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Diversidad gremial de alimentacin Aviar en las fincas de caf cultivado al sol y en la sombra en el valle de San Luis, Monteverde, Costa Rica
Avian feeding guild diversity in sun-grown and shade-grown coffee farms in San Luis Valley, Monteverde, Costa Rica
Three coffee farms were studied to determine avian feeding guild diversity differences between sun-grown and shade-grown plots in San Luis Valley, Monteverde, Costa Rica. Sun-grown and shade-grown plots were observed on three coffee farms, species were identified by sight, and separated into feeding guilds. Using the Shannon-Weiner Diversity Index, we found a significantly greater overall avian diversity in sun-grown plots (Modified t-test, t= -4.00, df = 267.36). We also found no significant difference in feeding guild diversity between sun-grown and shade-grown plots, but found a significant difference within insectivorous and omnivorous feeding guilds supporting greater diversity in the sun-grown plots (Modified t-Test, Insectivorous: p > 0.05 t = -2.28, df = 102.51, Omnivorous: p > 0.05, t = -2.84, df = 98.67). This comparison could indicate the sun-grown plots in San Luis Valley, Costa Rica to be a more productive system, whereas shade-grown plots are dominated by two species affecting overall diversity.
Se estudio tres fincas de caf para determinar la diferencia de la diversidad gremial de alimentacin aviar entre las parcelas cultivadas al sol y en la sombra en el valle de San Luis, Monteverde, Costa Rica.
Text in English.
Birds--Feeds and feeding--Costa Rica--Puntarenas--San Luis
Coffee plantations--Costa Rica--Puntarenas--San Luis
Aves--Alimentos y alimentacin--Costa Rica--Puntarenas--San Luis
Plantaciones de caf--Costa Rica--Puntarenas--San Luis
Tropical Ecology 2006
Ecologa Tropical 2006
t Monteverde Institute : Tropical Ecology
1 Avian feeding guild diversity in sun grown and shade grown coffee farms in San Luis Valley, Monteverde, Costa Rica Anna Richey Toria Waldron Department of Biology, Wofford College Department of Animal Science, University of Minnesota ABSTRACT Three c offee farms were studied to determine avian feeding guild diversity differences between sun grown and shade grown plots in San Luis Valley, Monteverde, Costa Rica. Sun grown and shade grown plots were observed on three coffee farms, species were identifie d by sight, and separated into feeding guilds. Using the Shannon Weiner Diversity Index, we found a significantly greater overall avian diversity in sun grown plots Modified t test, t= 4.00, df = 267.36. We also found no significant difference in feedi ng guild diversity between sun grown and shade grown plots, but found a significant difference within insectivorous and omnivorous feeding guilds supporting greater diversity in the sun grown plots Modified t Test, Insectivorous: p > 0.05 t = 2.28, df = 102.51, Omnivorous: p > 0.05, t = 2.84, df = 98.67. This comparison could indicate the sun grown plots in San Luis Valley, Costa Rica to be a more productive system, whereas shade grown plots are dominated by two species affecting overall diversity. RESUMEN Se estudiÃ³ tres fincas de cafÃ© para determinar las diferencias entre la diversidad de grupos de aves que se alimentan de lo mismo en parcelas con cafÃ© al sol y cafÃ© a la sombra en el valle de San Luis, Monteverde, Costa Rica. Se observÃ³ parcelas con cafÃ© al sol y a la sombra en tres fincas de cafÃ©, y las especies fueron identificadas por medio de la vista, y separadas en grupos de aves que se alimentan de lo mismo. Encontramos una diversidad de aves significativamente mayor en las parcelas con caf Ã© al sol al usa r el Ãndice de Shannon Weiner t test modificado, t= 4.00, df = 267.36. TambiÃ©n encontramos una diferencia no significativa en la diversidad de los grupos que se alimentan de lo mismo entre las parcelas con cafÃ© al sol y con cafÃ© a la so mbra, pero encontramos una diferencia significativa dentro de los grupos de aves insectÃvoras y de las omnÃvoras , habiendo mÃ¡s diversidad en las parcelas con cafÃ© al sol t Test modificado, insectÃvoras: p > 0.05 t = 2.28, df = 102.51, omnÃvoras: p > 0.0 5, t = 2.84, df = 98.67. Esta comparaciÃ³n podrÃa indicar que las parcelas con cafÃ© al sol en el valle de San Luis, Costa Rica son sistemas mÃ¡s productivos, mientras que las parcelas con cafÃ© con sombra son dominadas por dos especies que afectan la dive rsidad en total. INTRODUCTION Coffee production is an important aspect of the economy of Costa Rica, as it currently constitutes the largest percentage of the countryÂ€s total area of cultivated land MAG 2006. This crop is cultivated in sun grown or sha de grown systems, which can influence the surrounding flora and fauna. Sun grown plots are characterized by having few non herbaceous trees, resulting in an absence of shade. Previous studies in Latin America
2 have found that shade grown coffee farms exhib it higher avian diversity than sun grown farms e.g., Davidson 2005. Shade grown coffee may increase avian diversity by providing more resources and refuge for the avifauna there Johnson 2000. The traditional small scale system of shade grown coffee f arms places coffee plants into existing vegetation, creating a highly structurally diverse ecosystem. In such a system, avian diversity may be as high as that in a tropical forest Greenberg et al. 1997. Shade grown coffee plots scattered with old growth canopy and mid canopy non herbaceous trees have been shown to support greater avian diversity overall than sun grown coffee plots Wong 2005. In the Tropics, this great diversity is able to occur because of competition. Specialization on different resources, known as niche partitioning or differentiation, allows similar species to coexist Whittaker 1975. In the case of birds, it is possible to identify different feeding guilds, which are characterized by the food resources they utilize. In previo us studies, shade grown coffee farms have been found to harbor high arthropod species abundance Perfecto and Snelling 1995. This resource is utilized by insectivorous avian species, a highly abundant feeding guild of coffee farms. In the Tropics, howev er, little has been determined about the effects of sun grown and shade grown coffee farm habitats on avian feeding guild diversity. We hypothesized that since shade grown coffee plots harbor greater avian species diversity because of higher abundance of r esources and refuge, this results in greater avian feeding guild diversity as well. The purpose of our study was to determine 1 the overall avian species richness S and diversity HÂ€ of the avifauna in sun grown and shade grown coffee plots; 2 the d ifference in avian species richness S and number of individuals N between three coffee farms; 3 the richness or number of avian feeding guilds S G and the feeding guild diversity in sun grown and shade grown coffee plots; 4. the avian species rich ness and diversity within insectivorous and omnivorous feeding guilds of sun grown and shade grown coffee plots. MATERIALS AND METHODS Study Sites Study sites were located in the San Luis Valley, Monteverde, Costa Rica Fig 1. Three different coffee farms were observed. Each farm included sun grown and shade grown coffee plots Fig. 2. The land surrounding the study sites was a mixture of other farms, roads, forests, and pastures. Figure 2 graphically depicts surrounding area and structure. The elev ation range extended from 1065 to 1105 meters.
3 Legend Figure 1. Map of San Luis Valley, Costa Rica showing three observed coffee farms. Far ms observed belonged to Noe Vargas, Rafael LeitÃ³n, and Oldemar Salazar. All three farms had both sun grown and shade grown coffee plots. Noe Vargas farm Rafael LeitÃ³n farm Oldemar Salazar farm
4 a. Shade plot a. Sun plot l l l l l l l l Ã°Â¡ Ã°Â¡ Â§ Â§ Â§ Â§ Â§ Ã°Â¡ Ã°Â¡ Â§ Â§ Â§ Â§ Â§ l Ã°Â¡ Â§ Â§ Â§ Â§ Â§ l b. Shade plot b. Sun plot l l l l Ã°Â¡ Â§ Â§ Â§ Â§ Â§ Â§ Â§ Â§ Ã°Â¡ l _ Ã°Â¡ Ã°Â¡ Â§ Â§ Â§ Â§ Â§ Â§ Â§ Â§ Ã°Â¡ Ã°Â¡ _ Â§ Â§ Â§ Â§ Â§ Â§ Â§ Â§ l c. Shade plot c. Sun plot l l l Ã°Â¡ Ã°Â¡ l l Â§ Â§ Â§ l l Â§ Â§ Â§ _ _ Â§ Â§ Â§ _ _ _ Â§ Â§ Â§ _ _ Legend Large Tree l Coffee Plants Â§ Small Tree Ã°Â¡ Stream Bushes/Shrubs _ Pathway Ã°Â¡ Ã°Â¡ Ã°Â¡ Ã°Â¡ Ã°Â¡ Ã°Â¡ Ã°Â¡ Â§ Â§ Â§ _ _ Â§ Â§ Â§ _ l l l Ã°Â¡ _ _ _ l _ _ _ Ã°Â¡ Ã°Â¡ l l Â§ Â§ Â§ _ Ã°Â¡ Ã°Â¡ Ã°Â¡ l l _ l Â§ Â§ Â§ Â§ Â§ Ã°Â¡ Ã°Â¡ Ã°Â¡ _ l l Ã°Â¡ _ _ l _ Ã°Â¡ l l l l l l l l l l l l l l Ã°Â¡ Â§ Â§ l Â§ l Â§ Â§ l Â§ Â§ Â§ Â§ Â§ l Ã°Â¡ Ã°Â¡ Ã°Â¡ Ã°Â¡ Ã°Â¡ l _ Ã°Â¡ _ _ l Ã°Â¡ Ã°Â¡
5 Figure 2. Diagrams illustrating sun and shade plots of observed coffee farms in San Luis Valley, Costa Rica. a. Noe Vargas Farm b. Rafael Leiton s Farm c. Oldemar Salazar s Farm. Note: These figures are graphical representations and do not intend to show scale or accurately indicate how many of each component is present. Observing Avian Diversity Two 22 x 22 m plots were studie d on each of the three farms on 6 non consecutive observation days from July 15 to August 1, 2006. Sun grown plots, consisted of plants with up to five small interspersed trees creating shade. Shade grown plots consisted of coffee plants with greater t han five interspersed trees creating shade. On each farm, two days were allotted to observe avian activity during a morning period 7:00 7:30 AM and 7:30 8:00 AM and an afternoon period 2:30 3:00 PM and 3:00 3:30 PM. Each coffee plot type at each farm was viewed two times in the morning and two times in the afternoon. Avian species were identified primarily by using An annotated checklist of the birds of Monteverde and PeÃ±as Blancas Fogden 1993 and A Guide to the Birds of Costa Rica Stiles and Skutch 1989. Identified species were further separated into seven different feeding guilds consisting of nectivorous, small animals/insectivorous, granivorous species that feed almost exclusively on seeds, carrion feeders, frugivorous, raptors species that f eed almost exclusively on birds and/or small mammals, and omnivorous species that feed on insects, reptiles, seeds, fruits, and combinations thereof based on information in Stiles and Skutch 1989. Statistical Analyses Species richness and diversity over the sun grown and shade grown plots was calculated using the Shannon Weiner Diversity Index H . A modified t test was used to determine whether the diversity of the sun grown and shade grown coffee plots differed. The mean species richness per 30 m inute time interval in sun grown and shade grown coffee plots was calculated and a Mann Whitney U test was used to determine whether the means were significantly different. The Kruskal Wallace test was used to determine whether a significant difference ex isted in avian species richness and total number of individuals between the three farms studied. RESULTS Total Avian Diversity Using the Shannon Weiner diversity index, the overall avian diversity found on sun grown plots was found to be significantly hi gher than the overall avian diversity observed on shade grown plots Modified T test, P < 0.05, t = 4.00, df = 267.36. A total of 40 avian species were observed in sun and shade plots on the three farms studied. Of these species, five were unique to sh ade grown plots, whereas 17 were unique to sun grown plots. The remaining 18 species were common to both plots. Avian species richness S and number of individuals observed N were found to be greater on sun grown plots
6 Table 1. The significant diff erence was due to both species richness S and evenness E. TABLE 1. Avian species richness S, number of individuals N, Shannon Weiner Diversity Index H , and Evenness E for sun and shade coffee plots. Number of Individuals and Species Richness per Observation Period The difference between number of individuals observed per 30 minute time interval in shade grown and sun grown plots was not significant Fig. 3. The mean numbe r of avian individuals observed was 10.9 on shade grown plots compared to a mean of 11.4 on sun grown plots per 30 minute time interval. 0 2 4 6 8 10 12 14 Sun Shade Location Mean Number of Individuals FIGURE 3. The mean number of avian individuals observed on sun and shade coffee plots in San Luis Val ley, Costa Rica. There is no significant difference in the mean number of individuals on sun grown and shade grown coffee plots per 30 minute time interval Mann Whitney U Test, Ã°c 2 = 0.64, DF = 1, p = 0.42. Standard error bars are shown. Shade Sun S 23 34 H' 2.35 2.89 E 0. 75 0.82 N 131 137
7 The mea n species richness on shade grown plots was 4.9 species per time interval whereas the mean species richness on sun grown plots was 6.3 species per time interval. Mean species richness per 30 minute interval was significantly different favoring greater spe cies per 30 minute interval in sun grown plots Fig. 4. 0 1 2 3 4 5 6 7 8 Sun Shade Location Mean Species Richness FIGURE 4. The mean avian species richness observed on sun and shade coffee plots in San Luis Valley, Costa Rica. Sun coffee plots show significantly higher species richness than shade plots Mann Whitney U Test, Ã°c 2 = 4.02, DF=1, p=0.045. Standard error bars are shown.
8 Avian Species Richness and Abundance between Farms Kurskal Wallis test proved there was no significant difference in avian species richness and number of individuals between the three farms sampled Fig. 5. a 0 1 2 3 4 5 6 7 8 Noe Vargas Rafael Leiton Oldermar Salazar Farm Average Species Richness b 0 2 4 6 8 10 12 14 16 Noe Vargas Rafael Leiton Oldermar Salazar Farm Average Number of Individuals FIGURE 5. Average species richness a and number of avian individuals b observed at each farm. There was no significant difference in the average number of individuals observed between the three studied farms a Kruskal Wallis, Ã°c 2 = 1.49, DF = 2, p = 0.47. There was no significant difference in the average species richness between the three studied farms b Kruskal Wallis, Ã°c 2 = 0.073, DF = 2, p = 0.96. Standard error bars are shown. Feeding Guild Richness and Diversity Avian species in shade grown plots were represented by birds in six different feeding guilds and species in sun grown plots were represented by birds in seven different feeding guilds. There was no significant difference in the diversity of feeding guilds in sun grown and shade grown plots Table 2. TABLE 2. Feeding guild richness S G , number of individuals N, Shannon Weiner Diversity Index of feeding guilds H , and evenness E for sun and shade coffee plots. There is no significant difference in diversity of feeding guilds in sun and shade coffee plots Modified T test, p > 0.05, t = 1.21, df = 266.97. Shade Sun S G 6 7 H' 1.248 1.366 E 0.68 0.70 N 131 137
9 Diversity wi thin Omnivorous and Insectivorous Avian Feeding Guilds Sun grown plots supported a greater diversity within both insectivorous and omnivorous feeding guilds Table 3. The difference within the insectivorous feeding guild was due to a difference in evenn ess E sun > E shade . The difference within the omnivorous feeding guild was due to a difference in both species richness and evenness S sun > S shade , E sun > E shade . TABLE 3. Diversity within insectivorous and omnivorous feeding guilds. Species richness S, number of individuals N, Shannon Weiner Diversity Index H , and evenness E for sun and shade coffee plots calculated. There is a significant difference in the diversity within insectivorous and omnivorous feeding guilds with higher diversity in sun plots for both guilds Modified t Test, Insectivorous: p < 0.05 t = 2.28, df = 102.51, Omnivorous: p > 0.05, t = 2.84, df = 98.67. Insectivorous Omnivorous Shade Sun Shade Sun S 11 12 8 14 H' 1.56 2.1 1.17 1.82 E 0.65 0.85 0.53 0.69 N 57 46 53 62 DISCUSSION In Costa Rica, it is common to find shade coffee plantations that contain a variety of trees, such as fruit trees, mixed in with coffee plants, creating a habitat similar to the forest in terms of the number of strata and resources used by birds Greenburg et al., 1997. We, therefore, hypothesized that we would find a greater diversity of avian species and feeding guilds in the shade grown coffee plots. However, our results challenge this hypothesis. We found a significant differ ence in diversity in avifauna in the sun grown plots in the San Luis Valley, Costa Rica. These results counter previous comparisons of sun grown and shade grown coffee plantations. Greenberg et al. 1997 has found that shade grown coffee plots consisten tly harbor higher amounts of avian diversity. In addition, we found a significant difference in the species diversity of the insectivorous and omnivorous feeding guilds, in favor of sun grown coffee plots. These results suggest that in sun grown plots of coffee, other factors are more important than habitat structural complexity and resource base. This supports the needs of more diverse avian populations and greater diversity within omnivorous and insectivorous feeding guilds. In the sun grown plots, w e observed 34 different avian species with 17 of those species unique to the sun grown plots. Previous studies in the San Luis Valley, Costa Rica compare avian diversity in sun grown and shade grown coffee on a continuum of sun to shade coverage in struc tural complexity. A greater diversity of avian individuals was found in complex shade, but no significant difference was found between simple shade and complex sun Wong 2005. The sun grown plots we observed were somewhat similar to complex sun plots obs erved by Wong 2005. The increased species richness
10 of the sun grown coffee plots we observed suggests the sun grown systems in San Luis Valley to be more productive, in turn providing resources to support a greater amount of avian species. The greatest limit on primary productivity of a community is determined by the amount of incident radiation received by plants; without this radiation, no photosynthesis can occur Begon et al. 1990. A sun grown coffee plot opens forest area to greater abiotic resourc es such as sun energy and water, which can positively influence plant growth. This could create a more productive understory that may be preferred by birds. The sun grown plots studied here were all bordered by trees in windbreaks and forest patches. Al ong these edges, the changes in habitat structure, food availability and species interactions all influence different bird distributions Fletcher 2005. A variety of birds specialize in feeding in open forest gaps or edges because the gaps are often ecto thermically inviting to small creatures such as insects and lizards Forsyth and Miyata 1984. These creatures come to bask in open areas like that of a sun grown coffee plot, thus bringing in birds that prey on them. The species richness of avifauna in sun grown coffee plots was also coupled with a greater evenness in species abundance, thereby affecting the overall diversity Table 1. Shade grown coffee plots had a lower diversity because the avian assemblage was dominated by two species; the Clay Co lored Robin and the Rufous and White Wren. The domination by these species can be attributed to some of their biological characteristics. For example, the Clay Colored Robin prefers pasture areas with scattered trees or second growth forest, similar to t he shade grown coffee plots we observed. The Clay Colored Robin is also quite aggressive in the vicinity of its nest Stiles and Skutch 1989. The aggressive demeanor of the Clay Colored Robin may have served to chase out other species within the shade g rown plots, thereby affecting the relative abundance of species. The Rufous and White Wren is commonly found in open to scrubby woodlands, creeping along branches searching for insect prey Stiles and Skutch 1989. The preference for scrubby woodlands an d branches could lead it to spend a greater amount of time in the shade grown coffee plots. Its common presence in the shade would directly affect the evenness of the community. There was no significant difference in the diversity of the avian feeding guilds supported between sun grown and shade grown plots Table 2. This could indicate the resources available to different feeding guilds did not differ greatly between shade grown and sun grown plots. There was, however, a significant difference in di versity of species of insectivorous and omnivorous feeding guilds with greater diversity found in sun grown plots. This could, again, be due to a sun grown plot being a more productive system for small ectotherms such as insects and reptiles. If many typ es of insects prefer a sunny environment, many different insectivore avian species might be drawn there to forage on them. Further study to investigate the insect and reptile diversity in sun and shade plots would give insight into why there is such a hig h diversity within the insectivorous feeding guild. Our data suggest that forest edges along sun grown coffee plots can benefit avian diversity. From a conservation standpoint, it is important to realize that sun grown coffee plots in San Luis Valley, Costa Rica do harbor more avian diversity, but probably because they are on forest edge and near large trees. The vast diversity of avifauna we observed in sun grown plots depends on the forest edge as a place to find prey. The prey
11 found there often hav e ecological needs specific to the forest edge. Taking too much, through large scale deforestation, can be detrimental to the species of prey on the forest edge and thus avian diversity. Small sun grown plots within San Luis, Costa Rica can harbor greate r diversity indirectly because of the neighboring forests. In future studies, avian diversity can be looked at even closer in shade grown and sun grown coffee plots by taking a more exhaustive sample of coffee farms and incorporating more fully all bird v ocalizations heard. This could account for many of the species that were present but difficult to identify, especially in shade grown plots where large trees often blocked viewing area. Therefore, our shade avifauna data might be under represented here b ecause vocalizations should be employed more in identification. Also, it may be beneficial to determine a sun grown coffee plot s proximity to forest edge and its direct effect on avian diversity. This could go as far as to look specifically at landscape s urrounding plots and the relative plot size compared to the size of surrounding forest and the effects on avian diversity. Through future studies such as these, a greater understanding of avian diversity in coffee farm agro ecosystems may be obtained. AC KNOWLEDGEMENTS This study would not have been possible without the assistance of many people. We appreciate everyone who had any hand in helping us with this study. We would like to give a special thanks to the farm families of Noe Vargas, Rafael LeitÃ³n , and Oldemar Salazar in San Luis Valley, Costa Rica for allowing us to use their coffee farms as study sites. We would like to thank our dedicated professors, Karen L. Masters and Carmen Rojas for their answers to countless questions and their constant p ositive support and brilliant advice. Also, we would like to give a special thanks to Carmen Rojas for assisting us with her English Spanish translating skills in completing our Resumen . Thanks so much to our teaching assistants, Camryn Pennington and Tom McFarland for their relentless committal in providing the correct materials, computer statistics assistance, and most importantly, snacks and coffee in times of dire need. A special thanks to Matt Gasner for his avian expertise in PeÃ±as Blancas, introduci ng us to birding, and most of all, for his magnificent list of common San Luis birds of which we utilized daily. We would like to thank the Ecolodge of San Luis for providing a comfortable place for recording data and studying during our observation time. Finally, an extra special thanks to our loving families back home for corresponding through e mails and phone calls, listening to our birding experiences, and most of all for giving us the opportunity to study abroad and have this experience in Monteverd e, Costa Rica this Summer of 2006. LITERATURE CITED Begon, M., J.L. Harper, and C.R. Townsend. Ecology: Individuals, Populations, and Communities . 1990. Blackwell Scientific Publications, Boston, MA. Davidson, S. 2005. Shade Coffee Agro ecosys tems in Mexico: A Synopsis of the Environment Services and Socio Economic Considerations. Journal of Sustainable Forrestry. 21: 81 95. Fletcher, Robert J. 2005. Multiple edge effects and their implications in fragmented landscapes. Journal of Animal Ecology, 74: 347 352. Fogden, M. An annotated checklist of the birds of Monteverde and PeÃ±as Blancas . 1993. Litografia e Imprenta LIL, San JosÃ©, Costa Rica.
12 Forsyth, A. and K. Miyata. Tropical Nature. 1984. Touchstone, New York. G reenberg, R., P. Bichier, and J. Sterling. 1997. Bird populations in rustic and planted shade coffee plantations of eastern Chiapas, Mexico. Biotropica 29: 501 514. Johnson, M.D. 2000. Effects of shade tree species and crop structure on the winter a rthropod and bird communities in a Jamaican shade coffee plantation. Biotropica 32: 133 145. MAG. 2006. Infoagro website. San JosÃ©, Costa Rica, Minsterio de agricultura ganaderÃa SEPSA. < www.infoagro.go.cr > Perfecto, I, and R. Smelling. 1995. Biodiversity and the transformation of a tropical agroecosystem: ants in coffee plantations. Ecological Applications 5: 1084 1097. Stiles, F.G., A.F. Skutch, and D. Gardener. A Guide to the Birds of Cost a Rica . 1989. Comstock Publishing Associates, Ithaca, New York. Whittaker, R.H. Communities and Ecosystems . 1975. Macmillan Publishers, New York. Wong, C. 2005. The Impact of Avian Diversity on Insect Herbivory in Shande and Sun Coffee Plantatio ns. CIEE Symposium on Tropical Ecology and Conservation. EstaciÃ³n BiolÃ³gica Monteverde, Costa Rica.