Some tropical butterflies are flower ‘specialists’

Most tropical butterflies feed from a variety of flower types, but those that are “picky” about their flowers tend to prefer native plants, new research shows.

These selective butterflies also have more conspicuous wings and shorter proboscis and may be more dependent on forests, say the researchers.

The reduction in native plants due to urbanization affects the diet of such butterflies, and researchers suggest that intervention may be needed to manage their preferred flower resources.

“Butterfly species exhibit different levels of flower preferences and flower specialization,” says Anuj Jain of the National University of Singapore.

“Understanding the complex phenomenon of flower specialization of butterflies is important as butterflies are known to be important pollinators of tropical forests. Changes in vegetation structure due to urbanization could alter butterfly behavior, and in turn, result in changes in native plant pollination and reproduction,” explains Jain, who conducted the study as part of his doctoral research in the biological sciences department in the NUS Faculty of Science.

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“It is worrying that butterflies that are flower specialists may become increasingly dependent on fewer native flower sources. To conserve such butterflies, there is a need to develop intervention measures to maintain the availability of suitable flowering plants,” he adds.

Results of the study appear online in the journal Biological Conservation.

Forests and parks

When butterflies hunt for nectar, they collect pollen on their legs and body, which helps in pollination for the reproduction of plants. Studying the flowers that butterflies feed on is critical in understanding the reproduction and dispersal of different types of plants.

“So far, studies on the flower-feeding patterns of butterflies have been concentrated in temperate countries, such as the United Kingdom and Spain, but this area is not well-studied for the tropics. With massive landscape transformation that is happening in the tropics, there is a need to understand flower use by butterflies, to assess the implications on pollination and plant reproduction, as well as conservation of butterfly species,” says Edward Webb, associate professor in the biological sciences department, who supervised the study.

To address this research gap, Jain collaborated with Assistant Professor Krushnamegh Kunte from the National Center for Biological Sciences in India, and butterfly experts from the Nature Society in Singapore to look deeper into the flower-feeding patterns of tropical butterflies.

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Over a period of three years, the research team surveyed 62 sites in Singapore, which included both forested areas and urban parks, and recorded 3,092 flower visits by 190 butterfly species feeding on 149 plant species.

The researchers found that among the 190 butterfly species observed nectaring during the study, 30 were flower specialists who are picky about their diets, feeding only on selected flower species, while the rest feed from a wide array of flowers.

The pickiest of the picky

A few forest butterflies were found to be critically dependent on single native flower species. One of them is the Yellow Vein Lancer (Pyroneura latoia) butterfly, which fed on flowers of the native plant Leea indica in 74 percent of feeding observations. The team also found that the Lycaenidae family of butterflies, which is the most extinction prone and most habitat-specialized butterfly family in Singapore, is also the most flower-specialized.

Of the 19 butterfly species that made at least 10 flower visits in both forests and urban parks, five species expanded their diet when they are in urban parks, which have more non-native plants compared to forested sites. This suggests that non-native flowering plants may be benefitting some butterflies by providing extra nectar resources.

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“Native flowering plants in the forests of Singapore tend to be spatially dispersed and flowering events are short, sporadic, and few, except during times of mass flowering. The presence of non-native plants may make up for this shortfall in native flowering events. The impacts of non-native flowering plants can be complex, potentially benefiting generalist species while being detrimental to specialists,” says Jain.

Why the flashy wings?

The research team also studied the factors that made butterflies flower-specialists or generalists and found that butterflies that feed on fewer flower species (i.e. specialists) have wings that are more conspicuous.

“Our results suggest that the conspicuousness of the butterflies may be an important evolutionary adaptation to escape predators during feeding, explains Jain. “When butterflies are feeding, they tend to be vulnerable to predation. They will need to optimize foraging strategies or morphologies to reduce the time they spend on flowers, which may reduce exposure to predators and may lower predation.”

The study also found that butterflies that are flower generalists had longer proboscis lengths than specialists. Possession of a long proboscis is beneficial to butterflies because it widens food choices by allowing access to nectar in deep flowers, which typically secrete more nectar than short flowers.

In their current study, the research team could only quantify flower use by butterflies, but did not investigate the impact that the butterflies have on seed production, seed dispersal, and establishment of native plants.

To further their understanding on the true costs and benefits of non-native plant species to butterflies in tropical forests, the team hopes to carry out community-level experiments involving multiple plant species over the entire plant reproduction cycle.

Source: National University of Singapore

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Source: Futurity