The underestimated value of nectar resources for butterfly conservation

Background/Question/Methods

From monarchs and checkerspots to blues and browns, butterflies are no stranger to the list of taxa in need of enhanced conservation efforts. A major focus of these efforts is typically on ensuring sufficient host plant-containing habitats. It is well-known that nectar resources are important for butterflies as well, but the extent of their importance is often under-appreciated, and their availability taken for granted. Our research focuses on the importance of nectar availability for population persistence in the Baltimore checkerspot butterfly, a species of conservation concern in some parts of its range, and whose populations exist in habitats with great disparities in nectar plant presence. We reared checkerspot butterflies and fed adult females on varying amounts of nectar (ad libitum, limited, none). For butterflies from each treatment, we recorded the lifespan and the number of eggs laid, and incorporated these data into models to calculate effects on overall population viability. We incorporated our experimental data into population models to evaluate effects on overall population viability.

Results/Conclusions

While there was a nominal effect of the amount of nectar available to adult butterflies on the number of eggs laid, there was a significant effect on overall lifespan. These results suggest that, although butterfly fecundity per se may not be greatly affected by nectar availability (in our species at least), butterflies need to live long enough to find host plants on which to lay eggs. The interaction between lifespan and actual landscapes can therefore have very real effects on overall population viability. For example, our spatial population models suggest that in small, isolated patches, changes in longevity matter less because nearly butterflies leave patches before they die. However, reduced longevity changes the probability that those butterflies find new patches. These results have implications for managing butterfly populations, and suggest that “a change is gonna come” (or has gotta come!) in how we think about butterfly conservation, shifting from a more narrow focus on host plant availability as a major driver of population declines, to a more holistic view of the importance of resources across entire landscapes, particularly for motile species.