Monteverde Institute: Tropical Ecology and Conservation

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  Assortative mating of the halloween butterfly Dryadula phaetusa (Nymphalidae, Heliconiinae), November 2000

  Darin Reynaud

  Possible size-assortative mating was investigated in a captive population of the butterfly, Dryadula phaetusa (Nymphalidae) by comparing the forewing sizes of individuals of mating pairs to the average size of forewings in the whole population. It was postulated that females would prefer larger males because they deposit larger spermatophores, and females would thereby increase their fitness. Males would also prefer larger females because larger females have a better chance of fighting off predators and thus higher fitness. Individuals that were feeding or courting were also measured to document size variation and investigate size-dependent behaviors. There was no evidence for positive assortative mating in D. phaetusa but individuals of the mating pairs showed a significantly larger average forewing length than the average forewing length of the courting and feeding population (captive population mean = 3.878 cm, mating population mean = 3.983cm, feeding population mean = 3.573, courting population mean = 3.501 cm). This larger average in size of the mating pairs suggests that there is non-random mating. This sexual selection may be a preference to larger individuals due to their higher fitness or it may be an avoidance behavior to inbreeding. A significantly smaller population than average in the garden suggests that inbreeding is occurring and therefore mate choice may be observed because the butterflies are using it as an avoidance mechanism to inbreeding, which often results in reduced fitness.

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  Changes in hummingbird species richness and abundance in a forest fragment and agricultural ecotones, November 2000

  Stephen Smith

  Hummingbirds are important pollinators in tropical forests, and their behavior is vitally important to the plants they pollinate. As the tropics become more and more fragmented, hummingbirds will play the increasingly important role of long-distance pollination of many plants between isolated tracts of forest. This study looked at the different responses of hummingbirds to a forest fragment and the surrounding agricultural land. Hummingbirds preferred edge to open areas and forest, with three feeders out of 18 getting 126 of the 482 total visits, compared to 91 total visits of the second most visited feeder. Further, the birds preferred an open field and a coffee plantation to a banana plantation, the number of visits being 191, 171, and 120, respectively. Most interesting was the partitioning by two species of hummingbird, one preferring the forest and the other preferring open areas. The differing behavior of these two species could lead to very different pollination patterns in the open areas and the forest fragment, and could serve to isolate forest fragments in terms of gene flow for hummingbird pollinated plants.

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  Diversity, abundance, richness, and composition of avian communities and avian foraging behavior at Ficus pertusa, November 2000

  Heather Whelpley

  This study investigated differences in success between fruiting Ficus pertusa trees in a single pasture in Monteverde, Costa Rica. Success was qualitatively measured by the abundance, richness and diversity of avian dispersers and the total number of seeds dispersed (as measured by the number of visits by birds that swallow fruits). Each of the four sites was observed for five days from 7:00am – 11:00 am. Significant differences in diversity were found in five of seven comparisons between the sites, but neither diversity nor number of bird visits was related to dbh or crop size of the tree. Significant differences were found in the number of swallowing birds at each site, affecting the dispersal success of each tree. Proximity to forest patches and crop size may affect the overall success of a tree and differences in success are due to the interaction of several factors that change over very small spatial scales.

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  Diversity of arboreal and ground-dwelling ant species in a primary forest and grazed pasture, November 2000

  Mariel F. Bostrom

  Ants are very important to ecosystem function. They help to aerate soil, disperse seeds, distribute nutrients, and regulate other insect populations (Holldobler and Wilson 1990). Since a non-forested area will have a larger microclimate variation than a forest, it is expected to support more species (Torres 1984). In addition, arboreal ants can be expected to have a lower overall diversity than terrestrial ants, since there may be a smaller number of species adapted to tolerate the elevated range in abiotic conditions that occurs in arboreal environments (Nadkarni and Longino 1990). Ants were collected over eight days, using traps baited with tuna and honey. The ground-dwelling ant species were significantly more diverse than arboreal ant species (modified t test, t = 3.9172, P < 0.001), and had the highest richness and capture rates. No significant difference was found in the species diversity of pasture and forest ants (modified t test, t = 0.8785, 0.5 > P > 0.2). These results may indicate that there are a lower number of ant species adapted to tolerate arboreal conditions, or that the forest’s lack of microclimatic heterogeneity contributes to a lower richness and diversity of forest species.

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  Effects of elevation on pollinaria removal in Asclepias curassavica (Asclepiadaceae), November 2000

  Carolyn S. Weaver

  Pollinaria removal was studied in three populations of Asclepias curassavica located on an elevational gradient in and around Monteverde, Costa Rica (815m, 1175m, 1440m). The following plant characteristics were also studied: number of inflorescences, number of flowers per inflorescence, number of pollinaria removed per flower, number of pods. Pollinaria removal in plants with the presence of herbivory was compared to pollinaria removal in plants without herbivory at all three elevations. Pollinaria removal and the presence of aphids were compared the same way as herbivory. Data were collected over a nine day period during the misty season (October – November). Results showed a significant difference in pollinaria removal between all three elevations (ANOVA P- value < 0.0001). Pollinaria removal was lowest at the low elevation site, intermediate at the middle elevation site and highest at the high elevation site. These results may be explained by an increase in pollinators, specifically the Monarch butterfly (Danaus plexippus), as elevation increases, or the density of the plants per site. The highest numbers of pods per plant were observed at the high elevation site, which may indicate those plants also have the highest fitness. Significant differences in number of pods per plant were seen between high and low, and low and middle elevations (ANOVA P- value < 0.0001; Fisher’s PLSD both P-values < 0.0001). Neither the presence of herbivory nor presence of aphids had a significant effect on pollinaria removal. The number of flowers per inflorescence was highest at the high elevation site and lowest at the low elevation significantly affects pollinaria removal in Asclepias curassavica.

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  Effects of microhabitat on morphological adaptations of Pleurothallis sanchoi (Orchidaceae), November 2000

  B. J. Labay

  An abiotic gradient of wind, moisture and sun across a tree may directly affect morphological traits adapted for water conservation. In this study, Pleurothallis sanchoi was examined in a pasture near the Estación Biológica Monteverde, Costa Rica. I looked at how microhabitats affect morphological adaptations, including leaf thickness, toughness and stomata density. I tested two predictions of my hypothesis that individuals living in harsher conditions would show more adaptations for water conservation. The first is that individuals in a abiotic gradient along a tree will show variance in water conservation adaptations. The second is that in two distinct habitats, full sun, and full shade, I will find individuals in the harsher, full sun habitat to show more strategic against water loss. I found that individuals in trees vary greatly their adaptations for water conservation depending on microhabitat. I found that mean stomata density decreased in harsher, full sun habitats, and that thickness and toughness generally both increased in harsher, full sun habitats. The increase in stomata density and decrease in both thickness and toughness in full shade habitat is attributed to the reduced need to fight dessication.

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  Foraging preference of Atta cephalotes (Hymenoptera: Formicidae), November 2000

  Laurel Klein and Joseph Reid

  Leaf cutter ants, Atta cephalotes, were found to make distinct tree species choices as herbivores in the premontane wet forest of Cerro Plano, Costa Rica. One trail from each of six nests was studied. Trail lengths varied, ranging from 3.30 m to 40.40m. Trees were identified along the trail, as well as the host tree at the end of the trails. Three leaves were taken from each tree and tested for toughness, thickness, and percent water content. The results for each test for each tree along a trail were compared to those for the host tree. The ants selected for thinner leaves. A simple regression correlated leaf thickness and toughness. Because of the range of toughness per leaf thickness, however, the results for leaf selection based on toughness were not consistently significant with regards to being more or less tough than the host tree, suggesting that selection for toughness is secondary to selection to thickness. Selection for water content also yielded significant results, though; once again, not consistently significant with regards to having more or less water than the host tree. Our data suggests that other factors play a role in host selection of Atta, and further investigation of their selectivity would draw a more complete picture.

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  Nectar robbery and pollination by hummingbirds in relation to morphological and physiological features of Gesneriaceae, November 2000

  Catherine L. Hein

  Many flowers depend on hummingbirds for pollination. However, some hummingbirds are known to rob flowers rather than pollinate them. High robbery rates could decrease pollination reproductive fitness in these plants. Corolla length, bract coverage, nectar volume and sugar concentration, were hypothesized in this study to affect robbery rates. A long corolla, short bract, and high nectar volume and concentration were hypothesized to increase the rate of robbery. Pollination rates were also expected to increase with a high nectar volume and sugar concentration. Data were collected on Alloplectus tetragonus, Besleria formosa, and Drymonia rubra (Gesneriaceae) in the Santa Elena Reserve for 21 days. Alloplectus tetragonus had the longest corolla and shortest bract. Besleria formosa had the shortest corolla and D. rubra the longest bract. The nectar volume and concentration were examined daily for 16 days. All species varied significantly by day in nectar volume and concentration, except for D. rubra and B. formosa in nectar volume. Although there were significant differences between all characteristics examined, robbery and pollination rates were not significantly different. Thus, these characteristics were combined in different ways for each species, but resulted in the same outcome: low rates of robbery and pollination. A. tetragonus and B. formosa produced small amounts of dilute nectar and did not provide a great reward for nectar robbers while D. rubra had large bracts to protect against robbery.

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  Pollinia removal and visitation in Epidendrum radicans (Orchidaceae) and Asclepias curassavica (Asclepiadaceae), November 2000

  Nicholas J. Deacon

  The possibility of a floral mimicry complex between Lantana camara, Asclepias curassavica, and Epidendrum radicans sounds appealing based on their similarity in flower color and overlapping ranges in Central America. The pollinia removal in E. radicans and A. curassavica was observed under different conditions of scale and proximity. The conditions for increased pollinia removal in E. radicans are to have a large inflorescence, close proximity to A. curassavica or L. camara in a patch, isolation from other E. radicans, occurrence in less dense patches, and avoidance of patches that contain L. camara. Asclepias curassavica benefits when alone more than when with either E. radicans or L. camara and with increasing flower number in a patch. The findings for E. radicans are consistent with what would be expected for a Batesian mimic with A. curassavica as a model.

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  Preferred sucrose concentration in nectarivorous bats, November 2000

  Jeremy C. Sullivan

  Pollinators and plants are involved in a mutualism, where pollination takes place in exchange for some payment, usually in the form of nectar. One might assume that these nectar rewards would closely match a pollinator’s preference, but flowers may conserve energy by offering an unfavorable, but still suitable nectar reward. Bat pollinated flowers have been found to offer nectar of an 18% sucrose concentration, on average, over a range of 3%-51% (Baker 1998). Where in this range of sucrose concentrations do bat preferences lie? To find out, sucrose concentration preferences of a community of Neotropical bats were studied at the Hummingbird Gallery in Monteverde, Costa Rica. Four hummingbird feeders with solutions of 10%, 20%, 30% and 40% sucrose concentration were observed for 20 nights. Frequency of bat visitations to each feeder was recorded in ten-minute intervals. Bats visited the feeders of higher sucrose concentration (30% and 40%) more than feeders with lower sucrose concentration (10% and 20%). These findings support the idea that animal pollinated flowers may be providing a minimum reward to pollinators to ensure increased visitation frequency and cross-pollination.

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  Spider size, web location, and prey capture in the colonial orb-weaver Metabus gravidus, November 2000

  Jamie E. Potosek

  Metabus gravidus spiders live in colonies of five to 70 individuals and construct their webs over moving water. Buskirk (1975) found larger spiders can take over the webs of smaller spiders and suggested that certain sites within the colony may have greater prey capture rates. Therefore, I hypothesized that larger spiders should occupy these positions in the colony. Colonies of M. gravidus were studied at the Quebrada Máquina stream in Monteverde, Costa Rica. I measured spider size, web size, height from water, distance from bank, and prey capture rates for 198 total webs. Twenty-four artificial webs were created to determine prey capture and web position without the presence of spiders. Spider size and web area correlate positively (r² = 0.458, p < 0.0001). Larger spiders are found at locations closer to the water surface (r² = 0.212, p < 0.0001) and catch more prey than smaller spiders (r² =0.286, p< 0.0001). Larger spiders also show both a higher overall visitation rate by insects to their webs (r² = 0.231, p = 0.0032) and a higher proportion of hits that are successful (r² = 0.112, p = 0.0002). This data support the earlier idea that web placement within the colony and differential prey capture should place larger spiders in these areas. (Buskirk 1975a, Shannon 1996). However, there is no significance between spider size and distance of web from stream bank (r² = 0.017, p = 0.0672). Artificial webs showed no significant difference between upstream /downstream (p = 0.8614) and high/low positions over the water (p= 0.4218) within each colony, but they did show a significantly greater number of prey captures in the inner quadrants of the webs as compared to the outer quadrants (p < 0.0001). These findings support the notion that web position alone does not decide the success of prey capture. It is evident that spider size has tremendous influence on success of prey capture as well.

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  Sugar preferences of nectarivorous bats, November 2000

  Kristina L. Keppel

  Groups of flowers pollinated by the same subset of species will have general characteristics in common. These characteristics, when considered together, are called flower syndromes. For example, flowers that are bat pollinated open at night and are often drab, pale, and green with a musty odor, and contain hexose-rich nectar. Baker and Baker (1983) findings demonstrate that all bat-pollinated flowers have hexose-rich or hexose-dominated nectar. Four feeders were hung outside of the Hummingbird Gallery in the Monteverde Reserve. Each feeder contained a different type of sugar solution: one of fructose, one of glucose, the third of honey (a mixture of glucose and fructose) and the last, a solution of sucrose. The number of visits to each feeder was observed nightly. Results indicate a significantly greater preference for solutions of glucose and fructose (Kruskal Wallis, p = 0.0005). Number of visits to honey was not significantly higher over sucrose due to the lower concentration of the honey solution. Preference for hexose sugars in nectarivorous bats may reflect the evolution of nectarivory from frugivory.

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  The effect of plant location, and leaf position on the adult leaf form of Monstera tenuis in Costa Rica, November 2000

  Heather J. Allen

  Leaf morphology of Monstera tenuis (a tropical forest vine) differs greatly between growth stages. The mature leaf growth form has open areas presumably to prevent shading of the lower leaves on the same plant or to prevent overheating. Therefore, leaves highest on a plant, those exposed to most sun should show the most open area. Plants located on the edge of forest are exposed to more evenly distributed light; therefore, they are expected to have more open area per leaf on average. These ideas were tested in the forest and on the forest edge near the Estación Biológica Monteverde. One hundred and forty leaves were collected for analysis from twelve plants at each location. The edge plants had a significantly higher mean of open area per total leaf surface area (F1, 264 = 6.770, P= 0.0011). The forest site showed a significant correlation between leaf height and open area per total surface area (Rho = 0.0273, P=0.0011). These results suggest that the location of a plant and the placement of a leaf may explain leafmorphology, specifically the proportion of open area per leaf. Leaf height and leaf area has a significantly positive correlation, indicating that leaf size is likely a result of developmental changes. Leaf area appears to be independent of environmental conditions as determined by this study.

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  The effects of patch size on hummingbird visitation and pollination in Habracanthus belpharohachis, November 2000

  Monica Lisa Saldaña

  In tropical forests, plant species are sparsely distributed and in order to increase their probability of pollination they have developed bright, showy flowers that offer nectar to attract pollinators. In this study, I examined how the pollination rates are affected by the number of inflorescences present in patches of Habracanthus belpharohachis. In order to do this, I measured the percent of pollinated flowers from 22 small patches with one to five inflorescences, and flowers from 14 large patches with more than 15 inflorescences. I also recorded the number of visitations by the primary pollinator of H. belpharohachis, the Purple-throated Mountain-gem (Lampornis calolaema), along with two other hummingbird species to three different size patches of hummingbird feeders. Results showed a significantly greater percent of flowers were pollinated in large patches of H. belpharohachis than small patches. In addition, large patches of hummingbird feeders had significantly more visitations by all hummingbird species than small patches. This study showed that smaller patches of H. belpharohachis are less attractive than larger patches. In tropical forests, this behavior by pollinators may directly decrease the fitness of small patches.

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  The influence of leaf shape of Passiflora biflora in Heliconius spp. butterfly oviposition, November 2000

  Sarah M. Dempsey

  Between species the leaf morphology of Passiflora (Passifloraceae) differ greatly in leaf shape. These differences may be attributed to the presence of Heliconius larvae, who feed exclusively on Passiflora. Adult females may use leaf shape as an oviposition cue, thus the importance of the changing leaf morphology. This study was conducted in an enclosure in the Monteverde Butterfly Garden where I studied three species of Heliconius butterflies: Heliconius hecale, H. charitonius and H. erato. I studied the oviposition behavior on Passiflora biflora due to the varying leaf shapes present, which are two and three lobed leaves. Egg placement showed that Heliconius tend to deposit about half of their eggs on objects other than leaves, such as tendrils (49%) and other miscellaneous objects (8%), without regard to the nearest leaf. The remaining eggs, 43%, were deposited on leaves, with a majority of these deposited on newly unopened leaves. With these unopened leaves, ovipositing females were unable to use leaf shape in discriminating oviposition sites. Of the remaining 35% of the leaves, 2/3 was two lobed and 1/3 were three lobed. Comparing the relative frequencies of two lobed and three lobed showed no preference for one (X² = 93.73, D.F. = 1). Therefore, Heliconius butterflies do not rely on leaf shape to locate host plants and determine oviposition sites, at least in this study. Leaf shape may be a major factor in a more complex habitat with increased rates of other factors such as competition, climate and resource variability. Alternatively, leaf shape variability may be used for other purposes such as to prevent shading of lower leaves and predator avoidance by confusion.

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  A comparison in medicinal plant composition of primary and secondary growth stands by herbalist and medicinal literature references, September 2000

  Jill Jankowski and Nichole Leger

  We assessed the medicinal plant composition of a primary and secondary forest stand in lower montane wet forest in La Cruz, Costa Rica. Herbaceous and woody plant species above 45cm and below 200 cm in height (excluding vines and ferns) were collected identified and evidence for possible medicinal properties sought in both medicinal reference books and from local herbalist. We found approximately the same overall and medicinal diversity in both stands, but the species composition changed between primary and secondary forests. From our interviews with local herbalists, we found that herbalists knew more medicinal species in secondary growth than primary growth. This is expected since secondary forests are more accessible to local communities than undisturbed primary forest areas. From our comparison of local herbalist knowledge to medicinal information in book references, we found that herbalists know more medicinal species in both primary and secondary forest than what books report. However, book references report on average more medicinal uses per plant species. Studies of medicinal knowledge may be used to define a value for a forest area which could be critical for its conservation. Furthermore, it is essential for studies on medicinal composition of forests to include both scientific investigation and local herbalist knowledge in order to maximize the value assigned to a forest area.

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  Anti-predator behavior in birds: Reactions to raptor calls, September 2000

  Robin Elahi

  Birds display a number of defense mechanisms against their predators, including camouflage, mobbing, fleeing, and aggregational behavior. I studied the responses of 32 bird species to songbird and raptor calls to see if birds displayed anti-predator behavior in response to raptor calls in comparison with songbird calls. One focus of my study was avian defensive strategies, namely flocking and concealment, so observations took into consideration different conditions: whether the bird was solitary or in a group, and whether it was exposed or hidden in vegetation. A previous study showed that crows could distinguish between raptor calls of their predators and non-predators, so I examined if birds specifically recognized resident raptors, or if they had a general response to resident and non-resident raptor calls. I also attempted to correlate bird size with reaction, specifically to see if smaller birds flew away more often than larger birds due to a greater perceived threat. For each bird or group of birds. I played a songbird call, followed by a raptor call, and timed the raptor call to see how long the bird stayed till it flew away. Birds flew away 27% of the time in response to raptor calls, and only 3% of the time to songbird calls (X²= 16.11, df = 1, n = 26). Birds did not distinguish among resident and non-resident raptor calls, and had nearly equal flight frequencies (X² = 0.48, df =3, n=40). Trends showed that solitary and exposed birds tended to fly more often than birds in groups and hidden birds. Bird size was not a reliable indicator of reactions, although a trend demonstrate that average bird size was larger for flight reactions, than for no reactions or look reactions (One-way ANOVA, p = 0.1314). These results suggest that birds use the antipredator strategies of flocking and concealment, however, further research should be done on raptor call recognition on a single genus or species of birds to determine if raptor calls recognition is specific on a lower taxonomic level as previous studies have suggested.

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  Effect of fragment size on non-volant mammals in La Cruz and Monteverde, Costa Rica, September 2000

  Seema Sheth

  The purpose of this study was to examine the effects of fragment size on terrestrial, fruit-eating mammals. In this study, it was expected that there would be smaller mammals in small fragments than in large ones due to limited resources and fewer predators. In each of five fragments of different sizes and in a section of continuous forest, plantains were used to bait mammals, and each site was checked every other day for damage to bait. Based on observations of bite marks on plantains, for groups of mammals were identified: small rodents, opossums, agoutis and pacas, and coatis. Number of total visits to bait tended to decrease with increasing fragment size. Proportions of visits by small rodents were higher in smaller fragments. There was no significant difference between number of visits between fragments and continuous forest (Friedman test, p = 0.2409), but there was a significant difference between the different types of damage to bait in the six study sites (Friedman test, p = 0.0014). Specifically, multiple comparisons indicate that the number of plantains not found at the study sites (presumably because they were removed by larger mammals) was significantly higher than the number of visits by opossums (p < 0.05). These results suggest that fragmentation can influence relative abundances of fruit-eating mammals, which can be seed dispersers crucial to seedling recruitment.

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  Effects of entomopathonogenic fungus Beauveria bassiana on Plutella xylostella and Nymphalidae larvae, September 2000

  Kari L. Simmelink

  This study examined the use of the fungus Beauveria bassiana as a biological alternative to chemical insecticides for the cauliflower pest Plutella xylostella. Potential secondary effects of B. bassiana on several local wild butterfly pollinators in Monteverde, Costa Rica were also investigated. Larvae of P. xylostella (Plutellidae), Actinote leucomeles (Acraeinae), Pteronymia notilla (Ithomiinae) and a morpho species of Nymphalidae were collected and treated with the same concentration of B. bassiana fungus used on cauliflower crops in the Estación Biológica Monteverde greenhouse. Mortality of treated larvae was significantly higher than untreated larvae for P. xylostella (Chi-squared p < 0.001), while no difference was found for the three species of treated Nymphalidae larvae. These results support the idea that the use of biological alternatives such as B. bassiana may have fewer adverse secondary effects on the environment than chemical insecticides.

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  Hymenoptera diversity between pasture, ecotone, and secondary forest fragments, September 2000

  Mia E. Kiistala

  Deforestation and forest fragmentation has been shown to have varying effects on biodiversity. In general, invertebrate diversity is expected to increase in the edge areas created by forest fragments. This study looked at the diversity of Hymenoptera in pasture, ecotone and secondary forest fragment in La Cruz to observe the effects of different habitats in diversity. The Shannon-Weiner diversity index values for pasture, ecotone and forest were 1.146, 1378 and 1.674 respectively, indicating highest diversity in the forest. Significant differences were found between the Shannon-Weiner diversity index comparisons (p <0.001).

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  Impatiens walleriana (Balsaminaceae): Its effects on plant diversity and its abiotic habitat characteristics, September 2000

  Angela Braun

  Non-native species tend to proliferate in disturbed areas and may be well-suited to the conditions found there (Noss and Csuti, 1997). The effect of an exotic species, Impatiens walleriana, on plant species diversity at path edges was examined in the San Luis Valley, Monteverde, Costa Rica. Morphospecies of plants in 1m x 1m plots were collected and abundances for each recorded for 19 paired plots (38 total) with and without I. walleriana. Shannon-Wiener Diversity Indices were calculated twice for the plots with I. walleriana (accounting and discounting for the presence of I. walleriana) and once without I. walleriana (mean H’ values – 1.534, 1.754, and 1.767 respectively). No significant difference was found between the mean H’ values for the plots with I. walleriana (either accounting for or discounting for their abundance) and the plots without I. walleriana using a Paired Sign Test. An overall H’ was also calculated and compared with a modified t-test. A significant difference was found between the plots with I. walleriana (including their abundance) and the plots without, suggesting that the presence of I. walleriana affects the local species diversity. Additionally, light intensity and soil temperature were recorded a minimum of three times per plot at morning, noon and evening time periods. Only morning temperature exhibited any significant differences, but significant differences were found for all light measurements at all time periods with plots containing I. walleriana receiving higher amounts of light.

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  Rates of fungus infection in coffee plantations at varying distances from forest edge, September 2000

  Julia Crown

  Coffee (Coffea arabica, Rubiaceae) is an important economic crop for many small farmers in Monteverde, Costa Rica. The humid, cool and dark conditions near the forest as compared to the middle of a plantation provide an optimal habitat for fungal growth. In each of three different farms in Cañitas, three transects were set from the forest edge into the plantations. The amount of fungus on the coffee leaves was measured at varying distances away from the forests. A significant increase in the percent of fungus on the leaves between zero meters and five meters into the plantations was found (3-way ANOVA; p < 0.0001). These results suggest that farmers may find it more economically efficient to create a 10m buffer zone of non-host crops to reduce the impact of the forest microclimate in that area.

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  The effects of human-caused disturbances on water quality and the capability of river ecosystems to recover from disturbances: using benthic macroinvertebrates as indicators of water quality, September 2000

  M. P. Miller

  Degraded watersheds are considered a source of pollution input in rivers. The effects of human-caused disturbances and the abilities of rivers to recover from disturbances were analyzed in three rivers in the around the area of Monteverde, Costa Rica. This was done using benthic macroinvertebrate pollution tolerance levels (FBI), turbidity levels, and macroinvertebrate diversity. Diversity was found to be lowest in the disturbed sites of all three rivers (Modified T-test: 0.002 < p < 0.001). A pattern of maximum FBI values and turbidity levels at disturbance sites was also found to exist; and Escherichia coli were present at all sample sites in all rivers. The data from all rivers was combined for each site and regression analyses were performed. This data suggests that human-caused disturbances will result in decreased species diversity, increased FBI-values, and increased turbidity levels. The results also indicate that rivers have the ability to recover from small-scale human disturbances. The findings of this study support the idea that in order to maintain the diversity of both aquatic and terrestrial organisms as well as clean water for human use, humans need to take into account the effects of their actions on river systems.

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  The effects of patch size on hummingbird visitation and pollination in Habracanthus Belpharohachis, September 2000

  Monica Lisa Saldana

  In tropical forests, plant species are sparsely distributed and in order to increase their probability of pollination they have developed bright, showy flowers that offer nectar to attract pollinators. In this study, I examined how the pollination rates are affected by the number of inflorescences present in patches of Habracanthus belpharohachis. In order to do this, I measured the percent of pollinated flowers from 22 small patches with one to five inflorescences, and flowers from 14 large patches with more than 15 inflorescences. I also recorded the number of visitations by the primary pollinator of H. belpharohachis, the Purple-throated Mountain-gem (Lampornis calolaema), along with two other hummingbird species to three different size patches of hummingbird feeders. Results showed a significantly greater percent of flowers were pollinated in large patches of H. belpharohachis than small patches. In addition, large patches of hummingbird feeders had significantly more visitations by all hummingbird species than small patches. This study showed that smaller patches of H. belpharohachis are less attractive than larger patches. In tropical forests, this behavior by pollinators may directly decrease the fitness of small patches.