Influence of elevation, host species, and host size on the density of mistletoe, Phorodendron robustissmum (Viscaceae) Jessica Rochelle Price Department of Biology, Berea College ABSTRACT Phorodendron robustissmum is an aerial hemiparasitic plant, dispersed by bir ds, that parasitize their hosts by tapping into the hostÂ’s vascular tissue. This resea rch examines the density of mistletoe, Phorodendron robustissmum (Viscaceae) as a function of host species, host siz e, and elevation. This study was conducted in the M onteverde region in Costa Rica from 8801480 m. Data were co llected on host species, density of mistletoe on tw o host species, elevation, and the diameter at breast heig ht. ANCOVA and ANVOA showed that only host tree siz e influenced the clump density of Phorodendron robustissmum. Three different host species, Sapium glandulosum, Sapium laurifolium, and Sapium macrocarpum (Euphorbiaceae) harbor Phorodendron robustissmum in the study area. RESUMEN Phorodendron robustissmum es una planta hemiparsita area, dispersada por a ves, que parasita su hospedero tapping su tejido vascular. Esta investigacin exa mina la densidad del matapalo Phorodendron robustissmum (Viscaceae) en function de la especie, tamao del h ospedero y elevacin. Este studio fue hecho en la region de Monteverde, Costa Rica de 880 Â– 1480. Se tomaron d atos de densidad en dos hospederos, elevacin y di metro a la altura del pecho (DAP). ANCOVA y ANOVA muestran qu e solo el tamao del hospedero influye en la densid ad de Phorodendron robustissmum es una planta. Tres especies diferentes de hospede ro Sapium glandulosum, Sapium laurifolium, y Sapium macrocarpum (Euphorbiaceae) tienen Phorodendron robustissmum en el area de estudio. INTRODUCTION Mistletoes are diverse members of the Order Santala les that represent the largest group of parasitic woody angiosperms in the world (Kuijt, 19 68). They are found in four families Loranthaceae, Misodendraceae, Santalaceae, and Visc aceae (Amico, 2007). While being diverse in many regards, most mistletoe is bird-dispersed, often epiphytic plants that parasitize their hosts by tapping into the hostÂ’s vascular tissue (S argent, 1994), (Amico, 2007). There are some types of mistletoes that are dispersed balistically or by wind, but most are bird dispersed (Restrepo, 2002). Birds usually eat the viscous be rries from the mistletoes and then either defecate onto branches or in some cases rub the see ds from their beaks onto the branches of trees (Thompson, unpublished data). This method of seed d ispersal gives rise to the high diversity in
mistletoe species found throughout the world (Restr epo, 2002). When the birds disperse the mistletoe seeds onto tree branches, the seeds grow into the tree causing cankerous swellings to form in the branches. Then, mistletoe stems will gr ow out of the cankers and form clumps, multiple mistletoe stems growing from one location on the branch that range in size from small to large. Large infestations of mistletoe, meaning many clumps, can lead to the death of the host tree it inhabits but usually takes many years and d epends on the host tree it inhabits (Thompson, unpublished data). Host tree species vary with the mistletoe species that inhabit them. Meaning, a species of mistletoe will be host specific to a c ertain species or genus of tree and will only be found in that species or genus. Yet, not much is kn own about how or why mistletoe species are host specific but possible explanations are that mi stletoe distribution is 1) disperser dependent, or 2) host/mistletoe dependent. If mistletoe distribut ion is disperser dependent, then mistletoe would be able to grow in any tree species but would depend on the disperserÂ’s preference. Conversely, if it was dependent on the mistletoe/ho st species, then mistletoe would only grow in certain tree species even when dispersed in others. Mistletoes in the region of Monteverde, Costa Rica include Phorodendron robustissmum, a species that occurs on members of the genus Sapium that occurs from 0 m elevation to 2000 m elevation. It has been reported that Phorodendron robustissmum is host specific on Sapium oligoneurum in the Euphorbiaceae in the Monteverde region (Wil loughby, 1995). However, not enough research has been done to confirm that P. robustissmum is only found to inhabit the Sapium genus. Currently, there are four described Sapium spp found in the Monteverde region from 700-1500m (Fogden, 1993). These species differ in that they vary in elevation and size. For instance, Sapium glandulossum is found from 900-2000m and is 5-20m tall where as Sapium laurifolium is found from 0-1200 m and is 8-25 m tall. In addition to the host specificity of mistletoe sp ecies, more research needs to done to determine what influences mistletoe growth in host trees. The elevation and size of the host tree could also influence the growth of Phorodendron robustissmum and other mistletoe species The purpose of this study is to investigate whether mis tletoe clump density is influenced by the host species, diameter at breast height (DBH), elevation or some combination of these three. In this study, I determined the DBH, elevation, number of c lumps of mistletoe, and the species of host trees that Phorodendron robustissum was found to inhabit. With this information I dete rmined whether the clump density of Phorodendron robustissum is influenced by elevation, species, or host size. This research determines the host specie s of Phorodendron robustissimum found along an elevational gradient and the possible role of ho st size and species in determining mistletoe density. By determining, what factors can influence the growth patterns of Phorodendron robustissmum; future research can determine such things as the a ffects of mistletoe on its host species and how that interaction is affecting the c ommunity. MATERIALS AND METHODS This study took place in the Monteverde region, of Costa Rica from April 11-May 8, 2008. In area A and B the mistletoe observed was within 20 m from the road whereas in areas C, D, and E the mistletoe observed was in fields off of the mai n road (Figure 1). Eighty-eight host trees were
observed from 883 m elevation to 1481 m within thes e five areas. Observations were made by first identifying the mistletoe to ensure that it w as Phorodendron robustissimum In order to determine if the size of the host species influence s the clump density, the circumference at breast height was taken using a tape measure. The diameter was then calculated from the circumference measured for each tree. The trees that were branche d below the breast height diameter were still measured for each branch and then added together to get the diameter. The number of clumps was counted for each host tree containing Phorodendron robustissimum Clumps were determined by clearly separated clusters of mistlet oe in the host tree. In some instances, the clumps were so clustered together that they appeare d to be one huge clump. In these circumstances, the tree was marked as infested beca use the tree had so much mistletoe, I could not differentiate between the clumps. For testing, I reported the Â“infestedÂ” host trees containing approximately 20 clumps. The elevation was also recorded for each host tree with an altimeter to later use to determine if elevation influences that clump density or the growth of host species. The host species were identified by taking cut samples to William Haber. I ran an analysis of covariance (ANCOVA) between clump densities, elevation and species to determine whether clump density varied because of elevation, tree species, or the interaction of elevation and species. I also ran an ANCOVA between clump density, the diameter at breast height, and the species of tree to determine whether clump density varied with DBH, host species, or the interaction of host size and species. Lastly, I wanted to look at whether host species varied with their average diameter at breast height, which I tested with an analysis of variance RESULTS I identified three different host species of Phorodendron robustissimum specifically, Sapium glandulosum Sapium laurifolium and Sapium macrocarpum ( Euphorbiaceae). The data collected from Sapium laurifolium was not used in any of these tests because only two trees were found to be occupied with Phorodendron robustissimum The analysis of covariance (ANCOVA) relating clump densities to elevation, host Figure 1. Map of study site where Phorodendron robustissum was found in host species. Roads are signified by yellow. Each outlined box represents an area where mistletoe was found. Pink is Area A, teal is Area B, purple is Area C, green is Area D, and red is Area E.
species or the interaction of elevation and species was not significant (r2 = 0.05, F = 2.56, P = 0.0607, N = 85). However, the ANCOVA relating clump density to host species, host size, or an interaction was significant (r2=0.11, F for model 4.53, P 0.0055, N=85) (Figure 2) Lastly, an analysis of variance revealed that hosts differed s ignificantly in size, with S. glandulosum being larger than S. macrocarpum (r2 = 0.49, F = 83.22, P = 0.0001) (Figure 3) Figure 2. Regression of the density of clumps of Phorodendron robustissimum and DBH of the host trees Sapium macrocarpum and Sapium glandulossum (r2=0.110806, F = 4.5311, P 0.0055, N=85).
Figure 3. Average DBH for Sapium macrocarpum and Sapium glandulossum DISCUSSION My results showed that there is no effect of specie s or elevation on the density of Phorodendron robustissimum However, the diameter at breast height of host tr ees significantly affected the density of clumps of mistletoe. On ave rage, the greater the DBH, the greater number of clumps found. The ANOVA showed that there was a significant difference in average size between S. macrocarpum and S. glandulossum These results show that the larger the tree, the greater the density of Phorodendron robustissmum in Sapium and that on average, S. glandulossum is larger than S. macrocarpum These results support a previous study suggesting that the size of the substrate influences the growt h of the mistletoe yet adds new information that the size of the host tree influences the mistletoe growth. Still, the reason as to way is not answered in this study. Possible explanations could be 1) larger trees are larger targets for the disperser, 2) larger trees are healthier than small er trees, 3) larger trees are older trees, or 4) th at larger trees provide larger canopies. In the case of larger trees being larger target areas for dispersers would indicate that the disperser prefer s going to larger trees to perch or feed. This would make since because larger trees could provide more protection than smaller trees (Thompson, unpublished data). These findings could also suggest that larger trees are healthier trees, which would provide better substrate and nut rients to the mistletoe. Or, maybe larger trees are older which allow for more mistletoe to be esta blished which would account for a greater density of clumps in the host tree. Lastly, these r esults might indicate that larger trees have larger crowns have higher amounts of sunlight to support t he mistletoe. In a previous study, it was determined that the larger crowns support more mist letoe then smaller crowns and it was possibly do to 1) the amount of sunlight the mistle toe receives, or 2) larger crowns provide better branches for the mistletoe to grow (Thompson, unpub lished data). Whatever be the explanation of the factors that inf luence mistletoe growth, the first step in understanding mistletoe interactions is determin ing the host species and growth patterns of the mistletoe. Without that information, you cannot loo k at how that mistletoe species is influenced by the host species or the disperser and vice versa While seeming like an simple plant, the interactions that mistletoes have with its disperse r and host species is complex and needs much more research than it is given. While this research is only a small part in helping to better understand those interactions and how they work, it still is providing more information and possible explanations to explain this complex web. ACKNOWLEDGEMENTS I would like to thank Karen Masters for her time an d patience to help me work through my research project. I greatly appreciate William Habe r for taking the time to identify my mistletoe species and the host species. I would also like to thank Taegan McMahon for her understanding
and help. I would like to thank Martha Campbell and the Guindon Family for allowing me to use their property for my study sites. LITERATURE CITED Amico, G. C. 2007. Phylogenetic relationships and e cological speciation in the mistletoe Tristerix (Loranthaceae): the influence of pollinators, disp ersers, and hosts. American Journal of Botany 94(4): 558Â–567. Aukema, J. E. 2002. Mistletoes as parasites and see d-dispersing birds and disease vectors: current understanding, challenges and opportunitie s. Seed dispersal and frugivory: ecology, evolution and conservation D. J. Levey, ed. CABI Publishing, New York. pp. 99-110 Fogden, M. 1993. An annotated checklist of the bird s of Monteverde and Penas Blancas. Michael Fogden Monteverde, Costa Rica. 1993. Kuijt, J. 1968. Mutual affinities of Santalean fami lies. Brittonia 20, 136-147. Kuijt, J. 1969. The biology of parasitic flowering plants. Seed dispersal and frugivory: ecology, evolution and conservation. D. J. Levey, ed. CABI Publishing, New York, pp. 83 -98 Restrepo, C. 2002. The role of vertebrates in the d iversification of New World mistletoes. Seed dispersal and frugivory: ecology, evolution and co nservation Author. CABI Publishing, New York. pp. 83-98. Rowan, M. A. 1998. Mistletoe position in the host t ree Psidium guajava Tropical ecology and conservation Fall 1998. 1-8. Sargent, S. 1994. Dissertation: Seed dispersal of m istletoe by birds in Monteverde, Costa Rica. Cornell University. Thompson, R. L. Eastern Mistletoe ( Phoradendron leucarpum Viscaceae) in the City of Berea, Kentucky: a High Incidence of Infestation and Eig ht New Host Species for Kentucky. Unpubl. Data Willoughby, S. T. 1995. Preferential parasitism by mistletoe species on different host trees. UCEAP Tropical biology Spring 1995. 126-141.
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Price, Jessica Rochelle
Influencia de la altitud, las especies hospedadoras, y el tamao del hospedador en la densidad del matapalo, Phorodendron robustissmum (Viscaceae)
Influence of elevation, host species, and host size on the density of mistletoe, Phorodendron robustissmum (Viscaceae)
Phorodendron robustissmum is an aerial hemiparasitic plant, dispersed by birds, that parasitize their hosts by tapping into the hosts vascular tissue. This research examines the density of mistletoe, Phorodendron robustissmum (Viscaceae) as a function of host species, host size, and elevation. This study was conducted in the Monteverde region in Costa Rica from 880- 1480 m. Data were collected on host species, density of mistletoe on two host species, elevation, and the diameter at breast height. ANCOVA and ANVOA showed that only host tree size influenced the clump density of Phorodendron robustissmum. Three different host species, Sapium glandulosum, Sapium laurifolium, and Sapium macrocarpum (Euphorbiaceae) harbor Phorodendron robustissmum in the study area.
Phorodendron robustissmum es una planta hemi-parsita area, dispersada por aves, que parasita a su hospedador tocando en el tejido vascular del husped. Esta investigacin examina la densidad del matapalo Phorodendron robustissmum (Viscaceae) en funcin de la especie hospedador, el tamao del hospedador y la elevacin. Este estudio fue hecho en la regin de Monteverde, Costa Rica a una altura de 880-1480 metros.
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