. The impact of these changes in pollinator composition on plant-pollinator networks and the pollination function of communities is the main research theme from my doctoral course. Currently, I am conducting research on the impact of changes in species and functional diversity on interspecific interactions, regardless of the pollination ecosystem.
Like the blog post? Read the paper here
