Epiphyll community diversity on Anthurium and Philodendron Araceae Ellen Frondorf Department of Biology, Northern Michigan University ABSTRACT Little is known about epiphyll community diversity. This study compared epiphyll diversity gro wing on leav es from Anthurium and Philodendron . I hypothesized that the effect of a collecting vein, present on Anthurium , but not on Philodendron , would affect microhabitats and epiphyll species diversity. I predicted lower epiphyll abundance on Anthurium than on Philodendron . Fifteen leaves were collected from each plant species. Morphological species of epiphylls were counted for total percent cover, as well as the total area of the leaves. The Shannon Weiner Index was used, along with Margalof s index of ri chness. Analysis was done at metacommunity all the leaves of Anthurium and Philodendron and the local community individual leaves of Anthurium and Philodendron levels. Species richness was significantly greater in both communities, as well as the num ber of epiphyll occupied boxes for Philodendron . Evenness was equal at the metacommunity level E Philodendron = 0.62, E Anthurium = 0.61, but at the local community level, Anthurium had higher evenness of epiphyll species E Philodendron = 0.56, E Anthuri um = 0.67, Mann Whitney U ' = 163, p = 0.04. I hypothesized that the underlying reason is that the collecting vein gives a path for water to leave the leaf, resulting in a drier and more homogenous habitat of the leaf surface. Therefore, no niche special izing epiphylls can become too abundant. Further studies need to be conducted on collecting veins and homogeneity, coupled with the specialized niches of epiphylls. RESUMEN Se sabe muy poco s obre la diversi dad de la comunidad de epÃfilas . Este estudio c ompar Ã³ la diversidad de epÃfilas creci e ndo en hojas de Anthurium y Philodendron . Se predijo que el efecto de la vena de recolecciÃ³n , presente en Anthurium pero no en Philodendron , afectarÃ a a los microhÃ¡bitat s y a la diversidad de especie s de epÃfilas . TambiÃ©n se predijo un a abundancia inferior de epÃfilas en Anthurium que en Philodendron ; se recolectaron quince hojas de cada especie de planta. Se contaron las e specie s morfolÃ³gica s de epÃfilas de acuerdo al porcentaje total de cobertura, asÃ como el Ã¡re a total de las hojas. Se utilizaron los Ãndices de riqueza de Shannon Weiner y de Margalof . Los a nÃ¡lisis se realizaron al nivel de metacomunidad toda s las hojas de Anthurium y Philodendron y de comunidad local hojas individual de Anthurium y Philodend ron . La riqueza de es pecies fue significativamente mayor en ambas comunidades , asÃ como tambiÃ© n lo fue el nÃºmero de cuadros ocupados por epÃfilas en Philodendron . La uniformidad fue igual al nivel de metacomunidad E Philodendron = 0.62, E Anthurium = 0. 61 pero , a l nivel de la comunidad local, Anthurium presentÃ³ una uniformidad mayor de especies de epÃfilas E Philodendron = 0.56, E Anthurium = 0.67, Mann Whitney U ' = 163, p = 0.04. Se hip o te tizÃ³ que la razÃ³n fue que la vena de recolecciÃ³n suministra ba una vÃa de escape de la hoja para el agua , resulta n do en un hÃ¡bitat mÃ¡s seco y h omogÃ© n eo en la superficie de la hoja . Por lo tanto , las epÃfilas con especializaciones de nicho no pueden volverse mÃ¡s abundantes . Se requieren mÃ¡ s estudios sobre las venas d e recolecciÃ³n y la homogeneidad acopladas con los nichos especializados de las epÃfilas . INTRODUCTION E piphylls are mostly bryophytes that live on top of leaves. Bryophytes are nonvascular photosynthetic plants, including liverworts, lichens, and mosse s that prefer humid tropical regions Richards 1954, in Coley et al. 1993. Epiphylls are thought to be non host specific since epiphylls are very dependent on the abiotic factors of their environment. A majority of bryophytes obtain water and minerals f rom atmospheric
moisture; while a few can obtain these from the substrate they inhabit Schofield 1985. Therefore, epiphylls increase in abundance with moisture Drake 2005, decrease with increase fragmentation and sunlight, due to higher rates of evapo ration Hallen 2005, and likewise increase with elevation Drake 2005. Although they are non host specific, epiphylls are associated with certain leaf characteristics. They are more abundant on shorter lived leaves compared to long lived leaves Coley et al. 1993. Drips tips help to decrease water retention and are less overgrown with epiphylls than those without drip tips Jungner 1891, in Dean and Smith 1978. Substrate also affects epiphyll colonization. Epiphylls more easily colonize smooth surf ace leaves because they adhere to them better Morales 2000. Epiphylls have both positive and negative effects on host plant leaves. Lichens have high levels of terpenoids that deter herbivores Chopra and Kumra 1988, in Coley et al. 1993, while others help to fix nitrogen for the host plant Bentley 1987. However, there is evidence of the negative effects of epiphylls on host plant leaves. For instance, the epiphyll Radula flaccida , is considered a semi parasite because it obtains water and nutrients from its host plant, without any reciprocal benefit to it Berrie and Eze 1974. Another negative effect is that epiphylls can reduce th e amount of light an understory tropical plant receives by 55 85%, thus reducing photosynthesis of the host plant by 2 0% Coley 1993. Likewise, epiphylls could increase the likelihood of pathogenic infections, because they keep the leaf surface wet Gregory 1971, in Coley et al. 1993. Little is known about epiphyll assemblages or community diversity. Plants in the fa mily Araceae commonly known as aroids make good study subjects to analyze epiphyll community diversity. Aroids are common in tropical rainforests and are often colonized by epiphylls. Two aroids, Anthurium and Philodendron , have different leaf morpholo gies. Anthurium has a marginal collecting vein, while Philodendron does not. This may make differences in the surface humidity of leaves for the two species. Epiphylls are strongly affected by humidity and leaf surface moisture conditions and thus leaf m orphology differences, specifically a marginal collecting vein, may cause differences in diversity. The collecting vein should reduce epiphyll community abundance, in light of its possible role that it reduces water retention on the leaf. METHODS This s tudy was conducted April 15 th to May 8 th , 2006 along the Cerro Chomogo Ridge behind the EstaciÃ³n BiolÃ³gica Monteverde, Puntarenas, Costa Rica. Leaves were collected from individuals of one species of Anthurium and one species of Philodendron . A total of fifteen leaves were collected from fifteen individuals of each species, from heights of 1.5 meters and were never the three newest, uppermost leaves of the plant. This minimized possible differences in leaf age. All leaves were north facing, helping to minimize the affects of different abiotic factors. Direction of the leaf was determined by a compass, from the center of the plant to the tip of the leaf . Once removed, l eaves were individually placed into plastic bag s , marked as Anthurium or Philodendro n , n umbered sequentially, and kept refrigerated until analysis could be initiated. To examine the coverage and species of epiphylls on the leaves, they were taken out of the refrigerator and allowed to dry. A transparent 2mm by 2mm grid was placed over the entire leaf and examined under a dissecting scope at 40X magnification. The percent epiphyll coverage was calculated and the kinds of morphological species present
were noted. Morphological species of epiphylls were given its own color or pattern, usi ng permanent markers in order to quantify the abundance of each. If more than 50% of the grid was covered by an epiphyll species, the grid cell was counted as occupied , and marked with the color or pattern designated by which epiphyll was present; if le ss than 50% of the grid was covered, the cell was considered empty and not marked. In cases where more than one epiphyll was present, the dominant species was said to occupy the cell. The number of boxes was counted for each species of epiphyll occupan cy and the total number of boxes the leaf occupied. The data were analyzed on metacommunity all the epiphylls on all the leaves of Anthurium and Philodendron and local community individual leaves of Anthurium and Philodendron levels. The metacommunit y and local communities were evaluated using the diversity indices S marg Margalef s index, H ' Shannon Weiner Diversity Index, S species richness, E evenness, and N the number of boxes occupied by each epiphyll species. The Modified t test was us ed to evaluate the significance of H ' for the metacommunity and the Mann Whitney test was used to determine if the diversity indices of the local community were significant. RESULTS Sampling was exhaustive for both plant species Figure 1. There were 12 species of epiphylls found on Anthurium , with four more found on Philodendron , for a total of 16 epiphyll species. The percent epiphyll cover of the metacommunity was 24.59% for Anthurium and 26.63% for Philodendron . The average percent epiphyll cover o f the local community was 25.08% for Anthurium and 27.06% for Philodendron . The indices were compared between local communities of the two plant species Table 1. There was a significant difference in the averages of S, E, N, and S marg ; there was a hig her species richness S Philodendron = 8.6 Â± 2.261, S Anthurium = 5.6 Â± 1.298, Mann Whitney U ' = 198.5; p = 0.0003, n = 15; S marg Philodendron = 1.217 Â± 0.103 , S marg Anthurium = 0.859 Â± 0.062 , Mann Whitney U ' = 174; p = 0.0107, n = 15, less evenness E Philod endron = 0.559 Â± 0.145, E Anthurium = 0.673 Â± 0.152 , Mann Whitney U ' = 163; p = 0.0362, n = 15, and more boxes covered by epiphylls N Philodendron = 766.533 Â± 531.526 , N Anthurium = 239.333 Â± 135.699, Mann Whitney U ' = 196; p = 0.0005, n Philodendron = 11457 , n Anthurium = 3669 for Philodendron than Anthurium . Philodendron exhibited a higher diversity than Anthurium, but the indices were not significant H ' Philodendron = 1.206 Â± 0.372, H ' Anthurium = 1.147 Â± 0.312, Mann Whitney U ' = 134, p = 0.3725, n = 15. T he indices were also compared between metacommunities of the two plant species Table 2. Philodendron s epiphyll community was richer S Philodendron = 16, S Anthurium = 12; S marg Philodendron = 1.60, S marg Anthurium = 1.34 and was significantly more divers e H ' Philodendron = 1.72, H ' Anthurium = 1.51, Modified t test, t = 12.03, df = 7372.45, p < 0.001 than Anthurium . Philodendron had three times the number of boxes occupied by epiphylls N Philodendron = 11457, N Anthurium = 3669, but evenness was equal E Philodendron = 0.62, E Anthurium = 0.61. The most abundant epiphyll species for each leaf was noted Table 3. There were three most abundant epiphyll species in Anthurium and five most abundant epiphyll species in Philodendron .
0 5 10 15 20 0 5 10 15 20 Number of leaves sampled Cumulative number of epiphyll species Philodendron Anthurium FIGURE 1. The relat ionship between the number of leaves sampled and the cumulative number of epiphyll species. At n = 11 for Philodendron and n = 1 2 for Anthurium epiphyll species richness asymptotes, signifying that a sample size of 15 leaves for Philodendron and Anthurium was exhaustive of epiphyll species richness. 0 2 4 6 8 10 12 14 16 18 0 10000 20000 30000 40000 Number of boxes surveyed Cumulative number of epiphyll species Philodendron Anthurium Philodendron Anthurium FIGURE 2. The relationship between the number of boxes surveyed and the cumulative number of epiphyll species. The number of boxes is a proxy for the amount of area. Higher Philodendron epiphyll species ri chness S Philodendron = 16, S Anthurium = 12 is a strong consequence of the greater area surveyed. According to the highly similar trend lines RÂ² Philodendron = 0.9149, RÂ² Anthurium = 0.9539, as more area is surveyed, similar species richness would be fou nd in Anthurium .
TABLE 1 . Average diversity indices of the local communities of Anthurium and Philodendron . Philodendron had a greater average area covered by epiphylls. The epiphylls were significantly more abundant N, the number of epiphyll occupie d boxes, Mann Whitney U ' = 196; p = 0.0005, n Philodendron = 11457, n Anthurium = 3669 and had higher species richness S, species richness, Mann Whitney U ' = 198.5; p = 0.0003, n = 15 ; S marg , Margalef s index, Mann Whitney U ' = 174; p = 0.0107, n = 15 on Philodendron . There was significantly higher evenness of epiphylls on Anthurium compared to Philodendron Mann Whitney U ' = 163; p = 0.0362, n = 15 . There was not a significant difference in species diversity H ', Shannon Weiner Diversity Index, Mann Wh itney U' = 134, p = 0.65, n = 15. Anthurium Philodendron Signif ic ance p value Smarg 0.86 Â€ 0.06 1.22 Â€ 0.10 Yes 0.01 H' 1.15 Â€ 0.31 1 .21 Â€ 0.37 No 0.37 S 5.60 Â€ 1.30 8.60 Â€ 2.26 Yes < 0.0 1 E 0.67 Â€ 0.15 0.56 Â€ 0.15 Yes 0.04 N 239.33 Â€ 135.70 766.53 Â€ 531.53 Yes < 0.0 1 Average Percent Covered 25.08 % 27.06 % TABLE 2 . Diversity indices of the Metacommunities of Anthurium and Philodendron . Philodendron had a greater average area covered by epiphylls. The epiphylls were more abundant N, the number of epiphyll occupied boxes, had higher species richness S, species richness ; S marg , Margalef s index, and in consequence were significantly more diverse Modified t test, t = 12.03, df = 7372.45, p < 0.01 on Philodendron than Anthurium . The evenness o f epiphylls was equal for the two plant species. Anthurium Philodendron S marg 1.34 1.61 H' 1.51 1.72 S 12 16 E 0.61 0.62 N 3669 11457 Average Percent Covered 24. 59 % 26.63 %
TA BLE 3. The most abundant epiphyll species for each leaf of Anthur ium and Philodendron . Anthurium had three most common species. Philodendron had five most common species. Anthurium Philodendron Leaf Number Most Abundant Species Percent Area of Epiphyll Cover Most Abundant Species Percent Area of Epiphyll Cover 1 2maroon 16.089% 4red 41.156% 2 8light green 7.657% 3brown 12.798% 3 2maroon 5.361% 1purple 3.948% 4 8light green 14.659% 1purple 37.547% 5 2maroon 16.126% 2maroon 10.758% 6 8light green 12.411% 2maroon 12.266% 7 1purple 5. 463% 1purple 46.492% 8 1purple 19.251% 1purple 15.118% 9 8light green 15.234% 1purple 3.953% 10 8light green 5.464% 15dg w/brown 5.287% 11 1purple 16.808% 3brown 6.934% 12 1purple 6.367% 2maroon 11.210% 13 2maroon 8.691% 1pur ple 19.466% 14 1purple 17.066% 1purple 8.265% 15 2maroon 16.533% 2maroon 8.804% DISCUSSION The results for the local communit ies showed average community richness is greater on Philodendron than on Anthurium Table 1. This is due in part to Philodendron having larger leaves and higher epiphyll coverage Figure 2; Table 1. However, when the differences in coverage and area are accounted for , species richness on Philodendron is still greater. This will be discussed further below. Despite ha ving higher richness, epiphyll communities on Philodendron are, on average, equally diverse H' as those on Anthurium Table 1 . This is due to the fact that the average evenness of epiphyll communities on Philodendron is lower than Anthurium s epiphyll communities Table 1. This result suggests that individual Philodendron leaves are dominated by few species, whereas Anthurium epiphyll communities are not. The unevenness in Philodendron s epiphyll communities might reflect different competitive abilit ies of epiphylls . Because less evenness means, the identity of the common species changes from leaf to leaf Table 3, it seems more likely that chance and colonization are involved. The results for the metacommunities did not exactly mirror local commu nities. Species richness was again greater on Philodendron than on Anthurium Table 2. However, this time there was a significant difference in diversity and no difference in evenness Table 2. The evenness of Philodendron s epiphyll community for the metacommunity is higher than that for local communities. The increase in evenness means that on a per leaf basis epiphyll communities are dominated, but overall the domina n t species changes from leaf to leaf. The higher diversity of Philodendron s epi phyll community is a simple consequence of higher richness across the metacommunity. The per leaf richness is also
higher; suggesting that there is something about the individual leaf that allows many species to co exist. The presence or absence of a col lecting vein may influence how many species co exist by influencing leaf surface moisture. A vein, as present in Anthurium , may homogenize the surface moisture, making conditions uniform and drier. A uniform and drier habitat would lessen the advantage o f being competitive in more moist, heterogeneous conditions. The lack of a vein may result in such conditions, favoring different species with different microhabitat requirements. The differences in habitat, allows for niche specialization and greater sp ecies richness . Additional experimentation is needed to understand the role of a collecting vein in light of leaf surface conditions, and to determine if epiphylls have distinct niche specializations. Aroids and epiphylls are regularly interacting with ea ch other, especially in the humid tropics. Therefore further knowledge is essential to understanding epiphyll intraspecific interactions, and host plant epiphyll relations. ACKNOWLEDGMENTS I would like to thank Karen Masters, for her guidance and pati ence in advising; to Alan Masters and Javier MÃ©ndez for thoughtful insight to project ideas; to Maria Jost for her patience, statistical guidance, and appendix help; to her and Ollie Hyman for supplies; to Caroline Farrior for help with identifications of morphological species of epiphylls; and to the EstaciÃ³n BiolÃ³gica Monteverde. LITERATURE CITED Bates, J. W. 2000. Mineral nutrition, substratum ecology, and pollution. In: Byrophyte Biology. A.J. Shaw and B. Goffinet, eds. Cambridge University Press. Cambridge, UK. pp 171. Bentley, B.L. 1987. Nitrogen fixation by epiphylls in a tropical rainforest. Annals of the Missouri Botantical Garden 74: 234 241. Berrie, G. K. and J. M. O. Eze. 1975. The relationship between an epiphyllous liverwort and host leav es. Annals of Botany 39: 955 963. Chopra, R. N. and P. K. Kurma. 1988. Biology of bryophytes. John Wiley & Sons, New York, New York, USA In Coley, P.D., T. A. Kursar, and Jose Luis Machado. 1993. Colonization of tropical rain forest leaves by epiphylls: ef fects of site and host plant leaf lifetime. Ecology 74: 619 623. Coley, P. D., T. A. Kursar, and J. L. Machado. 1993. Colonization of tropical rain forest leaves by epiphylls: effects of site and host plant leaf lifetime. Ecology 74: 619 623. Daniels, J. D. 1998. Establishment and succession of epiphyllic bryophyte assemblages on the fronds of the neotropical understory palm Geooma seleri . Unpublished dissertation. University of North Dakota. Drake, J.E. 2005. Palm epiphylls response to elevation and mist frequency in a Costa Rican cloud forest: a possible bioindicator of local climate change. CIEE Spring 2005. pp 252. Gregory, P. H. 1971. The leaf as a spore trap. Pages 239 244 in R. F. Preece and C. H. Dickinson, editors. Ecology of leaf surface microorg anisms. Academic Press, New York, New York, USA In Coley, P.D., T. A. Kursar, and Jose Luis Machado. 1993. Colonization of tropical rain forest leaves by epiphylls: effects of site and host plant leaf lifetime. Ecology 74: 619 623. Hallen, J. 2005. Trail w idth and epiphyllous coverage of chameadorea spp. CIEE Spring 2005. pp 248. Jungner, J. R. 1891. Anpassungen der Pflanzen as das Kilma in den Gegenden der regenreichen Kamerungebirge. Bot. Zbl. 47: 353 360 In Dean, J. M., and A. P. Smith. 1978. Behavoria l and morphological adaptations of a tropical plant to high rainfall. Biotropica 10: 152 154. MacMillan, C. 1895. Current problems in plant morphology. Science, New Series 2: 481 482.
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