Monteverde Institute: Tropical Ecology and Conservation

Follow

• 

  Age-related mobbing behavior in brown jays, March 2003

  James W. Ford

  Mobbing behavior is one way birds respond to the threat of a predator. I studied the mobbing behavior of Brown Jays (Cyanocorax morio) in Monteverde, Costa Rica. Brown Jays are included in the 3% of bird species that breed cooperatively. I was curious whether the competitive nature of obtaining a breeding position was related to mobbing in any way. Were the jays mobbing to increase individual fitness or inclusive fitness? I divided the birds into three age groups (juvenile, sub-adult, and adult) and tried to measure aggression between the groups. I used myself, a rubber snake model painted to resemble a Boa constrictor, and an owl model to elicit a mobbing response. Results of Chi-square tests show that sub- adults were more likely to call first and more often in response to a predator model. It also showed that adults were more likely to fly, or swoop at the predator model. Results indicated that while sub-adults are more likely to mob to increase inclusive fitness, adults might be acting more to increase individual fitness. To support these results, however, further research is needed on banded individuals in order to determine sex and breeding status.

• 

  Aggregation formation in a neotropical harvestment (Opiliones: Cosmetidae), March 2003

  Crystal Fankhauser

  Neotropical harvestments are generally omnivorous, solitary nocturnal foragers. However, several species of harvestmen are known to form aggregations during the day, including a species of harvestmen (family Cosmetidae) that is common in open, grassy areasin Monteverde, Puntarenas, Costa Rica. This study focuses on how and under what conditions new aggregations are formed by marking and recapturing individuals in natural and artificially created sites. Proposed hypotheses for the purpose of forming aggregations include: limited site availability that provides protection from desiccation and exposure to light, an increase in defensive ability against predators by using the mass release of defensive chemicals and the dilution effect of reducing chances of predation by pure probability. This study has found support for the first hypothesis, that limited availability of suitable sites drives their choice in places to aggregate, based on their observed behavior and a strong statistical difference in temperatures above and below artificial sites (paired T-test; p-value < 0.0001). In addition, this species rapidly colonized the artificial sites, which was most likely motivated by optimal conditions beneath them. In both natural and artificial sites, individuals displayed high site fidelity due to a small range size. Also, estimated population densities between 0.2 and 2.6 individuals per m² in artificial sites suggest that this species of harvestmen is an important predator and prey item in open areas.

• 

  Algae as biological indicators of stream water quality in Monteverde, Costa Rica, March 2003

  Andrea Buckman

  Water quality is an issue of increasing importance as the growing population depletes and contaminates the Earth's natural resources. One example of this is in Monteverde, Costa Rica, where wastewater is directly discharged from homes and businesses into the many streams in the area, affecting the ecosystem within the streams. Runoff from the many farms and pastures that are treated with highly concentrated pesticides and fertilizers can also affect the natural freshwater ecosystems by adding nutrients and toxins. Seven streams in the Monteverde area were analyzed in order to determine if algae morphospecies can be used as reliable indicators of water quality. Two samples were taken from each stream, one at a point source and one in a pristine location. Water quality analyses, including dissolved oxygen content, pH, temperature, nitrogen and phosphorous content, and turbidity, were conducted for both samples. Algae morphospecies at each site were identified and recorded as well. There was also a significant difference (P = .0007) between the morphospecies found at the pristine sites and those at the point source sites. This shows that water quality has an effect on algae species composition, and that species composition can be used to indicate water quality. Studies similar to this one can be highly useful in identifying sources of water pollution or determining the health of a freshwater stream based on the algae species found there.

• 

  Anti-predator behavior of birds in response to call playbacks of the barred-forest-falcon and white-breasted wood-wren, March 2003

  Matthew R. Gasner

  Birds have evolved many different strategies to cope with varying predation. Birds throughout the world are known to respond to threats, in part related to their size, social preferences, and foraging habits. Since there is relatively little known about these mechanisms for tropical birds of Cloud Forests, I have performed the following study in the Monteverde area of Costa Rica. A total of 129 calls of two types were played to 33 species in the Monteverde area during the course of this study. Anti-predator responses were recorded for birds exposed to a call playback of the Barred Forest-Falcon (Micrastur ruficolli) and the scold call of a White-breasted Wood-Wren (Henicorhina leucosticta). The degree of response was compared to a bird’s size, social system, and foraging habits. Bird species studied tended to investigate wren calls more than raptor calls. Size was also found to be a factor influencing the type of response given to call playbacks. Heavier, longer, and “chubbier” birds tended to retreat from the call of the falcon. Longer birds tended to do nothing or call while moving towards the playback of the wren scold call. Response of birds was not related to social preference nor foraging habits, possibly because of small numbers of social birds found and the many foraging habits of Cloud Forest birds. Despite a relatively small sample size, this study has revealed a few basic trends in the anti-predator responses of a portion of Monteverde’s bird species and could possible provide the layout for possible larger future studies on this subject.

• 

  Biological responses of Platystele microtatantha and Specklinia aristata (Orchidaceae) to climate change in Monteverde, Costa Rica, March 2003

  Eleonore Wesserle

  The lifting of the cloud bank due to climate change in the Monteverde cloud forest has already caused discernible effects on the dry season mist regime. Epiphytes, including the most prevalent family of epiphytes, Orchidaceae, may serve as a useful indicator group of climate change. This study sought to fill the gap in knowledge about orchidaceous epiphytes and climate change by testing the response of the pleurothallid orchids Platystele microtatantha and Specklinia aristata to supplemental mist treatments simulating 1970s mist frequencies. Two sites were studied: P. microtatantha growing on an orchid frame and P. microtatantha and S. aristata individuals growing on tree trunks in a pasture. The frame P. microtatantha experienced an increase in leaf number for the supplemental mist treatment. The frame P. microtatantha and the S. aristata experienced significant increases in leaf thickness for the supplemental mist treatment. The pasture P. microtatantha individuals showed a trend significant to the p = 0.0540 level of higher fruitset frequency in the supplemental treatment. Both the S. aristata and the pasture P. microtatantha showed a significant correlation between total leaf number and inflorescence and flower number. These results indicate that the mist regime affected epiphytic orchids and these plants could possibly be used as climate change indicator species.

• 

  Colony size and its effect on forager polymorphism in Atta cephalotes (Hymenoptera, Formicidae), March 2003

  Matthew R. Wallrath

  Atta cephalotes or leaf-cutting ants (Hymenoptera, Formicidae) exhibit strong polymorphism over the life span of a single colony. This polymorphism effects foraging efficiency and is linked to overall social complexity. In this study, I quantified the degree of variance in head size and femur length in six colonies, as well as presence of a soldier class, and compared these results to the relative size of each nest as determined by a survey of foraging intensity. It was found that variance in the head and femurs and the presence of soldiers was significant different between small and large colonies, and this was related to increasing colony size.

• 

  Diversity, aggregation, leg mutilation and mite infestation of Costa Rican phalangida, Opiliones (Arachnida), March 2003

  Katherine Ayres

  Phalangida diversity, aggregation composition, leg mutilation and mite infestation were analyzed under a variety of substrates in a pasture and a forest fragment in Cañitas, Guanacaste, Costa Rica. Any solitary individual or group of individuals found on or under a substrate were collected and analyzed. For each aggregation, the number of individuals was recorded. Each individual was identified to family and morphospecies. The numbers of missing legs and the leg pair to which they belonged were analyzed for each individual. The number of mites and their locations on the body were also analyzed. Species diversity for each habitat was calculated using the Shannon-Wiener diversity index and the forest fragment was found to have a significantly higher Phalangida diversity (modified t-test; t = 10.96, p < 0.001). Aggregation sizes and species combinations revealed that Phalangida aggregations tend to be rare and smaller in the forest fragment. Of the aggregations containing two or more individuals, there was a higher percentage of multi-species aggregations (62.5%) than monospecies. Only one multi-species aggregation combination occurred more than once. Leg analyses indicated that species in the Palpatores suborder tend to lose legs at the coxae, while Laniatores have legs missing at various locations. Mite infestation analyses indicated that mites preferred legs to the body and will infest any part of the leg except the tarsus. No mite preference was observed between the cephalothorax and abdomen. This study was a preliminary investigation of Costa Rican Opiliones in hopes to learn more about the natural history of this poorly understood group of organisms. Overall, Opiliones appear to be a diverse suborder and this diversity may be threatened by deforestation.

• 

  Diversity and species breadth of carrion insect communities along an altitudinal gradient, March 2003

  James Dugan

  Detritivores play a crucial role in nutrient cycling within tropical forests by returning nutrients to the ecosystem. The purpose of this study was to inventory carrion feeding insect communities and show the change in insect diversity along an altitudinal gradient. Five sites were visited every 200m along the gradient from 800m to 1600m using carrion as bait to attract insects. A total of 1507 individuals were collected, representing 21 species. Six of the ten diversity comparisons using a variation of the Shannon- Weiner Diversity Index and modified t-tests were significantly different (p < 0.05). The number of individuals was found to decrease as elevation increased (simple regression, p = 0.0158, r2 = 0.01). It is believed that the lower elevations harbor a higher diversity and species richness due to unfavorable conditions at the higher elevations.

• 

  Effects of caste structure on Nasutitermes spp. (Isoptera) hindgut protozoan populations, March 2003

  Ruth Healey

  Evolutionary development of eusocial behavior in termite populations may be due to their symbiotic interaction with the protozoa that live in the hindgut and aid in cellulose digestion (Wilson 1971). In particular, the way in which protozoa are passed between individuals of different castes and the resulting variance in diversity could have led to the development of social interactions and specialization within castes over evolutionary time. This study looked at the hindgut composition of Nasutitermes spp. among three different castes across multiple nests to determine if a caste-dependent gradient of hindgut faunal diversity exists. Castes from six nest sites were collected and individual’s hindgut fauna was censused using a binocular microscope. Though data were not statistically significant in all cases, a trend of caste- dependent hindgut composition was documented. Soldiers and mature workers had a higher diversity of hindgut fauna than did recently molted workers, alates, or larvae. These data warrant further study into microorganism involvement in the development of the social structure of Nasutitermes spp. populations and the impact of termite behavior on the trophic structure of tropical habitats.

• 

  Effects of habitat type on predation rates, March 2003

  Erin Wilichowski

  High rates of habitat alteration increase the effects of fragmentation and creation of pasture. Degraded habitat can negatively affect predator abundance and hence predation. In this study, variation in predation rates between closed forest, open forest, and pasture were assessed for a matrix of degraded tropical premontane moist forest in Costa Rica. In order to compare predation rates in the different habitat types, non-toxic clay caterpillars were made, placed on understory leaves, and then rates of predation in each habitat type were determined. This study focused on three types of predators, insects, birds, and rodents, with insects as the most predominant predators. Overall percentages of predation were 15.6% ± 9.7 in closed forest, 19.1% ± 11.0 in open forest, and 19.0% ± 8.5% in pasture. No significant difference was found in the predation rates between the habitat types (F = 0.255, P = 0.7781). These results, are contrary to other research indicating that fragments and agricultural lands experience higher predation than continuous forest, and may have been caused by effects of the dry season on insect abundance.

• 

  Foraging behavior of Trigona fulviventris in a Costa Rican cloud forest, March 2003

  Tracy Noel Rogers

  Two colonies of Trigona fulviventris were studied in Monteverde, Costa Rica in April- May, 2003. Foraging patterns were analyzed within the nest and between nests. Nest EBM showed no significant foraging change from morning to afternoon and no proportional foraging difference over the course of the study. On the other hand, nest DM showed significant change morning vs. afternoon as well as a clear proportional change along the duration of observations (p < 0.0001). There was also a difference in behavior between both nests (p = 0.004) which leads to the speculation that the timing of brood production of these two nests are not equal even though they are located in the same region and studied over the same time span.

• 

  Freshwater crab density and demography in relation to water quality and elevation, March 2003

  Givonn D. Osterneck

  I investigated the effects of pollution and elevation on the population density of freshwater crabs as well as their age structure and sex ratio. This study gives insight into freshwater crabs as bioindicator of water quality as well as provides basic demographic information. Water quality was tested and crabs were collected at three different elevations, 1350 m, 1500 m, and 1650 m, at six different streams. Using a Kruskal-Wallis statistical analysis on the total crabs, the average male size, the average female size, the number of males, and the number of females were analyzed in relation to elevational change (table 2). There was a strong correlation between the total numbers of male and female crabs with a change in elevation (figure 3). The data on the total crab abundance suggests a pattern of crabs being most densely populated in higher elevations around 1650 m above sea level.

• 

  Niche partitioning and overlap in a cloud forest between two Neotropical warblers (Parulidae), March 2003

  Evan M. Adams

  The types of niche partitioning between two congener bird species Myioborus miniatus and M. torquatus (Parulidae) were studied in premontane wet and rain forest in Monteverde, Costa Rica. An altitudinal distribution showed that M. niniatus was found at an average height of 1568m and M. torquatus at 1612m. Foraging behavior was also different between the two species with M. miniatus foraging at an average height of 4.6m and M. torquatus at 7.2m off the ground. These findings indicate that there is a large amount overlap in altitudinal distribution and foraging height between the two species. Stronger partitioning with less overlap is seen in the foraging behavior of the species. Previous studies showed that interspecific competition between the two species was detrimental to M. miniatus and helpful to M. torquatus. Spatial overlap is therefore possible between the two species but it is undesirable for M. miniatus. While there is a large amount of niche overlap, the two species are different enough that they do not entirely exclude one another.

• 

  Parasites in scats of Nasua narica (Procyonidae), March 2003

  Mary E. Kutch

  The majority of animal species are parasites, and free-living animals almost certainly harbor at least one host- specific parasite species. This study surveyed the intestinal parasites in a Costa Rican population of white-nosed coatis (Nasua narica). Scat was collected and analyzed under a compound microscope using the direct smear technique, and parasite morphospecies were counted and identified. All samples contained endoparasites, the most abundant of which were nematodes. They were present in 95% of the samples and included the genera Enterobius, Strongyloides, and Dorylaimus, Physaloptera, Diphyllobothrium latum, and a ciliate- possibly Bresslaua vorax, were also observed. Members of this tropical population of N. narica are host to similar phyla and genera of intestinal parasites as individuals in temperate populations, but differ by species.

• 

  Plant preference and camouflage in Phasmid morphospecies, March 2003

  Jackie Prange

  Phasmids in the tropical and temperate zones are known to exhibit both polyphagous and monophagous behavior. Because more plants are better protected in the tropics, the expected number of host-plant specific insects, including Phasmids, should be higher. The diets of seven Phasmid morphospecies and a nymph group in the families Psuedophasmatidae and Phasmatidae of the Monteverde cloud forest, Puntarenas, Costa Rica, were studied. Results showed that these morphospecies consumed different amounts and different plant species (two-way ANOVA, P < 0.0001). Amount consumed increased with size as measured by tibia length. All morphospecies were polyphagous, but had differing plant preferences. Diet composition and breadth depended on morphospecies. Nymphs, however, were monophagous on Conostegia oerstediana. This study also investigated Phasmid camouflage. Phasmids of three color classes showed no significant difference in preferred resting substrate (two-way ANOVA, P < 0.0001). Phasmids most likely rely on other defense mechanisms, such as body shape and behavior, for protection.

• 

  Species diversity, activity, and behavioral variation in fireflies (Coleoptera: Lampyridae) along an elevational gradient, March 2003

  Emily J. Stirr

  Three aspects of firefly ecology were investigated including species diversity, activity and behavior of llampyrid species. Lampyrid species diversity was measured along an elevational gradient at five different sites (950m, 1100m, 1200m, 1450m, 1550m). Activity was measured along the same gradient between 6:00 PM and 8:45 PM. Behavioral diversity was studied in the context of species responses to disturbance by a simulated predator. Seven different species were collected including specimens of Aspisonia sp. and Photuris sp. Species diversity was found to be lowest at mid elevations and tended to increase at the outer ends of the gradient. Diversity was found to be greatest at 1550 m (Shannon-Weiner, modified t-test, p < 0.02). Activity was found to have a negative correlation to both elevation and time of night (ANOVA, time: F = 7.075, p < 0.0001; elevation: F = 10.987, p < 0.0001). Each species demonstrated varying responses to predatory disturbances and all species, with the exception of species A, maintained similar behavior for the full period of disturbance (Chi-square, p < 0.0001, 0.25 < p < 0.30; 0.95 < p < 0.975; 0.995 < p < 0.99, A, B, C, E). Species diversity was thought to be affected by habitat disturbance, while the negative correlation of activity with elevation was thought to be explained by decreasing ambient temperatures. The differing responses of various species to predatory disturbance sheds light on theories of flash behavior in fireflies.

• 

  The causes and effects of nest clustering in colonies of the chestnut-headed oropendola (Psarocolius wagleri), March 2003

  Jason Fisher

  Colonies of nesting birds are often subdivided into clusters of nests; the causes and effects of these clusters have profound impacts on the breeding strategies of colonial nesting birds. Five colonies of a Neotropical colonial nesting bird, the Chestnut-headed Oropendola (Psarocolius wagleri), were studied to identify trends in male and female intersexual competition, mating strategy, and brood parasitism in relation to colony and cluster size. The results were compared with data from studies by Webster (1994a, b) for another colonial nester, the Montezuma Oropendola (Psarocolius montezuma), which is known to use female-defence polygyny. The comparisons showed that while both the Montezuma and Chestnut-headed Oropendolas use female-defense polygyny, the degree to which a few males are able to monopolize copulations varies with cluster size and synchrony. Montezumas construct nests in larger colonies, more dense clusters, and as a result, males compete to defend nest clusters and copulate at the clusters, female aggression increases with cluster size, and nest parasitism decreases as clusters become larger. For the Chestnut-headed Oropendola, on the other hand, I found that males rarely compete near nests, guard clusters, or copulate near clusters. Female aggression and parasitism showed no significant relationship. Because copulations occur away from nests, and because there is partial synchrony of nest stage for all active nests in a colony, males must focus their breeding attention on one female at a time, which allows multiple males, rather than only a few, to successfully copulate. As a result, cluster sizes are smaller and more spread out.

• 

  Water quality and lichen coverage in Monteverde streams, March 2003

  Stephanie Payne

  This study examined lichen abundance and water quality in six streams in Monteverde, Costa Rica. By estimating lichen coverage on rocks over a 90 m transect, mean lichen coverage per stream was measured. Water quality was estimated by measuring temperature, dissolved oxygen concentration, pH, turbidity, nitrogen and phosphorous levels at each stream. Mean lichen coverage varied between each site, showing that the Quebrada Sucia had the smallest lichen coverage and the Quebrada Máquina had the highest lichen coverage. A significant positive correlation was found between percent lichen coverage and total dissolved oxygen concentration. There are at least four possible explanations for these trends: water enhances lichen growth, competition with algae limits lichen growth, interactions between source and sink populations affect lichen coverage, and pollution inhibits lichen growth in streams.

• 

  An analysis of three methodologies in determining family biotic index (FBI) values for benthic macroinvertebrates in the tropics, September 2002

  Victor J. Rini

  The use of living organisms to assess water quality is a century old approach (Cairns and Pratt 1993). Widespread use of this method of evaluation has been common in North America and Europe (Metcalf 1989), yet it has not been applied in the Tropics. Here I present a test and alternatives to Hilsenhoff’s (1977, 1982, 1987) methodology for assigning Family Biotic Index values (a measure of pollution tolerance) to macroinvertebrates in a tropical premontane moist/wet forest (Holdridge 1967). Samples of benthic macroinvertebrates were taken from seven streams in the Monteverde, Costa Rica area. Hilsenhoff’s methodology as well as two others are applied in constructing a preliminary formula for assigning FBI values according to a revised Water Quality Index (WQI) as originally provided by Mitchell and Stapp (1995) to tropical macroinvertebrates. The strongest correlation with abiotic WQI was with Hilsenhoff's methodology, suggesting this methodology is both applicable and most effective in assigning Family Biotic Index values for tropical ecosystems.

• 

  An evaluation of pre-lekking vocalization behaviors of adult-long-tailed manakins in Monteverde, Costa Rica, September 2002

  Jessie C. Thomas

• 

  Edge and pollution effects on lichen communities in the Monteverde area, September 2002

  Margaret Beswick

  Lichen has been used as a bioindicator of disturbance and pollution effects for over 100 years, however little is known about the relevance of lichen as a bioindicator in the tropics. Increasing fragmentation of tropical forest is leading to increased forest area along exposed edges. Also increased energy consumption is increasing levels of air pollution. Understanding the effects of pollution and edges on lichens in the tropics can have important implications for conservation. In the Monteverde area I tested edge effects and combined edge and pollution effects on lichen communities. A pasture, surrounded by forest, should show edge effects, and a parking lot surrounded by forest should show edge and pollution effects, on lichen communities. I analyzed the lichen communities for similarity and richness. I found 114 species of lichen in total, with more species in the unpolluted site. Similarity in lichen community structure was moderate between the two study sites. I conclude that the lichen community along the parking lot is different from the community along the pasture. I speculate that this is due to increased edge effects and pollution effects. To determine the impact of pollution and edge on lichen communities further studies of community composition are needed.

• 

  Effect of edge on the foraging of frugivorous birds and it's relation to palm composition, September 2002

  Christie Boser

  It has been observed that birds are more common in forest habitats then along the edge of pastures. This study investigates the idea that birds forage less frequently in pastures and along forest edges and therefore that fewer seeds are dispersed in pastures than in forest. This would affect forest composition along edges and duration of reforestation. Clay fruits were placed on a gradient from forest to pasture, and the number of “fruits” with peck marks at each distance was recorded. A palm census was done along the gradients to determine if the diversity of palms differed from the edge to the forest. It was found that there were significantly more fruits pecked in the forest then at the edge (one way ANOVA p = < 0.0001, F = 653.244, R² = 0.918). Therefore birds are not dispersing fruits at the edge as much as in the forest. This could affect the diversity of species at the edge. This was confirmed in the palm census. The diversity of palms was significantly greater in the forest then the pasture (one-way ANOVA p = 0.0093, F = 106.265, R² = 0.982). There is a correlation between the expected diversity of palms due to dispersal events and the actual diversity.

• 

  Environmental education and understanding: The case for elementary students in Monteverde, Costa Rica, September 2002

  Clara Householder

  Education is the key to preserving biodiversity throughout the world. Not just education, but the environment in which the education takes place. In an attempt to compare the effectiveness of the environmental education program, I surveyed the 5th and 6th grade students at four of the area schools in Monteverde, Costa Rica. I also talked to the teachers about the curriculum and made visual observations of the classroom settings. I found that the Monteverde Friends School, Quaker school, and Creative Learning Center, environmental education school, had better scores than the public or Adventist schools, but that their demographics were very different. The main differences were the ratio of Costa Ricans to non-Costa Ricans and the average monthly income for the families. The CEC and the public school, however, had very similar populations, and different test results. Since children with very similar backgrounds get such different results, it has to mean that something else is influencing them. My results show that the school is the other influencing factor and therefore, that environmental education can and does work.

• 

  Factors affecting arthropod loads on nectivorous phyllostomatidae, September 2002

  Jason Majewski

  Bats are known to host a wide range of both parasitic and non-parasitic arthropods on or around the pelage and wing membranes. The purpose of this study is to assess these macro and microscopic arthropod communities living on nectivorous bats, in an attempt to find patterns of arthropod load frequencies between sexes and among species. Bats were mist-netted at the Monteverde Hummingbird Gallery, for seven nights, with a total of 86 individuals examined from six different species. Macroparasites were counted and recorded; microparasites were then extracted from the bat by means of Scotch tape and aspiration. Analysis of Variance showed significant differences between white mites, bat flies, and total parasite load among Anoura geoffroyi, when compared to other species (white mites, mean = 2.513 ± 2.512, p = 0.0003. bat flies, mean = 6.282 ± 3.456, p = <0.0001. total parasites, mean = 9.395 ±4.126, p = <0.0001). Further, there are significant differences in bat flies, white mites, and total parasites, by sex, with female Anoura geoffroyi showing a significantly greater parasite load (bat flies, mean = 5.091 ± 3.456, p = <0.0001. white mites, mean = 2.333 ± 2.723, p = 0.0008. total parasites, mean = 7.879 ± 5.999, p = <0.0001). As predicted the greater arthropod load on Anoura geoffroyi was found to be directly related to roosting and mating habits.