Bird Diversity in Fragmented Forests in Monteverde, Costa Rica Heather Hulton Department of Biology, Carlow University ABSTRACT Due to deforestation, fragmented forests and secondary growth are replacing old growth forests. These fragments are reduced in biodiversity. In this study, bird diversity of a pre montane forest fragment, Bajo del Tigre, connected to the Monteverde Reserve through a corridor, and plus two other fragmented forests, Calandria and House Fragment, in Monteverde, Costa Rica were co mpared. It was expected that the fragment with the highest degree of protection and is connected to the Monteverde Cloud Forest Reserve should have a higher bird diversity. There is a difference between Bajo del Tigre and the two forest fragments in bird d iversity when the Shannon Weiner diversity index is calculated between Bajo del Tigre HÂ€ = 2.78 and Calandria HÂ€ = 2.04 Modified t test, t = 7.39, p = <0.001 along with Bajo del Tigre and House Fragment HÂ€ = 2.15 Modified t test, t = 5.52, p = <0. 001. RESUMEN Debido a deforestaciÃ³n, bosques fragmentados y de crecimiento secu ndario estÃ¡n reemplazando los bo sques primarios. Estos fragmentos estÃ¡n reduciendo la biodiversidad. En este estudio, se comparÃ³ la diversidad de aves de un bosque fragmen tado que estÃ¡ conectado a la Reserva de Monteverde a travÃ©s de un corredor y dos fragmentos mÃ¡s, Calandria y House Fragment, en Monteverde, Costa Rica. Se es p eraba que el fragmento con la mayorÃa de protecciÃ³n y conectado a la Reserva de Monteverde tendrÃa mÃ¡s diversidad de aves. Hay una diferencia entre Bajo del Tigre y los otros fragmentos en la diversidad de los pÃ¡jaros al utilizar el Ãndice de diversidad Shannon Weiner calculado entre Bajo del Tigre HÂ€ = 2,78 y Calandria HÂ€ = 2,04 t = 7,39, p = <0,0 01 y con Bajo del Tigre y House Fragment HÂ€ = 2,15 t = 5,52, p = <0,001. INTRODUCTION Natural habitats, especially regions located in the tropics, are being destroyed at frightening rates of 100,000 to 200,000 Km 2 per year Nason et al. 1997. Forest fragments of natural habitats are then left behind. These fragments are entwined with Âagriculture, secondary vegetation, and degraded landÂ‚ Kramer 1997. Rolstad 1991 defined a fragmented forest as an area that is any Âdetached, isolated, or incomplet e part broken away from a whole.Â‚
Forest fragments lead to the loss and alteration of landscapes. This causes an increase in edge effects, an isolation of a forest population, possible introduction of invasive species, and a new accessibility to hunting. Biotic components of tropical forest are highly vulnerable to habitat fragmentation because of this. Tropical forest biotas are forced to live in restricted and patchy distributions, which can increase their vulnerability to local extinction. The patchy co nditions can hinder species interactions, especially for the species that have coevolved with one another Laurance et al. 1997. There are multiple ecological factors that affect the abundance of a certain species in a given area Graham 2001. Fragme nts can vary in vegetation, density, and species abundance, even if they originated from the same old growth forest and were separated by deforestation Riiter et al. 2000. One of the main concerns of deforestation is the loss of biodiversity Kramer 1997 , which can occur when substantial amounts of natural land are reduced to forest fragments that ca nnot support the original flora or fauna Ehrlich and Ehrlich 1990. Forest fragmentation can cause a decrease in abundance or extinction of certain species while species that are well adapted to colonizing second growth to thrive have a chance to thrive MacArthur and Wilson 1967. The tropics inhabit seven percent of the earthÂ€s land surface area and contain an estimated ten to 30 million species, but the tropics are still being deforested Ehrlich and Ehrlich 1990. Each year, another 16 million hectares of forest disappear. It is estimated that only 22% of the world's old growth original forest cover remains intact Gurney et al 1993. According to Ehrl ich and Ehrlich 1990, bird and mammal extinction has rose to 40 to 400 timeÂ€s greater extinction rate in this last century mainly due to deforestation. In this study, bird diversity of three pre montane forest fragments was compared. It was hypothesized that the fragment with the highest degree of protection and is connected to the Monteverde Cloud Forest Reserve should have a higher bird diversity. It is expected that there will have higher bird diversity in the fragment, Bajo del Tigre, because it is connected to the Monteverde Cloud Forest Reserve through the corridor, Rio Guacimal, and because of the corridor, the fragment can maintain its biodiversity. MATERIALS AND METHODS One pre montane forest fragment with a corridor to the Monteverde Reserve a nd two forest fragments in Monteverde, Costa Rica were surveyed during three weeks in July during the rainy season. Bajo del Tigre Monteverde Conservation League protects the pre montane forest, Bajo del Tigre. This forest was once disturbed, but through conservation efforts, it is a thriving new growth fragment. It is connected to the Monteverde Cloud Forest Reserve through a corridor, Rio Guacimal. The forest is at approximately 1300 m in elevation. It is part of the ChildrenÂ€s Eternal Rainforest that e ncompasses 22,500 hectares of virgin and secondary forest. This forest has the greatest diversity of fruiting trees. The actual diversity was not calculated due to time restraints, but based on judgment, there were more species of fruiting trees available for frugivorous birds. Some of the fruiting trees surveyed include Besleria solanoides, Malvaviscus arboreus, Heliconia monteverdensis, Chamaedorea costaricana, Cecropia spp., Guetarda poasana, Ficus spp., and some wild raspberry bushes.
Calandria The seco nd fragment, The Calandria, is approximately 1300 m in elevation and is approximately 120 m 2 . It is 22 km away from the Monteverde Cloud Forest This distance was determined by the closest point on the map to the Monteverde Cloud Forest. The area and dist ance were measured using a topographical map. This fragment was second in diversity of fruiting trees. Once again, the actual diversity was not calculated due to time constraints. Some of the fruiting trees surveyed include Cecropia spp., Heliconnia montev erdensis, Chamaedorea costaricana , and a fruiting shrub from the family Solanaceae. House Fragment The third fragment is located behind a house in Los Llanos, which will be referred to as House Fragment. It is approximately 1300 m in elevation and is appro ximately 80 m 2 . It is 20 km away from the Monteverde Cloud Forest. The area and distance were measured using a topographical map. This fragment had the least diversity of fruiting trees. Much like the previous fragments, this was based off of judgment due to time constraints. There was one main fruiting genus, Conostegia spp . Surveying Bird Species For each fragment there were three separate occasions when bird species were surveyed: twice in the morning between 6:30 a.m. and 9:30 a.m. and once in the afternoon between 3 p.m. and 6 p.m. The field guide, The Birds of Costa Rica, by, Arrigues and Dean 2007, was used to identify bird species. The orange bellied trogon was identified by its unique call. Certain birds, such as the keel billed toucan an d the three wattled bellbird, were located by their distinct vocal calls, and they were quantified if not seen. They were counted as one individual unless there was an obvious difference such as individuals on different sides of the fragment. Once the data were collected, the percent of frugivorous birds of each forest fragment was calculated #S frugivorous/ total #S. Evenness, species richness, Smarg, and the Shannon Weiner Diversity Index were calculated. A student t test was used to determine the s tatistical significance of the results. RESULTS The percent of frugivorous birds was 63.94%, 69.23% and 57.14% for Bajo del Tigre, Calandria, and House Fragment, respectively Fig. 1. House Fragment has a corresponding low percentage of frugivorous bird s with the amount of different fruiting trees available. Since the abundance of each fruiting tree and a true measure of biodiversity was not calculated there is not sufficient evidence to say whether these data reflect a true difference. Evenness values for Bajo del Tigre, Calandria, and House Fragment were calculated to be 0.90, 0.81 and 0.78, respectively Table 1 and Fig. 2. Bajo del Tigre, the fragment connected to the Monteverde Cloud Forest Reserve, maintains the highest level of evenness. This ca n be expected due to cost benefit ratio for migration of the birds. Calandria and House Fragment can be expected to maintain similar diversity because they are similar in distance from the Monteverde Cloud Forest. There were 31 different species of birds observed in all three forest fragments Fig. 2 The number of species only found for Bajo del Tigre, Calandria, and House
Fragment are 14/22, 4/13, and 7/14, respectively Fig. 3. Bajo del Tigre has the highest number of species only spotted in that frag ment. Bajo del Tigre HÂ€ = 2.78 has a higher bird diversity compared with Calandria HÂ€ = 2.04 Modified t test, t = 7.39, p = <0.001. Bajo del Tigre has a higher bird diversity compared with House Fragment HÂ€ = 2.15 Modified t test, t = 5.52, p = <0.001 Table 1 and Fig. 4. There was not a significant difference in diversity HÂ€ values between the Calandria and House Fragment. DISCUSSION Deforestation can lead to forest fragments, which are land islands on the mainland MacArthur and Wilson 1967 . There are three to four species becoming extinct everyday by anthropogenic causes in Tropical Moist Forests Ehrlich and Ehrlich 1990, and when a part of the forest is isolated, the biodiversity is inevitably going to decrease faster than the three to four species a day in fragmented forests. Because of deforestation, bird diversity is decreased due to a lower carrying capacity, further distance from old growth forests, and an increase in vulnerability to extinction. I found similar results in my study. The smallest and the most isolated fragments Calandria and House Fragment maintain lower bird diversity than the fragment that is connected to the Monteverde Cloud Forest Reserve Bajo del Tigre through a corridor maintained the highest amount of biodi versity. Tropical tree species are vulnerable to fragmentation due to dispersal and genetic structure. Certain tree species must maintain a certain density for pollination and seed dispersal, and with decreased area and physical changes produced by fragm entation, many species are unable to survive landscape alteration Nason et al. 1997. Fruits are a main part of the diet of frugivorous species of birds, and with deforestation altering the composition of flora, there is bound to be a change in bird diver sity. In the tropics, there are more species that have coevolved together, and when one species is lost, it is just a matter of time before the other species becomes extinct. The species trapped by specialization are pressured by the shrinking habitats fro m deforestation Wilson 1992. Calandria and House Fragment contained less species of birds only surveyed in that fragment than Bajo del Tigre suggesting less species are willing to migrate to a further forest fragment. Pioneering species take over more vulnerable species after deforestation Lamb 1997. This further decreases biodiversity even further than after those species that have disappeared solely from habitat loss, especially when there is not a corridor between the fragment and the old growth. T his supports the theory that as a habitat is destroyed, biodiversity is being destroyed along with it Nason et al. 1997. With the loss of bird diversity in fragmented forests, it is obvious that to save biodiversity there needs to be protection of old g rowth forests. For those forests that have already been disturbed and turned into fragments, a corridor needs to be formed between the old growth forest and fragment. The connections will allow species to migrate into the fragments, which will help maintai n biodiversity. As explained by Wilson 1992, Âwhen an area is reduced to one tenth of its original size, the number of species eventually drops to one half.Â‚ If we want to keep biodiversity, such as bird diversity, there needs to be protection of old gro wth forests along with corridors to the fragments. Some suggestions for further studies would be to calculate the fruiting tree diversity and other resource diversities and compare with corresponding bird guild
diversities. Another fragment further from the Monteverde Cloud Forest Reserve should be compared with the three fragments to determine the loss of bird diversity with distance. ACKNOWLEDGMENTS A special thanks to my advisor, Tania Chavarria, for helping me with my project. I would also like to thank my professors, Karen and Alan Masters for teaching me about biodiversity and anthropogenic effects on natural habitats. I would like to thank Pablo Allen Monge and Jose Carlos Moncho CalderÃ³n for helping me at all times of the day. I would also lik e to thank the Conservation League for putting efforts into saving biodiversity at Bajo del Tigre.
Literature Cited: Ehrlich, A. H. and P. R. Ehrlich. 1990. Extinction: life in peril. Pages 95 105 in S. Head and R. Heinzman eds. Lessons of the rainf orest. Sierra Club Books: San Francisco. Garrigues, R. and R. Dean. The birds of Costa Rica: a field guide. Comstock Publishing Associates, Cornell University Press: Ithaca, New York. Graham, C. 2001. Factors influencing movement patterns of keel Bille d toucans in a fragmented tropical landscape in Southern Mexico. BioOne: Volume 3, Issue 104. Page 776 784. Gurney, R.J, J.L. Foster, and C. L. Parkinson. 1993. Atlas of satellite observations related to global change. Cambridge Press. Kramer, E. A. 1997 . Measuring landscape changes in remnant tropical dry forests. Pages 386 399 in William F. Laurance and Richard O. Bierregaard, Jr. eds. Tropical forest remnants: ecology, management and conservation of fragmented communities. University of Chicago Pre ss: United States of America. Lamb, D., J. Parrotta, R. Keenan, and N. Tucker. 1997. Rejoining habitat remnants: restoring degraded rainforest lands. Pages 366 385 in William F. Laurance and Richard O. Bierregaard, Jr. eds. Tropical forest remnants: ec ology, management and conservation of fragmented communities. University of Chicago Press: United States of America. LauranceW.F, R. O. Bierregaard, Jr., C. Gascon, R. K. Didham, A. P. Smith, A. L. Lynam, V. M. Viana, T. E. Lovejoy, K. E. Sieving, J. W. S ites, M. Anderson, M. D. Tocher, E. A. Kramer, C. Restrepo, and C. mortiz. 1997. Tropical forest fragmentation: synthesis of a diverse and dynamic discipline. Pages 502 514 in William F. Laurance and Richard O. Bierregaard, Jr. eds. Tropical forest remn ants: ecology, management and conservation of fragmented communities. University of Chicago Press: United States of America. MacArthur, R. H. and E. O. Wilson. 1967. The theory of island biogeography. Princeton University Press: United States of America . Pg.114. Nason, J. D., Preston Raldrick, and J.L. Hamrick. 1997. Dispersal and the dynamics of genetic structure in fragmented tropical tree populations. Pages 304 320 in William F. Laurance and Richard O. Bierregaard, Jr. eds. Tropical forest remnant s: ecology, management and conservation of fragmented communities. University of Chicago Press: United States of America. Riitters, K., J. Wickham, R. OÂ€Neil, B. Jones, and E. Smith. 2000. Global scale patterns of forest fragmentation. Conservation Ecol ogy 4 2: 3. [Online] URL: http://www.consecol.org/vol4/iss2/art3/ . Rolstad, J. 1991. Consequences of forest fragmentation for dynamics of bird populations: conceptual issues and the evidence. Biolo gical Journal of the Linnaean Society. 42: 149. Wilson, E.O. 1992. The diversity of life. W.W. Norton & Company: New York, New York. Pg. 229.
0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00 Bajo del Tigre Calandria House Fragment Forest Fragment Percentage % Figure 1. Percentage of Frugivorous birds species in the study sites. Bajo del Tigre had a 63.94% frugivorous bird species. Calandria had a 69.23%, frugivorous bird species. House Fragment had a 57.14% frugivorous bird species.
0.72 0.74 0.76 0.78 0.80 0.82 0.84 0.86 0.88 0.90 0.92 Bajo del Tigre Calandria House Fragment Forest Fragment Evenness Figure 2. Evenness for the three study sites. Bajo del Tigre has the highest evenne ss E = 0.90. Calandria and House Fragment have similar evenness with 0.81 and 0.78, respectively.
0 5 10 15 20 25 Bajo del Tigre Calandria House Fragment Forest Fragment Number of Species Figure 3. Spe c i es Richness for the three study sites. Bajo del Tigre has eight species seen in at least one other fragment wh ite and 14 species only seen in that fragment black. Calandria has nine species seen in at least one other fragment and four species only seen in that fragment species only seen in that fragment. House Fragment has seven species seen in at least one oth er fragment and seven species only seen in that fragment.
0 0.5 1 1.5 2 2.5 3 Bajo del Tigre Calandria House Fragment Forest Fragment H' Figure 4. H values for the three study sites. Bajo del Tigre has the highest Shannon Weiner diversity index H = 2.78. Calandria and House fragment have simi lar indexes, 2.04 and 2.15, respectively. The forest connected to the Monteverde Cloud Forest Reserve maintains higher bird diversity. Table 1. This table lists the evenness, species richness, Smarg, and Shannon Weiner diversity index for the three forests: Bajo del Tigre, Calandria, and House Fragment. Evenness Species Richness Smarg H' Bajo del Tigre 0.90 22 4.38 2.78 Calandria 0.81 14 17.00 2.04 House Fragment 0.78 13 2.56 2.15
Table 2. The following three tables list the specie s and number of individuals observed at Bajo del Tigre, Calandria, and House Fragment, respectively. Bajo del Tigre Number of Individuals Black Guan 5 Black Breasted Wood Gual 1 Orange Bellied Trogon 3 Lineated Foliage 2 Grey Breasted Wood Wren 5 Brown Jay 5 Slate Throated Redstart 3 Golden Browed Chlorophonia 4 White Tipped Dove 8 Silvery Throated Tapacula 1 Slaty Antwren 8 House Wren 13 Great Tailed Grackle 9 Blue Crowned Motmot 3 Turkey Vulture 4 Three Wattled Bellbird 1 Clay Colored Robin 12 Golden Crowned Warbler 7 Yellow Throated Euphonia 20 Long Tailed Manakin 5 American Swallow Tailed Kite 1 Hummingbird 1 N = 121 Calandria Number of Individuals Three Wattled Bellbird 26 Keel Billed Toucan 19 Great Tailed Grackle 3 Tu rkey Vulture 8 Short Billed Pigeon 4 Plain Wren 30 Crimson Fronted Parakeet 23 Squirrel Cukoo 1 White Collared Swift 7 Hummingbird 2 Brown Jay 12 Red Crowned Ant Tanager 7 N= 143 House Fragment Number of Individuals White Tipped Dove 9 Mottled Owl 1 White Collared Swift 11 Keel Billed Toucan 16 Great Kiskadee 2 Three Wattled Bellbird 19 Plain Wren 11 White Collared Seedeater 3 Yellow Billed Cacique 11 Turkey Vulture 4 Orange Chinned Parakeet 4 Orange Billed Nightingale Thrush 2 Clay C olored Robin 11 House Sparrow 5 N= 109
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Diversidad de aves en los bosques fragmentados en Monteverde, Costa Rica
Bird diversity in fragmented forests in Monteverde, Costa Rica
Due to deforestation, fragmented forests and secondary growth are replacing old growth forests. These fragments are reduced in biodiversity. In this study, bird diversity of a pre-montane forest fragment, Bajo del Tigre, connected to the Monteverde Reserve through a corridor, and plus two other fragmented forests, Calandria and House Fragment, in Monteverde, Costa Rica were compared. It was expected that the fragment with the highest degree of protection and is connected to the Monteverde Cloud Forest Reserve should have a higher bird diversity. There is a difference between Bajo del Tigre and the two forest fragments in bird diversity when the Shannon-Weiner diversity index is calculated between Bajo del Tigre (H = 2.78) and Calandria (H = 2.04) (Modified t-test, t = 7.39, p = <0.001) along with Bajo del Tigre and House Fragment (H = 2.15) (Modified t-test, t = 5.52, p = <0.001).
Debido a la deforestacin, los bosques fragmentados y de crecimiento secundarios estn reemplazando a los bosques primarios. Estos fragmentos estn reduciendo la biodiversidad. En este estudio, se comparo la diversidad de aves de un bosque fragmentado que esta conectado a la Reserva de Monteverde a travs de un corredor biolgico y dos fragmentos mas la Calandria y House Fragment, en Monteverde, Costa Rica.
Text in English.
Fragmented landscapes--Costa Rica--Monteverde Zone
Birds--Variation--Costa Rica--Puntarenas--Monteverde Zone
Deforestation--Costa Rica--Monteverde Zone
Paisajes fragmentados--Costa Rica--Zona de Monteverde
Aves--Variacin--Costa Rica--Zona de Monteverde
Deforestacin--Costa Rica--Zona de Monteverde
Tropical Ecology 2006
Ecologa Tropical 2006
Riqueza de especies
t Monteverde Institute : Tropical Ecology