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Respuesta del escarabajo coprfago en relacin a la ubicacin del estircol
Dung beetle response in relationship to manure location
Dung beetle ecology is an integral part of nutrient cycling within ecosystems around the world. Farms benefit from the decomposer action of dung beetles from the nutrients imputed into the soil and the breakdown of
helminthes parasites. This study analyzed the effects of varying dung location within pastures on dung beetle response. It was hypothesized that cow manure closer to forest edges would elicit a greater response than manure located further away. Also, manure located near an edge would elicit a greater beetle response overall when compared to manure in the middle of the pasture. Three pastures located in San Luis, Monteverde, Costa Rica were analyzed for beetle response. Two grid plots containing 30 2 X 2 meter squares were set up in each pasture, a corner plot and a middle plot, with eight-ounces of cow manure sample placed in each 2 X 2 square. An additional plot was set up in the forest. Using a simple linear regression it was found that the number of beetles did not correlate with distance from the forest. There were significantly less beetles located in 6-meters to 8-meters (ANOVA, p=0.005) and at 10-meters to 12-meters (ANOVA, p=0.004) groupings from the forest edge than in the woods. There were also significantly more beetles in the corner plots than in the middle plots (ANOVA, p = 0.0002). From these results, farms may be able to increase the amounts of beetles on their farms utilizing smaller fields with increased bordering forest, aiding in nutrient cycling and reduction of helminthes health risks.
La ecologa de escarabajos coprfagos es una parte importante del ciclo de nutrientes en los ecosistemas del mundo. Las fincas se benefician de la accin de los escarabajos de descomponer porque hay ms nutrientes que estn entrando al suelo y por la destruccin de los parsitos helmintos. Esta investigacin analiz los efectos en la respuesta de los escarabajos al cambiar la ubicacin de boiga de las vacas en los campos. Se hipotiz que la boiga ms cerca del borde del bosque provocara una mayor repuesta de los escarabajos que la boiga ubicada ms lejos. Tambin, la boiga localizada cerca de un borde provocara una mayor respuesta de los abejones en general en comparacin con la boiga ubicada en medio del potrero. Tres potreros localizados en San Luis, Monteverde, Costa Rica fueron estudiados para ver la respuesta de los escarabajos. Dos cuadrculas con 30 cuadrados de 2 X 2 metros se prepararon en cada potrero, en la parcela a la par del borde y en parcelas en el centro con ocho onzas de boiga ubicadas en cada cuadrado de 2 X 2 metros. Se prepar una parcela adicional en el bosque. Por medio de una regresin simple linear se mostr que el nmero de los escarabajos no se correlacionan con la distancia del bosque. Hubo menos escarabajos significativamente en las distancias de 6-metros a 8-metros (ANOVA, p = 0.005) y de 10-metros a 12-metros (ANOVA, p = 0.004) del borde del bosque que en el bosque. Hubo ms escarabajos significativamente en las cuadrculas al lado del bosque que en el centro de los potreros (ANOVA, p = 0.0002). A partir de estos resultados, es posible que las fincas puedan aumentar los nmeros de escarabajos usando potreros ms pequeos con mayor borde hacia el bosque, ayudando con el ciclo de nutrientes y la reduccin de parsitos helmintos que arriesgan la salud.
Text in English.
Costa Rica--Puntarenas--Monteverde Zone--San Luis
Costa Rica--Puntarenas--Zona de Monteverde--San Luis
Tropical Ecology Summer 2004
Ecologa Tropical Verano 2004
t Monteverde Institute : Tropical Ecology
1 Dung beetle response in relationship to manure location Margaret Quinn Department of Biology, University of Wisconsin Madison ABSTRACT Dung beetle ecology is an integral part of nutrient cycling within ecosystems around the world. Farms benefit f rom the decomposer action of dung beetles from the nutrients imputed into the soil and the breakdown of helminthes parasites. This study analyzed the effects of varying dung location within pastures on dung beetle response. It was hypothesized that cow man ure closer to forest edges would elicit a greater response than manure located further away. Also, manure located near an edge would elicit a greater beetle response overall when compared to manure in the middle of the pasture. Three pastures located in San Luis, Monteverde, Costa Rica were analyzed for beetle response. Two grid plots containing 30 2 X 2 meter squares were set up in each pasture, a corner plot and a middle plot, with eight ounces of cow manure sample placed in each 2 X 2 square. An addit ional plot was set up in the forest. Using a simple linear regression it was found that the number of beetles did not correlate with distance from the forest. There were significantly less beetles located in 6 meters to 8 meters (ANOVA, p=0.005) and at 10 meters to 12 meters (ANOVA, p=0.004) groupings from the forest edge than in the woods. There were also significantly more beetles in the corner plots than in the middle plots (ANOVA, p = 0.0002). From these results, farms may be able to increase the am ounts of beetles on their farms utilizing smaller fields with increased bordering forest, aiding in nutrient cycling and reduction of helminthes health risks. RESUMEN La ecologÃa de escarabajos coprÃ³fagos es una parte importante del ciclo de nutrimentos en los ecosistemas del mundo. Las fincas se benefician de la acciÃ³n de descomponer de los escarabajos porque hay mÃ¡s nutrimentos que estÃ¡n entrando al suelo y por la destrucciÃ³n de parÃ¡sitos helmintos. Esta investigaciÃ³n analizÃ³ los efectos en la respue sta de los escarabajos al cambiar la ubicaciÃ³n de boÃ±iga de vacas en los campos. Se hipotizÃ³ que la boÃ±iga mÃ¡s cerca del borde del bosque provocarÃa una mayor repuesta de los escarabajos que boÃ±iga ubicada mÃ¡s legos. TambiÃ©n, la boÃ±iga localizada cerca de un borde provocarÃa una mayor respuesta de los abejones en general en comparaciÃ³n con boÃ±iga ubicada en medio del potrero. Tres potreros localizadas en San Luis, Monteverde, Costa Rica fueron estudiados para ver la respuesta de los escarabajos. Dos cuad rÃculas con 30 cuadrades de 2 X 2 metros se prepararon en cada potrero, en la parcela a la par del borde y en parcelas en el centro con ocho onzas de boÃ±iga ubicadas en cada cuadrado de 2 X 2 metros. Se preparÃ³ una parcela adicional en el bosque. Por med io de una regresiÃ³n simple linear se mostrÃ³ que el nÃºmero de los escarabajos no se corelacionan con la distancia del bosque. Hubo menos escarabajos significativamente en los distancias de 6 metros a 8 metros (ANOVA, p = 0.005) y de 10 metros a 12 metros ( ANOVA, p = 0.004) del borde del bosque que en el bosque. Hubo mÃ¡s escarabajos significativamente en las cuadrÃculas al lado del bosque que en el centro de los potreros (ANOVA, p = 0.0002). A partir estos resultados, es posible que las fincas puedan aumen tar los nÃºmeros de escarabajos usando potreros mÃ¡s pequeÃ±os con mayor borde hacia el bosque, ayudando con el ciclo de nutrimentos y reducciÃ³n de parÃ¡sitos helmintos que arriesgan la salud. INTRODUCTION Dung beetle ecology is an integral part of ecosystem s around the world (Forsyth and Miyata 1984, Hanski and Cambefort 1991). In tropical ecosystems dung is a vital component to the nutrient cycle, quickly broken down by dung beetles and other insects that release nutrients
2 into the ecosystem (Dymock 1984, Hanski and Cambefort 1991). High temperature and humidity in the tropics also aid in rapid breakdown of dung, putting pressure on beetles to successfully find resources as quickly as possible. Colder temperatures in tropical montane systems cause dung to decompose less quickly; therefore, at higher altitudes dung beetles and other insects are the primary agents of decomposition (Janzen 1983). When a tropical ecosystem is disturbed by agriculture, the dung in the artificial ecosystem may not undergo the sa me breakdown, especially at higher altitudes. The cycling of nutrients from dung may help to sustain more productive pasturelands and curb the struggle that tropical farms face with high nutrient leaching after deforestation. Unfortunately, it has been found that deforestation may cause many dung beetle species to become extinct (Howden and Nealis 1975). Studies have found that when comparing continuous forest to pastures, dung beetle numbers and species richness are lower in the pastures (Estrada et a l. 1998, Roslin and Koivunen 2001). In fact, dung beetles have been found to serve as indicators of the degree of forest destruction (Halffter and Arellano 2002). Dung beetles are also beneficial to farmers because they combat the slow decay of manure that increases health risks to the livestock as they graze on soiled grass (Dymock 1993). The decomposer action of the beetles helps to clear the manure from the area and thus decreases contamination by compounds found in feces, as well as reducing fly and hel minthes related animal health problems (Dymock 1993). This potential transmission of parasites, particularly helminthes, could also infect man and other animals, including those in the natural ecosystem (Howden and Nealis 1975). To combat low nutrient c ontent in soils and health risks related to slow dung decomposition farmers may find ways to increase beetle numbers in their pastures by incorporating more forest and trees in their field. In order to assess dung beetle presence in pastures this study ex amined the level of dung beetle response to pasture manure located at different distances from forest edge. It was hypothesized that cow manure located closer to forest would have a greater beetle response than manure located further away from the forest , and that manure located in an corner plot would have a greater beetle response overall when compared to manure in the middle of a pasture plot. METHODS Three pastures located in San Luis Altos, Puntarenas, Costa Rica, near la trocha were selected for th is study. Criteria for selection included presence of cow manure and two sides of the field being bordered by forest. Two 3 X 10 meter grids were placed within each pasture: a middle plot location and a corner plot location placed 6 to 10 meters from th e edge of the forest (Figure 1). Each grid contained 30 2 X 2 meter squares; one eight ounce cow manure sample was placed in each square. Fresh cow manure used for samples was found at local dairy barns, and was examined to ensure that dung beetles were n ot already present. In addition 2 X 2 meter square plots were also prepared in the neighboring forest. All plots were examined three hours after set up and the number of beetles present in each grid square was recorded. Weather conditions were also not ed. Simple linear regressions were used to assess beetle response in relation to each bait distance from the forest edge in the middle plot location. Plot distances were clustered into
3 five groups (2 meter and 4 meter (n=18), 6 meter and 8 meter (n=18), 1 0 meter and 12 meter (n=18), 14 meter and 16 meter (n=18), and 18 meter and 20 meters (n=18)) so equal numbers of beetles would be compared between forest and pasture. The number of beetles present in each group was compared to the number of beetles in the wood plots (n=18) using a one way beetles found in particular plot groups. Differences in numbers of dung beetles recorded between corner and middle plots were also ev aluated using a one way ANOVA. RESULTS Pastures in San Luis were heterogeneous habitats with various grasses, clovers, and small shrubs. Cow manure drew a rapid response of a single dung beetle species, Onthophagus spp , subfamily Scarabaeinae. Beetle r esponse was not correlated with dung distance from forest edge (Simple linear regression, n=90). Mean beetle numbers in the middle pasture plot was found to be show ed significantly more beetles in the wood plot than both the 6 meter and 8 meter groups (p = 0.005) and the 10 meter to 12 meter groups (p = 0.004) (Figure 2). Beetle numbers did not vary significantly between forest and corner plots, but corner plots had significantly more beetles than middle plots (ANOVA, p = 0.0002) (Figure 3). DISCUSSION This study analyzed the effects of dung location in pastures on the degree of dung beetle response. It was hypothesized that there would be less dung beetles furt her from the forest edge in pastures bordering the forest. Contrary to the hypothesis, there was not a correlation between number of beetles and distance from forest edges. In the tropical rain forests, beetles are not adapted for pastures and therefore any dung beetles found in pastures theoretically originally came from the forest (Halffter and Arellano 2002, Hanski and Cambefort 1991). It was expected that there would be a greater density of beetles closer to the forest because less distance would ha ve to be traveled to find dung. It was also expected that there would be a lower density of beetles towards the middle of the field. Since there was no correlation between distance and response, the Onthophagus beetle may be semi adapted to pasture habit ats. However, further study would be needed to confirm this. When compared to the numbers of beetles in the forest, the pasture had significantly decreased levels of beetles in the 6 meter and 8 meter, and 10 meter and 12 meter groups. The variation o f beetles present between fields was great and may have lead to this significant finding. One field had very few beetles present compared to the other two fields, which may be attributed to cooler, windier weather on that particular sample day. Sasayama et al. (1984), found that beetle numbers decreased with increased wind speeds, which may explain why there was such variation in beetle response between sample days. While taking into account the lack of beetles in this field the significant dip between 6 meters and 12 meters resulted from only the other two fields, which may be due to chance and is not representative of pastures in
4 general. The overall trend in pastures was that manure further from the forest did not attract significantly less beetles, contradictory to past literature. There was no difference in the number of beetles in the corner plots and in the forest, showing that corner sites, with increased edge habitats, have similar amounts of beetles overall as do forest sites. The main diff erence found was between middle plots and corner plots, with corner having more beetles. In this study, corner plots were bordered by forest on both sides and samples were placed within 8 to 10 meters from the one side so the affect of two forest sides co uld be analyzed (Figure 1). The finding that more beetles were present in this location show that pastures with more surrounding wood cover will attract more beetles. The main limiting factor in this study was time. This study would have been enhanced b y a greater number of sampled pastures and by larger plots. Measuring beetle response further into the pasture would provide more information about the impacts of land alteration on dung beetles. Further studies could also include different types of pastu res, heterogeneous and homogeneous, and look at diversity by letting the manure baits sit for longer times, thus allowing more beetle numbers and species to find the bait. Although this study focused on pastures bordering continuous forest, study of wind break affects on the numbers of beetles found in pastures may also show more applications toward conservation and sustainability. It has been found that it is not feasible for beetles to remove all of the dung produced by livestock, causing it to accumu late and decompose more slowly in the field (Morelli et al. 2002). In San Luis the cooler temperatures combined with less beetle diversity due to altitude make dung decomposition an even more important concern for farmers. This study has shown that incre ased proximity to forest and forest edges increases dung beetle numbers. Therefore, smaller fields with larger percentages of the area as edge habitats should have increased amounts of beetles, aiding in nutrient cycling and reduction of helminthes health risks. ACKNOWLEDGEMENTS This study would not have been feasible without the help from Carlos Guindon and Carmen Rojas. Carlos worked with me after a first research project had failed and was able to help me set up an experiment that could be done in a short time period. Carmen inspired the idea for the second project as well as gave invaluable assistance in the first project with contacting farmers and communicating with the local vet. Statistical guidance was given by Carlos and Maria Jost. As well, Maria and Oliver Hymen gave indispensable critiques during the entire writing process. Thanks must also be given to the LeitÃ³n family for use of their fields in this study, and to the main contributors to my initial study including the Monteverde Cheese F actory Farm, Dr. Juan JosÃ© Monge, Joe Stuckey, JosÃ© RamÃ³n Fuentes, and Benito Guindon.
5 LITERATURE CITED Dymock, J. J. 1993. A case for the introduction of additional dung burying beetles (Coleoptera: Scarabaeidae) into New Zealand. New Zealand Jo urnal of Agricultural Research. 36(1): 163 171. Estrada, A., Coates, E., Rosamond, Dadda, A. A. and Cammarano, P. 1998. Dung and carrion beetles in tropical rain forest fragments and agricultural habitats at Los Tuxtlas, Mexico. Journal of Tropical E cology. 14(5): 577 593. Forsyth, A. and Miyata, K. 1984. Tropical Nature. Macmillan Publishing Company, New York, New York. Halffter, G. and Arellano, L. 2002. Response of dung beetle diversity to human induced changes in a tropical landscape. Bi otropica 34(1): 144 154. Hanski, I. and Cambefort, Y. 1991. Dung Beetle Ecology. Princeton University Press, Princeton, New Jersey. Howden, H. F., Nealis, V. G. 1975. Effects of clearing in a tropical rain forest on the composition of the coprohagous scarab beetle fauna (Coleoptera). Biotropica 7(2): 77 83. Janzen, D. H. 1983. Insects. In D. H. Janzen (Ed). Costa Rican Natural History, pp. 640 641. University of Chicago Press, Chicago, Illinois. Morelli, E., Gonzalez, V. P., and Baz, A. 2002. Co prophagous beetles (Coleoptera: Scarabaedoidea) in Uruguayan Prairies: Abundance, diversity and seasonal occurance. Studies on Neotropical Fauna and Environment. 37(1): 53 57. Roslin, T. and Koivunen, A. 2001. Distribution and abundance of dung beet les in fragmented landscapes. Oecologia 127: 69 77. Sasayama, K., Nakamura, K., Manda, M. and Kurohiji, I. 1984. Diurnal prevalence and its seasonal change of dung beetles relationshis to weather elements. Grassland Science 29(4): 362 367.
6 Figure 1. Grid plots containing 30 2X2 meter squares were set up in each pasture, at the edge and in the middle. One eight ounce cow manure sample was placed in each square.
7 Figure 2. A significant difference showing mo re beetle numbers in woods compared to pastures existed in groups 6 0.004). Figure 3. Analysis of dung beetle numbers in corner and middle plots showed significantly more beetles in corner plots than middle plots (ANOVA, p = 0.0002). Woods 2 4 m 6 8 m 10 12 m 14 16 m 18 20 m