– by Adolphe O. Debrot, Hannah Madden, Leontine E. Becking, Anna Rojer and Jacqueline. Y. Miller
Butterfly biogeography remains an interesting and active area of study, not only because the Caribbean fauna is relatively well-documented but also because the West Indies present an area with a complex biogeographic past as well as a rich gamut of ongoing ecological processes such as isolation, immigration, differentiation, speciation, and extinction that will continue to shape the biodiversity of the region for times to come.
For five years Hannah Madden, park ranger of STENAPA, monitored the common butterflies of St. Eustatius annually during the months of January-April in four distinct habitats. Her last collection took place early 2013. All her data are now being combined with earlier collection data by Dr. Miller and Anna Rojer for St. Eustatius, Saba and St. Maarten to provide an update and full assessment of the butterflies of the three Dutch islands.
The findings are proving to be very interesting. First of all, the four different habitats on St. Eustatius proved to have markedly different butterfly faunas. These differences are consistent with what is generally known about the habitat requirements of the various species. For instance, The Quill showed notably highest representation of both nymphalids and heliconiids than the drier and windier habitats of The Mountains and the coastal northeast flanks of the Quill. Lycaenids were notably absent inside the Quill crater while hesperids were more or less equally successful in all four contrasting habitats. Pierids were also well-represented in all habitats but tended to be more abundant in the lower dryer and windier habitats of The Mountains and the lower coastal northeast flank of the Quill.
The same contrasts also hold for individual species. For instance, Anaea minor was a species notably most strongly associated with the Quill. Densities in The Mountains area and in the still and humid Quill crater were a factor of four or more lower. Both Biblis hyperia (see picture left) and Heliconius charitonia were especially concentrated in the most wind-sheltered areas of the Quill, while Ephriades arcas was a hesperiid that was most important inside the Quill crater. New species records for Statia were also documented. These include Hypolimnas missipus and Papilio demoleus. Hypolimnas missipus occurs primarily in the Mountains area and was most seen on Gilboa and Signal Hill. The males are easier to spot than the females, though a female was also seen once on Gilboa Hill. Papilio demoleus is a recently introduced exotic species and was only found in the Lower Town area of the St. Eustatius port, with larvae on the limeberry, Triphasia trifolia. This plant of tropical southeast Asia has been introduced in tropical regions around the world for its edible berries. Papilio demoleus is relatively new to the Caribbean, but is gradually spreading. It is a known pest of citrus crops. The species may have come along to the region with imported crop plants. Island endemics are often vulnerable and rare. However, in November 2012 Debrot found the Lesser Antillean endemic butterfly Wallengrenia ophites (see picture below)to be abundant in the coastal areas of Venus Bay, Statia. Such abundance provides excellent opportunities to study the ecology of this poorly-known island endemic.
The butterfly species lists for St. Eustatius, Saba and St. Maarten now amount to 30, 28 and 25 species respectively. The total number of species documented for the three islands is: 39. This compares to a total of 61 species for all Leeward islands combined. Of the latter four are endemic species, nine endemic subspecies and one endemic genus. Three of the four lesser Antillean endemics are represented in the three Dutch Caribbean islands. Cluster analysis shows that the faunas of Saba and St. Eustatius cluster more closely with that of Nevis while the fauna of St. Maarten shares greatest similarity to the fauna of Anguilla, St. Barts and Barbuda.
The authors soon expect to submit the full study to a scientific journal for formal publication.
– by Hannah Madden (STENAPA Park Ranger)
Biological diversity has become a key issue in today’s world as people become more aware of the potential consequences of our actions and the intricate ways in which humanity is linked with nature. This has led scientists in many areas to begin a series of diversity inventories. These studies usually document the distribution and relative abundance of a small group of bio-indicator species, with the assumption that the results extrapolate to overall biodiversity.
Butterflies provide good indicator species for several reasons. For one, butterflies, in both the larval and adult stages, tend to have adapted to feed on only a few plant families, thus tightly joining butterfly and plant diversity. For researchers, butterflies are also relatively easy to spot, catch and identify, so that even an amateur naturalist can make initial observations. Finally, because butterflies are so beautiful and eye-catching, they are frequent research subjects, which means that historically, more is known about butterfly diversity, identification, and life history habits than is known about most other insects.
In 2009, former Botanical Garden intern Janet van Zoeren chose to do her personal project on butterflies. Her initial goal was to identify which species of butterflies are found on Statia and to create a distribution map showing where the different species are likely to be found. At the time, little formal information had been produced about the butterfly species of Statia or their distribution.
Janet established the monitoring protocols, which still remain in place today to ensure consistency. They consist of transects that sample eight locations in the Quill, two in the northern hills, and two locations in low-elevation, disturbed habitats. Each site is sampled at least three times, between January and April. While walking along the transect line, the observer identifies all butterfly species, which are noted down on a data sheet by the field assistant. Any butterflies that are not recognisable on sight are caught and identified in the net, or, if still unknown, are photographed or collected in order to be identified by a professional entomologist. Butterfly counts take between one and three hours at each site and additional criteria, such as date, start and end times, temperature, windspeed and cloud cover are noted at the start of each sub-section of every transect.
STENAPA’s National Park Ranger Hannah Madden continued the annual butterfly monitoring Janet set up in order to build a picture of the overall trends of the species. To date, STENAPA has five years’ worth of butterfly data, which was recently included in the Dutch Caribbean Biodiversity database and sent to IMARES for support with analysis. The full results of this analysis will be published shortly (see article within “Butterflies of St. Eustatius, Saba and St. Maarten”). In order to relieve an already heavy workload, STENAPA will reduce its butterfly monitoring to once every three years. The next surveys will take place in 2016.