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Nectarivorous bat (Anoura geoffroyi, Glossophaga soricina and Hylonycteris underwoodi) preference for nectar quality

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Title:
Nectarivorous bat (Anoura geoffroyi, Glossophaga soricina and Hylonycteris underwoodi) preference for nectar quality
Translated Title:
Preferencia del murciélago nectarívoro (Anoura geoffroyi, Glossophaga soricina y Hylonycteris underwoodi) por la calidad del nectar ( )
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Parsell, Madeleine
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Bats--Behavior   ( lcsh )
Nectaries   ( lcsh )
Pollination   ( lcsh )
Costa Rica--Puntarenas--Monteverde Zone   ( lcsh )
Murciélagos--Comportamiento
Nectarios
Polinización
Costa Rica--Puntarenas--Zona de Monteverde
Tropical Ecology Spring 2011
Ecología Tropical Primavera 2011
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Reports   ( lcsh )
Reports

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Abstract:
In pollination mutualisms, plants offer rewards for pollen delivery. In the case of nectarivorous bats, the reward is food, and in order to maximize net energy gain, bats need to forage optimally. Presumably, nectar offering a more balanced diet would allow the bat more time to forage at flowers. To see if bats prefer nectars of higher quality, 24 individuals comprising three species of nectarivorous bats were presented with a variety of solutions of variable sugar type and amount, with and without additional nutrients, like proteins and amino acids. Preference was determined by number of visits to each solution type and the amount (ml) consumed. This study took place in a flight cage at The Bat Jungle of Monteverde, Costa Rica, using Anoura geoffroyi(N=17), Glossophaga soricina(N=3), and Hylonycteris underwoodi(N=4). For all five experiments, there was statistical preference for sugar solutions without other added nutrients (chi-squared goodness-of-fit test, df=1, P<0.05). These results suggest that bats have not evolved to detect or prefer more balanced nectar. Thus, they must augment nectar-based diets with insects or other food items. Perhaps the cost is sufficiently low that this can be done with little compromise.
Abstract:
En los mutualismos de polinización, las plantas ofrecen recompensa por el transporte del polen, en el caso de los murciélagos nectarívoros, la recompensa es el alimento, y para maximizar la energía ganada, los murciélagos necesitan forrajear óptimamente. Presumiblemente, si el néctar ofreciera una dieta más balanceada podría permitir al murciélago más tiempo para forrajear en las flores. Para determinar si los murciélagos prefieren el néctar de alta calidad, 24 individuos de tres especies diferentes de murciélagos nectarívoros fueron expuestos a soluciones con diferentes tipos, y cantidades de azúcar, con y sin nutrientes adicionales, como las proteínas y los aminoácidos. La preferencia fue determinada por el número de visitas a cada solución visitada y la cantidad (ml) consumida. Este estudio se llevó a cabo en una jaula de vuelo en el museo de murciélagos en Monteverde, Costa Rica, usando Anoura geoffroyi (N=17), Glossophaga soricina (N=3), and Hylonycteris underwoodi (N=4). Para los cinco experimentos, existe una diferencia significativa sobre la preferencia por las soluciones de azúcar sin ningún nutriente añadido (chi-squared goodness-of-fit test, df=1, P<0.05). Estos resultados sugieren que los murciélagos no han evolucionado para preferir el néctar más balanceado. Por lo tanto, ellos complementan su dieta con insectos u otros alimentos. Sin embargo el costo es suficientemente bajo que esto se podría hacer con poco compromiso.
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Nectarivorous bat ( Anoura geoffroyi Glossophaga soricina & Hylonycteris underwoodi ) preference for nectar quality Madeleine Parsell Department of Biology, University of Puget Sound ABSTRACT In pollination mutualisms, plants offer rewards for pollen del ivery. In the case of nectarivorous bats, the reward is food, and in order to maximize net energy gain, bats need to forage optimally. Presumably, nectar offering a more balanced diet would allow the bat more time to forag e at flowers. To see if bats p refer nectars of higher quality, 24 individuals comprising three species of nectarivorous bats were presented with a variety of sol utions of variable sugar type and amount, with and without additional nutrients, like proteins and amino acids. Preference w as determined by number of visits to each solution type and the amount (ml) consumed. This study took place in a flight cage at The Bat Jungle of Monteverde, Costa Rica, using Anoura geoffroyi (N=17), Glossophaga soricina (N=3), and Hylonycteris underwoo di (N=4). For all five experiments, there was statistical preference for sugar solutions without other added nutrients (chi squared goodness of fit test, df=1, P<0.05). These results suggest that bats have not evolved to detect or prefer more balanced ne ctar. Thus, they must augment nectar based diets with insects or other food items. Perhaps the cost is sufficiently low that this can be done with little comprom ise. RESUMEN En los mutualismos de polinizacin, las plantas ofrecen recompense por el t ransporte de polen, En el caso de murcilagos nectarvoros, la recompensa es alimento, y para maximizar la energa ganada, los murcilagos necesitan forrajear ptimamente. Presuntamente, el nctar ofre cido en una dieta balanceada puede permitir al murci lago un mayor tiempo de forrajeo en las flores. Para determinar si los murcilagos prefieren nctar de alta calidad, 24 ind ividuos de tres especies diferentes de murcilagos nectarvoros fueron expuestos a soluciones con diferentes tipos de azcar y can tidades, con y sin nutrientes adicionales, como protenas y aminocidos. La preferencia fue determinada por el nmero de visitas a cada solucin visitada y la cantidad (ml) consumida. Este estudio se llevo a cabo en una jaula de vuelo en el Bat Jungle en Monteverde, Costa Rica, usando Anoura geoffroyi (N=17), Glossophaga soricina (N=3), and Hylonycteris underwoodi (N=4). Para los cinco experimentos, existe una diferencia significativa sobre la preferencia por soluciones de azcar sin ni ngn nutriente adi cionado (chi squared goodness of fit test, df=1, P<0.05). Estos resultados sugieren que los murcilagos no han evolucionado para preferir nctar ms balanceado. As, ellos complementan su dieta con insectos u otros alimentos. Sin embargo el costo es su ficientemente bajo que esto puede ser realizado sin mucho compromiso. INTRODUCTION In pollinator mutualisms both partners aim to maximize their relative fitness. For the plant attempts to provide the minimum reward that still maximizes the number of vi sits to flowers of the same species (Voigt & Speakman 2007). The pollinator must forage optimally by maximizing caloric intake and expending as little energy as possible (Heinrich 1975 Alcock 1984). Yet, optimal foraging is compromised by other behavior s, like attracting mates, predator avoidance, and achieving a balanced die t. Each of these processes has associated costs that reduce net gain of survival (Alcock 1984). Nectarivorous bats are impor tant pollinators of many tropical plants (Baker et al. 1998). Like Hummingbirds, nectarivorous bats require large energy intake relative to their body size (Voigt & Speakman 2007). Because sugar provides energy that is quickly expended, bats must make many visits to flowers; a bat weighing 10 grams will consume up to 150% of its body weight in nectar per night, (Heinrich 1975, Voigt & Speakman 2007). Bats prefer nectars with sucrose and in high concentrations some of the highest concentrations of sugar (Heinrich 1975). However, like all animals, bats need a balanced diet. This may cause the pollinator to spend more time away from the plant in search of food items that offer nutrients they need. F or example, it is known that nectarivorous bats eat fruit and protein rich insects and pollen to supplement their diet (Muchhala and Jarrin V. 2002; Heinrich 1975 ). Yet, m any plants provide nectar that contains nutrients, such as amino acids, lipids, anti oxidants and proteins, which may help meet this need (Freeman et al. 1991, Gardener et al. 2003). The obvious incentive for the plant to provide additional nutrients is to prevent pollinators from searching for other food items, so as to maximize the time pollinators spend on flowers of that

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species. Thus, consuming nectar with additional nutrients is beneficial to both the bat and the plant. Yet it remains unclear whether nectarivorous bats recognize the presence of such nutrients in nectar and if they select for them I conducted a study in which 24 nectarivorous bats of three species are presented with solutions with and without non sucrose nutrients, like proteins, amino acids, lipids and vitamins. I observed the number of visits to both solution ty pes and measured the quantities cons umed Because consuming higher quality nectar is potentially beneficial to both pollinator and plant, I predicted that nectarivorous bats would recognize and select for nectar with nutrients. METHODS STUDY SITE All exp eriments were conducted at The Bat Jungle of Monteverde, Costa Rica. Twenty four nectarivorous and seventy four frugivorous bats live together in a flight cage measuring 17m x 2 3m x 2.5m. Bats were on a reverse schedule, active from approximately 8:30am to 8:00pm. For the duration of my study, an additional two feeders (B 1 and A 2 ) were hung next to two permanent feeders (fig. 1). Feeders were always hung in an alternating order, so that both solution types were available at an outside and inside locatio n. STUDY ORGANISMS There are a total of 96 nectarivarous and fruit bats, which are kept together. The only visitors to my feeders were the 24 nectarivorous bats: 17 Anoura geoffroyi 3 Glossophaga soricina and 4 Hylonycteris underwoodi Given that A. geoffroyi was in the vast majority, the behaviors observed are most likely largely attributable to it. A. geoffroyi is a neotropical bats species that is primarily nectarivorous and visits flowers consistently throughout the year. Individuals of this sp ecies also supplement their diet with pollen (Muchhala and Jarrin V. 2002). Gut examination of A. geoffroyi also indicated that they consume insects which has been supported by the findings of other experts (Muchhala and Jarrin V. 2002 LaVal 200 2). Bot h G. soricina and H. underwoodi also consume pollen, insects and fruit in addition to nectar (LaVal 2002, Lemke 1984). 20% Sucrose vs. Juice with added nutrients (J+N) This comparison was conducted over two days. It e of two different nectar solutions: 20% sucrose (from table sugar) and a nutrient rich recipe regularly used by the Bat Jungle (Table 1), which is a mixture of Dos Pios Nctar Mixto de Frutas baby cereal, provimilk and wheat germ. Unfortunately, the fr uit juice did not allow a refractometer to measure percent sucrose, but it is likely about 12 14%, which is the standard for the industry (Azam Ali, 2008). Full feeders were in place in the flight cage when the bats entered at 8:30am and removed at 2:30pm During the experiment, feeders were hung in an alternate order, with the 20%S on the outside left and inside right feeders (A feeders in figure 1). Table 1. Bat Jungle Nectar Recipe. Nectar Recipe (J+N) 1L Nctar Mixto de Frutas 4 tbsp. Provimilk f or calves 4 tbsp. Mixed baby cereal 0.25 tsp. Wheat germ powder Observations were made between 8:30 and 10:30 am. Measurements (ml) of how much was consumed per feeder were made at 2:30pm and three feeders containing only J+N were promptly returned to t heir normal stations in the flight cage until the bats were released into their roost for the evening. Figure 1. Nectar feeders in flight cage at The Bat Jungle of Monteverde, Costa Rica. Two different solutions were kept in an alternate orderin g system (A vs. B). The distance between the two feeders in each pair was approximately the width of a feeder, with approximately 1 meter between the two pairs. A 1 B 1 A 2 B 2

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10% Sucrose vs. Juice with added nutrients (J+N) Experiment two ce for sugar solution of 10% sucrose (10%S) versus their normal J+N solution. The feeders were hung in the same locations in alternating order (fig. 1). For the first two days, 10%S was hung on the outside left and inside right feeders (A 1 and A 2 ). On t he third day the order was switched and J+N was hung on the outside left and inside right feeders to ensure that order preference was not a factor. Feeders were available to the bats when they entered the flight cage at 8:30am with a premeasured amount of liquid in each feeder; at 2:30pm the feeders were removed and the contents measured, after which three feeders were refilled with J+N and replaced into the flight cage. Observations were made from 8:30am until 10:00am. 10% Sucrose vs. 10% Sucrose wit h Added Nutrients and 10%S with nutrients (10%S+N), using the same form of nutrients and ratio s used in the J+N recipe (Table 1). The same feeders and locations were used, with two days of 10%S on the outside left and inside right, then switched for the third day with 10%S+N on the outside left. After observing a difference in preference on the third day, the order was switched back to the first order to determine if the trend remained. The feede rs, containing premeasured amounts of solution, were in the flight cage by 8:30am and observations were made until 10:00am. The feeders were only kept out until 11:30am, upon request of Dr. LaVal director of The Bat Jungle ; at which point, the contents w ere re measured to determine the amount consumed. Juice vs. Juice with Added Nutrients The fourth Nctar Mixto de Frutas (J) versus J+N. The experiment lasted two days; on the first day J was in the outside left and inside right feeders. On the second day, the order was reversed with J+N in the outside left and inside right. The feeders with premeasured contents were available to the bats by 8:30am, and observations were made until 10:00am. The feeders wer e removed by 11:30am and the contents measured. 16% Sucrose vs. Commercial Hummingbird Food (Sucrose plus added nutrients) Due to a calculation error, the first day of the final with 16% sugar c oncentration (16%S) versus Perky Pet Hummingbird Instant Nectar Concentrate with 13% sugar concentration (HB). This solution also has 3% other ingredients: sodium benzoate (preservative), tartaric acid (preservative), and artificial food coloring The fe eders on the outside left and inside right contained 16%S. The following day, the sugar solution was diluted to 13% (13%S) and was tested against HB, with HB in the outside left and inside right feeders. Observations on both days were made from 8:30 to 10 :00am. At 11:30am the remaining contents of the feeders were measured and three feeders containing J+N were replaced in the flight cage. RESULTS 20% Sucrose vs. Juice with added nutrients (J+N) Based on number of visits, there was a clear preference fo r 20%S over J+N (chi squared goodness of fit test, df=1, P<0.05; fig. 2); 20%S (2259) was visited more than 2.5 times more than J+N (849). This trend was also reflected in quantities consumed from the respective feeders. Figure 2. Nectarivorous bat vi sits to sugar water, 20% concentration, (20%S) and nutrient rich juice (J+N) for two days with error bars ( standard error). This study was conducted in the flight cage at The Bat Jungle of Monteverde, Costa Rica. 17 A. Geoffroyi present, 3 G. soricina and 4 H. underwoodi were used in this study. Observations of visits were conducted for two hours when the bats were first released form their roost at 8:30am. Significant preference was for 20%S over J+N, with more than 250% more visits to 20%S (chi squ ared goodness of fit test, df=1, P<0.05). Sugar solution was made with tap water and a 20% concentration of sucrose.

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Table 2. Mean quantities of sugar water, 20% concentration (20%S), and nutrient rich juice (J+N) consumed by nectarivorous bats with sta ndard deviation. Data compiled from two days. Species in study were : A. Geoffroyi G. soricina and H. underwoodi In general, more solution was consumed from outside feeders. 20%S J+N Feeder Location Inside Outside Inside Outside Mean 108.000 26 2.500 26.000 97.500 StDev 25.456 53.033 1.414 3.536 10% Sucrose vs. Juice with added nutrients (J+N) about 4.5 times more than the J+N feeder with 952 visits (chi squared goodness of fit test, df=1 P<0.05; fig. 3). Figure 3. Nectarivorous bat visits to sugar water, 10% concentration, (10%S) and nutrient rich juice (J+N) for three days with error bars ( standard error). Study subjects were A. Geoffroyi G. soricina and H. underwoodi Visits were observed for 1.5 hours when bats were released into the flight cage at The Bat Jungle of Monteverde, Costa Rica at 8:30am. There was significant preference for 10%S over J+N by almost 4.5 times (chi squared goodness of fit test, df=1, P<0.05). Order of feeders was switched after two days to control for potential location preference. Sugar solution was made using tap water and sucrose. 10% Sucrose vs. 10% Sucrose with Added Nutrients The greatest preference for sugar solution was demonstrated in ex periment three, with more than five times more visits to 10%S (5592) versus 10%S+N (1084) (chi squared goodness of fit test, df=1, P<0.05; fig. 4). Figure 4. Nectarivorous bat visits to sugar water, 10% sucrose concentration, (10%S) and sugar water w ith nutrients, 10% sucrose concentration, (10%S+N) for four days with error bars ( standard error). Species studied were A. Geoffroyi G. soricina and H. underwoodi Observations were made for 1.5 hours when the bats were released into the flight cage a t The Bat Jungle of Monteverde, Costa Rica. There were almost five times more visits to 10%S over 10%S+N (chi squared goodness of fit test, df=1, P<0.05). The order of the feeders was reversed for one day to account for any location preferences. Sugar sol utions were made using tap water and sucrose. Juice vs. Juice with Added Nutrients There were a little over 15% more visits to the J feeder (953) compared to the J+N feeder (820), which is statistically significant (chi squared goodness of fit test, df=1, P<0.05; fig. 5), though less impressive compared to the level of preference demonstrated in the other experiments. Figure 5. Nectarivorous bat visits to Nctar Mixto de Frutas (J) and Nctar Mixto de Frutas with nutrients (J+N) for duration of two d ays with error bars ( standard error). Species studied were A. Geoffroyi G. soricina and H. underwoodi Observations were made for 1.5 hours when the bats were released into the flight cage at The Bat Jungle of Monteverde, Costa Rica. There were signifi cantly more visits to J than to J+N, by about 15% (chi squared goodness of fit test, df=1, P<0.05). The order of the feeders was reversed the second day to account for any location preferences. Sugar solution was made using tap water and sucrose.

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16% Suc rose vs. Commercial Hummingbird Food (Sucrose plus added nutrients) PART A There were significantly more visits to the16%S (821) versus HB (506) by about 38% (chi squared goodness of fit test, df=1, P<0.05; fig. 6). Figure 6. Nectarivorous bat visits to sugar water, 16% sucrose concentration, (16%S) and Hummingbird nectar with amino acids (HB) for one day with error bars ( standard error). Species under observation were A. Geoffroyi G. soricina and H. underwoodi. Observations were made for 1.5 hours when the bats were released into the flight cage at The Bat Jungle of Monteverde, Costa Rica at 8:30am. There were significantly more visits to 16%S than to HB by about 38% (chi squared goodness of fit test, df=1, P<0.05). Sugar solution was made using ta p water and sucrose. PART B Similar to the findings of experiment 4, there were significantly more visits to the13%S (807) versus HB (704) by about 15% (chi squared goodness of fit test, df=1, P<0.05; fig. 7). Figure 7. Nectarivorous bat visits to su gar water, 13% sucrose concentration, (13%S) and Hummingbird nectar with amino acids (HB) for one day with error bars ( standard error). Species under observation were A. Geoffroyi G. soricina and H. underwoodi. Observations were made for 1.5 hours when the bats were released into the flight cage at The Bat Jungle of Monteverde, Costa Rica at 8:30am. There were significantly more visits to 16%S than to HB by about 15% (chi squared goodness of fit test, df=1, P<0.05). Sugar solution was made using tap wat er and sucrose. ADDITIONAL OBSERVATIONS In general, each day the bats went to the solution that had the nutrients first, but would quickly switch to the solution without nutrients. This trend was most prominent when J+N was present. In general, most vis its occurred at the outside feeders, but over time, this trend was less pronounced. Also notable, there was an observed change in behavior when the bats were drinking sugar solution. Observations prior to the study showed that the highest frequency of v isits were generally made when the bats first entered the flight cage and were the most hungry. When sugar was available there were many more visits to the feeders throughout and the bats exhibited excited behavior. This was particularly the case when 2 0%S was available. The bats were almost in constant motion and made more vocalizations at higher frequencies. There were even some events of minor aggression when more than one bat approached the feeder at the same time. There was less excitement when 2 0%S was replaced with 10%S; there was no aggression and vocalizations were reduced, but there was an increase in number of visits. DISCUSSION All comparisons showed that bats prefer nectars that are purely sugar. The addition of other nutrients always decreased number of visits and total amount of solution taken. Even a laboratory made hummingbird food was less attractive than pure sugar water. Pure sucrose solutions were preferred overall and 10% sucrose was preferred over 20%. More visits to 10%S o ver 20%S indicates it would sugar concentration to maximize visits to the plants, as discussed by Voigt & Speakman ( 2007 ). There are numerous possible explanations why there was constant preferen ce for plain sugar solutions. For instance, it is possible nectarivorous bats can get additional nutrients they need with low foraging costs relative to foraging for nectar. This is supported by Heinrich, who states there is no significant difference in energetic costs between foraging for pollen versus nectar (1975). Even finding insects may have little to no additional costs, because bats can consume the bugs caught on their wings or found on the plants they drink nectar from (Baker et al.

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1998). Easy access to nutrients may under mine the benefits of preferring nutrients in nectar. It is also possible the bats did not need the level of nutrients they were provided with during my study. Each day I observed initial preference for the nutrient solution, when they were hungriest, then they would shift their preference to the solutions without added nutrients. Thus, it is possible they satiate their need for nutrients by visiting the nutrient solutions first but feel they do not need to drink large amoun ts of the nutrient solution. Instead, they drink primarily from the simple sugar solution which more closely parallels their natural diet. It is also possible the bats have not evolved to seek specific nutrients in their nectar, even if it would increase their fitness. Perhaps, they are hardwired to seek the nectar with the highest perceived sugar concentration, preferably sucrose, and to seek nutrients in the form of fruit, pollen or insects. Finally, the preference the bats demonstrated for the plain su gar solutions may be because the nutrients provide an unsavory taste that makes the high quality nectar less attractive. This could be the case for all nutrient rich nectar, even those found in nature; yet, it might be specific to my experiment where the nutrients were in a form that was probably unrecognizable to their inherent palette. Though unquestionably good for them, baby cereal, provimilk and wheat germ may be too foreign to their natural palette for them to prefer nectars with these nutrients. S imilarly, HB contained preservatives, sodium benzoate and tartaric aid which may have provided an unappealing flavor that made HB less attractive. The simple sugar preference demonstrated by the bats may or may not have implications on the overall fitne ss of the individual and/or plant. If the bats do not have to spend more time away from the plant to seek additional nutrients, and can supplement their diet with fruit, insects, and pollen found on the plant it takes nectar from, there is probably no cos t to the fitness of the bat or plant. Alternatively, if the bats are supplementing their diet mainly with pollen and consume more than they pollinate then this is harmful to the plant and may be the incentive for plants to provide nutrient rich nectar. It is also possible, pursuit of added nutrients takes the bats away from the plant in search of insects and fruit and pollen of other species. In this case, the bats visit fewer flowers per unit time, which potentially decreases the fitness of both the ba t and the plant. Yet, if bats continue to select for low quality nectar, there is nothing to be done. In fact, providing more costly nectar that is selected against may decrease the fitness of the plant. The findings of this study were surprising and pr preferences. Future studies should provide bats with a choice of two sucrose solutions one with amino acids and one without for an extended period of time, to see if their choice changes over time It is important to provide the purest form of nutrients possible, without other ingredients such as preservatives that might impact their choice. ACKNOWLEDGEMENTS I have much gratitude towards The Bat Jungle of Monteverde, Costa Rica, for allowing me the use of their facilities and a special thank you to Dr. LaVal for all his help and guidance. Thank you Dr. Masters for all your time, energy and guidance as well! And thank you J se Carlos Calder n Ulloa. LITERATURE CITED Alcock, J. 1984. The ecology of feeding behavior. In Sinauer (Ed. 3). Animal behavior an evolutionary approach, pp. 261 273. Azam Ali, S. 2008. Fruit Juice Processing. Technical Brief, Practical Action, The Schumacher Centre, UK, http://practicalaction.org/practicalanswers/pro duct_info.php?products_id=94? Baker, H., Baker, I. and Hodges, S. 1998. Sugar composition of nectars and fruits consumed by birds and bats in the tropics and subtropics. Biotropica. 30: 559 586 Freeman, E., Worthington, R.D. and Jackson, M.S. 1991. Floral Nectar Sugar concentrations of some South and Southeast Asian spec ies. Biotropica. 23: 568 574 Gardener, M., Rowe, R. and Gillman, M. 2003. Tropical bees ( Trigona hockingsi ) show no preference for nectar with amino acids. Biotropica. 35: 119 125 Heinrich, B. 1975. Energetics of Pollination. Annual Review of Ecology and Systematics. 6: 139 170 LaVal, R. and Rodrguez H., B. 2002. Subfamily Glossophaginae. In INBio (Ed. 1). Murcilagos de Costa Rica bats, pp.148 150. Lemke, T. 1984. Foraging ecology of the long nosed bat, Glossophaga soricina with respect to resour ce availability. Ecology. 65: 538 548

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Voigt, C. and Speakman, J. Nectar feeding bats fuel their high metabolism directly with exogenous carbohydrates. Functional Ecology. 21: 913 921 Werner, E., and Hall, D. 1974. Optimal foraging and the size selection of prey by the Bluegill Sunfish ( Lepomis macrochirus ). Ecology. 55:1042 1052


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Preferencia del murcilago nectarvoro (Anoura geoffroyi, Glossophaga soricina y Hylonycteris underwoodi) por la calidad del nectar
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Nectarivorous bat (Anoura geoffroyi, Glossophaga soricina and Hylonycteris underwoodi) preference for nectar quality
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In pollination mutualisms, plants offer rewards for pollen delivery. In the case of nectarivorous bats, the reward is food, and in order to maximize net energy gain, bats need to forage optimally. Presumably, nectar offering a more balanced diet would allow the bat more time to forage at flowers. To see if bats prefer nectars of higher quality, 24 individuals comprising three species of nectarivorous bats were presented with a variety of solutions of variable sugar type and amount, with and without additional nutrients, like proteins and amino acids. Preference was determined by number of visits to each solution type and the amount (ml) consumed. This study took place in a flight cage at The Bat Jungle of Monteverde, Costa Rica, using Anoura geoffroyi(N=17), Glossophaga soricina(N=3), and Hylonycteris underwoodi(N=4). For all five experiments, there was statistical preference for sugar solutions without other added nutrients (chi-squared goodness-of-fit test, df=1, P<0.05). These results suggest that bats have not evolved to detect or prefer more balanced nectar. Thus, they must augment nectar-based diets with insects or other food items. Perhaps the cost is sufficiently low that this can be done with little compromise.
En los mutualismos de polinizacin, las plantas ofrecen recompensa por el transporte del polen, en el caso de los murcilagos nectarvoros, la recompensa es el alimento, y para maximizar la energa ganada, los murcilagos necesitan forrajear ptimamente. Presumiblemente, si el nctar ofreciera una dieta ms balanceada podra permitir al murcilago ms tiempo para forrajear en las flores. Para determinar si los murcilagos prefieren el nctar de alta calidad, 24 individuos de tres especies diferentes de murcilagos nectarvoros fueron expuestos a soluciones con diferentes tipos, y cantidades de azcar, con y sin nutrientes adicionales, como las protenas y los aminocidos. La preferencia fue determinada por el nmero de visitas a cada solucin visitada y la cantidad (ml) consumida. Este estudio se llev a cabo en una jaula de vuelo en el museo de murcilagos en Monteverde, Costa Rica, usando Anoura geoffroyi (N=17), Glossophaga soricina (N=3), and Hylonycteris underwoodi (N=4). Para los cinco experimentos, existe una diferencia significativa sobre la preferencia por las soluciones de azcar sin ningn nutriente aadido (chi-squared goodness-of-fit test, df=1, P<0.05). Estos resultados sugieren que los murcilagos no han evolucionado para preferir el nctar ms balanceado. Por lo tanto, ellos complementan su dieta con insectos u otros alimentos. Sin embargo el costo es suficientemente bajo que esto se podra hacer con poco compromiso.
546
Text in English.
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Bats--Behavior
Nectaries
Pollination
Costa Rica--Puntarenas--Monteverde Zone
4
Murcilagos--Comportamiento
Nectarios
Polinizacin
Costa Rica--Puntarenas--Zona de Monteverde
653
Tropical Ecology Spring 2011
Ecologa Tropical Primavera 2011
655
Reports
720
CIEE
773
t Monteverde Institute : Tropical Ecology
856
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