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Determinacin de los polinizadores ptimos de Stachytarpheta jamaicensis (Verbenaceae) basada en la produccin de nctar durante el transcurso del da
Determination of the optimal pollinator of Stachytarpheta jamaicensis (Verbenaceae) based on nectar production throughout the day
Stachytarpheta jamaicensis has been found to have various visitors but its actual pollinator is unknown. I Collected nectar from 22 individual plants during various times of the day and I determined that S. jamaicensis produces most nectar during 6:00 am and 6:00 pm. Observation of the visitors were recorded for each hour and ten flowers were collected for each potential pollinator after they were observed obtaining nectar from the flowers. Nectar production was found to be significantly abundant early morning and late afternoon, this suggests that S. jamaicensis produces nectar for hummingbirds and moths since this is when they are most active. Flowers used in order to determine how much pollen remained on the stamen after visitation by each potential pollinator. Observation of activity and statistical analysis showed that butterflies were the most abundant in visiting, but pollen amounts on the stamens did not show any significance for any of the species. Due to lack of sufficient data on moths, the amount of pollen left over after visitation of these species was unable to be determined.
Stachytarpheta jamaicensis ha sido documentada como una especie que atrae diferentes visitantes pero su verdadero polinizador es desconocido. Muestre nctar de 22 plantas individuales durante varias horas del da y determine que S. jamaicensis produce la mayor parte del nctar durante las 6:00am y las 6:00pm. La visita de los polinizadores fue registrada a cada hora, diez flores fueron reunidas para cada uno de los polinizadores potenciales despus de que ellos obtuvieran el nctar de las flores.
Text in English.
Pollination by insects
Pollination by animals
Polinizado por insectos
Polinizado por animales
Tropical Ecology 2006
Ecologa Tropical 2006
t Monteverde Institute : Tropical Ecology
1 Determination of the optimal pollinator of Stachytarpheta jamaicensis Verbenaceae based on nectar production throughout the day Stephanie Siemek Department of Biology, Villa Julie College ABSTRACT Stachytarpheta jamaicensis has been found to have va rious visitors but its actual pollinator is unknown. I Collected nectar from 22 individual plants during various times of the day and I determined that S. jamaicensis produces most nectar during 6:00 am and 6:00 pm. Observation of the visitors were record ed for each hour and ten flowers were collected for each potential pollinator after they were observed obtaining nectar from the flowers. Nectar production was found to be significantly abundant early morning and late afternoon; this suggests that S. jamai censis produces nectar for hummingbirds and moths since this is when they are most active. Flowers used in order to determine how much pollen remained on the stamen after visitation by each potential pollinator. Observation of activity and statistical an alysis showed that butterflies were the most abundant in visiting, but pollen amounts on the stamens did not show any significance for any of the species. Due to lack of sufficient data on moths, the amount of pollen left over after visitation of these spe cies was unable to be determined. RESUMEN Stachytarpheta jamaicensis ha sido documentada como una especie que atrae diferentes visitantes pero su verdadero poli nizador es desconocido. MostrÃ© el nÃ©ctar de 22 plantas individuales durante varias vec es del dÃa y determinÃ© que S. jamaicensis produce la mayorÃa de los nÃ©ctares durante las 6:00 am y 6:00 p.m. La visita de los polinizadores fue registrada por cada hora, diez despuÃ©s las flores fueron reunidas para cada potencial polinizador despuÃ©s de que el los obtuvieran el nÃ©ctar de las flores. La producciÃ³n del nÃ©ctar al principio de maÃ±ana fue apreciablemente abundante y tambiÃ©n al finalizar la tarde, esto sugiere que S. jamaicensis produce el nÃ©ctar para colibrÃs y polillas porque estas son los periodos cuando ellos son muy activos. Las flores utiliz adas para determinar cuÃ¡nto pol en habÃa quedado en el estambre despuÃ© s de cada visita por cada poten c ial polinizador mariposas fueron los polinizadores mÃ¡s abundantes vistos, pero la cantidad de polen removi do de los estambres no difiriÃ³ entre especies. Debido carecer de datos para las polillas, la cantidad de polen restante despuÃ©s de cada visita de las polillas no pudo ser determinada. INTRODUCTION Community dynamics include many different relationsh ips in which each species plays a distinct role. Angiosperms have been closely associated with pollinators, co evolving to ensure a consistent relationship between the form of the flower and the sensory perception of specific pollinators. Plants have evo lved to offer rewards, such as nutrient rich nectar, to ensure visitation by pollinators Heywood, 1993. As ranges of plant species have extended some have been found to adapt to new pollinators. Perez et al. 2006 found Schizanthus spp. Solanaceae t o have evolved new flower morphology in order to accommodate a new pollinator. They found evidence of this change by examining flower traits and DNA of Schizanthus spp . Ancestral data showed that bees pollinated the plant, whereas today, bees, moths, and hummingbirds, depending on location, pollinate the flowers.
2 The subject of this study, Stachytarpheta jamaicensis Verbenaceae, is a native flowering plant, visited by many potential pollinators Zuchowski 2005 and nectar robbers Miao & Dodd 2000. In order for plants to lessen competition between its pollinator and so called Â€nectar robbersÂ it has been suggested that plants may have specific flowering times Robertson 1895, in Little 1983. Charles RobertsonÂs results from his study on various Illinoi s woodland communities showed that flowering times were in sync with pollination Â‚guilds,Âƒ which suggests that native species may have adapted to attract a specific pollinator Robertson 1895, in Little 1983. PleasantsÂ 1980 study found significance fo r flowering times of different pollination guilds within a complex community, but it is still unknown if the difference in flowering times depends on competition between pollinators only, or if other biotic or abiotic factors have influenced the plants. A nother study, using herbaceous species, found that there was no relation between guild types and flowering times Thomson 1997, in Little 1983. The purpose of my study was to determine if S. jamaicensis has adapted to attract a specific pollinator by inve stigating the timing of nectar production. Determining the exact pollinator will establish which species is critical in the reproduction of S. jamaicensis . Although studies have been unable to determine if flower production is dependent on its pollinator, predictions of the pollinator will be based off of nectar production. If nectar production is most abundant in the morning, this will suggest that the flowers are attracting hummingbirds since this is when they are most active. If nectar production is hig hest during the afternoon, then this suggests that the flower is attracting insects since they are ectothermic and require the warmth of the day. If nectar production is greatest in the evening, then moths are implicated as pollinators. MATERIALS AND MET HODS My study was performed in CaÃ±itas, Puntarenas Providence, Costa Rica at the Finca de SantamarÃa 1300 m elevation. The subject of this study, S. jamaicensis , is a native, flowering plant species that is a popular ornamental in Monteverde and the su rrounding areas. It is visited by many potential pollinators such as butterflies, hummingbirds, moths, and bees that are attracted by its nectar, however, it has not been shown if any of these organisms pollinate the flowers Zuchowski 2005. S. jamaicensi s contains purple flowers that are 5 lobed with a narrow tube calibrated at 1.5 centimeters long that is light lilac or whitish Zuchowski, 2005. Â‚Nectar robbersÂƒ have been shown to lower the fitness of these flower by taking nectar without providing poll ination services to the plant. A previous study showed that S. jamaicensis was visited by species that participate in action of Â‚nectar robbing,Âƒ which resulted in a decrease in nectar production of those flowers Miao & Dodd 2000. My observations of vis itors were taken while sitting four meters away from 6:00 am to 6:00 pm on October 24 to October 30, for a total of 24 hours, taking note of which taxonomic group visited the flower for each specific hour. A species was considered a visitor if found to be taking nectar from a flower. I collected each flower in order to measure at a later time how much pollen was left on the stamen after visitation. Ten flowers were collected total for each taxonomic group, as well as ten flowers from branches that were co vered the night before in order to serve as controls. I used a total of 22 plants in order to test nectar production. Before taking measurements, I covered at least three branches that contained between 2 9 flowers for each plant the night before in ord er to keep potential pollinators from obtaining the nectar. The nectar
3 was withdrawn from the flower by use of a capillary tube and then measured with a ruler using centimeters. Nectar production was measured at 6:00 am, 9:00 am, 12:00 pm, 3:00 pm, and 6: 00 pm from October 24 to November 13 for a total of 30 hours. The plants were divided into six groups with three to five individuals in each group depending on the different locations of where they were found. The locations included disturbed areas, grassy fields, and Lower Montane Moist Forest. After I measured nectar production of all 22 plants and ten flowers for each visiting taxonomic group were collected, the amount of pollen for the control and experimental flowers was counted for each flower using a dissecting microscope Olympus SZ40. The flowers of each species and the control were split apart using tweezers in order to focus on the stamen. Once the stamen was in focus, the dissecting microscope was focused as narrow as possible on the stamen, an d the pollen grains were counted in this field of view. A Chi Square Test was used in order to determine if the visitation by a particular pollinator was significantly more frequent than visitation by the other pollinators. Nectar production was analyzed , along with the amount of pollen for each of the collected flowers, using an ANOVA test. A LSD test for the Post Hoc test was used as well in order to determine where the significant differences between nectar production was during the different hours. RESULTS I found that butterflies are the most abundant visitor to S. jamaicensis Chi Square Test, x 2 = 7.09; df = 2; p < 0.05 Figure 1. Bees are the second most abundant, and then hummingbirds. The results measuring nectar production showed that it was highest at 6:00 am and again at 6:00 pm ANOVA test, F = 15.77; df effect = 4; df error = 101; p = 0.00 Figure 2. When comparing the amount of pollen grains on each flower it was found that there was no significance among the pollinators ANOVA test, F = 1.09; df effect = 3; df error = 36; p = 0.37 Figure 3. When observing the stamens, however, almost all anthers of flowers visited by hummingbirds contained little or no pollen. DISCUSSION Since S. jamaicensis is known to have many hummingb ird visitors Zuchowski 2005, it was expected that nectar production would be highest at 6:00 am when these birds are most active. According to the results, a significantly greater amount of nectar is found during this time but again at 6:00 pm. This cou ld suggest that S. jamaicensis produces nectar in order to attract hummingbirds and moths because this is when they are most active. A study done on Centaurea scabiosa and Centaurea nigra, plants that have different insects as pollinators, found C. scabios a to produce nectar continuously until new flowers started to open. Similarly, C. nigra was found to produce nectar throughout the day until 6:00 pm Lack 1982. Since these plants accommodated to their numerous insect pollinators by producing nectar throu ghout the day there is reason to believe that S. jamaicensis has done the same in order to accommodate to hummingbirds and moths. It was found that butterflies are significantly more abundant than the other pollinators. This could be due to the fact that majority of my observations were taken during the times when it was sunny or partly cloudy, which is when butterflies are most active. Bees are second most
4 abundant, which could be because bees are quick learners and recognize colors, odors, and outlines very easily. In addition, since they are able to find flowers quickly they become consistent with visits to a particular flower if they find that flower to produce enough nectar Raven et al. 1986. Sunny weather may have had an effect of how many hummingb ird visitations were observed as well. Hummingbirds are active during any type of weather, while bees and butterflies are only active during sunny weather. Because I only made observations during sunny weather, my data could be skewed towards observations of bees and butterflies. By not observing hummingbird activity during bad weather, I may have underestimated the relative frequency of hummingbird visits, compared to other visitors. Moths were never seen visiting flowers, which could be due to cloudiness or lack of light in order to see the moths at night. When observing pollen grains in order to compare the amount of pollen missing from the stamens it was found that no significant amount of pollen was missing for any of the flowers visited. Although, re sults have found no difference in pollen amounts, I observed that most pollen was missing from stamens that were visited by hummingbirds. Pollination has been described as being a Â‚sloppy procedureÂƒ where pollen transfers do not always result between inter actions of plants and visitors Herrara and Olle 2002. Therefore, statistical analysis may have showed no difference between specific pollinators and amount of pollen missing from each of the visited flowers, there is reason to believe that at least one of these taxonomic groups is the actual pollinator of this plant. Since nectar production seemed to be most abundant at 6:00 am and 6:00 pm it is suggested that Stachytarpheta jamaicensis produces nectar in order to attract specific pollinators. Due to lac k of data, I was unable to determine whether or not moths collect pollen. Future studies may be needed in order to increase data on this particular theory. In addition, final results showed that butterflies were most abundant visitors, but difference in po llen grains did not show any significance between any of the taxonomic groups. Other studies that could be done in relation to this study include looking at other various flowers to determine nectar production in relation to when their pollinators are most active. This could then provide more evidence as to whether or not flowers, in general, produce nectar during certain times in order to attract their specific pollinator. ACKNOWLEDGEMENTS I would like to thank the SantamarÃa family for letting me use their farm and helping me find the plants that I used for my project. I would also like to thank them for the support and the coffee breaks in between working on my project and studying. I would also like to thank Camryn Pennington and Thomas McFarland fo r answering all of my questions and helping me obtain the materials needed in order to complete my project. I would like to thank Tania Pizarro for helping me with my data and interpretations of my statistical analysis and for being such a great advisor. A lso, a special thanks to Katherine Puzio and Lili Prahl for helping me collect my data before the rain and during those dark gloomy evenings. Thank you to Katherine Lulling and to Lili Prahl for proof reading my paper in order to make it the best it could be. Thank you to Alan and Karen Masters for answering my questions and helping me get through the semester. Lastly, thank you to the station and to all the students. You have made this experience worthwhile and I have enjoyed spending the semester with al l of you. LITERATURE CITED Bawa, K. S. 1990. Plant Pollinator Interactions in Tropical Rainforests. Annual Reviews Inc 21 :399 422.
5 Herrera, C. and O. Pellmyr. 2002. Plant Animal Interactions: An Evolutionary Approach. Blackwell Publishing: Massachus etts. Heywood, V.H. 1993. Flowering Plants of the World. Oxford University Press, New York. Lack, A. 1982. Competition for pollinators in the ecology of Centaurea scabiosa L. and Centaurea nigra L. II. Observations on nectar production. New Phytologi st 91 : 309 320. Miao, Darren and Athena Dodd 2000 Spring. Felony and the flowering plant: Effects of nectar robbery on Stachytarpheta jamaicensis pollen uses. OTS Ungraduate Semester Abroad Program: 33 35. Perez, F., M. T. K. Arroyo, R. Medel, and M. A. Hershkovitz. 2006. Ancestral reconstruction of flower morphology and pollination systems in Schizanthus Solanaceae. American Journal of Botany 93 : 1029 1038. Pleasants, J. M. 1980. Competition for bumblebee pollinators in Rocky Mountain plant commu nities. Ecology 61: 1446 1459. In: Handbook of Experimental Biology, Jones Little. Van Nostrand Reinhold Company Inc. New York, N.Y, pp. 282 283. Raven, P. et al. 1986. Biology of Plants. Worth Publishing Inc: New York. Robertson, C. 1895. The philoso phy of flower seasons, and the phaenological relations of the entomophilous flora and the anthophilous insect fauna. Am. Nat. 29:97 117. In: Handbook of Experimental Biology, Jones Little. Van Nostrand Reinhold Company Inc. New York, N.Y, pp. 282 283. T homson, J.D 1978. Competition and cooperation in plant pollinator systems. Doctoral dissertation, University of Wisconsin, Madison. In: Handbook of Experimental Biology, Jones Little. Van Nostrand Reinhold Company Inc. New York, N.Y, pp. 282 283. Zuchow ski, W. 2005. A Guide to Tropical Plants of Costa Rica. Distribuidores Zona Tropical, Miami, Florida.
6 0 20 40 60 80 100 120 140 hummingbird Butterfly Bees Pollinator Number of Pollinators Figure 1. Number of pollinators of different taxonomic grou ps visiting Stachytarpheta jamaicensis from 6:00 am to 6:00 pm during a two day period Chi Square, Ã°c 2 = 7.09; df = 2; p < 0.05.
7 Â€Std. Dev. Â€Std. Err. Mean HOUR NECTAR cm -0,04 0,00 0,04 0,08 0,12 0,16 0,20 6:00 am 9:00 am 12:00 pm 3:00 pm 6:00 pm Figure 2. Nectar production at different hours of the day of Stachytarpheta jamaicensis in CaÃ±itas, measured by length in capillary tube ANOVA, F=15.77; df effect= 4; df error= 101; p<0.05. Nectar cm
8 Â€Std. Dev. Â€Std. Err. Mean Pollinators # POLLEN 20 60 100 140 180 220 260 300 Control Bees Butterflies Hummingbirds Figure 3. Number of pollen grains found on flowers of Stachytarpheta jamaicensis after the visitation of potential pollinato rs ANOVA, F = 1.09; df effect = 3; df error = 36; p=0.37. # Pollen grains