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Diversidad de colepteros en un gradiente altitudinal en Monteverde, Puntarenas, Costa Rica
Coleopteran diversity on an elevational gradient in Monteverde, Puntarenas, Costa Rica
Most insect diversity decreases with increased altitude. However, little is known about how coleopteran (beetle) diversity changes with respect to altitude in tropical habitats (Hanski and Cambefort 1991).
Coleopterans were collected on the property of Estacin Biolgica Monteverde at three site locations at different elevations using pit-fall traps baited with mango, human scat, or soapy water. The number of
individuals and number of species collected were analyzed and divided by morphology into species by comparison with the collection of the Estacin Biolgica. A relationship existed between the abundance of
Coleoptera and the elevation at which they are found. There were no significant differences in species richness at each elevation. Eleven species of coleopterans were predominantly found at one particular
elevation more often than the others.
La mayor parte de la diversidad de insectos disminuye con el aumento en la altitud. Sin embargo, poco se sabe sobre cmo la diversidad de los colepteros (escarabajos) cambia con respecto a la altitud en los hbitats tropicales (Hanski y Cambefort 1991). Se colectaron colepteros en la estacin biolgica Monteverde en tres lugares a diferentes elevaciones usando trampas con mango, excremento humano, o agua jabonosa. El nmero de individuos y de especies colectados fueron analizados y divididos, de acuerdo a su morfologa, en especies con el fin de compararlas con la coleccin de la estacin biolgica. Se encontr una relacin entre la abundancia de colepteros y la elevacin en las cuales se encontraron. No hubo diferencias significativas en la riqueza de las especies en cada elevacin. Once especies de colepteros se encontraron en una elevacin particular ms a menudo que el resto de las especies.
Text in English.
Monteverde Biological Station (Costa Rica)
Diversidad de especies
Estacin Biolgica de Monteverde (Costa Rica)
Tropical Ecology Summer 2005
Ecologia Tropical Verano 2005
t Monteverde Institute : Tropical Ecology
Coleopteran Diversity on an Elevational Gradient in Monteverde, Puntarenas, Costa Rica Colin Weerts College of Biological Sciences, University of Minnesota Twin Cities ABSTRACT Most insect diversity decreases with increased altitude. However, little is known about how coleopteran (beetle) diversity changes with respect to altitude in tropical habitats (Hanski and Cambefort 1991). Coleopterans were collected on the property of Estacin Biolgica Monteverde at three site locations at different elevation s using pit fall traps baited with mango, human scat, or soapy water. The number of individuals and number of species collected were analyzed and divided by morphology into species by comparison with the collection of the Estacin Biolgica. A relationsh ip existed between the abundance of Coleoptera and the elevation at which they are found. There were no significant differences in species richness at each elevation. Eleven species of coleopterans were predominantly found at one particular elevation mor e often than the others. RESUMEN La mayor parte de la diversidad de insectos disminuye con el aumento en altitud. Sin embargo, poco se sabe sobre cmo la diversidad de colepteros (escarabajos) cambia con respecto a la altitud en hbitats tropicales (Ha nski y Cambefort 1991). Se colectaron colepteros en la estacon biolgica Monteverde en tres lugares a diferentes elevaciones usando trampas con mango, excremento humano, o agua jabonosa. El nmero de individuos y de especies colectados fueron analizados y divididos, de acuerdo a su morfologa, en especies con el fin de compararlas con la colecon de la estacon biolgica. Se encontr una relacin entre la abundancia de colepteros y la elevacin en las cuales se encontraron. No hubo diferencias signific ativas en la riqueza de las especies en cada elevacin. Once especies del colepteros se encontraron en una elevacin particular ms a menudo que el resto de las especies. INTRODUCTION Coleopteran diversity is extremely important and can be used as an in dicator for diversity in other plant and animal taxa (Halffter and Arellano 2002). Coleopterans can be found in nearly every environment and there are more than 400,000 species, which represent 25% of all described organisms on Earth (Nadkarni and Wheelwr ight 2000). Costa Rica is home to 110 coleopteran families of the 178 described worldwide; only 28 of the families found in Costa Rica are considered to be common. These 110 families contain 25,800 known species of an estimated 35,000 species in the coun try (Sols 2002), which is an indication of how little is known of the true number and diversity of coleopterans that inhabit the Monteverde area. Coleopterans are also important in terms of their ecological activities as pollinators, herbivores, and as a keystone food source for many higher predators (Sols 2002). Coleopterans found in varying abundance or species richness within an area would likely indicate variation in overall community diversity as well (Paarmann et al 2002).
Life zones are known to change greatly in sharp elevational changes, which could effect ecosystem compositions over short distances (Holdridge 1967). The Monteverde Cloud Forests has a very steep gradient and ecosystems in the area are known to change greatly over small distance s. In general, insect diversity is known to decline as elevation increases, a change that is often linked to decreases in moisture and temperature. This is exemplary of the fact that altitude is the single most important factor determining insect distrib ution (Nadkarni and Wheelwright 2000). Many other possible explanations for changes in diversity, abundance, and species richness exist, such as predation, composition of plant species, or available food sources (Janzen 1983). Searching for the trends tha t affect coleopteran populations now is very important because of the increased extinction rates. It has been hypothesized by Pounds et al (1999), that as global warming trends increase, many species are being found at higher altitudes than before. The M onteverde Cloud Forest is an ideal location to examine the effects of elevational change on population dynamics because of its great coleopteran diversity. This study examined what variations in coleopteran diversity, abundance, and species richness ex isted among three elevations (1355 m, 1465 m, and 1570 m) in the Monteverde Cloud Forest. Species composition at each altitude was also examined to determine whether or not different species exhibit different distributional patterns. It was hypothesized that there would be a decrease in coleopteran diversity, abundance and/or species richness. It was also hypothesized that some coleopteran species would be found more frequently at certain elevations, based on previously reported trends (Nadkarni and Wheel wright 2000). METHODS STUDY AREA This study was conducted on the property of Estacin Biolgica Monteverde in Monteverde, Puntarenas, Costa Rica between the dates of July 21 and July 30, 2005. The three collection sites were located slightly off of th e trails at elevations of 1355 m (at the end of the Catarata Trail), 1465 m (located 350 m along Sendero Principal), and 1570 m (located 785 m along Sendero Principal) (Fig. 1). These sites lie in a high altitude cloud forest which annually receives aroun d 3 m of rainfall and also receives moisture from wind borne mists and cloud cover (Haber et al 2000). Each site was chosen based on similar flora cover and terrain slope in order to compare similar habitats. METHODOLOGY Coleoptera were collected from traps two times, each after a five day period. Collection was done using pit fall traps similar to those described by White (1983). The traps consisted of a 900 g plastic pail with the bottom cut out and replaced with a wire mesh (Fig. 2). Two sizes of wire mesh (both squares, with a diagonal length of 3.5 cm and 1.5 cm) were used in order to capture a wide range of coleopteran species. One trap of the smaller mesh and two traps of the larger mesh were used for both scat and mango baits at each site. These traps allowed the beetles to crawl through the mesh to the bait, but did
not allow them to fly out of the trap because their wings made them too wide to pass through the openings in the mesh. The three sampling areas contained nine traps each, arrang ed in a circular pattern to randomize the collection at each site (Fig 3). The target species belonged to the Scarabaeidae family and are also known as dung beetles. Fruit beetles and species of leaf litter beetle were also considered. The traps were bai ted with either mango, human scat, or soapy water. Mango was chosen as bait to attract frugivorous beetles due to its availability and the fact that it is commonly found throughout Costa Rica. Human scat was chosen to attract dung beetles, based on known effectiveness from a study by Hays (2005). Soapy water was used to catch any beetle that may just happen to fall into the trap by chance. The three types of bait were selected to insure a varied sample of the local coleopteran fauna. The mango traps co ntained six similarly sized cubes of ripe mango each. The dung traps contained a trowel tip of scat in the bottom. The open traps consisted of a plain 900 g plastic pail filled with 4 cm water containing dish soap (Fig. 4). All the traps were buried so the top was level with the ground surface. The individuals were collected into zip lock bags separated by bait type and site location, resulting in a total of nine bags per collection. The coleopterans were separated into morphospecies based on shape, s ize, horn morphology and presence, leg shapes and antennae morphology. After separation, the morphospecies were identified using the beetle collection owned by the Estacon Biolgica as well as using identification plates (Sols 2002). RESULTS A total o f 719 individuals were collected representing 28 different species of Coleoptera. A total of 200 individuals from 21 species were found at the lowest elevation, 248 individuals from 20 species were found at the middle elevation and 271 individuals from 18 species were found at the highest elevation (Appendix 1). Coleopteran abundance was shown to be much greater at higher altitudes than at lower altitudes ( 2 = 10.95, c.v. = 5.99, df = 2). There were no significant differences in species richness among th e three elevations. Both species richness and abundance showed very high correlations in comparison with the different altitudes using linear regressions (Fig. 5) (abundance R 2 = 0.965, species richness R 2 = 0.969). Site overlap in the individual species was found to be fairly similar at all sites and no particular differences were found from one site to another (Sorenson coefficient for the lowest site compared to the middle site was 0.7805; for the middle site compared to the high site it was 0.7368; an d for the low site compared to the high site it was 0.7692). These results suggested that the low and middle sites are the most similar in species overlap and that the middle and high sites were the most different in species composition. Shannon Weiner d iversity indices indicated that the diversity was the highest at significantly diffe rent enough from each other to conclude that elevation had any correlation with species diversity. Chi squared analyses for differences in species presence at each site were calculated for each species found (Table 1). Deltochilum mexicanum and the speci es in
the family Cucujidae (morph A) had significant site differences, suggesting that D. mexicanum can be found much more often at higher elevations and that the species in the family Cucujidae (A) can be found much more often at lower elevations (for D. mexicanum 2 = 54.2, df=2, and for the species in the family Cucujidae (A), 2 =84.5, df=2). Eleven species were found to have significant differences in population at different elevations. DISCUSSION The data showed trends that suggest that the most d iversity among beetles was found at the middle elevations. Trends were also found that show that abundance in the number of individuals increased with altitude, but that the number of species decreased as the elevation increased (Fig. 5). This suggests t hat the original hypothesis was incorrect. A reasonable explanation for this may be that those beetle species found at higher elevations are more adapted to that location and have fewer competing species such as flies and other coprophagous insects. Ther efore, the site could potentially have an increased carrying capacity for those species still present (Hanski and Cambefort 1991). A majority of the beetles in this experiment were of the family Scarabaeidae. The biggest influence on the populations and diversity of Scarabaeidae likely corresponded with the type and amount of dung available; which are directly correlated to the number of mammals present at each altitude. The abundance of mammals sets the level of resource availability to dung beetles (Ha nski and Cambefort 1991). However, dung beetles have also been found to feed on other types of animal dung such as iguana and boa scat (Hanski and Cambefort 1991). This trend could suggest that there are more mammals or at least more dung or dung of high er quality at higher altitudes. The greater abundance at higher altitudes probably deals with specificity of those species present. Some dung beetles are known to prefer fresh dung that has not been contaminated by flies laying their eggs in it. The dec rease of flies as altitude increases likely leads to not necessarily more dung, but higher quality dung. D. mexicanum is a species known to prefer fresh dung. Its high population at greater altitudes can likely be attributed to the increase in their spec ialized food source (Hanski and Cambefort 1991). found at higher elevations and the species found only at lower elevations. Trends like that of species D. mexicanum that w ere shown to be significant (Table 1), indicate that some of the species are found more abundantly at higher altitudes whereas some species, such as the one in the family Cucujidae (A), were found mostly at lower altitudes. The Shannon Weiner diversity in dex did not measure solely the number of individuals and the number of species, but also how evenly they were distributed. The value at which the two trend lines (increase in abundance with altitude and decrease in species with altitude) intersect each ot Overlap is the highest between the lowest and middle elevation which supports this trend. However, because the Shannon Weiner diversity indices for these sites were not significantly di fferent in every case, the data did not have enough coleopteran diversity differences at each site to draw such robust conclusions. In this case, the differences found could be attributed solely to site location. Subtle trends in this study cannot be att ributed to altitudinal differences alone. Interestingly, similar results have been found
in previous studies. A study conducted in the French Alps at altitudes ranging from 1,750 m to 2,960 m in 1985 1987 and using similar baited pit fall traps, found th at species richness decreased as altitude increased. In the same study, abundance of those species still present at higher elevations greatly increased. A similar study on a tropical mountain in Borneo found a similar phenomenon (Hanski and Cambefort 1991 ). Both of these results were attributed to decreased competition for resources with other insects as elevation increased. These studies stated that decreased values in the equitability index (the comparison between the log of abundance and the species r ichness) showed a high degree of dominance by a few species at higher elevations. These studies further suggest that the results of the present study were not just a local phenomenon and that coleopteran populations seem to have similar trends in abundanc e and species richness in montane environments worldwide and not just in tropical wet habitats like that of Monteverde. Future studies should explore the possibility of vertical migrations toward higher elevations similar to those that have been found in N orops lizards and in many birds. Multiple sampling sites at more elevations than the ones considered in this study would add strength to future research. This would contribute in the avoidance of random events that may have occurred at one site, and did n ot truly reflect abundance and species richness for that elevation. ACKNOWLEDGEMENTS Thank you to Nathaniel Talbot for is efforts in identification of many of the coleopterans in this study despite the unbearable foul odor, as well as for his comical a ntics that helped lighten the mood during many stressful hours of researching and writing. Maria Jost for acquiring the many materials for which were needed for collection as well as trap construction and helping tweak my paper towards the direction of pe rfection. Thank you to Lucky and Wilfred Guindon for saving so many ice cream pails over the years and allowing me to use them in the construction of the pit fall traps. Thank you to Carlos Guindon for hauling the ice cream pails undoubtedly through much peril to the station on his motorcycle. Thank you to Javier Mndez for much insight and guidance in the creation of this study and for the supply of many articles related to this project. Thank you to all of my fellow students for their understanding of the fact that the foul odors produced during this project were all for the good of science. Special thank you to Elizabeth Hunter and Gina Rozinka for their valiant efforts in supplying the necessary bait for the traps. Thank you to Kent Melchiors for h is time in helping me finalize my paper. LITERATURE CITED Haber, William A., Willow Zuchowski and Erick Bello. 2000. An Introduction to Cloud Forest Trees Monteverde, Costa Rica 2 ed. Mountain Gem Publications. p. 11 Halffter, G. and Lucrecia Arellan o. 2002. Response of Dung Beetle Diversity to Human induced Changes in a Tropical Landscape. Biotropica 34(1): 144 154. Hanski, I. and Y. Cambefort. 1991. Dung Beetle Ecology Princeton Universit Press, Princeton, NJ. p. 242 254 Hays, Sasha. 2005. D ung and soil type as factors for niche partitioning in dung beetles (Scarabaeidae). CIEE. Monteverde.
Holdridge, L.R. 1967. Life Zone Ecology, revised edition. Tropical Science Center. San Jose, Costa Rica. pp. 17 30. Janzen, D. H., editor. 1983. Costa Rican natural history. Chicago: University of Chicago Press. p. 816 Nadkarni, N. M., and N. R. Wheelwright, editors. 2000. Monteverde: Ecology and conservation of a tropical cloud forest. New York: Oxford University Press. Fig 1.7, p. 95, 106 118 Paarmann, W., B. Gutzmann, P. Stumpe, H. Bolte, S. Kppers, K. Holzkamp, C. Niers, J. Adis, N. Stork, C.R.V. da Fonseca. 2002. The Structure of Ground Beetle Assemblages (Coleoptera: Carabidae) at Fruit Falls of Melastomataceae Trees in a Brazilian Ter ra Firma Rain Forest. Biotropica 34(3): 368 375. Pounds,J. Alan, M. P. L. Fogden, J. H. Campball. 1999, Biological response to climate change on a tropical mountain. Nature Vol 398 p. 611 614 Sampson, Emily. 2005. An Elevational Comparison of Coleopt eran Communities in a Riparian Forest in San Luis, Costa Rica. CIEE. Monteverde. Sols, A. 2002. Escarabajos de Costa Rica. 2 ed. Santo Domingo de Heredia, Costa Rica: Instituto Nacional de Biodiversidad, INBio. White, R. E. 1983. A Field Guide to the B eetles of North America. Boston: Houghton Mifflin Company. p. 23 26. Zar, J.H. 1984. Biostatistical Analysis. Prentice Hall, Englewood Cliffs, New Jersey. p. 146 147, 484 485