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The effect of hummingbird feeders on the pollen loads and diversity in nectarivorous bats (Glossophaginae) in a tropical cloud forest Benjamin Juan Padilla Department of Biology, Gordon College ___________________________________________________ _____________ ABSTRACT Bats are some of the most important pollinators in tropical regions. I studied the effect of hummingb ird feeders on pollen loads in nectarivorous bats in th e Monteverde region. I mist netted bats at two loc ations Selvatura Hummingbird Garden (deemed high feeder de nsity), and the Santa Elena Reserve (low feeder density). Pollen was removed from the bats back u sing clear scotch tape and placed directly onto microscope slides for examination. A Shannon-Weine r diversity index showed that there was a differenc e between the pollen diversities (Selvatura H=5.47, Reserve H= 4.63) although mean pollen diversity an d overall pollen count were not different. These dif ferences could have been attributed to the fact tha t Anoura geoffroyi was the main species caught at the Reserve while Glossophaga spp. was caught at Selvatura. RESUMEN Los murcilagos nectarivorous se encuentran entre l os mas importante polinizidores en los tropicos. Y o estudi la efecta de comedores de colibres en el p olen que encontr en los murcilagos nectarivorous en Monteverde, Costa Rica. Atrap murcilagos en dos lugares, El Jardn de Colibres en Selvatura, y La Reserva Santa Elena. Tom muestras de polen con ci nta transparente y lo puse en portaobjetos imediamente. Un ndice de diversidad Shannon-Weine r muestr que habia diferencia entre la diversidad de polen (Selvatura H=5.47, Reserva H= 4.63) aun pro medio diversidad de polen y total diversidad de pol en no produci ningun diferencia. Estos diferencias p ueden ser atribuido al hecho de Anoura geoffroyi era la mayoridad de los murcilagos captuado en La Reserv a, mientras Glossophaga spp. era captuado en Selvatura. INTRODUCTION Throughout tropical and semitropical zones worldwid e, bats are some of the most important pollinators and seed dispersers of flower ing plants. In the neotropics pollination by nectarivorous bats (Glossophaginae) has arisen independently in 27 different plant families affecting more than 500 di fferent species (Altringham 1996). Typical bat flowers are white, creamy, or greenish, open at night, often for only one night, and have deep nectaries which in some cases can hold up to 10 mL of nectar (Altringham 1996). When a bat visits a flower to d rink, the flowers strategically placed anthers deposit pollen onto the animals head, neck and back. Nectarivorous bats fill an ecological niche in the night that hummingbirds fill during the day. As a result of this similarity it is not surprising that Glossophaginae bats have been known to visit hummingbird feeders. Stud ies have shown that a pollinator will
leave a certain flower species when a source of hig her quality nectar is found elsewhere (Bronstien 1994). The amount of liquid and the con centration of sugars in hummingbird feeders far exceed any that could be found in a nat ural source. It is intuitive from this information that in the presence of hummingbird fee ders bats would choose them over the flowers. In study done on the effects of humm ingbird feeders on pollen dispersal by Heliodoxa jacula Hayes (2003) mist-netted hummingbirds at three di fferent locations: Monteverde Cloud Forest Reserve Hummingbird Garden, Estacion Biologica (no feeders), and Bajo del Tigre (no feeders). She dis covered that 21 morphospecies of pollen were found at the Estacion Biologica while o nly 14 were found at the Monteverde Cloud Forest Reserve. In a similar study done on nectarivorous bats, Grov er (2003) mist netted bats at the Monteverde Cloud Forest Reserve and at Bajo Del Tigre, a comparison of feeders vs. no feeders. She found that the diversity of pollen morphospecies found at the Cloud Forest Reserve was higher than that of Bajo Del Tig re. A large discrepancy in elevation could have had an affect on these results. The purpose of this study was to see if hummingbird feeders had a significant effect on the pollination behavior of Glossophagina e bats. Based on these prior studies I hypothesized there would be a difference in the pol len diversity at Selvatura and the Santa Elena Reserve. I predicted that Selvatura wo uld have lower pollen diversity because of the increased effect of humming bird fee ders on the bats diet. MATERIALS AND METHODS Bats were collected at the humming bird garden at S elvatura Adventure Park, and the walkway to the office at the Santa Elena Cloud Fore st Reserve between the first and the fifteenth of November. Selvatura Hummingbird galle ry is a very well established energy source for all sorts of nectarivorous animals. The garden has been in existence for nearly ten years, it has a stone tiled floor, benches, and as many as 20 active hummingbird feeders at one time. The other study site, Santa E lena Cloud Forest Reserve has a much smaller concentration of hummingbird feeders. The Reserve has roughly seven feeders set up about three meters apart on the path to the main office. These two study sites are located very close to each other. The Santa Elena Reserve is less than one kilometer away from Selvatura and situated on nearly the same elevation. Bats were caught at each site using one twelve mete r mist net. When a bat was caught it was removed from the net and identified u sing A Field Key to the Bats of Costa Rica by Robert M. Timm and Richard K. LaVal (1998). On ce identified the forearm length in millimeters and mass in grams was recorde d with a Pesola 50 g scale. Pollen was removed from the bat with using clear scotch ta pe on the head, neck, and back of the bat for a total of ten pats per bat. The tape cont aining the pollen was then stuck to a blank microscope slide and labeled with the number of the bat and the location of capture. Slides were then set aside for later exam ination. The slide was scanned on the 10x lens to detect the presence or absence of pollen. When a pollen grain, or group of pollen grains was found it was examined on the 40x lens to determine which morphospecies it belonged t o. Morphospecies were drawn and given a letter for identification ranging from A th rough EE (letters were doubled once AZ was seen).
The diversity of pollen was analyzed using a Shanno n-Wiener diversity index, and a T-test was used to look for significance. I also calculated s-marg and evenness for the same data. RESULTS For both locations there were a total of thirty one different pollen morphospecies discovered. The Selvatura Hummingbird Garden yield ed twenty six morphospecies while the Santa Elena Reserve had only twenty. An equal number of bats (19) were caught at each sight however there was only a limit ed amount of species over lap. Seventeen of the nineteen individuals caught at Sel vatura were identified as Glossophaga spp,. two were fruit bats of the genus Sturnia spp. At the Santa Elena Reserve five of the nineteen bats were identified as Glossophaga spp. two were Loncophylla robusta and the remaining twelve were Anoura geoffroyi The pollen diversity found on bats in the Selvatur a Hummingbird Garden (H= 2.76) was significantly higher than the pollen dive rsity at the Santa Elena Reserve (H= 2.41) (t = 2.58, df = 181.8, p = 0.01). I found mo re morphospecies at Selvatura (26) than the Reserve (20). Morphospecies C was found in eve ry pollen sample at both locations, morphospecies G was extremely common as well found in 33 of the 38 samples. Eleven morphospecies were unique to the Selvatura Hummingb ird Garden, while only five were distinctive at the Santa Elena Reserve. Pollen mor phospecies L found in 27 of the total 38 pollen slides was later identified as a lepidopt eron wing scale The Selvatura Hummingbird Garden had higher values for all three numbers calculated H, E, and Smarg. A t-test was done us ing these values and concluded that the differences were indeed significant with a p-va lue of 0.01 < 0.05. The mean morphospecies count per bat was calculated and test ed for significance using a t-test. The mean for Selvatura was 5.47 while the mean for the Reserve was 4.63. The t-test yielded a p-value of 0.0974 at 36 degrees of freedo m and a t-value of 1.701. The p-value of 0.0974 is insignificant because it is greater th an the desired p-value of 0.05 (see Figure 1). In all different morphotypes were seen a total of 107 times at Selvatura and 86 at the Santa Elena Reserve. A Chi-square test resulte d in a chi-value of 2.285 with one degree of freedom. This yielded an insignificant p -value of 0.131 (see Figure 2). DISCUSSION My data showed that although there was a difference in the amount and abundance of pollen morphotypes between the two sites, this diff erence was not significant. The Shannon-Wiener diversity index did find a significa nt result, but the difference in mean pollen count, and total pollen count were insignifi cant. This data did agree with my hypothesis that there would be a significant differ ence in pollen at the two sites, the pollen abundance however did not differ. Many fact ors could have had an effect on these trends. Although it was originally thought that the Selvat ura Hummingbird Garden would have more of an effect on the bats feeding, observ ations seemed to point otherwise. At
Selvatura the hummingbird feeders were often empty, or had fallen on the ground. Time spent observing the feeders by moonlight showed tha t visitors were few and far between. The Santa Elena Reserve on the other hand, although there were fewer feeders, and the feeders were spaced farther apart, always had plent iful solution available. Feeder observations at the Reserve were also very differen t. There was hardly a moment when a bat wasnt feeding or flying low and fast along the trail. This difference in feeding activity could explain why the Reserve had slightly lower pollen diversity than Selvatura. The difference in species caught could have also ha d an effect on the results. Only Glossophaga spp. was caught at Selvatura, while Anoura geoffroyi was the most commonly captured species at the Reserve. Hajducze k (1997) studied the pollen carried by Anoura geoffroyi She found only thirteen different morphospecies on thirty-two individual bats (I found only 16 morphospecies on A. geoffroyi ). It is possible that A. geoffroyi is merely more of a specialist pollinator and the h ummingbird feeders themselves have little effect. The fact that morphospecies L is a lepidopteron wi ng scale is intuitive because like hummingbirds, nectarivorous bats must suppleme nt their diet of nectar with insects for protein. Soto-Centano and Kurta (2006) studied the diets of two Puerto Rican nectarivorous bat species and concluded that 75% of fecal matter examined contained insect material. Unlike the results found by Grover (2003), my data showed a difference between the pollen found at my two locations. I eliminated the altitudinal differences found in Grovers study and as a result found significant re sults. My two study sites unlike Grovers both had hummingbird feeders in high and l ow concentrations. In order to make a more detailed study, a comparison of forest to hummingbird garden on the same elevation would be more descriptive. I did not hav e time enough to search for a suitable netting site on the same elevation as Selvatura tha t was entirely out of range of hummingbird feeders. Future studies should look at the pollen diversity of a single species over a wide range of habitats comparing not only feeders vs. no feeders but also altitudinal differences, and changes in life zones. ACKNOWLEDGEMENTS I would like to thank Selvatura and La Reserva Sant a Elena for letting me net on their properties. Thanks to the night guard at Selvatura for keeping me company. Laurel and Danny for coming bat catching with me. Thanks Tani a for helping me with everything when I needed it, and thanks Moncho for teaching me everything I know about bat catching. LITERATURE CITED Altringham, J.D. 1996. Bats: Biology and behavior. Oxford University Press, New York, New York. Bronstein, J.L. 1994. Conditional outcomes in mutu alistic interactions. Trends in Ecology and Evolution, 4.
Grover, C. 2003. The effects of hummingbird feeders on pollen loads of Costa Rican nectarivorous bats (Subfamily Glossophaginae). UCEap Instituto Mont everde. Hajduczek, B. Poellen carried by nectarivorous bat s Anoura geoffroyi UCEap Instituto Monteverde. Hayes, C. 2003. Effects of hummingbird feeders on pollen dispersal performed by Heliodoxa jacula (Trochilidae) in Monteverde, Costa Rica. UCEap Ins tituto Monteverde. Hoeh, J. Pollen diversity on male Hylonycteris underwoodi (Glossophaginae). Tropical Ecology and Conservation, CIEE. LaVal, R.K. and B. Rodruiguez-H. 2002. Murcielagos de Costa Rica. Editorial INBio, Costa Rica. Soto-Centeno, J.A. and K. Allen. 2006. Diet of two nectarivorous bats, Erophylla sezekorni and Monophyllus redmani (Phyllostomidae) on Puerto Rico. Journal of Mammalogy 87, 19-26. Timm, R. M. and R.K. LaVal. 2000. Mammals of Mont everde. In Nadkarni, N. M. and N. T. Wheelwright (Ed.) Monteverde: Ecology and conserva tion of a tropical cloud forest. Pp. 553-557. Oxford University Press, New York, New Y ork. Mean number of morphospecies per bat 4.632 5.474 0 1 2 3 4 5 6 7 8 SelvaturaSanta Elena Reserve Figure 1. Mean number of morphospecies per bat: th e mean number of different morphospecies of pollen found on each bat.
107.000 86 0.000 20.000 40.000 60.000 80.000 100.000 120.000 1 2 Location Amount of Pollen Series1 Figure 2. Total pollen count: The number of diffe rent morphospecies on each bat was added up to give total pollen count. 107 at Selvatura vs. 86 at the Reserve.
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Padilla, Benjamin Juan
El efecto de los comederos para colibres en las cargas de polen y la diversidad de murcilagos nectarvoros (Glossophaginae) en un bosque tropical nuboso
The effect of hummingbird feeders on the pollen loads and diversity in nectarivorous bats (Glossophaginae) in a tropical cloud forest
Bats are some of the most important pollinators in tropical regions. I studied the effect of hummingbird feeders on pollen loads in nectarivorous bats in the Monteverde region. I mist netted bats at two locations Selvatura Hummingbird Garden (deemed high feeder density), and the Santa Elena Reserve (low feeder density). Pollen was removed from the bats back using clear scotch tape and placed directly onto microscope slides for examination. A Shannon-Weiner diversity index showed that there was a difference between the pollen diversities (Selvatura H=5.47, Reserve H= 4.63) although mean pollen diversity and overall pollen count were not different. These differences could have been attributed to the fact that Anoura geoffroyi was the main species caught at the Reserve while Glossophaga spp. was caught at Selvatura.
Los murcilagos son algunos de los polinizadores ms importantes en las regiones tropicales. He estudiado el efecto de los comederos para colibres en las cargas de polen en los murcilagos nectarvoros en la regin de Monteverde.
Text in English.
Bats--Costa Rica--Puntarenas--Monteverde Zone
Pollen--Costa Rica--Puntarenas--Monteverde Zone
Monteverde Cloud Forest Reserve (Costa Rica)
Cloud forest ecology--Costa Rica
Murcilagos--Costa Rica--Puntarenas--Zona de Monteverde
Pollen--Costa Rica--Puntarenas--Zona de Monteverde
Reserva Bosque Nuboso Monteverde (Costa Rica)
Ecologa del bosque nuboso--Costa Rica
Tropical Ecology 2008
Hummingbird feeders, effect on bats
Santa Elena Reserve
Ecologa Tropical 2008
Comederos para colibres, efecto en los murcilagos
Reserva de Santa Elena
t Monteverde Institute : Tropical Ecology