Where have all the Good Butterflies Gone?: Introduction
Butterfly conservation is a vital but complicated endeavor. These charismatic pollinators are adapted for several ecosystems, including wide and open grassland environments with many nectar plants reliant on them. They act as flagship species, where the conservation of butterflies will benefit all pollinators that coevolved with the native fauna and are thus more vulnerable and a potential indicator of widespread pollinator declines, with cascading ecosystem effects. Unfortunately, these areas have become increasingly restricted by urbanization, improper management, changes in agricultural practices, and suburban sprawl, reducing butterflies to varying patches of habitat few and far between. This isolation is exacerbated by the usage of broad-spectrum pesticides and herbicides. Ecologically, these flowering patches act as islands, from which butterflies are locked within or around, without any suitable habitat between them, within the sea of unusable habitat, such as monoculture lawns, buildings, and farms. Understanding the dynamics between these patches is imperative for effective conservation.
Butterflies interact with their environment in two ways because they are holometabolous insects, with a complete metamorphosis. Thus, their habitat needs must be considered in two ways for conservation, focusing on ample amounts of larval host plants for caterpillars (ranging from wildflowers, grasses, trees, and vines) as well as nectar plants as adults (i.e., milkweed, thistles). Policy makers and land managers must understand the interactions these butterflies have with available plants to diagnose the direct cause of the butterfly decline. Is a lack of host plants the limiting factor? Is it the nectar plants? Is it genetic isolation from isolated patches?
A previous case study in the National Guard training center, Fort Indiantown Gap, has diagnosed one rare native butterfly’s decline as a product of a decline in available nectar plants (Swartz et al. 2015), however replicant studies must be done elsewhere to assess if this is the case elsewhere and for other species.
Northeastern butterflies exist in a fragile space. The grasslands they live in require frequent disturbance to prevent the growth of a deciduous forest due to the high amount of rainfall we receive in the Pennsylvania area. Therefore, optimal butterfly habitat exists in the middle of secondary ecological succession, a state referred to as a sere (Latham et al. 2007). Historically, this state was kept stable by the now extinct buffalo population (or “iron bison”), trampling and rolling over larger flora, maintaining an open space of wildflowers and grasses (Ferster and Vulinec. 2009).
The Gettysburg National Military Park (GNMP) provides an excellent opportunity to study the make-up of these vulnerable habitat patches, with several long-maintained wet meadows and old successional fields (dating back to the early 1800s) at a larger size than seen elsewhere in the Gettysburg area. Creating inventories and long term surveying of plants and butterflies can answer our core research questions: How do butterflies interact with the plants around them? How can we use our information in the conservation of northeastern grassland butterflies?
(Butter) Fly Me to the Moon: About Our Field Surveys
Once a week, we conduct field surveys of butterfly and flowering plant species across six field sites in the Gettysburg regional area. We hope that through our surveys, we will better understand how butterflies use nectar resources throughout the year, and if this relationship is changing over time (phenology). In order to monitor these trends, we follow specified criteria which are dependent on the weather. These conditions include:
- Temperatures between 68 and 98 Fahrenheit degrees
- Between 9AM and 2PM
- Wind Speed less than 10mph
- Cloud Cover less than 50%
These criteria are inspired by techniques from Ferster and Vulinec (2009) as well as Harker and Shreeve (2008), and altered to fit field conditions of the national park and surrounding areas.
With a modified Pollard walk technique (Pollard 1977), we follow the same paths each week and record which species of butterflies and plants we observe (GIS figure). Each member of the lab has a specialized job in order to ensure the data collection process runs smoothly. Jamie walks towards the front of the group, and scans the area for any butterfly observations. We try and take a photo of every butterfly species we see to cross reference identifications (photos). To do so, we use two websites: iNaturalist.com a citizen science database, and butterfliesandmoths.org where observations are verified by lepidopterists (butterfly experts). Zach walks alongside Jamie as a second pair of eyes to make sure that she doesn’t miss any (which can happen from time to time since some butterflies, such as low flying grass skippers, can be so small!).
Gabe and Dr. Ferster are the designated botanists of the group, and are able to identify flowering plant species through their acquired knowledge, supplemented occasionally by conforming species in the lab using our “Plants of Pennsylvania Guide”. In our plant surveys, we look at flowering plants which may contribute to the nectar resource pool. We identify every flowering plant by species and record where it was found. This information helps us understand nectar resource diversity and it allows us to understand the relationship between nectar resource presence and diversity to butterfly abundance and diversity over time. Our plant data also serves as a phenological record or life cycle of the plants in Gettysburg.
We’re about to take you through an island getaway, and not necessarily an island off the coast, but biogeographical islands we have designated in order to compare biodiversity.
Our six field sites: Sherfy Garden, The Wheatfield, New Jersey Brigade, Adams County Agricultural Center, The Painted Turtle Farm, and our own curated Pollinator Garden vary in both land management as well as other site characteristics such as size and age.
All of our survey sites are uniquely different, from the management practices that go into maintaining the sites or the geography and features of each site such as presence of highways and proximity to other nectar resources. All of these factors affect the ability of butterflies to spread as well as their survival rates, both aspects of the ecology which we are interested in understanding. We have put sites into three categories depending on how survey sites are maintained: minimally managed sites, human maintained food gardens, and pollinator gardens. We used this information to better understand the differences and similarities of sites that are alike in terms of management and to understand how management affects biodiversity.
In order to understand how our sites are related to each other we use Geographical Information Systems (GIS) to see how islands are related in space. This will help us understand the movement of butterflies between our resource (nectar and larval host plant) “islands” (survey sites) by allowing us to visualize the habitat patches between sites.
We encourage you to download iNaturalist on your phone so you can help us contribute to our data collection! Due to the limitations of our surveys, we may miss species sightings. We have created an iNaturalist project page that selects observations that fall inside the national park or college boundary so we can see butterfly species that citizen-scientists upload! Although we don’t factor these observations into our biodiversity calculations, we track where species sightings have occurred in order to make comparisons of the habitat where butterflies may occupy. Please view our iNaturalist page via this link!
Every Rose has its Thorns: Results
We have used our 2021 field data to calculate butterfly diversity via three diversity metrics as well as a calculation to determine butterfly species evenness. If you’re curious how to interpret each of these indices, we have assembled an equation table for your convenience!
We hypothesize that butterfly diversity will be greater in the old maintained grasslands of Gettysburg National Military Park (GNMP) when compared with cultivated gardens. Although man-made gardens may have a higher species richness, the abundance of the nectar plants in these man-made gardens is significantly lower than in natural areas of the battlefield. For example, we found 174 stems of common milkweed at Sherfy Garden and 1,343 stems at our New Jersey Brigade field site. From an island biogeography perspective, the chance that a butterfly will find a smaller habitat island farther away from the mainland is small. The largest and the oldest of our field sites, the Wheatfield and the New Jersey Brigade, had the highest butterfly diversity in 2021 as predicted. We are curious to determine why Sherfy Garden has the lowest diversity, given that it is older than our other garden sites, and its distance to the “mainland” sites (the Wheatfield and New Jersey brigade) is relatively small.
We did not find a significant difference in butterfly diversity among sites by category of our field sites; maintained Grassland (Battlefield Sites), Food Gardens (PTF and Sherfy garden), and Pollinator Gardens (pollinator garden and Agriculture center). We performed two distinct ANOVA tests to evaluate if site classification has an effect on butterfly species evenness (F=2.18, df=2, p=0.26) and diversity: Shannon-Wiener (F=3.87, df=2., p=0.15). We fail to reject the null hypothesis that species diversity and evenness differs among site classifications. However, the trends we see indicate still are beneficial in comparing the species composition of our “islands”.
We began surveying these fields in 2020 and found no significant difference between diversity between 2020 and 2021. We plan to conduct these same analyses at the conclusion of our 2022 field season.
Understanding the plant diversity in our sites can help characterize our surveyed areas, to begin looking for differences which may explain butterfly diversity and abundance. The data collected from our plant surveys helps us understand the proportion of native and exotic flowering plant species plant resources and the number of unique plant species per site.
In both 2020 and 2021, the Wheatfield had the highest percentage of native plant species, yet the lowest number of unique species, followed by the New Jersey Brigade and the Pollinator Garden. These sites contrasted with the Adams County Agricultural and Natural Resource Center Garden and Sherfy Garden, which both had a low percentage of native species, but a high number of unique species.
I Heard it Through the Grapevine: Our Pollinator Garden
Using our survey data and the butterfly literature, our lab is constructing and maintaining a pollinator garden on campus, located next to the Painted Turtle Farm. We spend most mornings maintaining this plot when we aren’t conducting our field surveys. Planting began in April of 2021, when the plot looked open and empty.
We emphasize a diversity of native host and nectar plants, following pollinator garden recommendations by the Penn State Master Gardener program and the Xerxes society. This literature stresses having a high diversity of larval host and nectar plants to ensure that there is no period during the spring or summer where flowering nectar plants are not available. However, these butterfly garden recommendations don’t address resource abundance. Adopting a scientific model, our aim with this garden is to have a greater abundance of important plants than other pollinator gardens we survey for comparison. Using other gardens as a control (Adam’s County Agricultural and Natural Resource Center Garden and Sherfy Garden), we predict that having a higher abundance of important native plants, primarily milkweeds and thistles, will attract a greater abundance and diversity of butterflies.
Looking at our pollinator garden through the lens of theory of island biogeography, our “island” of butterfly habitat should accrue a higher diversity over time, thus it is early to see significant differences between monitored gardens to support our hypothesis. Despite this expected lag period, the Gettysburg Pollinator Garden has optimistically shown a slightly higher diversity than our two control gardens (Figure). Shown below are some of the species we’ve observed:
The process of succession from the starting monocultural field has had radiating ecosystem effects, benefiting more than just pollinators. Observing plant colonization post disturbance in the garden hints at the process of succession. Invasives, such as teasel and canada thistle, have proliferated, however, native milkweeds and blue vervain have also proliferated. Ground nesting birds have settled between patches of blue vervain which may act as protection from predators, while feeding on caterpillars which thrive in such areas. Additionally, painted turtles have laid eggs within the garden due to its proximity to Quarry Pond.
Although early on in our long-term surveying, our pollinator garden has shown more than just promise. High densities of important nectar plants within our garden have attracted a higher diversity of butterflies in a shorter time than other pollinator gardens in the same area, and we predict that these numbers will increase with time. Using the same principles, we have been growing seedlings in the greenhouse to be planted in Gettysburg professors’ and faculties’ backyards, increasing butterfly habitat even more. Combatting butterfly biodiversity loss will take more than just one garden, and using the observations we have made about what works well in our garden will inform us about what constitutes good butterfly habitat, allowing the widespread planting of pollinator plants in backyards.
Thank you for reading! Enjoy this sweet video.
Ferster, B. & Vulinec, K.(2008). Population size and conservation of the last eastern remnants of the regal fritillary, Speyeria idalia (Drury) [Lepidoptera, Nymphalidae]; implications for temperate grassland restoration. J Insect Conserv. DOI: 10.1007/s10841-009-9222-5.
Harker, R. & Shreeve, T. (2008) How accurate are single site transect data for monitoring butterfly trends? Spatial and temporal issues identified in monitoring Lasiommata megera. J Insect Conserv.DOI: 10.1007/s10841-007-9068-7
Latham, R.E., Zercher, D., McElhenny, P., Mooreside, P., Ferster, B. (2007). The role of disturbance in habitat restoration and management for the Eastern regal fritillary (Speyeria idalia idalia) at a military installation in Pennsylvania. Ecological Restoration. 25:2. 103-111.
Pollard, E. (1977). A method for assessing changes in the abundance of butterflies. Biological Conservation. 12(2). 115-135. https://doi.org/10.1016/0006-3207(77)90065-9
Swartz, M.T, Ferster, B., Vulinec, B., Paulson, G. (2015). Measuring Regal Fritillary Butterfly (Speyeria idalia) Habitat Requirements in South-Central Pennsylvania: Implications for the Conservation of an Imperiled Butterfly. Northeastern Naturalist. 22(4). 812-829.