The effects of patch size on hummingbird visitation and pollination in Habracanthus Belpharohachis Monica Lisa Saldaa Departments of Biology and Chemistry, Santa Clara University, 500 El Camino Real, Santa Clara, Ca 95053, USA Abstract In tropical forests, plant species are sparsely distributed and in order to increase their probability of pollination they have developed bright, showy flowers that offer nectar to attract pollinators. In this study, I examined how the pollination rates ar e affected by the number of inflorescences present in patches of Habracanthus belpharohachis In order to do this, I measured the percent of pollinated flowers from 22 small patches with one to five inflorescences, and flowers from 14 large patches with mo re than 15 inflorescences. I also recorded the number of visitations by the primary pollinator of H. belpharohachis the Purple throated Mountain gem ( Lampornis calolaema ), along with two other hummingbird species to three different size patches of humming bird feeders. Results showed a significantly greater percent of flowers were pollinated in large patches of H. belpharohachis than small patches. In addition, large patches of hummingbird feeders had significantly more visitations by all hummingbird specie s than small patches. This study showed that smaller patches of H. belpharohachis are less attractive than larger patches. In tropical forests, this behavior by pollinators may directly decrease the fitness of small patches. Resumen En el bosque tropical, las especies de plantas son poco densas y necesitan estrategias para mejorar su capacidad de reproduccin. Una estrategia es tener las flores brillantes que producen nctar para atraer visitantes. En este estudio examin como el nme ro de inflorescencias de una parcela Habracanthus belpharohachis afecta la habilidad de la planta para atraer visitantes. Med el porcentaje de polinizaciones de las flores en 22 parcelas pequeas que tienen una a cinco inflorescencias, y 14 parcelas gran des tienen 15 o ms inflorescencias. Tambin observ cuantos colibres visitaron a las parcelas con comederos de colibres de tres tamaos. Los resultados indican que las flores tienen significativamente ms polen en las parcelas grandes que en las parcela s pequeas y haba una diferencia significativamente en cuanto al nmero de visitantes a los comederos de colibres. Las plantas pequeas sufran de menos habilidad para atraer polinizadores. La razn por esto es que las pequeas tienen un grado ms alto d e reproduccin con otros individuos que tienen diferente informacin gentica. Introduction Pollination, an integral part of the process of sexual reproduction in Plants, is the transfer of pollen from the anther to the stigma. Because pollination plays s uch an essential role in
reproduction, plants have evolved many different systems to effectively accomplish this transfer of genetic information. Pollen, the carrier of the males genetic information, is made of nitrogen rich proteins, fats, nucleic acids, and vitamins, and is costly to produce (Raven 1999). For this reason, it is beneficial for plants to evolve a system of pollination in which little pollen is wasted, but instead has a high rate of being transferred to other individuals of the same species In a tropic al forest, it is c ommon for species to be spa rsely distributed. Animals provide plants a means of long distance selective dispersal when plants of the same species may be separated by long distance In order to increase the probability of successful pollinati on, plants in the tropic s have de veloped ways to attract pollinators and to insure th e pollin a tor will visit another individual of the sa me sp ecies (Forsyth & Miyata 198 4). One possible method use d by p lants to attract pollinators is to produce bright, showy f lowe rs. These f lowers often offer nectar or some ot her re ward so the pollinator will vis it more f lowers of the sa me species. Habracanthus belpharohachis (formerly called Hansteinia belpharohac his ) is a small understory shrub in the Acanthaceae family and utilizes up to 20 orange red flowers arranged on an inflorescence to attract its pollinators. It is pollinated by L. calolaema 84.9% of the time (Feinsinger et al, 1986). It has an average coro lla length of 22 mm and the stigma and anthers are spatially separated. This species is not apomictic and is cross compatible with Razisea spicata (Acanthaceae) but there is almost no overlap in their polli nators (Feinsinger et al. 1986). Habracanthus bel pharohachis was the study organism because it is hummingbird pollinated, is common, and its flowers are accessible and unlikely to self pollinate without the intervention of a hummingbird. In addition, large patches are not defended as a feeding territory (Linhart 1973). Therefore, the effects of territoriality on outcrossing and pollen flow do not complicate my results. Large patches of H. belpharohachis might benefit from having many inflorescences because this would increase the number of visitations (A uspurger 1980, 1981, as cited in Feinsinger et al. 1986; Feinsinger and Tiebout 1991). It can be expected that as visitation rates increase so will rates of pollination. I also conducted a hummingbird feeder experiment to show the effects of patch size on pollinator visitation. Hummingbird feeders have been used in past studies to observe and document the behavior of hummingbirds as pollinators (Aide 1986). A hummingbird may view a feeder as an inflorescence of a plant (Aide 1986). The visitation behavior of hummingbirds to different size patches of feeders may help explain hummingbird behavior that occurs at natural patches of plants. In Monteverde, as elsewhere in the ne otropics (Feinsinger 1978), tw o distinct kinds of interactions occur betwee n hummingbirds and plants. The tw o extreme s of foraging behaviors are traplining (moving among widely spaced patches) and territoriality (remaining at a single patch). Territorial behavior should occur when there is abundance in nectar (flowers) in a small enough area to defend. These foraging behaviors are important because plants need outcrossing. In small patches, a hummingbird would have to visit many patches because of their high energetic needs and the limited quantity
of nectar provided by few inflorescences. In contrast, in a few large patches a hummingbird could visit many inflorescences and benefit from the energetic value. The focus of this study was to assess which patch size of H. belpharohachis is more likely to have greater fitness. To determine this, I measured the percentage of flowers that were pollinated in both small and large patches. I also conducted a hummingbird feeder experiment to measure if larger patch sizes have the ability to attract more pollinators than smaller patches. I predict that t he patch with the larger number of inflorescences (feeders) would have a greater ability to attract pollinators and therefore, would have a greater ability to be pollinated. Materials and Methods This study was conducted from 18 October 2000, until 12 November 2000 in Lower Montane Wet Forest (Holdridge 1967) in the Elfin Forest behind the Estacin Biolgica Monteverde, Provincia de Puntarenas, Costa Rica. In order to determine if larger patches have a higher percent of flowers pollinated, I examined 3 6 natural patches of H. belpharohachis with characteristics given in Table 1.I defined a large patch as being a group of at least 15 inflorescences that had open flowers, and a small patch as that containing between one and five inflorescences. All patches were at least 1 km away from the ne xt closest patch. Two randomly chosen flowers from each inflorescence in all patches were examined for the presence of pollen on the 12 November. Pollen receipt was quantified by clipping the stigma, placing it on a microscope slide, and looking for the pr esence of pollen grains. I analyzed the relationship between patch size (number of inflorescence in a patch) and the presence of pollen with a chi squared test of independence. I also conducted a hummingbird feeder experiment to evaluate pollinator visita tion to patches of different sizes. Three different size patches of hummingbird feeders (small, 1 feeder; medium, 3 feeders; large, 6 feeders) were created in the Elfin Forest by suspending feeders on ropes tied between tree trunks. All feeders within a pa tch were 1.5 to 2m from the next closest feeder in the patch. Feeders were suspended at a uniform height of 1.5 to 2m. Distances between patches were at least 1km. Two days after patches were established (to allow feeders to be discovered by hummingbirds) ; I made two 30 minute observations at each patch daily, recording the number of hummingbird visitations and the species. Observations were generally made between 0600 and 0900, and 1300 and 1600. I defined a visit as having occurred when a hummingbird ins erted its beak into a feeder. On the fourth day of patch establishment, after observations were made, all three patches were relocated at least 1km away from previous patches. The above process was repeated five times, so there were six patches (N=6) of ea ch size that existed for four days. Hummingbird feeders were filled with 20% sucrose solution.
The feeder experiment was not conducted in or near the natural patches of H. belpharohachis This was to prevent hummingbirds that pollinated H. belpharohachis patches from visiting patches of feeders and neglecting the flowers of H. belpharohachis I focused primarily on the relationship between patch size (number of feeders in a patch), L. calolaema traplining and territorial hummingbirds, and visitations by all hummingbird species. The relationships were examined by Kruskal Wallis nonparametric analysis of variance. In addition, I used a two way ANOVA to assess the effects of the rates of discovery of feeders by hummingbirds. Results Pollination was signifi cantly higher for the 14 large patches of H. belpharohachis (X = 76.7, + SE 2.1) than the 22 small patches (X = 56.4, + SE 2.2) (X = 33.3, P < 0.0001, chi squared test of independence, Fig. 1). In addition, there were only four stigmas (two in the small patches and two in the large patches) that received foreign pollen grains. Large patches (x = 30.7, + SE 3.3) of hummingbird feeders had the gr eatest total visitations by L. calolaema Medium size patches (x = 16.6, + SE 3.3) had the next greatest total visitations, and small patches (x = 1.1, + SE 0.6) had the least total visitations (Fig. 2a). Differences in total visitations by L. calolaema to the three patch sizes were significant (H = 47.1, P < 0.0001, Kruskal Wallis nonparametric analysis of variance, Fig. 2a). As shown in Figure 2b, large patches of feeders had the greatest total visitations of all three hummingbird species together (x=63. 8, + SE 0.4), then medium size patches had the next greatest total visitations (x = 34.6, + SE 0.2), and small patches had the least total visitations (x = 2.8, + SE 0.5). Differences in total visitations of all three species together to the three patch si zes were significant (H = 46.3, P < 0.0001, Kruskal Wallis nonparametric analysis of variance, Fig 2b). Large patches of feeders had more total visitations (x = 31.8, + SE 0.5) by territorial species ( L. calolaema and Heliodoxoa jacula ) than medium patche s (x = 17.4, + SE 0.3), and medium patches had more total visitations than small patches (x = 1.6, + SE 0.8) of feeders (Fig. 2c). Differences in total visitations of territorial species to the three patch sizes were significant (H = 47.1, P < 0.0001, Krus kal Wallis nonparametric analysis of variance, Fig. 2c). In addition, large patches (x=31.9, + SE 0.5) of feeders had more total visitations by traplining species ( Phaethornis guy ) than medium patches (x = 17.7, + SE 0.5), and medium patches had more tota l visitations than small patches (x = 1.2, + SE 0.9) of feeders (Fig. 2d). Differences in total visitations of traplining species to different size patches were significant (H = 47.4, P < 0.0001), Kruskal Wallis nonparametric analysis of variance, Fig. 2d) Differences in daily visitations over three days showed no trend among all three patch sizes of hummingbird feeders. Differences in visitations among days were not significant (F= 1.2, P = 0.3, two way ANOVA, Fig. 3).
Discussion Most pollination ecologi sts expect some relationship to exist between patch size and pollination success, even if they disagree on the exact nature of the relationship (e.g. Rathcke 1983 and Waseler 1983). In this study, results showed that significantly greater percent of flower s were pollinated in large patches of H. belpharohachis than small patches. This may be the direct result that small patches of H. belpharohachis are less attractive to pollinators than large patches. Different size patches of hummingbird feeders affect the number of visitations by hummingbird species. Larger patches of feeders have a greater number of visitations by all three species ( L. calolaema P. guy and H. jacula Fig. 4) than smaller patches. These behaviors of humm ingbirds visiting larger patches of feeders with greater frequency may reflect foraging behaviors at natural occurring patches. A natural patch may benefit from having many inflorescences because it would increase the number of visitations and therefore, i ncreasing the percent of flowers pollinated. Although I observed three hummingbird species foraging at feeders, one was of primary importance. The males and females of the L. calolaema because they provided nearly 100% of pollination of H. belpharohachis (Aide 1986). Lampornis calolaema were attracted to larger patches of feeders than smaller patches. If feeders are seen by L. calolaema as inflorescences in patches than these results may reflect their behavior at natural occurring patches of H. belpharoha chis Although I did not study visitation rates of L. calolaema to patches of H. belpharohachis larger patches may have more visitations, which would correspond to my finding that large patches of H. belpharohachis had a greater percent of flowers pollina ted than small patches (Fig. 1.). Competition among hummingbird-pollinate d neotropica l plants is the subje ct of many de bates. The c hief point of c ontention is whether foraging behavior of hummingbirds and patch size c an affect visitations among indivi dual s and outcrossing (Real 1983, Sc hemske 1981). The re sults of this study s howed that territorial species ( L. calolaema and H. jacula ) and traplining species ( P. guy ) had similar number of visitations a t all three p atch sizes (Fig. 2c d). These interactions are not releva nt to the pollination success of H. belpharohachis because several past studies have found that 84.9% of H. belpharohachis is pollinated by L. calolaema (Feinsinger et al. 1986) andthat large patches of H. belpharohachis are not defended as feeding territories (Linart 1973). If, in fact, there was no competition among individuals, than the number of visitations by L. calolaema should be correlated with the number of visitations that would occur at natural patches of H. belpharohachis. Therefore, it can be said that large patchesof H. belpharohachis do not suffer from insufficient outcrossing even though it was notdirectly studied. The data from the hummingbird feeder experiment eliminated the potential fault that larger patches wou ld be discovered faster but not necessarily proportionately more than smaller patches because daily visitations of hummingbirds did not increase as the days of patch persistence increased (Fig. 3). This is because in reward producing animal pollinated plan ts, small populations are likely to be less attractive to pollinators than large
patches. It is more beneficial for foragers to concentrate their efforts in a few large patches than in many small patches. In short, small patches of H. belpharohachis are le ss attractive to L. calolaema than large patches. This may directly decrease the fitness of small patches. These results confirm my predictions that large patches of H. belpharohachis would have a greater percent of flowers pollinated than small patches, and that larger patches of feeders would have a greater number of visitations. Nevertheless, to better understand the role that patch size plays in the fitness of H. belpharohachis it is necessary to expand the scale of study, both by including more patche s and by continuing research over many plant generations. Further studies need to be conducted on nectar production of H. belpharohachis and visitation of L. calolaema to different size patches. Finally, local floral neighborhoods (flowers of other species that surrounded the patch) of H. belpharohachis may also affect the foraging behavior of hummingbirds and the pollen loads they carry. Acknowledgements I would like to thank all those that have contributed time, resources, and encouragement to this project. I especially would like to extend gratitude to Karen and Alan Masters, Mauricio Garca, Tim Kuhman, and Andrew R odstrom f or their continual e ncouragement, advice, a nd never-ending pa tience. A t hanks a lso goes out to the Vargas family. Finally, I w ould like t o let t he o ther 29 CIEE s tudents a nd our pr ofessors know w hat a n unforgettable e xperience t hey ha ve made t hese last f our m onths. Literature Cited Ai de, T.M. 1986. The influence of eind and animal pollination on variation in outcrossing rates. Evolution 40: 434 435. Augsp urger, C.A. 1980. Mass flowering of a tropical shrub ( Hybanthus prunifolius ): Influence on pollinator attraction and movement, Evolution 34: 475 488. ---------. 1981. Reproductive synchrony of tropical shrub: experimental studies on effects of pollinators and seed predators on Hybanthus prunifolius (Violaceae). Ecology 62: 775 788 Feinsinger, P., K.G. Murray, S. Kinsman, and W.H. Busby. 1986. Floral neighborhood and pollination success in four hummingbird pollinated cloud forest species. Ecology 67(2): 4949 464. Feinsinger, P., and H.M. Tiebout III. 1991. Do Tropical Bird Pollinated Plants Exhibit Density dependent interacti ons? Field experiments. Ecology. 72(6): 1953 1963. Feinsinger, P. 1976. Organization of a tropical guild of nectarivorous birds. Ecology 56:333 345. ----------. 19978. Ecological interactions between plants and hummingbirds in succession tropical comm unity. Ecology 48: 269 287 Handel, S. 1983. Pollination and population structure. Pp. 163 202. In Leslie Real (ed.) Pollination biology. Academic press Inc. New York, New York, USA. Holdridge, D.R. 1967. Life zone ecology. Tropical Science Center, Sa n Jos, Costa Rica. Linhart, Y.B. 1973. Ecological and behavioral determinants of pollen dispersal in hummingbird pollinated Heliconia American Naturalist 107: 511 523.
Rathche, B. 1983. Competition and facilitation among plants for pollination. Pages 2 87*329 in L.A. Real, editor. Pollination biology. Academic Press, New York, New York, USA. Raven, P.H. 1999. Biology of Plants W.H. Freeman and Company Woth Publisher, New York, New York. Real, L.A. 1983. Microbehavior and macrostructure in pollinator pl ant interactions. Pages 287 304 in L.A. Real, editor. Pollination biology. Academic press. New York, New York, USA. Schemske, D.W. 1981. Floral convergence and pollinator sharing in two bee pollinated tropical herbs. Ecology 62: 946 954. Waseler, J. 1 983. Pollination intensity and potential seed set in Passiflora vitifolia Oecologia 55: 231 237.
Table 1. Characteristics of 36 natural patches of Habracanthus belpharohachis examined. Two randomly chosen flowers from each inflorescence present in a patch were examined for the presence of pollen. Patch number Number of Inflorescence Patch Size Patch Area (m 2 ) Number of flowers sampled Percent of flowers pollinated 1 1 S 0.5 2 50 2 1 S 0.5 2 100 3 2 S 1 4 50 4 2 S 1 4 50 5 2 S 0.5 4 75 6 2 S 2 4 75 7 2 S 1 4 75 8 2 S 1 4 25 9 3 S 1 6 67 10 3 S 1.5 6 67 11 3 S 1 6 50 12 3 S 1 6 83 13 3 S 1 6 66 14 4 S 1 8 50 15 4 S 1 8 50 16 4 S 1 8 50 17 4 S 1 8 62 18 4 S 1.5 8 25 19 4 S 1 8 25 20 5 S 1 10 25 21 5 S 1 10 70 22 5 S 1 10 50 23 15 L 2 30 83 24 16 L 2 32 72 25 17 L 2.5 34 74 26 17 L 2 34 71 27 18 L 1.5 36 69 28 19 L 2 38 89 29 22 L 3.5 44 75 30 22 L 1.5 44 72 31 23 L 2 46 74 32 25 L 2 50 74 33 26 L 2 52 69 34 26 L 1.5 52 81 35 27 L 2 54 76 36 31 L 4 62 95
Figure 1. Mean percent of flowers of Habracanthus belpharohachis pollinated. Differences between small and large patches and pollination were significant (X 2 = 33.33, P = 1, chi squared test of independence).
Figure 3. Mean number of daily visitations by three hummingbird species ( Phaethornis guy, Heliodoxa jacula, and Lampornis calolaema ) to different size pa tches of hummingbird feeders (small, 1 feeders; medium, 3; large, 6) on three consecutive days. Differences in visitation between days were not significant (F = 1.2, P = 0.33, two way ANOVA).
Figure 4. (a) Flower of Habracanthus belpharohachis and (b) its pollinator, Lampornis calolaema Two other hummingbird species, (c) Phaethornis guy and (d) Heliodoxa jacula that made visitations to patches of hummingbird feeders.