Frequency and Distribution of Fruit-Feeding Butterflies in a Costa Rican Cloud Forest: from Grazeland to Primary Forest
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Frequency and Distribution of Fruit-Feeding Butterflies in a Costa Rican Cloud Forest: From Grazeland to Primary Forest Gabrielle C. Duong & Ashley J. Junger Abstract To determine whether the frequency and distribution of fruit-feeding Nymphalid butterflies change through a habitat’s succession from pasture land to primary forest, as well as to determine whether Cloudbridge’s reforestation efforts were expediting the growth of primary forest butterfly populations, a community of fruit-feeding Nymphalid butterflies was sampled daily for 6 weeks by trapping 174 individuals of 27 species in the understory of four habitat types: primary forest, natural secondary regrowth forest, planted secondary regrowth forest, and pastureland. We found the whole study area had a species evenness of 0.5, and a Simpson’s Index of Diversity of 0.88. Planted regrowth had the highest species richness (20), diversity index (0.9), and a relatively high evenness (0.58). Therefore, of the successional habitat types studied, planted regrowth is the most diverse and rich, indicating that the process of planting climax species in secondary forests improves community diversity and richness. This increase in community diversity and richness may lead to higher diversity and richness in the climax community. We also conclude that a large number of species are being found out of their natural elevation range, which could indicate that butterflies in this area are experiencing the effects of climate change. Key words: nymphalidae, butterfly, species abundance distribution, species richness, environmental monitoring, habitat disturbance, tropical, conservation. INTRODUCTION Natural habitats in the tropics continue habitats, and sensitivity to microclimate to be globally threatened by habitat loss and heterogeneity and disturbance (New, 1997; climate change, leading to the massive loss of DeVries et al., 1997). Butterflies are the best- species. Remediation efforts are being known group of insects (DeVries et al., 1997), undertaken globally in an effort to reduce and giving them great potential to provide reverse the effects of habitat loss and climate understanding of insect diversity and change. In order to focus these efforts and to conservation. The study of fruit feeding determine their effects on biological diversity, butterflies has additional advantages, reliable monitoring programs that assess including their ability to be vigorously changes in biodiversity and ecosystem sampled with the use of fruit-baited traps. function are needed. The choice of organism Therefore, fruit-feeding butterflies provide a investigated is crucial to this process due to standard means for comparing species overall lack of funds and available expertise. diversity within and among tropical insect Trapping butterflies is often the communities (DeVries et al., 2012). method of choice in tropical forests (Aduse- Bait trapping is an inherently biased Poku et al., 2012). Advantages of using method for assessing butterfly fauna. Issues butterflies (Lepidoptera) as a target species include: some butterflies are never captured in include: their relatively large size, colorful traps, and some butterflies are more strongly appearance, relative ease of identification to attracted than others, thus relative abundances species level, their presence in all terrestrial captured do not necessarily reflect the relative Duong and Junger, 2015 1 abundances of fruit feeding species in the industry, and both legal and illegal timbering region (Hughes et al., 1998). Despite these (Borges-Méndez, 2008). During this period drawbacks, bait trapping provides the most the national area covered with forests dropped effective and efficient method for monitoring from about 70% to about 10% (United States changes in species abundances, and measuring Agency for International Development diversity of tropical butterfly communities. [USAID], 1996). In fact, between 1950 and Reforestation is an essential step in 1994, the pace of deforestation in Costa Rica restoring forest health. Monitoring and was one of the fastest in the western assessment of the effects of reforestation on hemisphere, with a decrease of 40,000-50,000 communities within remediated areas is hectares annually (Watson et al., 1998; essential to gaining an understanding of its Borges-Méndez, 2008). Given this rapid and short- and long-term effects. Few studies drastic loss of forested areas throughout the investigate the changes in species abundance country, reforestation programs will be and diversity through various levels of essential to restoring the country’s former succession in tropical forests. Most studies in biodiversity. this area focus on the differences between Costa Rican forests have sufficiently disturbed and undisturbed habitats. Disturbed diverse fruit-feeding butterfly fauna to warrant habitats have been found to have higher their use as target organisms for monitoring species richness and more unique species changes in biodiversity. There are (DeVries et al., 1997). Additionally, vertical approximately 543 butterfly species present in stratification is reduced in disturbed forests, Costa Rica (DeVries, 1987). Of these, at least trapping canopy species in the understory, 40% feed exclusively upon rotting fruits as leading to overestimates of species richness in adults (DeVries, 1987). understory trapping in disturbed areas The aim of this study is to quantify the (DeVries & Walla, 2001; Fermon et al., 2005; differences in diversity and abundance of Aduse-Poku et al., 2012). Rapid monitoring fruit-feeding butterflies within habitats at programs will allow assessments of the different stages of succession. We performed changes in diversity and abundance within a butterfly trapping study on the Cloudbridge different stages of succession, allowing for Nature reserve in Costa Rica during the onset more effective and focused remediation of the rainy season, studying four habitat types efforts. (grazeland, natural regrowth, planted Between the 1940s and 1980s regrowth, and primary forest). In each of these deforestation in Costa Rica was caused by habitat types three traps were established in government-sponsored land colonization the understory. schemes, expansion of the agricultural frontier, cattle ranching to support the beef MATERIALS AND METHODS Study Site over a million hectares spanning northern This research was conducted at the Costa Rica and southern Panama. Together Chirripó Cloudbridge Nature Reserve, San with the adjoining La Amistad International Isidro de General, south central Costa Rica. Park, Chirripó National Park is comprised of Located in a cloud forest on one of the tallest the largest unspoiled forest in the country. mountains of Central America, Cloudbridge is Cloudbridge started off as privately a 700 acre nature reserve on the northern end owned land in 2002, owned by Ian Giddy and of one of the most important biological zones Genevieve (Jenny) Giddy, who made the first of all Central America, and lies within a of many subsequent purchases of cattle farms designated “biological hot spot” on the Meso- bordering the Chirripó National Park to American Biological Corridor. Cloudbridge is impede the appalling denuding and erosive part of an area of forested land that includes effects that cattle grazing has had on the land. Duong and Junger, 2015 2 Since then, their reserve has grown to We chose to place our traps along the encompass 700 acres of reclaimed pasture natural regrowth areas of the River Trail. Trap land and is used to re-build a corridor where 1 was located near the bench by the river, and deforestation has left a gap between the large next to a very small, narrow stream that Chirripó National Park, and the smaller nature crossed over the trail. Traps 2 and 3 along the reserve of 4,000 acres on the other side of the River Trail were farther from the river and did river. Our study was conducted within a not have any streams of water flowing past contiguous patch of the Cloudbridge reserve them. Trap 2 was placed in an open pocket of that formed a disturbance gradient composed forest under a tree surrounded by plants that of 3 contiguous habitat types: primary forest, produced fruit. Trap 3 was placed in a more natural secondary regrowth forest, and planted open section of forest under a tree; no fruit- secondary regrowth forest, as well as the growing species were observed. pasture of a nearby cow farm. Planted Regrowth Forest Trap Sites A Planted regrowth, or secondary, Each habitat type was fitted with 3 forest is defined here as one that, in addition to butterfly traps, whose locations were selected having naturally regrown after a major based on elevation, walking distance, and disturbance, is replenished through accessibility (Appendix B). In steeper hiking reforestation efforts. During reforestation, areas, such as in the primary forest (PF) and climax species are manually planted to planted regrowth (PR) forest, traps were facilitate the transition of a secondary forest spaced, on average, 117 meters apart in into what more closely resembles a primary elevation. In flatter and lower areas, such as forest. on the grazeland (GL) and along the natural We chose to place our traps along the regrowth (NR) forest, traps were spaced, on planted regrowth areas of the El Jilguero Trail. average, 14 meters apart in elevation. All Grazeland latitude, longitude, and elevation A grazeland is a grassy field suitable measurements were taken using GIS with an for grazing by livestock. In our study,