Human activities like planting crops or managing land changes landscapes for wild animals. For butterflies, these changes might reduce access to food like wildflowers. When faced with a changing food supply, certain butterflies may be able to survive in environments with reduced resources if, for example, they have lower metabolic rates that would reduce the energy required to maintain their bodily functions. This is exactly what interested Julie Lebeau, Renate Wesselingh and Hans Van Dyck of Université Catholique de Louvain, Belgium. They used wild meadow brown butterflies to test whether human-modified landscapes affect the physiological characteristics of wild butterfly populations.
Butterflies typically live in meadows with plentiful nectar-rich flowers. However, some butterflies live on land fragmented for human use with fewer available flowers. Butterflies then have to travel to find a single flower resource. Lebeau and her colleagues were specifically interested in the effects of different landscape habitats on butterfly energy budget and flight ability. The researchers went to the field and collected butterflies: half from unmanaged wild meadows with infrequent mowing and abundant flowers, and half from managed meadows that were mowed frequently, had fewer flowers and were surrounded by agricultural land.
The researchers then placed the butterflies in flight cages to test their responses to environments of differing nectar quality. Each cage was provided with flowers to create conditions that varied from a high-quality environment simulating a wild unmanaged meadow – the butterflies were provided with 100 flowers of their preferred species (brown knapweed, Centaurea jacea) – to the poorest quality setting simulating a managed meadow – where the butterflies were provided with only 10 flowers of a species that they would not normally visit (red clover, Trifolium pratense). After 2 days in the cages, the researchers measured the butterflies’ resting metabolism – the amount of energy consumed for baseline bodily functions – as well as their flight capacity using a flight mill that measured the distance flown by each butterfly in 10 min.
Looking at the effects of the different settings on the physiology of the insects collected from the managed and unmanaged settings, the team found that butterflies that had been collected from the managed meadows were physiologically better suited to a harsher lifestyle. To start, they had lower metabolic rates than the butterflies from wilder areas, required less energy to maintain baseline bodily functions and potentially used more energy when moving to find mates or flower resources in the wild. The butterflies that originated from the managed landscapes were also able to fly greater distances in the flight mill; on average, they flew 2.5 times farther than butterflies from the wilder areas. Being able to fly longer distances would be helpful when looking for infrequent nectar-bearing flowers in their managed habitat.
Interestingly, the team found that the quality of the nectar in the different cages (the number and type of flowers available) had little impact on the butterflies’ metabolic rates and flight distances, except when the nectar was of the poorest quality (10 flowers of a non-preferred flower). On this occasion, the butterflies from the wild areas had lower metabolic rates and flew very little. The authors suggest that butterflies from the wilder meadows are not prepared for poor-quality nectar and must reduce their metabolism and the amount of energy that they expend on flight, while butterflies from managed environments can maintain their physiology in the face of varying nectar quality.
This work shows that intensive land management can select a specific subset of butterflies that have a well-adapted physiology to persist in such environments and we are therefore shaping the characteristics of wild animal populations with our activities.
