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Distribucin y abundancia de Epidendrum parkinsonianum (Orchidaceae) en relacin con el hbitat y el tipo de micro hbitat.
Distribution and abundance of Epidendrum parkinsonianum (Orchidaceae) in relation to habitat and microhabitat type
Orchid distribution and abundance are likely functions of both abiotic and biotic factors. Forty host trees were surveyed, 20 in a closed forest site and 20 in an open area, in Monteverde, Costa Rica. The distribution and abundance of Epidendrum parkinsonianum were examined in order to better understand how they are spatially distributed across habitats and microhabitats, and to suggest possible explanations for this distribution. Epidendrum parkinsonianum was significantly more common in the open area than the closed forest, with more orchids found per tree. Trees were divided into five tree zones to compare the distribution of orchids along abiotic gradients within microhabitats. Epidendrum parkinsonianum followed a random distribution in the open site, however in the closed site there were more orchids than expected in zone two and less than expected in zone four. In addition a significant correlation was found between the percent occupied by other vascular epiphytes and the E. parkinsonianum. Further investigation needs to be done in order to better understand exactly which factors are affecting the distribution and to what degree.
La distribucin y abundancia de las orqudeas es probablemente una funcin de factores tanto biticos como abiticos. Cuarenta rboles fueron considerados, 20 en un bosque cerrado y 20 en un rea abierta en Monteverde, Costa Rica. Este estudio examin la distribucin y la abundancia de Epidendrum parkinsonianum para entender mejor como se distribuan entre los hbitats y micro hbitats, y para sugerir algunas explicaciones para esta distribucin. Epidendrum parkinsonianum fue significativamente ms comn en el rea abierta que el bosque, con ms orqudeas en cada rbol. Los rboles fueron divididos en cinco zonas que correspondan al gradiente de los factores abiticos para comparar la distribucin de las orqudeas en los micro hbitats, Epidendrum parkinsonianum sigui una distribucin aleatoria en el sitio abierto; pero hubo ms orqudeas que las esperadas en la zona dos del bosque, y menos que las esperadas en la zona cuatro. Tambin se encontr una relacin significativa entre el porcentaje ocupado por otras epfitas vasculares y E. parkinsonianum. Se necesitan ms estudios para entender exactamente qu factores afectan la distribucin de las orqudeas.
Text in English.
Costa Rica--Puntarenas--Monteverde Zone
Costa Rica--Puntarenas--Zona de Monteverde
Tropical Ecology Spring 2005
Ecologa Tropical Primavera 2005
t Monteverde Institute : Tropical Ecology
1 Distribution and abundance of Epidendrum parkinsonianum (Orchidaceae) in relation to habitat and microhabitat type. Alyson Mohan Lucas Dept. Global Studies and Environmental Sciences, University of Minnesota Twin Cities _________________________________ _______________________________________ ABSTRACT Orchid distribution and abundance are likely functions of both abiotic and biotic factors. Forty host trees were surveyed, 20 in a closed forest site and 20 in an open area, in Monteverde, Costa Rica. The distribution and abundance of Epidendrum parkinsonianum were examined in order to better understand how they are spatially distributed across habitats and microhabitats, and to suggest possible explanations for this distribution. Epidendrum parkinsonianum was significantly more common in the open area than the closed forest, with more orchids found per tree. Trees were divided into five tree zones to compare the distribution of orchids along abiotic gradients within microhabitats. Epidendrum parkinsonianu m followed a random distribution in the open site, however in the closed site there were more orchids than expected in zone two and less than expected in zone four. In addition a significant correlation was found between the percent occupied by other vascu lar epiphytes and the E. parkinsonianum. Further investigation needs to be done in order to better understand exactly which factors are affecting the distribution and to what degree. RESUMEN La distribuciÃ³n y abundancia de las orquÃdeas es probablament e una funciÃ³n de factores tanto biÃ³ticos como abiÃ³ticos. Cuarenta Ã¡rboles fueron considerados, 20 en un bosque cerrado y 20 en un Ã¡rea abierta en Monteverde, Costa Rica. Este estudio examinÃ³ la distribuciÃ³n y la abundancia de Epidendrum parkinsonianum para entender mejor como se distribuÃan entre hÃ¡bitats y microhÃ¡bitats, y para sugerir algunas explicaciones para esta distribuciÃ³n. Epidendrum parkinsonianum fue significativamente mÃ¡s comÃºn en el Ã¡rea abierta que el bosque, con mÃ¡s orquÃdeas en cada Ã¡rbol. Los Ã¡rboles fueron divididos en cinco zonas que correspondÃan al gradiente de los factores abiÃ³ticos para comparar la distribucion de las orquÃdeas en los microhÃ¡bitats, Epidendrum parkinsonianum siguiÃ³ una distribuciÃ³n aleatoria en el sitio abierto; pero hubo mÃ¡s orquÃdeas que las esperadas en la zona dos del bosque, y menos que las esperadas en la zona cuatro. TambiÃ©n se encuentrÃ³ una relaciÃ³n significativa entre el porcentaje ocupado por otras epÃfitas vasculares y E. parkinsonianum. Se necesitan mÃ¡s estudios para entender exactamente que factores afectan la distribuciÃ³n de las orquÃdeas. INTRODUCTION The factors that determine the distribution and abundance of a given epiphytic orchid species are complex and numerous. They may involve chance, histo ry, adaptations to abiotic parameters, as well as interactions with other species, including hosts, pollinators, and competitors. (Walter, K.S., 1983.) This study examines the distribution and abundance of Epidendrum parkinsonianum in order to better under stand how they are
2 spatially distributed across habitats and microhabitats, and to suggest possible explanations for this distribution. Orchids are known to respond to variation in abiotic factors that differ between habitats and microhabitats, this makes them good candidates to study a variety of abiotic factors. In addition to the abiotic factors that affect the distribution of orchids interspecific interactions may also impact the distribution. Examples of possible species interactions could be with myco rrhize fungi, with pollinators, or with other competitive vascular epiphytes. (Walter, K.S., 1983.) Epidendrum parkinsonianum is a large conspicuous epiphyte that is locally abundant in adjacent patches of woods that differ in age and light conditions. Fu rther, due to the large size and long pendant leaves it is easily seen, even in the top of the crown, from the ground. These aspects make it a good candidate for documenting spatial patterns both across habitats and within the tree zones, which may differ in abiotic as well as biotic factors. Documentation of the spatial dispersion both systematically and quantitatively, will make it possible to hypothesize explanations that can be tested in future observational or experimental studies. METHODS AND M ATERIALS Study Orchid Epidendrum parkinsonianum is a large epiphytic orchid. The long pendant leaves are lanceolate shaped and can reach up to one meter long. Epidendrum parkinsonianum has a large green to white flower that ranges from 7 7.5 cm long. As the flower matures it gradually turns from white to yellowish orange. (Dressler, 1993.) There are usually 1 3 long lasting flowers, with one long ovary. Plants become reproductive year round, most frequently from spring to summer. (Simon and Schuster, 1988 .) Study Site The study site was located in a secondary growth lower montane wet forest. (Nadkarni and Wheelwright, 2000.) Data were taken both from property owned by the Monteverde Institute as well as neighboring private property, owned by Rachel and D wight Crandall. The Crandall site consisted of second growth forest scattered with large Cedrela trees, a driveway and a yard, it was considered the open site. The adjacent closed forest site consisted of secondary growth forest as well, with scattered lig ht gaps. Orchids were found on trees that lined the edges of light gaps. All surveyed trees ranged from elevations of 1500 m to 1650 m. Data Collection Data were collected from April 20 to May 8 th , 2005. The first 20 trees found in each site containing E pidendrum parkinsonianum were chosen. These trees were selected without
3 regard for host tree size or species. First the trees were numbered and labeled, their zones, correspo nding to the life zones laid out by Johansson (1996). (Figure 1). Using binoculars to aid in orchid identification, orchids in each zone were counted and plant. Plant s that were longer than 0.3 meters or with flowers were considered reproductive. Next using a compass the branch facing in the northern most direction was identified. The tree was then surveyed for vascular epiphytes within zones one and two, past zone two the previously mentioned branch was only considered. The branch length and percent of vascular epiphytes other than E. parkinsonianum were estimated. Percent occupied was determined by visually dividing the branch into halves and then breaking down the h alves until vascular epiphytes other than E. parkinsonianum could be easily described. If a branch was found to have fewer than five epiphytes it was considered to have 5% coverage. Data Analysis I ran a simple linear regression to compare Epidendrum par kinsonianum abundance to DBH, a contingency table analysis to compare the frequency of E. parkinsonianum across tree zones, and regression analyses for the number of E. parkinsnianum vs. the percent area occupied by other vascular epiphytes. RESULTS A total of 347 Epidendrum parkinsonianum were sampled between the two sites, 33 in the woods and 314 in the open area. The average number of orchids per tree in the open area +/ 1S.E. 15.7, in the woods site +/ 1 S.E. 1.65. (Figure 2.) The simple linear regression of the number of E. parkinsonianum versus host tree DBH was not significant for the open area compared to the woods. (Figure 3.) The distribution of Epidendrum parkinsonianum across tree zones is non random: Zone two host trees within the wood s site had more orchids than expected, while Zone four hosts had fewer than expected. (Table 1.) DISCUSSION The overall abundance of Epidendrum parknsonianum was higher in the open area when compared to the woods, with more orchids found per tree. The majority of the orchids within the open area were found in higher tree zones in the open area compared to the light gap trees in the woods. Within the microhabitats the orchids were randomly distributed in the open area site. However distribution within th e woods site was not random, zone two had more than expected and zone four had fewer that expected. Which is the opposite than what would have been expected if orchid distribution were only of function of light. There are many factors that could have affe cted the distribution and concentration of the orchids. A logical first explanation is that the higher orchid concentration in the
4 open area is a function of light. Clearly there was more available light in the open area than the closed woods. Further all of the host trees within the woods site were found along light gaps. If Epidendrum parkinsonianum were in fact a good colonaizer it would follow that it would reach high densities quickly in the open area. Therefore the decreased amount of light in the woo ds area might be a possible explanation for the decreased abundance of E. parkinsoniaunm . This pattern may also explain the less even distribution of E. parkinsonianum within the wood site. The orchids in the woods site were mainly concentrated in zone two ; it is possible that due to the host trees location on the edge of a light gap that zone two may have been high in light levels. However, it is highly unlikely that there was limited light in Zone four. Therefore it is likely that there is another factor that is affecting the abundance and distribution of E. parkinsonianum within the woods site. Species interactions were considered as a possible pressure affecting the distribution of Epidendrum parknsonianum. These interspecies interactions may be mutuali stic, competitive or something in between, and especially important in zone four. Many vascular epiphytes thrive in zone four where they have horizontal structural support in addition to proper light and nutrient rich precipitation. If many epiphytes are in fact better adapted to survive in zone four that competition for space could be especially strong there. Within this study there is evidence that is consistent that competition for free space may be important. If Epidendrum parkinsonianum distribution were in fact a function of a competitive species interaction, it would follow that when there are higher levels of vascular epiphytes coverage there are decreased levels of E. parkinsonianum and vice versa, more E. parkinsonianium would result in decrease d coverage of other vascular epiphytes. Future studies should considerlimiting their host trees to a sngle species, this will help to eliminate some factors, such as bark type, fissure depth, and pH. In addition it would be helpful to survey more trees an d take light, mist, and temperature to more accurately establish the gradients within each of the tree zones. ACKNOWLEDGEMENTS First thank you Karen for sharing you love of Orchids with me, without your support and guidance I would have never been abl e to spend so much time with such beautiful flowers. Thank you to Matt and Ollie for helping with every single aspect of my project. Alan thank you for the hug the night before the symposium, I was near a breakdown. Thank you Jave for always being there fo r me. Thank you to Patty Ortiz for letting me look at your orchids. Thank you to the Estacion Biologica de Monteverde for providing me with a home and an amazing forest. Gracias a mi familia tica, Viki y Andres y para todo su carino. And thank you to all o f my gringos for helping me and sharing computers with me near the end. Lastly thank you to my wonderful artist friend, Elissa, for helping me to draw trees.
5 LITERATURE CITED Dressler, R.L. 1993. Field Guide to the Orchids of Costa Rica and Panama. Coms tock Publishing Associates. Ithaca, New York. Hietz, P and U. Heitz Seifert. 1995. Intra and interspecific relations within an epiphytic community in a Mexican humid montane forest. Selbyana 16: Johansson (1996). In Freiburg. Spatial distribution of vascular epiphytes on three emergent tree species. in French Guiana. Biotropica 28: 345 355. Nadkarni, N.M., N.T. Wheelwright. 2000. Monteverde. Oxford University Press, New York, New York. Raich, J. 1988. Seasonal and Spatial Variation in the Light Envi ronment I a Tropical Diptocarp Forest and Gaps. Isotropic 21(4): 299 301. Schuster, S. Orchids. 1988. Simon and Schuster INC. New York, New York. Walter, K.S. 1983. Orchids. In Janzen, D. (Ed.) Costa Rican Natural History. University of Chicago Press, C hicago, Illinois.
6 ________________ ____________________________________________ Figure 2. Abundance of Epidendrum parkinsonianum compared to host tree DBH (cm). There is no correlation. Open site, R 2 = 0.0743, N = 20, P = 0.8016. Woods site, R 2 = 0.0913, N = 20, P > 0.05. _____________ _______________________________________________ _____________________________________________________________ Table 1. Comparison of expected Epidendrum parkinsonianum frequencies to the observed, in both an open and woods site. Number of Epidendrum p arkinsonianum was counted in three microhabitat zones, zones one and five were omitted due to low abundance of orchids from either site. ( 2 = 30.91; P < 0.05.) See Figure 1 for tree zone descriptions. ___________________________________________________ __________ Tree Zone Open Site Open Site Woods Site Woods Site Expected Observed Expected Observed Zone 2 104.73 90 13.28 28 Zone 3 115.38 122 14.68 8 Zone 4 63.9 72 8.1 0
7 Figure 3 . Relative numbers of Epidendrum parki nsonianum per tree found in two adjacent sites. _____________________________________________________________
8 ________________________________________________________________________ Figure 4. Plot of total number of Epiden drum parkinsonianum against percentage occupancy of other vascular epiphytes, within zone two of the closed forest site. Total E. parkinsonianum I zone two of woods, R2 = 0.2505, N = 28, P = 0.0150. Reproductive E. parkinsonianum , R 2 = 0.1869, N = 21, P = 0.0327, Pre reproductive E. parkinsonianum , R 2 = 0.2670, N = 7, P = 0.0422. ________________________________________________________________________