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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 for the unprecedented rate of tropical forest destruction. Coffee, in terms of ar ea, 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-fores t coffee plantation than in the far forest. However, there was no significant difference in herbivory or ins ectivory between the two site s. These results suggest that forest stands are important to the conservation of avian diversity in coffee plantations. Resumen La transformacin del bosque en parcelas de agricultura, plantaciones, y fincas ganaderas es un de las razones ms importantes de la destruccin del bosque tropical. El caf es el cultivo ms importante en Costa Rica y por lo que amenaza la so brevivencia del bosque existente (L ean 1990). Este estudio examin como el efecto de la proximinidad de los cafetales a el bosque influye sobre la diversidad de los aves, depradacin de larvas, y el porcentaje de herbivoria del caf. Estudi la diversidad de aves en dos cafetales, uno cerca del bosque y uno lejos del bosque. La diversidad fue ms alta en el cafetal cerca del bosque que en el cafetal lejos del bosque. Sin embargo, no encontre una differencia significantiva en el/ de herbivoria y en la depradacin de larvas entre los dos sitios. Estos resultados sugieren que el bosque es importante para la conservacin de la diversidad de los aves en los cafetales. Introduction For the past 10,000 years humans have been tr ansforming natural ecosystems in Central America to agricultural ecosystems, resulting in the extermination of large herbivores and top predators that would ot herwise compete for food res ources (Naylor and Ehrlich 1997). The further intensificati on 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 humanitys most important competitors for food and fiber (Naylor and Ehrlich 1997). In order to compete with these pests, farm ers apply roughly 2,500,000 tons of synthetic pesticides annually to crops worldwide (Nay lor and Ehrlich 1997). This practice is economically and environmentally expensive and could be replaced by natural ecosystem services (Harvey, 2005). 1
In Costa Rica, the introduction of new s un tolerant, high yiel ding 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 environmental 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 (Perfecto et al. 2004). MacArthur and Wilsons theory of island bi ogeography states th at the number of species on an island is determined by a ba lance between immigra tion and extinction, which are affected by island size and distan ce 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 dive rsity 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 dive rsity decreases with distance from forest as the theory of island biogeography would suggest, I studied shade-grown coffee at different distances from the forest. The purpose of this study wa s to examine distance from forest affects avian diversity in shade grown coffee plan tations, and how avian diversity affects insectivory and coffee herbivory. I predicted that avian dive rsity would be higher in the coffee farm near forest and as a result, in sectivory and herbivor y would decrease. 2
Materials and Methods Figure 1. Map of sites in San Luis, Cost a 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 Reserv e 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 24th to November 16th 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 sp ecies using Stiles gu ide to the birds of Costa Rica and then categorized species into classes of o ccurrence 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 insectivory, I tagged ten coff ee 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 (i ndicating avian predation) once a week. To measure herbivory, I took three leaves, each bein g 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 herbivory for each leaf I used a transparent grid (1cm x 1cm), placed it over th e leaf, and then calcu lated the percent of grid cells with any amount of herbivory out of to tal grid cells. 3
Statistical Analysis Avian diversity was calculated for each farm using the Shannon Weiner diversity index and a modified T-test and was used to compar e 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 insectivory. A chi-squared test was also used to determine if number of total individuals for all species was significantly different, 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 (Shannon-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 gr eater in the near fore st site (chi-squared test x= 23.49, df=1, p < 0.05). In total, I sa w 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 avian communities at both farms were largely composed of omnivorous species, consisting of about half (48%) of the total sp ecies. 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 ri ch although there was no significant difference in insectivorous species richness between th e 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 grea ter number of species (s = 34) than the far forest site (s = 32). There was no signifi cant 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 a nd the far-forest site (15%, 14 %) while rare species had the highest percentages of birds in both sites (56%, 55%)(Table 2). 4
Percentage of species in each feeding guild for each site 0% 10% 20% 30% 40% 50% 60% 70%Fr ugivorous/Granivoro us Om niv o r ous Insec t ivorous Ne c t ivorousFeeding Guild Near Far Figure 2: Feeding guild percentage for each site 5
Table 2. Bird species for both sites ca tegorized by feeding guild based on my observations (Stiles, 1989) and commonalit y. Commonality: C=common, F=fairly common, U=uncommon, 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) Whit e 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 Reds tart (U) Steely Vented Hummingbird (R) Green Backed Heron (R) House Wren (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) Common 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 Parakeet (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 per cent herbivory between the near forest site and the far from forest site (t-tes t t= .036, df = 176, p = 0. 972)(Figure 3). 6
Std. Dev. 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 herbiv ory 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 amount of peck marks than the far site which had an average of 0.26. However, no significant difference was found between the two sites (c hi-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 Figure 4. Mean number of pecks per site. 7
Discussion Previous studies have shown that avian dive rsity increases while herbivory decreases in shade grown coffee when compared with sun grown coffee (Perfecto et al. 2004, Sekercioglu, 2002). Although av ian diversity and abundance wa s significantly greater in the near than in the far forest site, there was no significant difference in insectivory or herbivory. It is possible that avian diversity was great er in the near forest site because the forest is providing more resources and a more diverse habitat, whic h has the potential to support a greater number of species. It could also be that the near fo rest site is not as exposed to the elements as the far from fore st site. My study i ndicates 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 cons istent with the result s of another study that found that diversity of frugivorous bird species decreased with distance from the forest (Luck et al. 2004). It is also possible that the bi rds seen only in the near forest site may not have been able to disperse to the site that was furt her from the forest (Emlen 1984). Fifteen bird species were found exclusively in the near fore st site while only four species were found exclusively in the far forest site. These fi ndings agree with another study that found that the best determinant of the persistence of understory insectivor ous birds in small fragments is their ability to disperse through deforested countryside habitats (Sekercioglu et al. 2001). Some of the speci es found exclusively in the co ffee farm near the forest are species that prefer forest e dge and second growth areas. On the other hand, all but one of the species found only in the coffee farm far from the forest are adapted to highly disturbed areas (Stiles 1989). These results suggest that, in orde r 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 longer 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 in sectivory and herbivory decreased, would be shown. This suggests that with conservation of avian diversity, the billions of dollars spent on pesticides each ye ar could be greatly reduced. Decreasing use of pesticides will also reduce the amount of indirect damages associated with their use including negative health effect s, ecosystem effects, and de velopment 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, than ks to Tom and Cam for being at my beck and call the whole time I was writing my paper! 8
9Literature 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 valu e of shade-grown coffee: A biological perspective using neotropical birds. Endangered Species Update 68: 122. Emlen, J. 1984. Population Biology: The Coe volution 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. Ma drigal. 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. A tlas 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. Natures Services: Natural Pest Control 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.
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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