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La proximidad del bosque, la diversidad de aves y la herbivora de insectos en el caf de sombra
Forest proximity, avian diversity and insect herbivory in shade grown coffee
Conversion of forest to agricultural plots, plantations, and pastureland is one of the top two reasons for the unprecedented rate of tropical forest destruction. Coffee, in terms of area, is the most important crop in Costa Rica and continues to threaten remaining forest (Lean 1990). This study examined how proximity of coffee plantations to forest stands affects avian diversity, and the role of avian insectivores on coffee herbivory. Avian diversity was studied at two coffee plantations, one near and one far from the forest. Avian diversity was significantly higher in the near-forest coffee plantation than in the far forest. However, there was no significant difference in herbivory or insectivory between the two sites. These results suggest that forest stands are important to the conservation of avian diversity in coffee plantations.
La transformacin del bosque en parcelas de agricultura, plantaciones y fincas ganaderas es uno de las razones ms importantes de la destruccin del bosque tropical. El caf es el cultivo mas importante en Costa Rica y por lo que amenaza la sobrevivencia del bosque existente (Lean 1990). Este estudio examino como el efecto de la proximidad de los cafetales al bosque influye sobre la diversidad de las aves, depredacin de larvas y el porcentaje de herbivora del caf.
Text in English.
Rain forest plants--Costa Rica--Puntarenas--San Luis
Coffee plantations--Costa Rica--Puntarenas--San Luis
Plantas del bosque tropical--Costa Rica--Puntarenas--San Luis
Plantacioned de caf--Costa Rica--Puntarenas--San Luis
Tropical Ecology 2006
Ecologa Tropical 2006
t Monteverde Institute : Tropical Ecology
1 Forest proximity, avian diversity and insect herbivory in shade grown coffee Frannie Peterson Department of Geography, University of Texas Abstract Conversion of forest to agricultural plots, plantations, and pastureland is one of the top two reasons f or the unprecedented rate of tropical forest destruction. Coffee, in terms of area, is the most important crop in Costa Rica and continues to threaten remaining forest Lean 1990. This study examined how proximity of coffee plantations to forest stands affects avian diversity, and the role of avian insectivores on coffee herbivory. Avian diversity was studied at two coffee plantations, one near and one far from the forest. Avian diversity was significantly higher in the near forest coffee plantation th an in the far forest. However, there was no significant difference in herbivory or insectivore between the two sites. These results suggest that forest stands are important to the conservation of avian diversity in coffee plantations . Resumen La transf ormaciÃ³n del bosque en parcelas de agricultura, plantaciones, y fincas ganaderas es un de las razones mÃ¡s importantes de la destrucciÃ³n del bosque tropical. El cafÃ© es el cultivo mÃ¡s importante en Costa Rica y por lo que amenaza la sobrevivencia del bosque existente Lean 1990. Este estudio examinÃ³ como el efecto de la proximidad de los cafetales al bosque influye sobre la diversidad de las aves, depredaciÃ³n de larvas, y el porcentaje de herbivorÃa del cafÃ©. EstudiÃ© la diversidad de aves en dos cafet ales, uno cerca del bosque y uno lejos del bosque. La diversidad fue mÃ¡s alta en el cafetal cerca del bosque que en el cafetal lejos del bosque. Sin embargo, no encontrÃ© una diferencia significativa en el/ de herbivorÃa y en la depredaciÃ³n de larvas en tre los dos sitios. Estos resultados sugieren que el bosque es importante para la conservaciÃ³n de la diversidad de las aves en los cafetales. Introduction For the past 10,000 years humans have been transforming natural ecosystems in Central America to agricultural ecosystems, resulting in the extermination of large herbivores and top predators that would otherwise compete for food resources Naylor and Ehrlich 1997. The further intensification of agriculture has resulted in a decrease in competitors and has created outbreaks of small herbivores that act as crop pests. These and other pests, which destroy an estimated 25 50 % of crops before and after harvest, are humanity s most important competitors for food and fiber Naylor and Ehrlich 1997. In order to compete with these pests, farmers apply roughly 2,500,000 tons of synthetic pesticides annually to crops worldwide Naylor and Ehrlich 1997. This practice is economically and environmentally expensive and could be replaced by natural ecosystem s ervices Harvey, 2005 .
2 In Costa Rica, the introduction of new sun tolerant, high yielding coffee varieties led to the conversion of many traditional shaded farms to un shaded farms. This shift has led to increased economic costs for farmers, as well as e nvironmental and biological degradation Albertin et al. 2004, Dietsch 2000. The insurance hypothesis states that high biodiversity insures ecosystem vitality in response to environmental fluctuations Perfecto et al. 2004. Previous studies have shown that shade grown coffee farms contain higher arthropod and avian insectivore diversity and experience less herbivory than sun grown coffee Wong 2005, Greenburg 2000. These studies indicate that birds can potentially protect against pest outbreaks Perfe cto et al. 2004. MacArthur and Wilson s theory of island biogeography states that the number of species on an island is determined by a balance between immigration and extinction, which are affected by island size and distance from mainland Emlen 1984 . For every island the mainland serves as a source of immigrants. In my study, shade grown coffee farms are islands in a sea of development with a mainland, or species pool, of forest. According to island biogeography, avian diversity on the island, or coffee farm, should decrease with distance from the mainland suggesting that isolated systems will be less diverse than systems near the mainland, or forest. In order to see if avian diversity decreases with distance from forest as the theory of island bi ogeography would suggest, I studied shade grown coffee at different distances from the forest. The purpose of this study was to examine distance from forest affects avian diversity in shade grown coffee plantations, and how avian diversity affects insectivore and coffee herbivory. I predicted that avian diversity would be higher in the coffee farm near forest and as a result, insectivore and herbivory would decrease.
3 Materials and Methods Figure 1. Map of sites in San Luis, Costa Rica. Near forest site is ~1km away from forest while far from forest site is ~3km away. Site Description I chose two similarly sized eight hectares shade grown coffee farms in San Luis, Costa Rica for my study sites Figure 1. My near forest site was approximately one kilometer from the Monteverde Cloud Forest Reserve while my far from forest site was approximately three kilometers away. Procedure I made a 15 m transect at 17.5m from the road across each plot. From October 24 th to November 16 th I observed birds for 30 minutes at every five meters along the 15m transect. From 6:00 am to 8:00 am species richness and abundance was recorded for perched birds along the transect. I identified species using Stiles guide to the birds of Costa Rica and then categorized species into classes of occurrence using the Fogden List based on my observations Fogden 1993. Species were then classified by diet: insectivorous, frugivorous, nectarivorous, omnivorous and granivorous also using Stiles guidebook. To quantify insectivore , I tagged ten coffee trees along each transect and placed a clay caterpillar green with black stripes at mid level branches on each of the tagged trees. I measured caterpillar peck marks indicating avian predation once a week. To measure herbivory, I took three leaves, each being the third leaf from the branch tip, one taken from crown, mid level or breast height, and close to trunk branches from each of the ten tagged coffee trees. To calculate percent herbivor y for each leaf I used a transparent grid 1cm x 1cm, placed it over the leaf, and then calculated the percent of grid cells with any amount of herbivory out of total grid cells.
4 Statistical Analysis Avian diversity was calculated for each farm using the Shannon Weiner diversity index and a modified T test and was used to compare differences in avian diversity between the two farms. A t test was used to determine if there was a significant difference in herbivory between the two farms. A chi square test was used to determine if there was a significant difference in the number of peck marks between the two farms as a proxy for insectivore . A chi squared test was also used to determine if number of total individuals for all species was significantly differe nt, if insectivorous species were significantly different, and if abundance of common species were significantly different between the two sites. Results Avian Diversity and Abundance Avian diversity was shown to be greater at the near forest site Shann on Weiner H =1.06 than at the far forest site Shannon Weiner H =. 72, Modified t test t=4.83, df = 100, p<. 05. Avian abundance was also significantly greater in the near forest site chi squared test x= 23.49, df = 1, p < 0.05. In total, I saw 34 bird species and 116 individuals in the near site while only 22 species and 53 individuals at the far site. Fifteen bird species were found exclusively in the near forest site, while only four species were found exclusively in the far site. I observed that av ian communities at both farms were largely composed of omnivorous species, consisting of about half 48% of the total species. Omnivorous species richness was greatest for the far site while insectivorous species was greatest for the near site Table 2. Insectivorous species, consisting of about %30 of total species in both sites, was the second most species rich although there was no significant difference in insectivorous species richness between the two sites chi square, x = 0.0005, df = 1, p, 0.05. Figure 2. Commonality of Bird Species I observed that the near forest site had a greater number of species s = 34 than the far forest site s = 32. There was no significant difference in common species between the sites chi square, x = 0.008, df = 1, p < 0.05. Fairly common species were similar between the near forest site and the far forest site 15%, 14% while rare species had the highest percentages of birds in both sites 56%, 55% Table 2.
5 Percentage of species in each feeding gui ld for each site Figure 2: Feeding guild percentage for each site 0% 10% 20% 30% 40% 50% 60% 70% Frugivorous/Granivorous Omnivorous Insectivorous Nectivorous Feeding Guild % of species Near Far
6 Table 2. Bird species for both sites categorized by feeding guild based on my observations Stiles, 1989 and commonality. Commonality: C=common, F=fairly common, U=unc ommon, and R=rare Fogden, 1993. A Near Frugivorous/Granivorous Omnivorous Insectivorous Nectivorous Red Billed Pigeon R Brown Jay C Wilson's Warble C Green Hermit C Olive Throated Parakeet C Great Tailed Grackle R White Breasted Wood Wren F Rufous Tailed Hummingbird F Long Tailed Manakin R Mistle Toe Tyrannulet R Yellow Billed Cacique R Coppery Headed Emerald R Turkey Vulture F Slate Throated Redstart U Steely Vented Hummingbird R Green Backed Heron R House Wr en R Blue Tailed Hummingbird R Wood Thrush U Slate Headed Tody Flycatcher R Keel Billed Toucan U Worm Eating Warbler R Clay Colored Robin U Squirrel Cuckoo R Great Kiskadee F Bronzed Cowbird R Dusky Capped Flycatcher R Co mmon Tody Flycatcher F Masked Tityra U White Eared Ground Sparrow R Short Tailed Hawk R Western Wood Peewee R White Tipped Dove R B Far Frugivorous/Granivorous Omnivorous Insectivorous Nectivourous Crimson Fronted Parake et F Blue Gray Tanager U White Breasted Wood Wren U Green Hermit C Yellow Crowned Tyrannulet R Yellow Crowned Euphonia R Common Tody Flycatcher F Yellow Faced Grassquit U Wilson's Warbler C Great Kiskadee U Yellow Warbler R Brown Jay C Black Burnian Warbler R Tennessee Warbler R Dusky Capped Flycatcher R Turkey Vulture F Red Eyed Vireo R Slate Headed Tody Flycatcher R White Tipped Dove R Clay Colored Robin R Hoffman's Woodpecker R Yellow Tyrannulet R Herbivory There was not a significant difference in percent herbivory between the near forest site and the far from forest site t test t= .036, df = 176, p = 0. 972Figure 3.
7 Â€Std. Dev. Â€Std. Err. Mean % herbivory -0,03 -0,01 0,01 0,03 0,05 0,07 NEAR FAR Figure 3. Site vs. % Herbivory in San Luis, Costa Rica. There was no significant difference in the mean percent herbivory between the near and far sites. Avian Insectivorous Activity With an average of 0.5 peck marks, the near forest site had almost twice the am ount of peck marks than the far site which had an average of 0.26. However, no significant difference was found between the two sites chi squared x= 2.13, df= 1, p>.05 Figure 4. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Near Forest Far Forest Site Mean number of peck marks Figure 4. Mean number of pecks per site.
8 Di scussion Previous studies have shown that avian diversity increases while herbivory decreases in shade grown coffee when compared with sun grown coffee Perfecto et al. 2004, Sekercioglu, 2002. Although avian diversity and abundance was significantly gre ater in the near than in the far forest site, there was no significant difference in insectivore or herbivory. It is possible that avian diversity was greater in the near forest site because the forest is providing more resources and a more diverse habita t, which has the potential to support a greater number of species. It could also be that the near forest site is not as exposed to the elements as the far from forest site. My study indicates that the coffee grown near forest is sustaining a more divers e population of bird species than the coffee grown far from forest. My results were consistent with the results of another study that found that diversity of frugivorous bird species decreased with distance from the forest Luck et al. 2004. It is also p ossible that the birds seen only in the near forest site may not have been able to disperse to the site that was further from the forest Emlen 1984. Fifteen bird species were found exclusively in the near forest site while only four species were found ex clusively in the far forest site. These findings agree with another study that found that the best determinant of the persistence of understory insectivorous birds in small fragments is their ability to disperse through deforested countryside habitats Sek ercioglu et al. 2001. Some of the species found exclusively in the coffee farm near the forest are species that prefer forest edge and second growth areas. On the other hand, all but one of the species found only in the coffee farm far from the forest a re adapted to highly disturbed areas Stiles 1989. These results suggest that, in order to conserve avian diversity near coffee plantations, we must work to preserve stands of forest in the area. For future studies, my study should be repeated over a lo nger period of time because I believe that the trend that was shown in the sun versus shade study, where avian diversity was greater in the near forest site and as a result insectivore and herbivory decreased, would be shown. This suggests that, with cons ervation of avian diversity, the billions of dollars spent on pesticides each year could be greatly reduced. Decreasing use of pesticides will also reduce the amount of indirect damages associated with their use including negative health effects, ecosyste m effects, and development of resistance to chemicals in vectors of human disease Naylor, 1997. Acknowledgements Thanks to Odileo and Gilbert for being so kind and letting me use their farms for my study. A big thanks goes to Tania for making the trek out to San Luis to help me bird watch. Also thanks to Katie Mac and Ellen for revising my paper. Last but not least, thanks to Tom and Cam for being at my beck and call the whole time I was writing my paper!
9 Literature Cited Albertin, A., P.K.R.Nair. 2004. Avian diversity in sun and shade grown coffee. Human Ecology: 32: 443 Dietsch, T. 2000. Assessing the conservation value of shade grown coffee: A biological perspective using neotropical birds. Endangered Species Update 68: 122. Emlen, J. 1984 . Population Biology: The Coevolution of Population Dynamics and Behavior. Macmillian Publishing Company, New York, NY. Fogden, M. 1993. An annotated checklist of the birds of Monteverde and Penas Blancas. Litografia e Imprenta LIL, San Jose, Costa Rica . Greenburg, R.,P. Bichier, A, Angon, C. Macvean, R,Perez, E, Cano. 2000. The Impact of avian insectivory on arthropods and leaf damages in some Guatemalan coffee plantations. Ecology 81: 1750 1755. Harvey, C., F. Alpizar., M. Chacon, R. Madrigal. 2005 . Assessing Linkages between Agriculture and Biodiversity in Central America: Historical Overview and Future Perspectives . The Nature Conservancy. San Jose, Costa Rica. Lean, G.,D. Hinrichsen, A. Markham. 1990. Atlas of the Environment. Prentice Hall Press, New York, NY. Luck, G., G. Daily. 2004. Tropical countryside bird assemblages: Richness, composition, and foraging differ by landscape context. Ecological Applications 13: 235 247. Naylor, R., P. Ehrlich. 1997. Nature s Services: Natural Pest Co ntrol Services and Agriculture. Island Press, Washington, DC. Perfecto, I., J.H. Vandermeer, G.L. Bautista, G.I. Nunez, R. Greenberg, P. Bichier and S. Langridge. 2004. Greater predation in shaded coffee farms: the role of resident neotropical birds. Ecology 85: 2677 2681. Sekercioglu, C.H., P. Ehtlich, G. Daily, D. Aygen, D. Goering, R. Sandi.2002. The disappearance of insectivorous birds from Tropical forest fragments. Ecology:119 263 267. Stiles, F.G., A.F. Skutch, D. Gardener. 1998. A guide to the birds of Costa Rica. Comstock Publishing Associates, Ithaca, NY.