1Avian 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 Minneso ta ABSTRACT Three coffee farms were studied to determine avian feeding guild diversity differences between sun-gro wn and shade-grown plots in San Luis Valley, Monteverd e, Costa Rica. Sun-grown and shade-grown plots were observed on three coffee farms, species were i dentified by sight, and separated into feeding guil ds. Using the Shannon-Weiner Diversity Index, we found a significantly greater overall avian diversity in sungrown plots (Modified t-test, t= -4.00, df = 267.36 ). We also found no significant difference in feed ing guild diversity between sun-grown and shade-grown p lots, but found a significant difference within insectivorous and omnivorous feeding guilds support ing greater diversity in the sun-grown plots (Modif ied 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 Sa n 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 q ue se alimentan de lo mismo en parcelas con cafÃ© al sol y cafÃ© a la sombra en el valle de San Luis, Montever de, 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. Econtramos una diversidad de aves significativament e mayor en las parcelas con cafÃ© al sol al usar 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 sombra, pero encontramos una diferenc ia significativa dentro de los grupos de aves insectivoras y de las omnivoras, habiendo mÃ¡s diver sidad en las parcelas con cafÃ© al sol ( t-Test modificado, insectÃvoras: p > 0.05 t = -2.28, df = 102.51, omnÃvoras: p > 0.05, t = -2.84, df = 98.67) . Esta comparaciÃ³n podrÃa indicar que las parcelas con caf Ã© al sol en el valle de San Luis, Costa Rica son sisttemas mÃ¡s productivos, mientras que las parcela s con cafÃ© con sombra son dominadas por dos especie s que afectan la diversidad en total. INTRODUCTION Coffee production is an important aspect of the eco nomy 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 shad e-grown systems, which can influence the surrounding flora and fauna. Sun-grown plots a re characterized by having few nonherbaceous trees, resulting in an absence of shade. Previous studies in Latin America
2 have found that shade-grown coffee farms exhibit hi gher avian diversity than sun-grown farms (e.g., Davidson 2005). Shade-grown coffee ma y increase avian diversity by providing more resources and refuge for the avifaun a there (Johnson 2000). The traditional small-scale system of shade-grown coffe e farms 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 tropica l forest (Greenberg et al. 1997). Shade-grown coffee plots scattered with old-growth canopy and mid-canopy nonherbaceous trees have been shown to support greater avian diversity overall than sungrown coffee plots (Wong 2005). In the Tropics, thi s great diversity is able to occur because of competition. Specialization on different resources, known as niche partitioning or differentiation, allows similar spe cies 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 previous 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 feed ing guild of coffee farms. In the Tropics, however, little has been determined about the effects of sun-grown and shadegrown coffee farm habitats on avian feeding guild d iversity. We hypothesized that since shade-grown coffee plots harbor greater avian speci es diversity because of higher abundance of resources and refuge, this results in greater avian feeding guild diversity as well. The purpose of our study was to determine 1) the ov erall avian species richness (S) and diversity (HÂ’) of the avifauna in sun-grown and shade-grown coffee plots; 2) the difference in avian species richness (S) and number of individuals (N) between three coffee farms; 3) the richness (or number of) avian feeding guilds (SG) and the feeding guild diversity in sun-grown and shade-grown coffee plots; 4.) the avian species richness and diversity within insectivorous and omnivorous f eeding guilds of sun-grown and shade-grown coffee plots. MATERIALS AND METHODS Study Sites Study sites were located in the San Luis Valley, Mo nteverde, Costa Rica (Fig 1). Three different coffee farms were observed. Each farm inc luded sun-grown and shade-grown coffee plots (Fig. 2). The land surrounding the st udy sites was a mixture of other farms, roads, forests, and pastures. Figure 2 graphically depicts surrounding area and structure. The elevation range extended from 1065 to 1105 mete rs.
3 Legend Figure 1. Map of San Luis Valley, Costa Rica showi ng three observed coffee farms. Farms observed belonged to Noe Vargas, Rafael LeitÃ³ n, and Oldemar Salazar. All three farms had both sun-grown and shade-grown coffee plo ts. Noe Vargas farm Rafael LeitÃ³n farm Oldemar Salazar farm
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5Bushes/Shrubs _ __ _ Pathway Figure 2. Diagrams illustrating sun and shade plot s of observed coffee farms in San Luis Valley, Costa Rica. a.) Noe VargasÂ’ Farm b.) Rafae l LeitonÂ’s Farm c.) Oldemar SalazarÂ’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 studied on each of the thr ee farms on 6 non-consecutive observation days from July 15 to August 1, 2006. Â‘ Sun-grown plots,Â’ consisted of plants with up to five small interspersed trees creating s hade. Â‘Shade-grown plots consisted of coffee plants with greater than five interspersed t rees 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 Ri ca (Stiles and Skutch 1989). Identified species were f urther separated into seven different feeding guilds consisting of nectivorous, small ani mals/insectivorous, granivorous (species that feed almost exclusively on seeds), ca rrion-feeders, frugivorous, raptors (species that feed almost exclusively on birds and/ or small mammals), and omnivorous (species that feed on insects, reptiles, seeds, fru its, 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 (HÂ’). A mo dified t-test was used to determine whether the diversity of the sun-grown and shade-gr own coffee plots differed. The mean species richness per 30-minute time interval in sun -grown and shade-grown coffee plots was calculated and a Mann-Whitney U test was used t o determine whether the means were significantly different. The Kruskal-Wallace test was used to determine whether a significant difference existed in avian species ric hness and total number of individuals between the three farms studied. RESULTS Total Avian Diversity Using the Shannon-Weiner diversity index, the overa ll avian diversity found on sungrown plots was found to be significantly higher th an 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
6 species, five were unique to shade-grown plots, whe reas 17 were unique to sun-grown plots. The remaining 18 species were common to bot h plots. Avian species richness (S) and number of individuals observed (N) were found t o be greater on sun-grown plots (Table 1). The significant difference was due to bo th species richness (S) and evenness (E). TABLE 1. Avian species richness (S), number of ind ividuals (N), Shannon-Weiner Diversity Index (HÂ’), and Evenness (E) for sun and shade coffee plots. Number of Individuals and Species Richness per Obse rvation Period The difference between number of individuals observ ed per 30-minute time interval in shade-grown and sun-grown plots was not significant (Fig. 3). The mean number 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 LocationMean Number of Individuals FIGURE 3. The mean number of avian individuals obs erved on sun and shade coffee plots in San Luis Valley, Costa Rica. There is no s ignificant difference in the mean number of individuals on sun-grown and shade-grown coffee plots per 30-minute time interval (Mann Whitney U Test, c2 = 0.64, DF = 1, p = 0.42). Standard error bars ar e shown. Shade Sun S 23 34 H' 2.35 2.89 E 0.75 0.82 N 131 137
7 The mean species richness on shade-grown plots was 4.9 species per time interval whereas the mean species richness on sun-grown plot s was 6.3 species per time interval. Mean species richness per 30-minute interval was si gnificantly different favoring greater species per 30-minute interval in sun-grown plots ( Fig. 4). 0 1 2 3 4 5 6 7 8 SunShade LocationMean 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, 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 s ampled (Fig. 5). a) 0 1 2 3 4 5 6 7 8Noe VargasRafael LeitonOldermar SalazarFarmAverage Species Richness b) 0 2 4 6 8 10 12 14 16Noe VargasRafael LeitonOldermar 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) (Krusk al-Wallis, c2 = 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, 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 represente d 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 (SG), number of individuals (N), Shannon-Weiner Diversity Index of feeding guilds (HÂ’), and evennes s (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 = 2 66.97). Shade Sun
9 S G 6 7 H' 1.248 1.366 E 0.68 0.70 N 131 137 Diversity within Omnivorous and Insectivorous Avian Feeding Guilds Sun-grown plots supported a greater diversity withi n both insectivorous and omnivorous feeding guilds (Table 3). The difference within th e insectivorous feeding guild was due to a difference in evenness (Esun > Eshade). The difference within the omnivorous feeding guild was due to a difference in both species richn ess and evenness (Ssun > Sshade, Esun > Eshade). TABLE 3. Diversity within insectivorous and omnivor ous feeding guilds. Species richness (S), number of individuals (N), Shannon-We iner Diversity Index (HÂ’), and evenness (E) for sun and shade coffee plots calcula ted. There is a significant difference in the diversity within insectivorous and omnivorous f eeding guilds with higher diversity in sun plots for both guilds (Modified t-Test, Insecti vorous: 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 pl antations that contain a variety of trees, such as fruit trees, mixed in with coffee pl ants, creating a habitat similar to the forest in terms of the number of strata and resourc es used by birds (Greenburg et al., 1997). We, therefore, hypothesized that we would f ind a greater diversity of avian species and feeding guilds in the shade-grown coffe e plots. However, our results challenge this hypothesis. We found a significant difference in diversity in avifauna in the sun-grown plots in the San Luis Valley, Costa R ica. These results counter previous comparisons of sun-grown and shade-grown coffee pla ntations. Greenberg et al. (1997) has found that shade-grown coffee plots consistentl y harbor higher amounts of avian diversity. In addition, we found a significant diff erence in the species diversity of the insectivorous and omnivorous feeding guilds, in fav or 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. T his supports the needs of more diverse
10 avian populations and greater diversity within omni vorous and insectivorous feeding guilds. In the sun-grown plots, we observed 34 different a vian species with 17 of those species unique to the sun-grown plots. Previous s tudies 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 structural complexity. A g reater diversity of avian individuals was found in complex shade, but no significant diff erence was found between simple shade and complex sun (Wong 2005). The sun-grown p lots we observed were somewhat similar to complex sun plots observed by Wong (2005 ). The increased species richness of the sun-grown coffee plots we observed suggests the sun-grown systems in San Luis Valley to be more productive, in turn providing res ources to support a greater amount of avian species. The greatest limit on primary produc tivity of a community is determined by the amount of incident radiation received by pla nts; without this radiation, no photosynthesis can occur (Begon et al. 1990). A sun -grown coffee plot opens forest area to greater abiotic resources 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. Along these edges, the changes in habitat structure, food availability and species interactions all influence different bird d istributions (Fletcher 2005). A variety of birds specialize in feeding in open forest gaps or edges because the gaps are often ectothermically 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 who prey on the m. The species richness of avifauna in sun-grown coff ee plots was also coupled with a greater evenness in species abundance, thereby af fecting the overall diversity (Table 1). Shade-grown coffee plots had a lower diversity beca use the avian assemblage was dominated by two species; the Clay-Colored Robin an d the Rufous-and-White Wren. The domination by these species can be attributed t o some of their biological characteristics. For example, the Clay-Colored Rob in prefers pasture areas with scattered trees or second growth forest, similar to the 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-grown plots, the reby affecting the relative abundance of species. The Rufous-and-White Wren is commonly found in open to scrubby woodlands, creeping along branches searching for in sect prey (Stiles and Skutch 1989). The preference for scrubby woodlands and branches c ould lead it to spend a greater amount of time in the shade-grown coffee plots. It s common presence in the shade would directly affect the evenness of the community. There was no significant difference in the diversi ty 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 signifi cant difference in diversity of species of insectivorous and omnivorous feeding guilds with greater diversity found in sungrown plots. This could, again, be due to a sun-gr own plot being a more productive system for small ectotherms such as insects and rep tiles. If many types of insects prefer a
11 sunny environment, many different insectivore avian species might be drawn there to forage on them. Further study to investigate the i nsect and reptile diversity in sun and shade plots would give insight into why there is su ch a high 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 i mportant 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 tree s. The vast diversity of avifauna we observed in sun-grown plots depends on the forest e dge as a place to find prey. The prey found there often have ecological needs specific to the forest edge. Taking too much, through large-scale deforestation, can be detriment al to the species of prey on the forest edge and thus avian diversity. Small sun-grown plo ts within San Luis, Costa Rica, can harbor greater diversity indirectly because of the neighboring forests. In future studies, avian diversity can be looked at even closer in sha de-grown and sun-grown coffee plots by taking a more exhaustive sample of coffee farms and incorporating more fully all bird vocalizations heard. This could account for many o f the species that were present but difficult to identify, especially in shade-grown pl ots where large trees often blocked viewing area. Therefore, our shade avifauna data m ight be under-represented here because vocalizations should be employed more in id entification. Also, it may be beneficial to determine a sun-grown coffee plotÂ’s p roximity to forest edge and its direct effect on avian diversity. This could go as far as to look specifically at landscape surrounding plots and the relative plot size compar ed to the size of surrounding forest and the effects on avian diversity. Through future stu dies such as these, a greater understanding of avian diversity in coffee-farm agr o-ecosystems may be obtained. ACKNOWLEDGEMENTS 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 fa milies of Noe Vargas, Rafael Leiton, and Oldemar Salazar i n San Luis Valley, Costa Rica for allowing us to us e their coffee farms as study sites. We would like t o thank our dedicated professors, Karen L. Masters and Carmen Rojas for their answers to countless questio ns and their constant positive support and brillian t advice. Also, we would like to give a special than ks to Carmen Rojas for assisting us with her Englis hSpanish translating skills in completing our Resume n. Thanks so much to our teaching assistants, Camry n Pennington and Tom McFarland for their relentless c ommittal in providing the correct materials, comput er 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, in troducing 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 pl ace 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 b irding experiences, and most of all for giving us t he opportunity to study abroad and have this experienc e in Monteverde, Costa Rica this Summer of 2006. LITERATURE CITED
12 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-ecosystems i n Mexico: A Synopsis of the Environment Services and Socio-Economic Considerations. Journal of Sust ainable Forrestry. 21: 81-95. Fletcher, Robert J. 2005. Multiple edge effects a nd their implications in fragmented landscapes. Jo urnal 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. Forsyth, A. and K. Miyata. Tropical Nature. 1984 . Touchstone, New York. Greenberg, R., P. Bichier, and J. Sterling. 1997. Bird populations in rustic and planted shade coffe e plantations of eastern Chiapas, Mexico. Biotropica 29: 501-514. Johnson, M.D. 2000. Effects of shade-tree species and crop structure on the winter arthropod and bir d communities in a Jamaican shade coffee plantation. Biotropica 32: 133Â—145. MAG. 2006. Infoagro website. San JosÃ©, Costa Ric a, 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 Guid e to the Birds of Costa 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 I nsect Herbivory in Shande and Sun Coffee Plantations. CIEE Symposium on Tropical Ecology a nd Conservation. EstaciÃ³n BiolÃ³gica Monteverde, Costa Rica.
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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