This collection contains the findings of scientific studies of tropical terrestrial and marine ecosystems, their components, and their conservation from Monteverde, Cuajiniquil, and other areas of Costa Rica.
This digital collection is a service of the Monteverde Institute, whose mission is to catalyze social, ecological and economic sustainability by integrating community initiatives with education, research and conservation.
Esta colección contiene los hallazgos de estudios científicos de ecosistemas tropicales terrestres y marinos, sus componentes y su conservación de Monteverde, Cuajiniquil y otras áreas de Costa Rica.
Esta colección digital es un servicio del Instituto Monteverde, cuya misión es catalizar la sostenibilidad social, ecológica y económica integrando iniciativas comunitarias con educación, investigación y conservación.
Karen Leigh Sonnenblick
The purpose of this study was to look at the frequency of infection and percent root infection of vesiculararbuscular mycorrhizae present in saplings of Sapium glandulosum in pasture and gaps. Saplings in the pasture had a significantly higher frequency of infection than saplings in the gaps (Two-by-two contingency table, X² = 27.855, p < 0.0001). Saplings in the pasture also had a significantly higher mean percent infection than saplings in the gaps (Mann-Whitney U test, U = 370.00, tied p-value = 0.0013). These findings indicated that the amount of disturbance that an area has been subjected to strongly influences the levels of VAM growth on S. glandulosum.
Plants are an extremely important contributor to many medicines throughout the world. Because of the amount of forest destruction that is occurring, it is becoming important to find a rapid way to assess forests for their potential of having medicinal plants. Two such methods for assessing areas for medicinal plants, chemotaxonomic and ethnopharmacological are discussed in this paper. A biological survey of an area of premontane wet forest in Monteverde, and interviews of local people were done to compare which would better assess possible medicinal plants in the area. The end result indicates that the biological inventory would be the best way to proceed in Monteverde, although other regions might find it beneficial to use a method that combines both approaches.
Limitation of nutrients can greatly reduce the success of plants. Such stresses can be caused by invasive species that can outcompete other plant species trying to establish themselves in the vicinity. This can lead to reduced species richness. This study investigates the relationship between Chusquea pohlii culm density and species richness around the clumps. Clump area, number of species within and immediately around each clump was recorded and analyzed by regressing culm density on species density around the clumps (p = < .0001, R^2 = .493). Results showed that increasing culm density reduced species richness in and around the clumps suggesting that C. pohlii may be an invasive species that reduces species richness in the forest. Observations also showed that certain hemiepiphytic and herbaceous species occurred more often than other species.
Meg Seifert and Ambrose Tuscano
The purpose of this study was to determine hummingbird preference between protein and higher sugar concentrations, and how any preference affects competition and memory. We hung three sets of three feeders in triangular patterns and observed hummingbird visits and interactions. We also, noted solitary feedings on the days directly following both site establishment and feeder rotation. Our results showed that there was an overall preference for the feeder with higher sugar concentration, that larger species and newcomers were generally dominant and that birds did not take longer to learn the values of established leaders that had been rotated than feeders whose contents were unknown. We concluded that larger, more aggressive birds had a stronger preference tor the feeder with the highest sugar concentration, smaller birds tended to take more dips per feeding, birds with curved beaks showed less interest in the feeder with fruit flies present, it is easier tor a newcomer to dominate a feeder and to maintain control of it after an interaction and spatial location of feeders is the most important memory cue.
Kristin C. Young
Disturbances to continuous forest such as roads or cleared patches of land often cause forest fragmentation. Resulting tracts of forest are often too small to support populations of top predators. As a result of this, mesopredators populations are left unchecked and increase to unnatural abundances. One consequence of this is increased predation on tropical bird nests, which may put them at risk for extinction. I constructed 120 artificial bird nests and placed two quail eggs in each nest. Nests were situated along 12 transect lines that ran into the forest, perpendicular to a road in Monteverde, Costa Rica. Predation was observed over a period of 27 days. Chi Squared Tests revealed that distance from the road had no effect on predation levels (p > 0.05 at above ground level; p > 0.05 at ground level). However,ground nests suffered significantly higher predation than did above ground nests (2-Way ANOVA; p <0.0001). This study cannot conclude that an edge effect is present, but it suggests the possibility of an increase in predator pressure from opportunistic mesopredators due to reductions in the populations of higher trophic levels.
The use of indicator species in conservation biology has proven to be an effective means of gauging the biointegrity of communities and ecosystems. Nymphalid butterflies are excellent bioindicators of forest and forest edge habitats. Their varied microhabitats required during different stages of development make them excellent subjects for studies in vertical and elevational niche partitioning. This study examines the vertical niche partitioning of Nymphalid butterflies along an elevational gradient in the Estación Biológica Reserve in Monteverde, Costa Rica. This forest contains both fragmented and continuous forest sections, thus making it a good representation of presently protected forests. The study was conducted over a fifteen day period in late November. Fruit traps were set at three elevational points within the reserve at three heights above the ground. Eighty-three butterflies were caught representing six subfamilies and fourteen species. Sixty-eight percent of the sample was represented by Manataria maculata in the subfamily Satyrinae. Butterflies were found to significantly prefer the lowest elevation (1550m) in an understory habitat. One species of butterfly was found to only occur at the highest elevation (1750m). These results signify elevational niche partitioning but not necessarily vertical. This trend may be due to small sample size and a short study period. Comprehension of niche partitioning within tropical forests will lead to a greater understanding of the ecology and biointegrity of presently protected areas.
I studied feeding preferences of hummingbirds in the presence and absence of a simulated predator at feeders with varied nectar concentration. Using nectar concentration of 15% and 25% with and without predators, I counted visits over eleven sessions of one hour apiece. I found no significant patterns in number of visits (p= .379) or number of species visiting (p= 0.413) across all treatments. The hummingbirds showed no avoidance of the predator nor preference for nectar concentration. Although no statistically significant patterns were found, these findings are biologically relevant because they indicate possible behavioral responses to fragmentation and environmental disturbances.
Bonita S. Thibault
Fallen tree logs provide an ideal moist habitat for Arachnids in the Order Opiliones. This study compares pasture and forest logs to determine which of the two habitat types Opiliones prefer. Log size and degree of decomposition were examined to determine their effect on Opilion abundance and species richness. Logs in pasture and forest sites at Monteverde and Cañitas, Costa Rica were overturned and searched for Opiliones. Opiliones were found to be more abundant and species rich in the pasture than in the forest. However, forest logs have a higher index of diversity than pasture logs. A positive correlation was found between volume (size) and species richness (forest: p = 0.024, r = 0.0207; pasture: p = 0.001, r = -0.295) and between volume and Opilion abundance in pasture logs (p < 0.0001, r = 0.401) but not in forest logs (p = 0.063, r = 0.171). No correlation was found between degree of decomposition and Opilion abundance (forest: p = 0.839, r = 0.019; pasture: p = 0.598, r = 0.048) or species richness (forest: p = 0.916, r = 0.01; pasture p = 0.875, r = 0.014). Negative effects of deforestation on Opilion diversity were looked at in global terms and reasons for these effects were hypothesized and discussed.
Protandry has been known to promote outcrossing in many species of plants (Lloyd & Webb 1986, in Endress 1994), but in asynchronously flowering plants other mechanisms are needed to reinforce outcrossing (Endress 1994). This study investigates the flowering system of Columnea microcalyx (Gesneriaceae) to determine what mechanisms the plant may be using to promote outcrossing. Nectar production, floral characteristics, and the effects of pollination on nectar production were measured in 36 flowers of C. microcalyx. It was found that C. microcalyx flowers are protandrous; they open asynchronously on a plant and have delayed nectar production. It was also found that they reduce amount and concentration of nectar if pollinated prior to nectar production, and have more highly concentrated nectar than most hummingbird-pollinated flowers. These characteristics may act as mechanisms to promote outcrossing in C. microcalyx.
In this study I looked at reproductive strategies of Besleria princeps (Gesneriaceae). I took population sex ratios from 100 randomly chosen plants over a nine day period and found that individual flowers as well as the population as a whole were protandrous. There was a significant difference in the ratios of males to females from day one to day two. This protandrous system promotes outbreeding thereby reducing the negative effects of inbreeding. In a separate group of plants, I bagged 94 individuals including 162 buds. When the buds opened, I noted their sex and separated them into groups in which I either probed for nectar, removed pollen, or left them alone. I monitored them daily, noting when the sex change occurred from male to female to determine if the plants responded to simulated visitation by pollinators. The group that I probed for nectar switched sex sooner than the control group, which suggests that the flowers switch after their pollen has likely been removed and therefore the chance of inbreeding is reduced. There was a trend among flowers whose pollen was removed to switch sex earlier than the control but it was not statistically significant.
James J. Garnsey
Many tropical plants show age-related morphological and chemical changes that are adaptive to a particular environment. Generally, leaves of young plants have drip tips and increased secondary compounds while leaves of mature plants lack drip tips and are tougher. Cecropia polyphlebia and Cecropia obtusifolia are common pioneer tree species in Monteverde, Costa Rica that exhibit morphological and chemical changes with age. Here, I study how water content, herbivory, toughness and concentration of alkaloids change in the leaves of Cecropia as the plants age. Leaves from young, medium and mature aged plants were collected from gaps near the Estación Biológica Monteverde (1500m) for C. polyphlebia and below the road to Monteverde (1300m) for C. obtusifolia. Percent water content, percent herbivory, toughness and alkaloid concentration was then determined for each leaf. The leaves of the young plants displayed the highest percent water content (83.2 ± 2.8) and alkaloid concentration (3.6 ± 9.5), decreasing significantly with plant age. It is likely that the young Cecropia are utilizing greater amounts of water for rapid growth and investing in more renewable defenses such as alkaloids. Toughness showed a significant increase with plant age, with the leaves of mature plants having an overall mean 91.0 ± 26.2. This provides evidence that as the Cecropia age and sunlight is less available, they will invest in longer-lived defenses. However, further research is needed in order to elucidate the mechanisms that determine plant anti-herbivory investment.
The effect of acorn weevils (Curculionidae: Curculioninae) as seed predators of Quercus insignis (Fagaceae) in a tropical montane forest
Timothy R. Kuhman
The effect of seed predation by acorn weevils on the acorns of Quercus insignis was assessed in the context of frequency of infestation and the extent of damage incurred by the larvae on individual acorns. The effect of such damage on early fruit abscission and germination potential of infested acorns was also examined in this study. Acorns were collected from five Q. insignis trees in the lower montane forest of the Cordillera de Tilarán in Costa Rica. Frequencies of infestation varied greatly among the five trees, from 3.3% to 75%. However, there was no evidence for early abscission of infested acorns by the parent trees. Finally, the larvae were found to produce considerable damage to individual acorns after abscission that could potentially limit recruitment rates of Q. insignis.
Vegetative fragmentation within two microhabitats along an altitudinal gradient in the Monteverde cloud forest, Costa Rica
Reproduction by vegetative fragments of cloud forest plants was studied at Monteverde, Costa Rica. The relative frequency of reproduction via seeds and plant fragments was quantified on trail edges and in forest understories, along an elevational and east-west gradient encompassing the Continental Divide. The proportion of young plants that originated from fragments in the understory increased with elevation and on the east-facing slope. A similar trend was found along the trail edge, with the highest proportion of fragments at the Continental Divide. The diversity and composition of plants that reproduce via fragmentation was compared among three sites (west-facing, Continental Divide, and east-facing). No significant species diversity overlap was found using the Sorenson quantitative index, and a modified t-test showed no significant differences in diversity between each of these three sites. Occurrence of fragmentation is related to levels of wind, moisture, sunlight, nutrients, density of the understory, terrain, and decomposition rates of specific sites and elevations.
Vertical niche partitioning between Gray-breasted wood-wrens (Henicorhina-leucophrys) and Ochraceous wrens (Troglodytes ochraceus)
The study of competition is important because the presence of one of the competing species reduces the fitness of the other; therefore, one of the species eventually will go extinct. This leads to the idea that all species must occupy different niches in order to coexist. Theories on niche partitioning in tropical forests have become important in order to explain their immense species richness and biodiversity. Two very similar species in the Monteverde area are the Gray-breasted Wood-Wren (Henicorhina leucophrys) and the Ochraceous Wren (Troglodytes ochraceus). These sympatric species are both foliage gleaners and are often found together in insectivorous mixed species foraging flocks, making them potential competitors. The purpose of this study was to determine if Gray-breasted Wood-Wrens and Ochraceous Wrens were partitioning their habitat in order to preclude competition. Preliminary data suggested that Ochraceous Wrens would be found higher vertically than Gray-breasted Wood-Wrens. Observations of these wrens were made visually and by call in the Monteverde Cloud Forest Reserve. Vertical height was divided into three zones: understory, middle, and canopy. Zone and altitude were recorded for each wren sighting. A significant difference was discovered in vertical height between the two species of wren but no altitudinal preference was found. Gray-breasted Wood-Wrens preferred to live in the understory while Ochraceous Wrens preferred the canopy. Therefore, these two species are able to coexist in the same environment by vertical habitat partitioning.
Ithomiine (Nymphalidae) butterflies are vertically stratified by color pattern in neotropical forests. Each of the five color patterns recognized represents a mimicry complex of several sympatric species. Vertical stratification between color complexes of Ithomiines has been attributed to crypticity and host plant stratification. Here, I study stratification between the clearwing and golden-translucent complexes in Monteverde, Costa Rica. As in other studies, clearwings tend to fly lower than golden-translucents. Host plants do not correspond well to flight heights for these species, however. Within complexes species are also vertically stratified with most similar species tending to separate, possibly to aid in mate location.
Vesicular-arbuscular mycorrhizal fungi among different growth stages of cecropia polyphlebia (Cecropiaceae)
Mycorrhizal fungi are important in the survival and growth of most plants, tropical trees in particular. Yet little research has been done on the abundance of mycorrhizae throughout the life span of plants. I collected root samples from 15 seedlings, 15 saplings, and 15 adults of Cecropia polyphlebia in order to determine the variance in abundance of mycorrhizae among the three growth stages. Root samples were stained and scored for vesicular-arbuscular mycorrhizae by comparing the number of infected roots to non-infected roots. Three morphologies of mycorrhizae were observed under examination of stained roots; random, hyphal, and sheathing infection. Two-way ANOVA’s and post-hoc analyses showed that there was no significance among the three types of growth stages compared to the frequency of infection (p = 0.6626). However, there were significant differences among the three types of infection (p = < 0.0001) and between the type of leaf (growth stage) and the type of infection (p = 0.0001) and between the type of leaf (growth stage) and the type of infection (p = 0.0001). Results indicate a relationship between optimal infection time and type of fungal infection. This leads one to believe there may be a limited amount of mycorrhizae allowed by the tree to maximize the tree’s own production.