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Diversidad de pajaros en el bosque fragmentario de 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).
Text in English.
Birds--Bajo del Tigre--Costa Rica--Puntarenas--Monteverde Zone
Corridors (Ecology)--Bajo del Tigre
Fragmented landscapes--Bajo del Tigre--Costa Rica--Monteverde Zone
Pajaros--Costa Rica--Puntarenas--Zona de Monteverde
Corredores(ecologia)--Bajo del tigre
Paisajes fragmentarios--Bajo del Tigre--Costa Rica--Puntarenas--Zona de Monteverde
Tropical Ecology--Summer 2008
Ecologia Tropical--Verano 2008
t Monteverde Institute : Tropical Ecology
Bird Diversity in Fragmented Forests in Monteverde, Costa Rica Heather Hulton Department of Biology, Carlow University ABSTRACT Due to deforestation, fragmented forests and second ary growth are replacing old growth forests. These fragments are reduced in biodiversit y. In this study, bird diversity of a premontane forest fragment, Bajo del Tigre, connected to the Monteverde Reserve through a corridor, and plus two other fragmented forests, Ca landria and House Fragment, in Monteverde, Costa Rica were compared. It was expect ed that the fragment with the highest degree of protection and is connected to th e Monteverde Cloud Forest Reserve should have a higher bird diversity. There is a dif ference between Bajo del Tigre and the two forest fragments in bird diversity when the Sha nnon-Weiner diversity index is calculated between Bajo del Tigre (HÂ’ = 2.78) and C alandria (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 deforestacin, bosques fragmentados y de crecimiento secundario estn reemplazando los busques primarios. Estos fragmento s estn reduciendo la biodiversidad. En este estudio, se compar la diversidad de aves d e un bosque fragmentado que est conectado a la Reserva de Monteverde a travs de un corredor y dos fragmentos ms, Calandria y House Fragment, en Monteverde, Costa Ri ca. Se eseraba que el fragmento con la mayora de proteccin y conectado a la Reser va de Monteverde tendra mas diversidad de aves. Hay una diferencia entre Bajo d el Tigre y los otros fragmentos en la diversidad de los pjaros al utilizar el ndice de diversidad Shannon-Weiner calculado entre Bajo del Tigre (HÂ’ = 2,78) y Calandria (HÂ’ = 2,04) (t = 7,39, p = <0,001) 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 Km2 per year (Nason et al. 1997). Forest fragments of natural habitats are then left behind. These fragments are entwined with Â“agriculture, secondary vegetation, and degraded la ndÂ” (Kramer 1997). Rolstad (1991) defined a fragmented forest as an area that is any Â“detached, isolated, or incomplete 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 huntin g. Biotic components of tropical forest
are highly vulnerable to habitat fragmentation beca use of this. Tropical forest biotas are forced to live in restricted and patchy distributio ns, which can increase their vulnerability to local extinction. The patchy conditions can hind er species interactions, especially for the species that have coevolved with one another (L aurance et al. 1997). There are multiple ecological factors that affect t he abundance of a certain species in a given area (Graham 2001). Fragments can vary i n vegetation, density, and species abundance, even if they originated from the same ol d-growth forest and were separated by deforestation (Riiter et al. 2000). One of the main concerns of deforestation is the lo ss of biodiversity (Kramer 1997), which can occur when substantial amounts of natural land are reduced to forest fragments that cannot support the original floral o r fauna (Ehrlich and Ehrlich 1990). Forest fragmentation can cause a decrease in abunda nce or extinction of certain species while species that are well adapted to colonizing s econd growth to thrive have a chance to thrive (MacArthur and Wilson 1967). The tropics inhabit seven percent of the earthÂ’s la nd surface area and contain an estimated ten to 30 million species, but the tropic s are still being deforested (Ehrlich and Ehrlich 1990). Each year, another 16 million hectar es 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 Ehrlich and Ehrlich (1990), bird and mammal extinction has rose to 40 to 400 times 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 high est degree of protection and is connected to the Monteverde Cloud Forest Reserve sh ould have a higher bird diversity. It is expected that there will have higher bird div ersity in the fragment, Bajo del Tigre, because it is connected to the Monteverde Cloud For est 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 and two forest fragments in Monteverde, Costa Rica were sur veyed during three weeks in July during the rainy season. Bajo del Tigre Monteverde Conservation League protects the pre-mon taine 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 F orest 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 encompasses 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, ther e were more species of fruiting trees available for frugivorous birds. Some of the fruiti ng trees surveyed include Besleria solanoides, Malvaviscus arboreus, Heliconia monteve rdensis, Chamaedorea costaricana, Cecropia spp., Guetarda poasana, Ficus spp., and some wild raspberry bushes. Calandria The second fragment, The Calandria, is approximatel y 1300 m in elevation and is approximately 120 m2. 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 distance were measured using a topographical map. This fragment was second in diversity of fruiting trees. Once aga in, the actual diversity was not calculated due to time constraints. Some of the fru iting trees surveyed include Cecropia spp., Heliconnia monteverdensis, Chamaedorea costar icana 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 eleva tion and is approximately 80 m2. It is 20 km away from the Monteverde Cloud Forest. The area and distance were measured using a topographical map. This fragment had the le ast 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 occasio ns when bird species were surveyed: twice in the morning (between 6:30 a.m. and 9:30 a. m.) and once in the after noon (between 3 p.m. and 6 p.m.) The field guide, The Birds of Costa Rica, by, Arri gues 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 and t he three-wattled bellbird, were located by their distinct vocal calls, and they were quanti fied if not seen. They were counted as one individual unless there was an obvious differen ce (such as individuals on different sides of the fragment). Once the data were collected, the percent of frugi vorous birds of each forest fragment was calculated (#S frugivorous/ total #S). Evenness, species richness, Smarg, and the Shannon-Weiner Diversity Index were calcula ted. A student-t test was used to determine the statistical significance of the resul ts. 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 birds w ith the amount of different fruiting trees available. Since the abundance of each fruiti ng tree and a true measure of biodiversity was not calculated there is not suffic ient 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 R eserve, maintains the highest level of evenness. This can be expected due to cost-benef it ratio for migration of the birds. Calandria and House Fragment can be expected to mai ntain similar diversity because they are similar in distance from the Monteverde Cl oud 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 (F ig. 3). Bajo del Tigre has the highest number of species only spotted in that fragment. Bajo del Tigre (HÂ’ = 2.78) has a higher bird diver sity 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 signi ficant difference in diversity HÂ’ values between the Calandria and House Fragment. DISCUSSION Deforestation can lead to forest fragments, which a re land islands on the mainland (MacArthur and Wilson 1967). There are three to fou r 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 fores ts. Because of deforestation, bird diversity is decreased due to a lower carrying capa city, further distance from old growth forests, and an increase in vulnerability to extinc tion. I found similar results in my study. The smallest and the most isolated fragments (Calan dria and House Fragment) maintain lower bird diversity than the fragment that is conn ected to the Monteverde Cloud Forest Reserve (Bajo del Tigre) through a corridor maintai ned the highest amount of biodiversity. Tropical tree species are vulnerable to fragmentat ion due to dispersal and genetic structure. Certain tree species must maintain a cer tain density for pollination and seed dispersal, and with decreased area and physical cha nges produced by fragmentation, many species are unable to survive landscape altera tion (Nason et al. 1997). Fruits are a main part of the diet of frugivorous species of bir ds, and with deforestation altering the composition of flora, there is bound to be a change in bird diversity. 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 ext inct. The species trapped by specialization are pressured by the shrinking habit ats from deforestation (Wilson 1992). Calandria and House Fragment contained less specie s of birds only surveyed in that fragment than Bajo del Tigre suggesting less s pecies are willing to migrate to a further forest fragment. Pioneering species take ov er more vulnerable species after deforestation (Lamb 1997). This further decreases b iodiversity even further than after those species that have disappeared solely from hab itat loss, especially when there is not a corridor between the fragment and the old growth. This supports the theory that as a habitat is destroyed, biodiversity is being destroy ed along with it (Nason et al. 1997). With the loss of bird diversity in fragmented fore sts, it is obvious that to save biodiversity there needs to be protection of old gr owth 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 maintain biodiversit y. As explained by Wilson (1992), Â“when an area is reduced to one tenth of its origin al size, the number of species eventually drops to one half.Â” If we want to keep b iodiversity, such as bird diversity, there needs to be protection of old growth forests along with corridors to the fragments. Some suggestions for further studies would be to c alculate the fruiting tree diversity and other resource diversities and compar e with corresponding bird guild diversities. Another fragment further from the Mont everde Cloud Forest Reserve should be compared with the three fragments to determine t he loss of bird diversity with distance.
ACKNOWLEDGMENTS A special thanks to my advisor, Tania Chavarria, fo r 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) Caldern for helpin g me at all times of the day. I would also like to th ank the Conservation League for putting efforts int o 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. Hein zman (eds). Lessons of the rainforest. 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 patte rns of keel-Billed toucans in a fragmented tropical landscape in Southern Mexico. BioOne: Volume 3, Iss ue 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 i n 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 communiti es. University of Chicago Press: United States of America. Lamb, D., J. Parrotta, R. Keenan, and N. Tucker. 19 97. Rejoining habitat remnants: restoring degraded rainforest lands. Pages 366-385 in William F. Laurance and Richard O. Bierregaard, Jr (eds). Tropical forest remnants: ecology, management and conservation of fragmented communities. University of Chicago Press: United States of Amer ica. 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. Sites, 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 remnants: 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 struct ure in fragmented tropical tree populations. Pages 304320 in William F. Laurance and Richard O. Bierregaard, Jr. (eds). Tropical forest remnants: 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 Ecology 4 (2): 3. [Online] URL: http://www.consecol.org/vol4/iss2/art3/ Rolstad, J. 1991. Consequences of forest fragmentat ion for dynamics of bird populations: conceptual issues and the evidence. Biological Journal of the Linnaean Society. 42: 149. Wilson, E.O. 1992. The diversity of life. W.W. Nort on & Company: New York, New York. Pg. 229.
n rrrrr n Figure 1. Percentage of Frugivorous birds species i n 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 specie s.
n n n n n nn rrrrr n Figure 2. Evenness for the three study sites. Bajo del Tigre has the highest evenness (E = 0.90). Calandria and House Fragment have similar ev enness with 0.81 and 0.78, respectively.
rrrrr n Figure 3. Speices Richness for the three study sit es. Bajo del Tigre has eight species seen in at least one other fragment (white) and 14 speci es only seen in that fragment (black). Calandria has nine species seen in at least one oth er 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 other fragment and seven speci es only seen in that fragment.
rrrrr n Figure 4. HÂ’ values for the three study sites. Baj o del Tigre has the highest ShannonWeiner diversity index (HÂ’ = 2.78). Calandria and House fragment have similar indexes, 2.04 and 2.15, respectively. The forest connected t o the Monteverde Cloud Forest Reserve maintains higher bird diversity. Table 1. This table lists the evenness, species ri chness, Smarg, and Shannon-Weiner diversity index for the three forests: Bajo del Ti gre, Calandria, and House Fragment. r n n n n n n
Table 2. The following three tables list the spec ies and number of individuals observed at Bajo del Tigre, Calandria, and House Fragment, r espectively. n r Black Guan Black Breasted Wood Gual Orange Bellied Trogon Lineated Foliage Grey Breasted Wood Wren Brown Jay Slate Throated Redstart Golden Browed Chlorophonia White Tipped Dove n Silvery Throated Tapacula Slaty Antwren n House Wren Great Tailed Grackle Blue Crowned Motmot Turkey Vulture Three Wattled Bellbird Clay Colored Robin Golden Crowned Warbler Yellow Throated Euphonia Long Tailed Manakin American Swallow Tailed Kite Hummingbird n r"#$r% 'r(rr(r') )*+n,"#-r$ #-rr) ,.) $"#r,/0 % /1r* 2#/3rr n n r$"#445678/$"#r,/0 &'r (r&)r "#$r%-r$ $"#r,r 9/#r'. )*+ 8r#"-rr) 8r# "r ""r*#2%,4r/