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Allen, Cierra Y
La disponibilidad de nutrientes y la abundancia de protistas en bromelias del bosque nuboso
Nutrient availability and protist abundance in cloud forest Bromeliads
Protists are microscopic organisms which play a vital role in nutrient degradation in tank bromeliads (Carrias et al. 2001). Their communities provide good subjects of study for the effects of nutrient availability in an ecosystem. One hypothesis says that the number of individuals that an ecosystem harbors is determined by the total energy that enters. This study tested the prediction that there will be a relationship between nutrient availability and abundance of protists in tank bromeliads. Data were collected among 25 bromeliads located within the Monteverde Cloud forest, Cerro Plano, Costa Rica and the following parameters were estimated: the number of protists and nutrient resources (canopy density, water volume, tank diameter, and detritus dry weight). Regressions analyses showed there were only significance between detritus weight by water volume and number of detritivores by number of photosynthetic protists. This study shows that none of the resources tested were significant in determining protist abundance in bromeliad tank communities, however, further study is needed.
Los protistas son organismos microscpicos que desempean un papel vital en la degradacin de nutrientes en el tanque de las bromelias (Carrias et al. 2001). Sus comunidades proporcionan buenos temas de estudio para los efectos de la disponibilidad de nutrientes en un ecosistema. Una hiptesis dice que el nmero de los individuos que un ecosistema abriga est determinado por la energa total que entra. Este estudio prob la prediccin de que habr una relacin entre la disponibilidad y la abundancia de nutrientes de protistas en los tanques de las bromelias.
Text in English.
Tropical Ecology 2006
Ecologa Tropical 2006
Puertos del ecosistema
t Monteverde Institute : Tropical Ecology
Nutrient Availability and protist abundance in Cloud Forest Bromeliads Cierra Y. Allen Department of Biology, Spelman College ABSTRACT Protists are microscopic organisms which play a vital role in nutrient degradation in tank bromeliads (Carrias et al. 2001). Their communities provide good subjects of study for the effects of nutrient availability in an ecosystem. One hypothesis says that the number of individuals that an ecosystem harbors is determined by to total energy that enters. This st udy tested the prediction that there will be a relationship between nutrient availability and abundance of protists in tank bromeliads. Data were collected among 25 bromeliads located within the Monteverde Cloud forest, Cerro Plano, Costa Rica and the following parameters were estimated: the number of protists and nutrient resources (canopy density, water volume, tank diameter, and detritus dry weight). Regressi ons analyses showed there were only significance between detritus weight by water volume and number of detritivores by number of photosynthetic protists. This study shows that none of the resources tested we re significant in determining protist abundance in bromeliad tank communities, however, further study is needed. RESUMEN Protists es los organismos microscpicos que desempean un papel vital en la degradacin nutriente en los bromeliads del tanque (Carrias y otros. 2001). Sus comunidades proporcionan buenos temas del estudio para los efectos de la disponibilidad nutriente en un ecosistema. Una hiptesis dice que el nmero de los individuos que un ecosistema abriga est determinado cerca para sumar la energa que entra. Este estudio prob la prediccin que habr una relacin entre la disp onibilidad y la abundancia nutrientes de protists en bromeliads del tanque. Los datos fueron recogidos en tre 25 bromeliads situados dentro del bosque de la nube de Monteverde, Cerro Plano, Costa Rica y los parmetros siguientes eran estimados: el nmero de protists y de recursos del alimento (densidad del pabelln, volumen del agua, dimetro del tanque, y peso seco del detritus). Los anlisis de las regresione s demostrados all eran sola mente significacin entre el peso del detritus al lado de volumen del agua y nmero de detritivores por el nmero de protists fotosintticos. Este estudio demuestra que ningunos de los recursos probados eran significativos en la determinacin de abundancia del protist en comunidades del tanque del bromeliad, sin embargo, el estudio adicional es necesario. INTRODUCTION Tank bromeliads are considered keystone species, especially in tropical forest (Carrias et al. 2001). Bromeliads are plants whose leav es are arranged spirally, forming a rosette that enables some species to store water that falls from the canopy as well as hold decaying materials; this tank provides the plant with both water and essential nutrients (Morales 2000). Fallen debris is caught by the bromeliads rosette formation serves as one of the main sources of nutrients for the plant. These nutrients are absorbed by the roots and trichomes growing inside of th e tank (Morales 2000). Thus, these tank
bromeliads create their own phytotelm communitie s. Phytotelmata refers to small bodies of water within leaves, flowers, and tree ho les. The phytotelm communities within these tanks represent almost all major groups of fres hwater organisms (Carri as et al. 2001). Though there are many macro and micro organisms represented in these communities, protists are one of most significant contributors. Protists are unicelluar eukaryotes that obtain their energy and nut rients by heterotro phy, although some may contain chloroplasts for photos ynthesis (Patterson 1998). They are essential in phytotelm communities because of the role they play in releasing nutrients to the plant by acting as pathways for dissolved organic matter, a nd by consuming bacteria (Spaulding 2005). Despite their small size, protists play a v ital role in these tank bromeliad ecosystems, therefore, playing a vital role in tropical forest ecosystems. The tanks of bromeliads are isolated communities, meaning that, protist inhabitants cannot move freel y from one bromeliad to another. Therefore, these communities can be used as model systems to understand factors that influence the structure of natural communities, such as nutri ents or weather patterns (Armbruster et al. 2002). Also, because of the tanks small size, the whole community from each plant can be collected and quantified w ith a degree of accuracy not pos sible in larger ecological systems (Richardson et al. 2000). Thus, brom eliads allow for accurate study of the cause and consequence of nutrient availability in ecosystems. Nutrient availability should have a huge impact on the number of individua ls according to the More Individuals Hypothesis. This states that a more nutri ent-rich habitat has more individuals and species, because in productive habitats even scarce species are sufficiently abundant to resist extinction (Srivastava & Lawton1998). Th erefore, bromeliads with more nutrients according to this hypothesis should have mo re individuals. This study will explore patterns between the numbers of individuals in protist communities and the amount of nutrients. It tests the More Individuals Hypothesis with the prediction that the number of protists will increase in a tank as the amount of nutrients increases. MATERIALS AND METHODS This study was conducted in closed canopy cl oud forest in Cerro Plano, Costa Rica located behind the Monteverde Biological Sta tion at an altitude of 1540-1750m. A total of 25 bromeliads were sampled for this st udy which included a variety of tank species and sizes. Only one bromeliad was sampled from each tree in order to keep the samples as independent as possible. There were four parameters estimated : canopy density, tank diameter, volume of water in the tank, and detritus dry weight. Canopy density was quantified using a canopy densiometer. Tank diameter was meas ured (mm) using a caliper. The water within the tank was drained using a pipette, then gravity filtered, placed in a graduated cylinder, and the volume (mL) recorded. The collected water was homogenized by shaking the sample and two drops were view ed under a microscope at a magnitude of 400x. The number of protists was quantified usi ng a five point system of analysis. With this system of analysis, five different fields of view of the micros cope were viewed and the protists were counted in each individual fiel d. Two groups of protists were identified: photosynthetic protists (possessing pigmentation) and detritivores (lacking pigmentation). The five fields of view were summed giving the total number of protists. The detritus
that was filtered plus the detr itus that was initially colle cted was dried and weighed. With those measurements, a regression analysis was run to identify possible relationships between the aforementioned parameters and the numbers of individuals. RESULTS Of the nineteen regressions run, only volume of water by the detritus weight and the number of detritivores by the number of photosynthetic protist was significant (Table 1, Fig. 1&2). The number of detritivores by the detritus weight, the number of photosynthetic protist by the detritus weight, and the to tal protist abundance by the detritus weight were very cl ose to significant (Fig. 3, 4, & 5). There was no significant regression between canopy density and photosynthetic protists (Table 1). One noticeable pattern during data collection were the fluctu ations in the daily volume of water and the number of protists in tanks. DISCUSSION Overall, these results do not support the or iginal hypothesis that there will be a relationship between the amount of nutrient s and the number of protist individuals. Interestingly, detritus dry we ight had no significant effect on the abundance of protists (Fig. 3, 4, & 5). These communities are supposed to be detritus based, so it is interesting that detritus did not have a great er effect on the number of pro tist. It is also intriguing that the other nutrients did not have a significant effect on protist abundance (Table 1). For instance, Rosenzweig (1995) considered habitat area to be the factor that most influences number of individuals and species richness, with larger areas supporting more individuals because of low extinction rate s. My results, however, show no significance between number of protists and tank diameter (Table 1). It was also intriguing that there was no significance between canopy density and am ount of photosynthetic protists (Table 1). This could be due to protists being su ch efficient converters of energy, with many species showing gross growth efficiencies of 50% or more. Ther efore photosynthetic protists may only need small amounts of light (Covich &Thorp 1991). There was a significant relationship be tween the number of photosynthetic protists and the number of de tritivores (Fig. 2). Every bromeliad sampled had more detritivores than photosynthetic protists and no bromeliads were found soley with detritivores, there were either bromeliads with both types of protists or no protists. This may indicate a case of diffuse mutualism between the two groups of protists. There were also great fluctuations in the number of pro tists in each bromeliad. During the collection period, however, there were great fluctuations in the weather as well. There were periods of dry, hot days and periods of cool, rainy days. The protist communities seemed to be affected by these trends illustrating Foxs ( 2002) view that natura l communities might not be closed dynamic systems at all, but rather open systems with structures reflecting the influence of the surrounding biogeogra phical region. Tank bromeliad protist communities may illustrate this statement if protist community successive composition is effected by the conditions, such as weathe r, of the surrounding cloud forest. Further research needs to be done to see exactly how phytotelm communities are affected by the surrounding biogeographical region.
ACKNOWLEDGMENTS I would like to thank Karen Masters for challenging me beyond my expectations. I would like to thank Alan Master for going out of his way to help with this project. I would also like to express my gratitude to Cam Pennington and Tom McFarland for being extremely helpful with all of my questions. Finally, I would like to thank the Monteverde Biological Station for allowing me to use their land for this project. LITERATURE CITED Armbruster, P., Cotgreave, P., Hutchinson, R.A. 2002. Factors influencing community structure in a South American tank bromeliad fauna. Oikos 96 (2): 225-234. Carrias, J, M.E. Cussac, and B. Corbara. 2001. A preliminary study of freshwater protozoa in tank bromeliads. Journal of Tropical Ecology 17: 611-617. Covich, A.P. & Thorp, J.H. 1991. Ecology and Classification of North American Freshwater Invertebrates. Academic Press, Inc, pp. 60-61. Fox, J.W., 2002. Testing a simple rule for dominance in resource competition. American Naturalist 159: 305-319. Morales, J.F. 2000. Costa Rica Bromeliads INBio, Costa Rica, pp. 10-15. Patterson, D.J. 1998. Free-Living Freshwater Protozoa John Wiley & Sons, New York, pp.181-193. Richardson, B.A., Richardson, M.J., Scatena, F.N. & Mc Dowell, W.H. 2000. Effects of nutrient availability and other elevational changes on bromeliad populations and their invertebrate communities in a humid tropical forest in Puerto Rico. Journal of Tropical Ecology 16: 348-356. Rosenzweig, M.L. 1995. Species Diversity in Space and Time. Cambridge University Press, Cambridge. Spaulding, J. 2005. Protist community diversity in relation to resources in bromeliads. CIEE Spring Tropical Biology and Conservation, pp 1-9. Unpublished. Srivastava, D.S. & Lawton, J.H. 1998. Why more productive sites have more species: an experimental test of theory using tree-hole communities. American Naturalist 152: 510-529.
Table 1. Regression analyses for the relationshi ps between water volume, tank diameter, detritus weight, canopy density, and protist abundance in Monteverde bromeliads. Sample size equals 25 bromeliads. Aste risks indicate signifi cant relationships. R2 P % Photsythetic pro tist by Tank dm 0.02 0.54 by volume of water 0.06 0.23 by detritus dry weight 0.02 0.54 by canopy density 0.00 0.98 Detritivores by Tank dm 0.00 0.97 by volume of water 0.03 0.42 by detritus dry weight 0.13 0.08 by canopy density 0.00 0.94 Photosynthetic protis t by Tank dm 0.00 0.78 by volume of water 0.02 0.48 by detritus dry weight 0.14 0.06 by canopy density 0.00 0.98 Total protist by Tank dm 0.00 0.95 by volume of water 0.03 0.44 by detritus dry weight 0.13 0.07 by canopy density 0.00 0.97 Canopy density by detritus dry weight 0.04 0.31 Detritus dry weight by volume of water 0.36 0.002* # of detrivores by # of photosynthetic protist 0.98 0.0001* 0 2 4 6 8 10 12 14 16 02040608010012 Water Volume (mL)Detritus Dry Weight (g)0
Figure 1. The simple regression for the detritus dry weight and water volume. The data were taken from cloud forest bromeliads. This regression was found to be significant (R^2 = 0.36, P value = 0.002, n =25). 0 20 40 60 80 100 120 140 160 180 01020304050607080 # of photosynthetic protist# of detrivores Figure 2. The simple regression for the numbe r of detritivores and number of photosynthetic protist. The data were taken from cloud forest bromeliads. This regression was found to be significant (R^2 = 0.98, P = 0.0001, n = 25). 0 20 40 60 80 100 120 140 160 180 024681012141 detritus dry weight (g)# of detritivores6 Figure 3. The simple regression for the # of detr itivores and detritus dry weight. The data were taken from cloud forest bromeliads This regression was not significant (R^2 = 0.13, P = 0.08, n=25).
0 10 20 30 40 50 60 70 80 0246810121416 Detritus Dry Weight (g)# of photosynthetic protist Figure 4 The simple regression for the # of photosynthetic protist and detritus dry weight. The data were taken from cloud fo rest bromeliads. This regression was not significant (R^2 = 0.14, P = 0.06, n = 25). 0 50 100 150 200 250 300 0246810121416 detritus dry weight (g)total # of protist
Figure 5. The simple regression for the total # of protist and detritus dry weight. The data were taken from cloud forest bromeliads This regression was not significant (R^2 = 0.13, P = 0.07, n = 25).