Monteverde Institute: Tropical Ecology and Conservation

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  Hummingbird size, pollen load and pollination efficiency, December 2003

  Andrew Gapinski

  Pollinators are an important selective agent and play a role in the evolution of certain floral characteristics (Fenster, 1991). This is often the case with flower corollas, which have closely coevolved with the length and curvature of the bill or tongue of its pollinators (Stiles 1989) The purpose of this study was to determine the specificity of the coevolution between hummingbirds as pollinators and the species on which they forage. I also hope to examine the bill length- body size relationship, pollen loads and their placements. I hypothesize that short-billed hummingbirds will carry pollen from plant species with short corollas, and long-billed hummingbirds will carry pollen from plant species with longer corollas, even though they are capable of getting nectar from shorter corolla flowers. Hummingbirds for this study were collected between October 20 and November 14, 2003 around the Estación Biológica Monteverde, Puntarenas, Costa Rica. When number of pollen species was plotted against bill length in a simple regression (Fig. 6), the relationship turned out to be significant (P = .0021). As bill length increases the number of pollen species found on a bird also increased. Species richness on the bill was significantly different then on the chest with a P-value of 0.0324 and bill vs. total species of pollen was also found to be significant (P = 0.0015) (Fig. 8). Chest and bill vs. total were also showed a significant difference in species richness, both having Pvalues of < 0.0001. So the females are carrying significantly more pollen species than males. When looking at body parts the greatest amount of pollen species is being carried on the bill, followed by the head and then chest. Females were determined to carry greater pollen loads then male due to male territorial behavior. Also, long-billed humming birds feed mainly on long corolla flowers.

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  Microhabitat use and escape behavior of male, female and juvenile Norops oxylophus (Polychrotidae), December 2003

  Nathan Dappen

  The intraspecific distributions of microhabitats in territorial lizard species is determined largely by differing behavior among sexes and age classes. In this project I study a population of Norops oxylophus along the Río Alondra of the San Luis Valley towards the end of the rainy season. I caught individuals, recording their age, sex, size, perch substrate and location, and escape method. I found that adult males prefer to be perched on live tree branches overhanging the water; the larger the individual, the higher he is above the stream. Juveniles are found to inhabit lower areas along the stream banks. Males mean vertical perch height was 123cm and juveniles were 58cm. Females are found to vary dramatically in location, however are most common in live trees overhanging the water. Male territoriality affects the distribution of juveniles, but not females, because territory is primarily for maintaining exclusive access to females. Male, female and juvenile escape behavior differs depending on where they are found because of differences in ecological and reproductive interests.

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  Patterns of seasonal and altitudinal change in Monteverde bird communities, December 2003

  Eric Palm

  Previous studies in Monteverde, Costa Rica, have shown that numerous bird species are moving upslope in response to climate change. While there are an increasing number of such studies that address climate change, most fail to incorporate seasonal climatic variation. I censused the birds in three elevational zones in the Monteverde area not only to assess these distributional shifts, but also to determine the effects of season on bird communities. Compared to Michael Fogden’s data from 1979-1992, I found a number of species that have moved into higher zones where they were previously less common or absent. However, the results showed less upslope movement than those found by Donnelly (1998), during the dry season, likely due to downslope migrations during the non-breeding season. My findings suggest that not only are birds continuing to move up in elevation, but also that the effects of global warming on such movements in birds are less pronounced during the wet season than in the dry season. Also, this study indicates that future studies of species responses to climate change must account for seasonal variation.

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  Reproduction of Besleria princeps in Monteverde cloud forests, December 2003

  Michelle Murphy

  The purpose of this study was to show the occurrence of asexual versus sexual reproduction in lower premontane cloud forest, on the Atlantic slope and the Pacific slope of the Tilarán Mountain range near the Monteverde Biological Station. Eight hundred plants, 400 on the Atlantic slope and 400 on the Pacific side, were examined at their roots for fragmentation and seeding. The elevations of each slope and a comparison of the two slopes were examined using a chi-squared two-way contingency test. The results showed that asexual reproduction (fragments) is more common in Besleria princeps than sexual reproduction (from seeds). The Atlantic slope and the highest elevations of each slope, showed a higher frequency of fragments to seeds in the windier and wetter conditions. The chi-squared results of the Pacific slope elevations were significant, x² = 29.609; df = 3, and a p-value <.0001. The Atlantic slope elevations chi squared test had significant results, x² = 21.212, df = 2, and a p-value <.0001. The results of the Atlantic slope versus the Pacific slope showed significant chi squared results, x² = 41.439, df = 1, and a p-value <.0001.

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  Spatial distribution patterns of mistletoe (Antidaphne viscoidea: Eremolepidaceae, and Phoradendron undulatum: Viscaceae) on Psidium guajava (Mrytaceae) in Monteverde, Costa Rica, December 2003

  Matthew Greenfield

  Spatial distributions of mistletoe are noticeably clustered but unexamined in Monteverde, Costa Rica. To better understand their spatial structure, I examined the dispersion of two species of epiphytic mistletoe (Antidaphne viscoidea: Eremolepidaceae and Phoradendron undulatum: Viscaceae) within and between host trees. Six sites on one hill in Cañitas, Costa Rica were surveyed for data relating to dispersion structure (nearest neighbor distance and frequency within host trees). Additional study was done on the spatial dispersion on the host tree Psidium guajava, and it was found to have clustered dispersions. Indices of dispersion and tests comparing observed results to Poisson distributions showed A. viscoidea and P. undulatum were distributed contagiously within host trees and between host trees. I suggest this may be due to bird disperser foraging behavior.

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  Stomata densities of Pleurothallids (Orchidaceae) in different microhabitats of Monteverde, December 2003

  Chelsea Beebe

  The purpose of this study was to test whether there is a difference in the number of open and closed stomata on the northeast and southwest facing sides of trees among seven species of Pleurothallids and one pseudobulb species. Stomata impressions were taken from the leaves using clear finger nail polish and they were then examined under a microscope. The results showed that there was a significant difference between the number of open and closed stomata for every species, always with a higher frequency of closed stomata. Significant affects of species type and position on the tree on stomata density was also found with branch tip orchids having a lower stomata density then nonbranch tip species. A possible explanation for the low frequency of open stomata is that they might only open in the rain, when water loss is at a minimum.

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  Structural habitat preferences in Norops tropidolepis in the presence and absence of Norops humilis, December 2003

  Greg Maximov

  Interspecific and intraspecific competitions are effectively reduced in populations of Anoline lizards through the use of niche separation. While much research has been done on this phenomenon, not much research addresses what happens to niche structure in the absence of a species. This project studies the effects of the absence of Norops humilis on the structural habitat preferences of N. tropidolepis in an area of cloud forest in Monteverde, Costa Rica. Between the 25th of October and the 14th of November 2003, an area of cloud forest above the Estación Biológica de Monteverde was searched thoroughly for Norops (Zones 3 and 4, above 1470m in elevation). When a lizard was found, perch height and diameter were measured. These results were then compared against findings by J. Alan Pounds (1988) with N. humilis present. Adult N. tropidolepis were found to significantly shift their perch height down in the absence of N. humilis. Significant differences were also found in stem diameter preference. I conclude that N. tropidolepis and N. humilis experience facultative niche separation on the basis of structural habitat preference.

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  The effects of morphology on feeding behavior in the Family Sphingidae, December 2003

  Andrew S. Lima

  The purpose of this field experiment was to examine how morphological characteristics like proboscis length, weight, and wing surface area, affect diet breadth in the family Sphingidae (order Lepidoptera) intropical premontane wet forest in Monteverde, Puntarenas province, Costa Rica. I collected 60 hawkmoths from 11 species between October 18 and November 18 from the Estación Biologica de Monteverde and the Cerro Plano Jardin de Mariposas, taking morphological measurements and pollen samples from their proboscises. There was not a significant relationship between proboscis length and pollen richness (p = 0.9049), nor between species (p = 0.4358). A significant correlation was seen between proboscis length and forewing area in a ratio of about 1:1 (p = 0.0083). Weight, proboscis, andforewing area were significantly different between species (p < 0.0001 for all parameters). I found that morphological features did not seem to directly affect pollen richness but that seasonal changes in the abundance of flowers and a combination of morphological and metabolic factors may be the cause of diet differentiation between sphingid moth species.

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  The role of metachrosis in thermoregulation of Sceloporus malachiticus, December 2003

  Joel Patrick Napier Stonedale

  Metachrosis is a change in color, common to many amphibians and reptiles. The purpose of this study was to determine if rate of metachrosis correlates with weight in Sceloporus malachiticus. Twenty-one lizards were collected and photographed every half hour, and the change in reflected light in the photographs was measured. There was a significant negative correlation between rate of metachrosis and weight (Simple Regression, P < 0.02), which is an indication that metachrosis aids in thermoregulation. Larger lizards must remain darker longer in order to absorb heat more quickly, because their lower surface area to volume ratio causes them to need more heat for their large bodies that have limited ability to absorb heat due to their proportionately lower surface area. This need for larger lizards to be darker may also explain why other reptiles such as Clelia clelia, Clelia ceytalia, Ctenosaura similis, and Iguana iguana become darker as they grow older and increase in size.

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  Trail length and nutritional value for Atta cephalotes, December 2003

  Erin Jacubec

  The leaf-cutter ant Atta cephalotes has a complex society including workers who forage for leaf fragments used to grow fungus for food. The purpose of this project was to find if A. cephalotes’ head size and foraged leaf fragment size and quality changes with trail length. Twelve trail lengths were measured and fifty leaf fragments and ant head measurements were collected per trail. The leaf fragments and whole leaf samples were measured for nitrogen content and toughness. Results showed negative relationships between trail length and wet weight (simple regression, P=.0083) and trail length and dry weight (simple regression, P=.0007). Increasing trail length led to increased leaf toughness (simple regression, P=.2008) and nitrogen content (simple regression, P=.2250). Results relating foraging trail length to ant head size showed a negative relationship (simple regression, P=.0199). These trends suggest that A. cephalotes are able to selectively choose both workers and plants on different trails to increase foraging efficiency.

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  Tree fern (Dicksoniaceae and Cyathaceae) allelopathy in the Monteverde cloud forest, December 2003

  Katie Heckendom and Melody Saeman

  The purpose of this experiment was to look at the effects of Allelopathy between six species of tree ferns in the Monteverde Cloud Forest. We analyzed these effects by comparing plant abundances under the tree ferns to controls. We also compared controls to germination of seeds and spores grown with water or leachate made from the tree fern fronds. We found significantly higher plant abundances in controls than under the tree ferns. Also significantly less seed and spore germination than controls was found. There was not a significant difference between species of tree ferns in their inhibition of plants under the tree ferns. We did observe a difference in allelopathic effects on germinating tomato seeds and Dicksonia gigantea spores, though not for Lophosoria quadripinnata spores. These results lead us to conclude that Allelopathy in nature is affected by other factors such as facilitation or competition but different species of tree ferns do show differing levels of Allelopathy. Allelopathy in tree ferns inhibits spores more than seeds indicating that more closely related species inhibit each other more, at least in this case. Also we confirmed previous studies that found Allelopathy in tree ferns.

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  Vertical stratification of moss-dwelling arthropod communities in the elfin forest of Monteverde, Costa Rica, December 2003

  Joe Northrup

  The purpose of this study was to determine the community composition, S, H, E, N, and Smarg of arthropods living in epiphytic moss mats on vertical gradients, in the elfin forest of Monteverde, Costa Rica. Past studies have shown that moss mats alter biotic factors of the surrounding environment by increasing moisture and decreasing temperature variation. Moss samples were collected from 1 m, 7 m, and 15 m from nine trees between 1725 m and 1800 m and dried using Berlese funnels. Arthropods were separated by order and morphospecies. N was highest at 15 m, Smarg and S were highest at 1m, and H1 and E were highest at 7 m. High abundance of arthropods at 1m and 15m, stems from the presence of one morphospecies of arthropod found in high numbers at each height but in patchy distributions. These results point to variable resource distribution at 1m and 15m rather than height as the main factor behind moss-dwelling arthropod community makeup.

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  Effects of Cecropia obtusifolia leaf ingestion on lung capacity, September 2003

  Catherine Ross

  People in developing countries have traditionally used forests as sources of local, cheap medicines. One plant used throughout the Neotropics is Cecropia spp., most notably for asthma. The purpose of this study was to determine if tea made from Cecropia obtusifolialeaves increases lung capacity and in what time frame this takes place. This was accomplished by treating a group of people with Cecropia tea for five days and another group with a placebo treatment and comparing the change in lung capacity of the two. The short term change in the placebo group had a statistically insignificant decrease of 2% while the Cecropia showed a significant increase of 4%. This indicates that C. obtusifolia leaves do in fact contain medicinal chemical properties. Hence, while further clinical test should be performed, Cecropia provides a good example of the importance of local plants and their conservation for human health.

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  Affects of nest availability on behavior of Crawfordapis luctuosa, a solitary bee, May 2003

  Erika Blackwell

  Intra-specific interference competition behavior arises when one organism prevents another from utilizing a resource (Begon, et al. 1990). This resource can be mating partners, a food source, or habitat, but it is often less expensive for the organism to defend the resource than to find another. In this study, 60 nest hole entrances were barred in percentages of 25%, and 50%, in order to study the interactions of Crawfordapis luctuosa (Apoidea, Colletidae, Diphaglossinae) in the presence of depleted nest hole availability. The study was conducted in Monteverde, Puntarenas Province, Costa Rica, at a large nest aggregation approximately 1740 meters in elevation on Cerro Amigos. It was found that with an increasing number of holes covered, the mean lengths of visits increased (t-Test, F = 3, 452, P = .032), as well as the incidence of long visits (Fisher’s PLSD post hoc, MD = .407, P = .044), and long visits from 25% of 50% coverage (Fisher’s PLSD post hoc test, MD = .612, P = .003). It was also found that with an increasing percentage of holes covered, crawling and digging behavior increased (chi-square test, X2 = 6.533, df = 2, P = .038), as well as the overall incidence of aggressive interactions (chi-square test, X2 = 25.609, df = 2, P < .05). Also, twenty-six new nest holes were constructed during the study. It was hypothesized that the bees who spent the most time digging were also the main participants in aggressive interactions. These were “provisioning” females with a high energetic investment in a single nest. These aggressive interactions in C. luctuosa are previously unobserved, and therefore makes C. luctuosa an excellent subject for the study of competition and evolution of sociality.

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  Distribution and anti-herbivoral role of extra extrafloral nectaries and leaflet pair number on Inga sierrae (Fabaceae: Mimosaceae), May 2003

  Andraya Gough

  The purpose of this project is to investigate the distribution and anti-herbivore impact of extra-extrafloral nectaries (EEFNs) and leaflet pair number on Inga sierrae (Fabacaeae: Mimosaceae) in Monteverde, Costa Rica. I recorded the number of EEFNs and leaflet pairs per leaf for forty leaves collected from sixty trees from three different locations. EEFNs, though not commonly found on I. sierrae, did significantly reduce the percent herbivory on leaves (1-way ANOVA, P < 0.0001 and Exponential Regression Analysis; R2 = 0.0001). The most commonly encountered leaflet pair number was three. However, when the number of leaflet pairs decreased, percent herbivory increased (Exponential Regression Analysis, R2 = 0.9905, P < 0.0001 and 1-way ANOVA, P < 0.0001). Heavy herbivory pressure could be causing a species change toward increased production of EFNs.

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  Distribution of stingless bees (Meliponinae) at two elevations and their reaction to deforestation on the Pacific slope of Costa Rica, May 2003

  Christina Murphy

  The distribution and abundance of Meliponinae and Apidae, as well as the effects of deforestation on Meliponinae, at two elevations on the Pacific slope of Costa Rica were studied. All apids were collected using a pan trap method at 700 m and 1700 m in forest and pasture. The low elevation had higher diversity of Apidae and Meliponinae than the high elevation. These findings are consistent with InBIO (Instituto Nacional de Biodiversidad) data on overall elevational trends in Meliponinae and Apidae, yet four species of Meliponinae found in this study add new elevational ranges to InBIO’s records. This study found that apids and stingless bees had more diversity in pastures than in forests. Also there was no significant difference in Meliponinae diversity between the forest and pasture at the low elevation but more diversity was found in the pasture while individuals of species were more abundant in the forest. This was probably due to forest-nesting stingless bees foraging in pasture. These results show that deforestation could change the behavior of stingless bees and thus have drastic consequences for the pollination of forest plants and ecosystems as a whole. This study found that Meliponinae and Apidae are more diverse at lower elevations and that Meliponinae are affected by deforestation.

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  Liana size class diversity across three forest habitats, May 2003

  Janelle Burke

  The purpose of this study was to see how forest edge, primary and secondary habitats affect average size and size class diversity of lianas in a cloud forest in Monteverde, Costa Rica. Three 625 m² sites were studied in primary and secondary forests, and along the edge of a forest. Exhaustive sampling of lianas was taken of four continuous plots within each habitat: all individuals were measured for PBH (perimeter at breast height). The primary forest was the most diverse according to the Shannon- Weiner index of diversity (H’ = 0.918), and the oldest judging by mean perimeter (3.87 ± 0.34 cm). In terms of significant differences in diversity indices, the secondary habitat differed significantly from the edge and primary habitats, while the primary and edge did not. The mean age of the primary varied significantly from the other two habitats, while the secondary and edge did not show significant variation. Furthermore plot 1 varied significantly from plot 3 and 4 within the primary habitat. These results are probably a consequence of the ecotone qualities of the edge site and the small-scale heterogeneity of disturbance history within the primary site.

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  Resource partitioning and niche differentiation of nectarivorous bats in a Monteverde cloud forest, May 2003

  D. Morris Cohen

  Plant-pollinator interactions are an important part of tropical ecosystem function and diversity. In this paper, I present the results of a month-long study comparing the three nectarivorous Phylostomid bat species, Anoura geoffroyi, Glossophaga commissarisi, and Hylonycteris underwoodi, and the their plant resource base within the cloud forest of Monteverde, Costa Rica. Bats were mistnetted, and their pollen loads were removed and later measured for richness, abundance, and diversity. The extent of Niche overlap between the three species was also assessed. I found G. commissarisi to carry the most diverse pollen loads (H'=0.648) and to also have the most consistent floral visitation patterns. Pollen load analysis revealed similar visitation patterns for the morphologically analogous H. underwoodi, and different patterns for the larger and more distinct A. geoffroyi. Niche overlap was high between H. underwoodi and G. commissarisi and low between both of these species and A. geoffroyi. Although capture rates were too low for significant conclusions regarding H. underwoodi, resource partitioning was found to occur between the other two species.

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  Resource partitioning between Trigona fulviventris and Scaptotrigona mexicana with overlapping flight ranges, May 2003

  Michelle H. Averbeck

  The theory of resource partitioning predicts that congeneric species are allowed to coexist by a division of the available resources. This study looks at the possibility of resource partitioning between Trigona fulviventris and Scaptotrigona mexicana on fine temporal scales in Cloud Forest habitat, a region in which stingless bee pollen diets has not been extensively studied. Workers from one T. fulviventris and one S. mexicana nest, located 200 m apart, were studied synchronously over six days. Capture-mark and release experiments verified that the foraging areas of these two nests indeed overlap. Of the 14 morphotypes of pollen brought in by S. mexicana and the 16 morphotypes brought in by T. fulviventris, seven morphotypes were found in common between the two species (Sørenson index = 0.3).

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  Rolled-leaf hispine herbivory of Heliconia spp. (Heliconiaceae) over an altitudinal gradient, May 2003

  Sarah Bachman

  Hispine beetles (Coleoptera: Chrysomelidae, Hispinae) are herbivores of the Order Zingiberales (Strong 1977a). In Monteverde area there are three known species of Heliconiaceae (Zingiberales): Heliconia monteverdensis, H. tortuosa, and H. vaginalis (Haber, 1990). H. monteverdensis is a high elevation species (1500 – 1800m) whose range does not overlap with H. vaginalis, a low elevation species (700-1300m). H. tortuosa occurs along the elevational gradient from San Luis (1000m) to the forest behind the Estación Biológica de Monteverde (1760m) where this study was performed, and overlaps in geographical range with the other two species. In this study I looked at patterns of hispine herbivory between Monteverde Heliconia species as well as leaf age, and altitude. I did not find turnover in hispine herbivory between species of Heliconia, but found that the amount of herbivory changed between species, elevation, and between leaves of different ages. H. vaginalis had significantly lower herbivory than the other two species (Fisher’s PLSD, p < 0.0001). H. tortuosa and H. monteverdensis showed higher herbivory in older leaves (Fisher’s PLSD, p = 0.0119). Herbivory in H. tortuosa increased with elevation in older leaves (simple regression, p < 0.0001). Elevational trends are best explained as responses to temperature and water availability during the dry season, while differences between Heliconia spp. in amounts of herbivory may be due to differences in leaf phenology.

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  The effect of pedicel length in regulating seed and wasp production in the fig-wasp oblígate mutualism of Ficus tuerkheimii (Moraceae) and Agaonidae., May 2003

  Tova Jacobovits

  Pedicel and style lengths of fig flowers were measured in order to determine their role in regulating seed and wasp production within a Ficus tuerkheimii fig. Figs were collected in two groups at two different stages in development. Foundress number, foundress ovipositor length, pedicel lengths, and style lengths were measured (to the nearest micrometer) in the younger figs. Flower pedicel lengths were measured (to the nearest micrometer) and flower occupancy was recorded in mature, but unripe figs. Young figs: In a sample size of 10 young figs, 60% had two foundresses, 20% had one, and 20% had three. The average ovipositor length in 20 foundresses was 10.16 micrometers. Average style length was about 11 micrometers. Based on style length frequency, the predicted wasp: seed ratio is 44%: 55% respectively. Mature figs: the observed wasp: seed ratio is 45.9 female, 4.3% male, 37.35% vacant, and 12.45% seeds. A significant negative correlation was found between style lengths and pedicel lengths (r2 = .495, P < .0001). A simple regression analysis between the number of flowers at each pedicel length and between the proportion of female wasps, male wasps, seeds, and vacancies. There is a significant negative correlation between flower number and percent females (n = 118, r2 = 0.81, P = .0376). There are not enough male wasps to draw a significant correlation (n = 11, r2 = .02, P = .3103) between flower number, pedicel length, and percent males, even though the graph does show a less defined, but very similar negative trend for the male wasps. There are also not enough seeds to draw a significant correlation (n = 32, r2 = .009, P = .4926) between the amount of flowers and pedicel length, however the graph shows a slight positive correlation. There is however a strong positive correlation between percent vacancies and flower number (n = 96, r2 = .134, P = .0066). As flower number increases, there are more flowers with short pedicels and long styles which produce a high number of vacancies. In conclusion, this study demonstrates that pedicel length and thus style length do play a major role in regulating seed and wasp production and are therefore important factors in maintaining the mutualism; however, many other factors such as foundress number, ovipositor length, egg limitation, and pollen limitation are confounded with style length and must be taken into consideration. Currently, in F. tuerkheimii, wasps have the upper hand.

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  The role of height and flower symmetry in bat pollination of Mucuna urens (Papilionaceae), May 2003

  Callie Vincent

  The flowers of plants in the tropics have evolved mechanisms that attract bats and ensure that pollination is deposited on the bat for transfer to the next flower (Altringham 1996). In particular, a recent study has shown that flowers in the Mucuna genus attract bats using an acoustic nectar guide (vonHelverson and vonHelverson 1999). In order to test additional factors that could possibly play a role in the pollinator-plant relationship involvingMucuna, inflorescence height, infructescence height, and flower symmetry were studied for fiveMucuna urens patches in the Monteverde (Puntarenas, Costa Rica) cloud forest. A simple regression showed no significant relationship between flowers pollinated and inflorescence height (Simple Regression; p = 0.1724, R2 = 0.021). Alternatively, a regression of fruits per infructescence versus infructescence height showed a positive relationship (Simple Regression; p < .0001, R2 = 0.254). It is likely that this significance can be attributed to moreplant clutter around lower inflorescences, making it more difficult, but not impossible, for the bats to locate them. Finally, unpaired t-tests used to analyze the relationship between flower symmetry and pollination revealed that there was not a significant difference betweenpollinated and non-pollinated flowers for any of the points measured (unpaired t-tests; (a) p = 0.5557, (b) p = 0.4036, (c) p = 0.4511). Possible reasons for this involve the trap lining behavior of nectar bats and nectar peaks in the flower throughout the night. High differences in variation between pollinated and non-pollinated flowers for the point at the top of the flower can possibly be attributed to effects of pollination on floral attraction and longevity.

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  Tree size and habitat effects on stream gall abundance in Conostegia oerstediana (Melastomataceae), May 2003

  Priya Shashidharan

  The moth Mompha sp. (Coleophoridae, Lepidoptera) is known to induce a stem gall on the tree Conostegia oerstediana (Melastomataceae). There is little known about the distribution and abundance of galls. This study tested the difference in stem gall abundance between varying tree sizes and between two different habitats- pasture and secondary forest. Trees from each habitat were sampled and measured for diameter at breast height (DBH), height, number of branches, and number of galls. A significant difference was found between pasture and forested areas (unpaired t-test, p < 0.0001), with pasture trees having more galls. No relation was found relating tree size (DBH, height, number of branches) to gall abundance. I conclude from these results that tree size is not directly related to stem gall abundance. Instead, differences in habitats, such as predator and parasite abundance and host density, may be important factors that influence gall abundance.

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  Advantageous development of buttresses displayed in Quercus spp., March 2003

  Mariel Platt

  The many hypotheses aimed at describing the physiological, morphological, environmental forces contributing to buttress development have not clearly shown definitive evidence regarding what selective forces are responsible for buttress formation. One hypothesis that has little documented research available is that the presence of buttresses allows for an increased abundance of organic matter and inhibits nutrient leaching from the soil, thus providing the tree with a greater quality soil for localized growth. Twenty-five different soil samples were collected and analyzed for potassium, nitrogen, phosphorus, and pH from both the base of buttressed Quercus spp. and a control site in the cloud forest of Monteverde, Costa Rica. No significant difference was found in the relationship between the presence of buttresses and an increased amount of N, P, K, or a more suitable pH. Results found may be due to nutrient use by the roots of buttressed trees or a slower rate of decomposition due to decreased temperatures in lower montane wet forests verses lowland tropical forests.