Community composition and diversity of lichens along a disturbance gradient in San Luis, Costa Rica Sarah Hosford Department of Zoology, Colorado State University ABSTRACT This research was conducted to better understand lichen morphology and diversit y in different habitats in San Luis, Costa Rica. Lichens on trees in adjacent pasture, forest edge, and mature forest areas were identified to morphospecies and the species richness, diversity and total coverage per tree was compared across habitats. 18 di fferent morphospecies were found across all three habitats. The forest trees had the lowest species richness and diversity, while the forest edge and the pasture had the highest. Resumen Esta investigaciÃ³n se condujo para entender la morfologÃa y divers idad de lÃquenes en distintos hÃ¡bitats de San Luis, Costa Rica. Los lÃquenes en los Ã¡rboles en tres distintos hÃ¡bitats: potrero adyacente, orilla del bosque y bosque primario fueron identifi cados por especies morfolÃ³gicas . La riqueza de especies, la divers idad y el area total cubierta por Ã¡rbol se compararon entre hÃ¡bitats. Dieciocho especies morfolÃ³gicas se encontraron entre los tres hÃ¡bitats. Los Ã¡rboles del bosque tuvieron una riqueza y diversidad de especies menor, en tanto que la orilla del bosque y e l potrero presentaron las riquezas y diversidades mÃ¡s altas. INTRODUCTION Lichens are organisms taxonomically classified in the Kingdom Fungi. However, they are actually composed of a fungal partner (mycobiont) and one or more photosynthetic partners (ph otobiont) (Nash, 1996). Photobionts have been observed as either a green algae (Kingdom Plantae) or a cyanobacteria (Kingdom Protista)(Nash, 1996). Lichens exist in an obligate relationship in which the fungus provides the photobiont with protection from d esiccation in return for carbohydrates (Umana et al. 2002). The majority of their nutrients are absorbed across their surface because they lack a vascular system. They are also poikilohydric and therefore they rely on precipitation for moisture (Wolseley e t al. 1997). These two factors result in lichens responding strongly to environmental variation in light, moisture, temperature, and air quality. Lichen richness and abundance across the tropics seem to be related to physical parameters, such as temperat ure and humidity. In Ecuador the most species rich area was found in the moist cloud forest around 3000m above sea level. Lichens at this level did with mosses, filmy f not as abundant (Arvidsson 1977). In New Guinea, where the climate is generally warm and humid year round, lichens dominate the mid montane forests (1500 2000m) but are richer in the lower montane zone (1000m) (Lambley 1991). Trees in more open areas,
such as pastures and roadsides, are usually found covered in lichens in most elevations across the tropics (Lambley 1991, Krog 1991). A study done in the Monteverde zone in CaÃ±itas, Costa Ric a(20 compared lichen communities between pasture and pristine forest areas (Bedell Stiles 2004). Coverage on host trees between areas was not significantly different, but the lichen species in the forest had to compete with moss and epiphytes, resulting i n lower total coverage. Species richness in the pasture area was significantly higher than the forest. Species composition of the two communities was very different with a very low percentage of species overlap. This brings up the question if the egde of the forest, where the two habitats overlap, would have overlapping species as well. This study is similar to Bedell Stiles study by comparing lichen communities in different habitats, but at a lower elevation. The lower elevation is hypothesized to conta in a larger amount of lichen coverage in the forest with the low abundance of epiphytes and moss. The edge area is included in this study and is hypothesized to have the highest species richness having species from both areas. MATERIALS AND METHODS This study was conducted in San Luis, Costa Rica where the intact habitat is classified as a premontane wet forest (Holdridge 1967). Twenty trees were chosen in each habitat: pasture, forest edge, and mature forest. The habitats were each approximately 100m x 100m and were located adjacent to one another. Trees were chosen on the basis of having a DBH (diameter at breast height) greater than fifteen centimeters and harboring at least one species of lichen. To have a representative sample of the lichens, a varie ty of host species were used. The relative area occupied by each lichen species per tree was estimated by counting the occupied grid cells (0.5 x 0.5cm) on a laminate of 20.5 x 30.5 cm. The area of the host tree censussed was located on the trunk, at a hei ght on 1.5 m, on the South East facing side. With information on lichen taxonomy lacking, each morphospecies was assigned a unique letter. Photographs of each species were taken using a Sony Cyber shot DSC S85 to create a visual database. S (species rich ness) was quantified at each location. A Shannon Weiner Index Qualitative Index was calculated for the similarity of species composition between sites. RESULTS Diversity and Number of Species Per Tree A total of 18 morphospecies of lichens were found across the three habitats. The average diversity per tree between all three areas was found to be significantly different (Figure 1, The average number of species per tree was also significantly different in each area (Figure 2, F = 14.891, P < .0001, df = 2). The pasture had an average of 2.85 species per tree, the edge had 1.95, and the forest had 1.25.
Species Richness Species richness across the three habitats was the same in the pasture and edge, but vastly lower in the forest. 14 morphospecies were found in the pasture and edge (Appendix 1a and 1b respectively), with the forest only having four (Appendix 1c). Abundance The abundance of lichen per tre e was found by dividing the total number of grid squares covered by lichens divided by the total number of squares on the grid (2,080). The average abundance of lichen across habitats was only marginally significant (F = 1.427, P = .2485, df = 2). Species Composition and Evenness value is given from 0 1, with 0 indicating no similarity and 1 indication complete homogeny between sites. The forest and pasture, as well a s the forest and edge habitats, had four species in common (Sorenson Index = 0.44). The pasture and edge habitats showed higher similarity with 10 species in common (Sorenson Index = 0.714). An eveness value was assigned to each habitat to represent how e venly species are distributed by abundance, with 1 being perfectly even and 0 completely uneven. The average evennes of species was significantly different across all three habitats (F = 4.627, P = .0137, df = 2). The pasture was the most even (E = 0.653) followed by the edge (E = 0.411), and lastly the forest (E = 0.308). DISCUSSION The lichen communities of San Luis were shown here to be most species diverse, species rich, and most evenly distributed on pasture trees, followed by edge trees, and lastly , on interior forest trees. As figure 3 shows, the forest had few species relative to the other two habitats. Two of the four total species in this area were dominant, with the other two being rare. This resulted in the species being disproportionately dis tributed across the host trees. The edge area was dominated by one of the dominate species in the forest, but had higher abundances of other species as well. Species richness in this area was considerably higher with 14 total species. These species were mo re evenly distributed than the forest, but significantly less than the pasture (Figure 3). The pasture had no dominant species, but instead a relatively even abundances of each species. Despite the prediction that edge communities would be most diverse, r ich, and even, my results do not support this. One possible explanation could be intraspecific competition . The species in the forest could be fighting for limited sunlight in which to two dominant species could have an advantage over the others and are dr iving them to extinction. This would explain the small diversity in the forest habitat. The edge is only partly shady , so lichens living on hosts that do receive sun would not need to compete while those in shady parts would. This could explain the higher abundance of more species and fewer dominating species. In the future, studies concentrating on sun exposure between hosts in edge habitats could be beneficial . In the pasture , sun light is abundant so compe ti ti on is not necessary, resulting in the higher diversity. Another explanation for the higher diversity in the pasture could potentially be the sun itself. Higher exposure to sun results in more productivity as well as higher biodiversity. Usually this fact is coupled with another factor.
A third e xplanation , which could be coupled with sun exposure, is based on chance more than anything. Lichens use water, wind, and small animals, such as mites in birds, to move to new locations with favorable conditions (Purvis 2000). For the forest, species that like shadier habitats, have a higher chance of dispersing to new favorable conditions being that hosts are so close together. They do not have to travel very far and have a higher chance, when depending on wind and rain, to hit another tree. Also, a bottle neck effect could be in effect for this forest area in particular. The dominant species found could be a result of the dominant becoming more dominant and the rarer becoming rarer . This is possible because of the trees being so close, probably having high interconnectance, resulting in the most fit lichens taking over. For the pasture, trees are further apart and could potentially be acting like islands. Connectance between trees is probably less frequent because lichens have to depend on chance events to m ove around. The chance of hitting another tree is less probable than the forest were the trees are close together. This would slow down any one species dominating, creating a more diverse population. Also, if lichens are depending on wind and rain to dispe rse, their overall dispersal could be limited to a certain range. This could be restricting lichens species from dispersing in to other areas, explaining the lack of overlap found between habitats (Figure 3). Further research in dispersal ranges would furt her this hypothesis. The forest trees having the highest overall coverage of trunk surface area, even though it was mostly dominated by only one or two species could be explained by a combination of the previous hypotheses. If the lichens are competing f or sunlight, then like other understory organisms, the more surface area they have available for sunf lecks the better. The other expla nation could have to do with their dispersal. The closer trees could be allowing for more individual lichens to colonize a cross host species. Both of these factors could be playing into the large coverage of lichens on forest trees. Overall , lichen communities might not be reflecting environmental conditions as much as chance events. Further research into dispersal ranges a nd lichen comp e tition could help the study on lichen communities. ACKNOWLEDGEMENTS I must start with my parents with their help in getting me to Costa Rica to even be doing this study. Then, thank you to the five million flies that so nicely made sure I was never lonely while collecting data. I also must credit the family of Macho Leiton Salazar for housing me, putting up with my dirtiness, as well as letting me use their farm, even though I could hardly communicate with them. Maria, oh Maria, for the c razy hours in front of the computer with me and all my ridiculous questions. Alan must be recognized for helping me keep my sanity with random hugs at all the right times. Last, but definitely not least, my guiding light through it all, Karen, whom with ou t I would be lost in the forest somewhere. LITERATURE CITED Arvidsson, L. 1991 On the importance of botanical gardens for lichens in the tropics. In Tropical Lichens: Their Systematics, Conservation, and Ecology . (ed. D.J. Galloway), Systematics Associa tion Special Volume No. 43, pp. 193 9. Clarendon Press, Oxford, 1991 Bedell Stiles, Jenny. 2004. The Effects of Edge and Pollution on Lichen Richness, Abundance, and Distribution in Caitas, Costa Rica. CIEE Fall 2004. Tropical Biology and Conservation. Brodo, Irwin M. and Sharnoff, Sylvia D. and Stephen, Sharnoff. 2001. Lichens of North America. New Haven: Yale University Press. Holdridge, L. 1967. Life zone ecology: revised edition. Tropical Science Center, San Jose , Costa Rica.
Lambley, P.W. 1991 L ichens of Papua New Guinea. In Tropical Lichens:Their Systematics, Conservation, and Ecology . (ed. D.J. Galloway), Systematics Association Special Volume No. 43, pp. 1 16. Clarendon Press, Oxford, 1991. Krog, H. 1991. Lichenological observations in low montane rainforests of eastern Tanzania. In Tropical Lichens Their Systematics, Conservation, and Ecology . (ed. D.J. Galloway), Systematics Association Special Volume No. 43, pp. 193 9. Clarendon Press, Oxford, 1991 Purvis, William. 2000. Lichens. Smi thsonian Institution Press, Washington, D.C. Umana, Loengrin and Sipman, Harrie. Costa Rica Lichens. INBio. Santo Domingo de Heredia Wolseley, P. and Aguirre Hudson, B. 1997. The Ecology and Distribution of Lichens in Tropical Deciduous and Evergreen Fore sts ofNorthern Thailand. Journal of Biogeography 24 Figure 1. The average Shannon three habitats in San Luis, Costa Rica for lichen species on twenty trees in each ha bitat in San Luis, Costa Rica. ANOVA, F = 10.076, P = .0002, df = 2
Figure 2. The average number of lichen species found on 20 trees in three habitats in San Luis, Costa Rica. ANOVA, F = 14.891, P < .0001, df = 2 a.
b. c. Figure 3. Relative abundance of each lichen species on 20 trees in three habitats in San Luis, Costa Rica (a = pasture, b = edge, c = forest). ANOVA, F = 4.627, P = .0137 , df = 2
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Composicin de la comunidad y diversidad de los lquenes a lo largo de un gradiente de perturbacin en San Luis, Costa Rica
Community composition and diversity of lichens along a disturbance gradient in San Luis, Costa Rica
Digitized by MVI
This research was conducted to better understand lichen morphology and diversity in different habitats in San Luis, Costa Rica. Lichens on trees in adjacent pasture, forest edge, and mature forest areas were identified to morphospecies and the species richness, diversity and total coverage per tree was compared across habitats. Eighteen different morphospecies were found across all three habitats. The forest trees had the lowest species richness and diversity, while the forest edge and the pasture had the highest.
Esta investigacin se condujo para entender la morfologa y la diversidad de los lquenes en los distintos hbitats de San Luis, Costa Rica. Los lquenes en los rboles en tres distintos hbitats: potrero adyacente, orilla del bosque y bosque primario fueron identificados por especies morfolgicas. La riqueza de especies, la diversidad y el rea total cubierta por el rbol se compararon entre hbitats. Dieciocho especies morfolgicas se encontraron entre los tres hbitats. Los rboles del bosque tuvieron una menor riqueza y diversidad de especies, mientras que la orilla del bosque y el potrero presentaron las riquezas y diversidades ms altas.
Text in English.
Costa Rica--Puntarenas--Monteverde Zone--San Luis
Comunidades de lquenes
Costa Rica--Puntarenas--Zona de Monteverde--San Luis
Tropical Ecology Fall 2005.
Ecologa Tropical Otoo 2005.
t Monteverde Institute : Tropical Ecology