The Effects of Intrinsic and Extrensic Factors on F loral Visitation of Xanthosoma undipes in Monteverde, Costa Rica. Kirsten Martin Department of Biological Aspects of Conservation University of Wisconsin, Madison Abstract: Both intrinsic and extrinsic floral characteristics exert important influences on floral visitation. T he average distance between flowering plants, the number of fl owering plants, and the spadix temperature were assessed to determine the influence of these intrin sic and extrinsic floral factors on floral visitati on in Xanthosoma undipes in Monteverde Costa Ri a. Observations were made for seven nights in whi h the distan es between all flowering plants, abundan es of all morphospe ies of arthropods present and spadix temperatures were taken. Both the number of plants in flower and the average distance between flowers did appear to have an affect on flower visitation among pollinators. As the number of male inflores en es open in a night in reased, the number of s arabs per inflores en e tended to de rease (p = 0.0687). It was also found that as the average distan nrnrnrn rr rn (p = 0.0374). On the other hand, arthropod abundan es showed no orrelation with either the number of plants in flower (p = 0.1911) or the aver age distan e between flowering plants (p=0.1881), whi h suggests a lower degree of spe ialization among interlopers than the Cy lo ephala pollinators. The inflores en es sexual identity, an intrinsi fa tor, did have an affe t on visitor omposition. Diversity in male inflores en es was signifi antly higher than diversity in female inflores en es (HÂ’males=1.5097, HÂ’females=0.6466. t= 15.826, F = 1.964). This study showed t hat both intrinsic and extrinsic factors are important in floral visitation in X. undipes and different floral factors have differing affec ts on interloper and scarab visitation. Understanding the effects of both intrinsic and extrinsic factors in floral vis itation is important because plant pollination directly affect s plant reproduction and therefore directly affects plant fitness. Resumen: Tanto caractersticas florales intrnsecas como ext rnsecas ejercen influencias importantes en la visi tacin floral. La distancia promedio entre plantas con fl ores, el nmero de flores por planta y la temperatu ra del espdice fueron tomados para medir la influencia de estos factores intrnsecos y extrnsecos en la vis itacin floral en Xanthosoma undipes en Monteverde, Costa Rica. Se realizaron observac iones durante siete noches en la cual la distancia entre todas las plan tas con flores, abundancia de todas las morfoespeci es de artrpodos presentes y la temperatura de espdice f ue tomada. Tanto el nmero de plantas con flores c omo la distancia promedio entre flores parece tener un efecto en la visitacin de flores por parte de polinizadores. En cuanto el nmero de inflorescenc ias masculinas abiertas por noche aumenta, el nmer o de escarabajos por inflorescencia tiende a disminui r (p= 0.0687). Se encontr tambin que al aumentar la distancia entre plantas, el nmero de escarabajos p or planta tambin aumenta (p= 0.0374). Por otro la do, la abundancia de artrpodos no muestra correlacin con el nmero de plantas en flor (p= 0.1911) o la distancia promedio entre plantas con flor (p= 0.188 1), lo que sugiere un bajo grado de especializacin entre otros organismos que visitan la planta que los pol inizadores Cyclocephala La identidad sexual de las inflorescencias, factor intrnseco, tiene un efecto en la composicin de visitantes. La diversidad en inflorescencias masculinas es mayor que la diversid ad encontrada en las femeninas (HÂ’males=1.5097, HÂ’females=0.6466. t= 15.826, F = 1.964). Este estudio muest ra que tanto los factores intrnsecos como los extrnsecos son importantes en las visitas a X. undipes y diferentes factores florales tienen diferentes
efectos en la visitacin por escarabajos y otros or ganismos. Entender los efectos de ambos factores en la visitacin floral es importante debido a que la pol inizacin afecta directamente la reproduccin de la planta, por lo tanto afecta directamente tambin su xito r eproductivo. Introduction: Floral visitation is affected by many factors, both intrinsic and extrinsic (Garcia-Robledo et al 2005). Intrinsic factors include factors such as fl ower size, color, temperature, or sexual identity of the flower. Some extrinsic facto rs include climate, neighboring plant species and pollinator abundance as well as floral distribution and the number of plants in flower. The effects of floral distribution and the number of plants in flower are unclear and may change depending on the pollination system of the plant in question (Bosche & Waser 2001, Garcia-Robledo et al 2005). In the bumblebee pollinated flower Alstroemeria auria density did not explain variations in pollen rece ipt (Aizen 1997), but in the beetle pollinated flower Xanthosoma daguense rates of pollinator visitation have been shown to increase with increasing average dist ance between inflorescences (GarciaRobledo et al. 2005). Floral offer, or the number of flowers in a given area, is an important extrinsic factor that has been shown to h ave an effect on floral visitation. For example, an increase in floral offer leads to a dec rease in the number of pollinators per inflorescence in Xanthosoma dangues (Garcia-Robledo et al 2005). Limited research exists on the effects of the number of plants in fl ower and distance between inflorescences on visitation in X. undipes. Many aroids possess a thermogenic inflorescence, me aning that the inflorescence heats up to above air temperature. In Xanthosoma undipes temperatures peak around 35 degrees Celsius (Goldwasser, 1987). This suggests t hat inflorescence temperature may be an important intrinsic factor in determining flower visitation. It is commonly believed that heat itself does not provide the primary attra ctant to the pollinators; rather a sweet odor, which is volatized by the heat, is believed t o attract the pollinators (Dormer 1960 in Goldwasser 1987). Few studies have directly measure d how differences in spadix temperature may affect pollinator visitation in X. undipes Sexual identity may also be an important intrinsic factor in plant visitation. In the bumblebee pollinated plant Alstroemeria auria it was found that female biased patches had higher rates of visitation than male dominated patches. On the other hand, sexual identity did not explain variations in pollen recei pt (Aizen 1997). Although Alstroemeria and Xanthosoma have very different pollination systems and therefo re flower sex may effect visitation differently in the two plants (Bo sche & Waser 2001, Garcia-Robledo et al. 2005). In addition to pollinators, many interlopers visit Xanthosoma inflorescences (Cochran 1997, Goldwasser 1987). An interloper is a n organism that takes advantage of and benefits from a mutualism to the detriment of t he mutualist (Goldwasser 1987). This high abundance and visibility of interlopers in X. undipes provides a unique opportunity for the study of the interaction between intrinsic and extrinsic factors and interloper visitation rate. Previous research on inflorescence temperature and interloper communities in Xanthosoma jacquinii has shown no correlation between the two (Cochran 1997). No previous research on interloper visitation and any other intrinsic or extrinsic floral factor was found.
In this study I will assess the affects of intrinsi c and extrinsic factors on inflorescence visitation by looking at inflorescenc e temperatures, inflorescence sex, floral distribution and the number of inflorescences in fl ower. I hypothesized that su h intrinsic and extrinsic factors would have an effe t on floral visitation in X. undipes I predicted that differences in inflorescence temperatures, inf lorescence sex, average distance between inflorescences and the number of infloresce nces in flower would be correlated with changes in the abundance of pollinators and in terlopers in X. undipes Materials and Methods: Study Organisms: X. undipes is pollinated by beetles of the genus Cyclocephala in the family Scarabidae (Goldwasser 1987, Goldwasser 2000) Two species of Cyclocephala pollinators are found in the Monteverde region, C. sexpunctata which is a dirty yellow color with dark spots and C. nigerrima which is completely black. Both pollinators are s imilar in size and behavior (Goldwasser 2000). The inflorescence is in flower for two nights, on the first night the inflorescence opens and the spadix begins heating up around 4:00 pm, volatizing a sweet odor. The scarabs, attracted by this odor, land on the spadix and descend into a closed, kettle-like structure formed by the spathe at the base of the flower, where they cannot be seen by an outside observer. W hile in the kettle the scarabs eat a ring of sterile flowers provided by the inflorescen ce, mate, and feed on nectar. Late the next afternoon the spadix heats again, and the male flowers begin to grow pollen. The heat signals the scarabs to leave the kettle, and c rawl up the spadix, which is covered in pollen. The beetle then flies to another flower; th us completing pollen transfer (GarciaRobledo et al. 2005;Goldwasser 1987; Goldwasser, 2000). Study Site: The plot was found in Monteverde Costa Rica, near t he Monteverde Cloud Forest Preserve. The site measured approximately 80m squar ed and was mostly cleared of its primary vegetation. The distance between neighborin g X. undipes plants varied, with some plants clumped and others standing alone. Procedure: Upon arrival, the site was systematically searched for open flowers. The number of open inflorescences as well as the distance between all flowering plants was measured, and the open inflorescences were sexed. Females were disti nguished by having a clean, white spadix. Males had a slightly yellowed spadix, often with arthropods present. Next one male and one female inflorescence were chosen at ra ndom by assigning numbers to all the plants in flower and picking a numbered card ou t of a stack of cards of corresponding numbers. If only one sex was present, two randomly chosen flowers from the same sex were observed. If only one flowering plant was pres ent, that inflorescence was observed alone, for twice the number of observations. Once o ne male and one female were
selected, the selected plants were marked with whit e flagging tape in order to facilitate finding them in the dark. Inflorescences were observed in 10 minute intervals between 4:00 and 6:30pm. Inflorescences were observed starting on the quarte r hour and observed for 10 minutes. All observations after dark were made with a red li ght, in order to avoid disturbing the arthropods present. After 10 minutes of observation I moved to the randomly chosen flower of the opposite sex, and started observation s on that flower at the next quarter hour. The abundance of each morphospecies present i n each inflorescence during the time of observation, as well as the temperature of the spadix was recorded during each observation. All nonCyclocephala species were considered interlopers. On two separate occasions a male inflorescence was collected after the nightÂ’s observations were made in order to facilitate arthr opod identification. A male inflorescence was chosen so as not to affect the ra tio of male to female inflorescences that would be present the following night. The infl orescence was cut off the plant, put in a large zip lock bag and put in the freezer over ni ght. The following day the arthropods contained in the inflorescence were counted and ide ntified to morphospecies. Analysis: The average distance between flowering plants and a verage inflorescence temperatures were calculated. Abundances for each observation pe riod were standardized for differing observation numbers by interpolating to the smalles t number of observations. The Spearman rank correlation was run between the total number of flowers in a night and the total abundance of scarabs in the same night. In ad dition the Spearman rank correlation was run between intrinsic and extrinsic plant facto rs (the number of male flowers, average distance between plants, total number of fl owers, average temperature of male inflorescences, average temperature of female inflo rescences) and abundances of different arthropod communities (Abundance of scara bs per night, abundance of arthropods per night, abundance of scarabs in both male and female inflorescences and abundance of interlopers in male and female inflore scences). The overall community diversity of male inflorescence communities and fem ale inflorescence communities were compared using the Shannon-Weiner index and results were compared using a modified t-test. Total abundances of each species of arthrop od in males and female communities were compared using a Chi-squared test for independ ence. Results:
Extrinsic Factors and Visitation: TABLE 1: The number of plants in flower was recor ded on seven separate nights and the average distance between all flowering plants w as calculated. The averages on days 5 and 6 were not calculated due to the presence of on ly one flowering plant. It was found that the total number of plants in flo wer and the average distance between plants were not correlated (Rho = -0.7016, p = 0.1203, df = 6). The number of male inflorescences open in a night w as not correlated with total arthropod abundance in male plants on that night (R ho= -0.3381, p = 0.5122, df = 5). In addition the number of male inflorescences in a nig ht was not correlated with total abundance of scarabs in a night, but the data did s how a negative trend (Rho = -0.7775, p = 0.0687, df = 5). nr FIGURE 1: Number of male inflorescences open on a given night correlated with the abundance of scarabs observed in male inflorescence s that same night. A negative trend was found (Rho = -0.7775, p = 0.0687). Night # Total # of open inflorescences Males open Females open Average distance between flowering plants 1 6 4 2 24.94 m. 2 2 1 1 47.80 m. 3 2 1 1 53.80 m. 4 5 3 2 29.72 m. 5 1 1 0 6 1 1 0 7 3 0 3 22.18 m.
The number of plants in flower per night was not co rrelated with the total number of arthropods found that night (Rho = 0.6179, p = 0.19 11, df = 5). On the other hand, a negative trend was observed between the number of p lants in flower on a given night and the abundance of scarabs observed on the same night (Rho = -0.6910, p = 0.0856, df = 6). FIGURE 2: The total number of plants flowering on a given night correlated with the total abundance of scarabs on the same night. A neg ative trend was found between the two (Rho = Â–0.6910, p = 0.0856). The average distance was not correlated with the ab undance of scarabs in males (Rho = 0.80, p = 20, df = 3) or females (Rho = -0.6325, p = 0.3675, df=3). Finally, the average distance was not correlated with the abundance of a rthropods (Rho = 0.700, p = 0.1881, df = 4), but an increase in the average distance be tween inflorescences did correlate with an increase in the total abundance of scarabs (Rho = 0.900, p=0.0374, df=4). ___________________________________________________ _____________________ FIGURE 3: Average distance between flowering plant s on a given night correlated with the total abundance of scarabs found on the sa me night. A positive correlation was found (Rho = 0.900, p = 0.0374).
Intrinsi fa tors and visitation: There was no correlation found between average temp erature of the male inflorescence and either interloper abundance (Rho = -0.3143, p = 0.5441, df = 5) or scarab abundance (Rho = 0.2571, p = 0.6228, df = 5). Diversity was significantly higher in Male inflores cences than female inflorescences (HÂ’males = 1.5097, HÂ’females = 0.6466. t = 15.826, F = 1.964). The morphospecies present in male and female inflo rescences as well as the number of inflorescences in which they were present, their mi nimum and maximum abundances in the inflorescences and their mean abundance are sum marized in Table 2. TABLE 2: Arthropod community composition of both male and female inflorescences. Percent of inflorescences of the given sex in which the specie s is found, minimum and maximum abundances of the s pecies in a night in the given sex and the mean abundance of th e arthropod species in one night in the given sex. Male Inflorescences (N=6) Females (N=4) ________________________________ ______________ __________________ % Present Min-Max Mean % Present Min-Max Mean Cyclocephala nigerrima 42.86 0-21 4.67 25 0-1 0 .25 Cyclocephala Sexpunctata 100 2-27 7.83 75 0-1 0.75 Diptera sp. 28.57 0-14 2.33 50 0-1 0.25 Diptera larvae 14.28 0-2 0.33 0 Drosophila 85.71 0-44 22 100 5-44 16.25 Hemipteran sp. 100 11-101 42.33 0.25 0-4 0.25 Miridae 100 39-134 93.33 100 35-184 94.5 Mite 100 2-157 45.83 75 0-5 1.2 5 Mosquito 14.28 0-1 0.17 25 0-1 0.25 White Moth 14.28 0-1 0.17 0 0
___________________________________________________ _____________________ FIGURE 4: The total abundance, for all seven nights of different arthropod morphospecies in male and female inflorescences is depicted in this graph. Male inflorescences had greater abundances of individual s in the following groups: Miridae (x2=9.3074, p=0.0023,df=1), O. Hemiptera (x2 =199.9 6, p < 0.0001, df = 1), Drosophila sp (x2=11.5714, p= 0.00067, df=1), mites (x2 = 214.5 9, p < 0.001, df = 1), Cyclocephala sexpunctata (x2 = 31.02, p < 0.0001, df = 1) and Cyclocephala nigerrima (x2 = 20.50, p < 0.0001, df = 1). The sexes did not differ in abundances of individua ls of the O.Diptera found in their inflorescences (x2=1.82, p=0.1776, df=1), Diptera l arvae (x2=1.67, p=0.1967, df=1), mosquitoes (x2=0.015, p=0.920, df=1), or white moth s (x2=0.833, p=0.3613). Discussion: I predicted that both intrinsic and extrinsic facto rs would show an effect on arthropod visitation to X. undipes I found that average distance between flowering p lants on a given night was not correlated with the number of i nflorescences on that same night. This allowed me to treat them as independent variables a nd assess both separately. Extrinsic Factors: The negative trend found between the number of plan ts on a given night and the number of scarabs found per inflorescence on that night sh ows that the more inflorescences on a given night, the fewer scarabs tended to be found i n each inflorescence. Similarly, the negative trend observed between the number of male inflorescences on a given night and the number of scarabs per male inflorescence on the same night shows that the more male inflorescences open on a given night the fewer scar abs that were present per inflorescence. Based on the pollination biology of the plant, a negative trend between the number of female flowers on the previous night and the number of scarabs arriving at them is probable. It is likely that this trend was not observed in female flowers due to nrrrnrrr r !"r !r# $ % &
small sample size (seven nights) as well as the inh erent difficulty of seeing the scarabs arrive, as opposed the relative ease of seeing the scarabs congregating on the male spadix. Further study is needed to see if these trends are significant, but these data support the observation of Garcia Robledo et. al 2005 that on nights with a low number of flowering plants Cyclocephala beetles appear to be congregating in the few availa ble inflorescences. The positive correlation found between the average distance between flowers and the number of scarabs found per inflorescence is co nsistent with previous results found in Xanthosoma daguense (Garcia-Robledo et al. 2005). I suggest that this positive correlation is due to increasing distances effectiv ely lowering floral availability from the scarab point of view. Cyclocephala spp. have been shown to go to the first available inflorescence of the appropriate sex in some aroids in this case females (Young 1986). Therefore, with increased distance between inflores cences, it is likely that the number of inflorescences detected by the scarabs decreases, d ecreasing the floral availability to the beetles and increasing the number of scarabs found in each inflorescence. Arthropod abundance was not correlated with either the number of flowering plants or the average distance between flowering pl ants. This could be explained by a lack of host specificity among the interlopers pres ent. If this is the case, then other factors such as the other plant species in the area may be more important. The interloper may be looking for any place to go, and not necessarily an other Xanthosoma flower. Intrinsic factors and visitation: No correlation was found between average temperatur e of inflorescences and abundances of either scarabs or all arthropods. This is consis tant with previous observations on the subject (Cochran 1997, Goldwasser 1987) and suggest s the role of heating is indirect. Visitors are likely attracted to the odor volatized by the heat and not the heat itself (Dormer 1960 in Goldwasser 1987). Male inflorescences displayed higher community dive rsity than female inflorescences. This difference was due to increase d abundance in a few species. This was consistent with field observations, where the s padix of the male flower was often covered with interloper species, while the spadix o f the female inflorescence was often clean. These differences, especially in scarabs, may also be due to the arthropod visibility in the different inflorescences. For exa mple, upon arriving at a female inflorescence a scarab would go into the kettle for med by the spathe and was usually not seen again for the remainder of the night, so if th e scarab was not seen arriving it would not be documented in the female inflorescence. On t he other hand, in the male inflorescence the scarabs would spend extended peri ods of time on the spathe and hence were easier to observe. This pattern appeared to be less important among the interloper species present, they appeared to spend more time o n the spadix of the female inflorescence and would less often disappear into t he kettle of the flower. In conclusion, both intrinsic and extrinsic factors were important in floral visitation in X. undipes and different factors had differing affects on in terloper and scarab visitation. Future study should increase sample size, in order to find out if any of the trends
observed are significant. In addition further study on the visitation patterns and host specificity of the interlopers present in X. undipes are needed to fully understand the results shown in this study. This study furthered b otanical knowledge of the unique pollination process of X. undipes Understanding the pollination process is extremel y important in this, or any other flowering plant, be cause it directly affects plant reproduction and as such directly affects the fitne ss of the plant. Acknowledgements: I would like to thank Tania Chavarra for the endle ss help finding study sites, coming up with project ideas and running statistics. Also a huge thank you to Ka ren Masters for peaking my interest in the Xanthosoma pollination system and helping me gain access to my study site. Thank you to the Morrison, Tandy and Calvert property owners for generously allowing me to use their land to conduct this study. Also, an e xtra huge thank you to Pablo Allen for helping me identi fy arthropods and run my statistical analyses Final ly, thank you to Moncho Calddern for helping me deal w ith all my computer problems throughout the process. Literature cited: AIZEN, M.A. 1997. Influence of local floral density and sex ratio on pollen receipt and seed output: empirical and experimental results in dichogamous Alstoemeria aurea (Alstromemeriaceae). Oecologia. 111:404-412. BOSCH, M., and N.M. Waser. 2001. Experimental manip ulation of plant density and its effect on pollination and reproduction of two cofamilial mon tane herbs. Oecologia. 126:76-83. COCHRAN, C.M. 1997. Elephant Ear ( Xanthosoma jacquinii: Araceae) Pollinators and the Effect of Heat as an Attractant. CIEE Tropical Ecology and Conser vation, Monteverde, Costa Rica. DORMER, K.J. 1960, The truth about pollination in Arum In : Goldwasser L.P. 1987. Mutualism and its Ecological and Evolutionary Consequences. Doctoral Dissertation: University of California, Berkley. GARCIA-ROBLEDO,C., G. Kattan, C. Murcia, and P. Qui ntero-Marin, 2005. Equal and Opposite Effects of Floral Offer and Spatial Distribution on Fruit Production and Predispersal Seed Predation in Xanthosoma daguense (Araceae).Biotropica. 37(3):373-380. GOLDWASSER, L.P. 1987. Mutualism and its Ecological and Evolutionary Consequences. Doctoral Dissertation: University of California, Berkeley. GOLDWASSER, L.P. 2000. Scarab beetles, Elephant Ear ( Xanthosoma robustum ) and their Associates. In: Monteverde: Ecology and conservation of a tropi cal cloud forest. N.H. Nadkerni and N.T. Wheelwright, ed. Oxford University Press, Oxford, N Y, pp. 268-271. YOUNG, H.J. 1986, Beetle Pollination of Diffenbachia Longispatha (Araceae). Amer. J. Bot. 73(6):931941.
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Los efectos de los factores intrnsecos y extrnsecos respecto a las visitas florales de Xanthosoma undipes en Monteverde, Costa Rica
The effects of intrinsic and extrensic factors on floral visitation of Xanthosoma undipes in Monteverde, Costa Rica
Both intrinsic and extrinsic floral characteristics exert important influences on floral visitation. The average distance between flowering plants, the number of flowering plants, and the spadix temperature were assessed to determine the influence of these intrinsic and extrinsic floral factors on floral visitation in Xanthosoma undipes in Monteverde Costa Rica. Observations were made for seven nights in which the distances between all flowering plants, abundances of all morphospecies of arthropods present and spadix temperatures were taken. Both the number of plants in flower and the average distance between flowers did appear to have an affect on flower visitation among pollinators. As the number of male inflorescences open in a night increased, the number of scarabs per inflorescence tended to decrease (p = 0.0687). It was also found that as the average distance between plants increased, the number of scarabs per inflorescence increased (p = 0.0374). On the other hand, arthropod abundances showed no correlation with either the number of plants in flower (p = 0.1911) or the average distance between flowering plants (p=0.1881), which suggests a lower degree of specialization among interlopers than the Cyclocephala pollinators. The inflorescences sexual identity, an intrinsic factor, did have an affect on visitor composition. Diversity in male inflorescences was significantly higher than diversity in female inflorescences (Hmales=1.5097, Hfemales=0.6466. t= 15.826, F = 1.964). This study showed that both intrinsic and extrinsic factors are important in floral visitation in X. undipes, and different floral factors have differing affects on interloper and scarab visitation. Understanding the effects of both intrinsic and extrinsic factors in floral visitation is important because plant pollination directly affects plant reproduction and therefore directly affects plant fitness.
Tanto las caractersticas florales intrnsecas como extrnsecas ejercen influencias importantes en la visitacin floral. La distancia promedio entre las plantas con flores, el nmero de flores por planta y la temperatura del espdice fueron tomados para medir la influencia de estos factores intrnsecos y extrnsecos en la visitacin floral en Xanthosoma undipes en Monteverde, Costa Rica.
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Species diversity--Costa Rica--Puntarenas--Monteverde Zone
Species diversity--Monteverde Cloud Forest Reserve
Diversidad de especies--Costa Rica--Puntarenas--Zona de Monteverde
Diversidad de especies--Reserva Bosque Nuboso de Monteverde
Tropical Ecology 2008
Tall elephant's ear
Ecologa Tropical 2008
Estado fsico de las especies
t Monteverde Institute : Tropical Ecology