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.
Prey preference of Megaphobema mesomelas (theraphosidae) in relation to prey abundance and chemical defense
Food preference is an integral part of what defines a species’ niche. Predators within the arthropod community must be able to deal with a variety of anti-predatory defenses. Because spiders vary in their responses to prey defenses, it is difficult to predict how each spider species will cope with them. This knowledge is important because spiders are common in nearly all ecosystems. In this experiment, I studied the feeding preference of Megaphobema mesomelas, a tropical spider of the family Theraphosidae, in relation to the abundance of potential prey species and prey chemical defenses. I found that cockroach nymphs were the most common potential prey item available, but that M. mesomelas typically did not eat this prey, preferring the less abundant crickets instead. I also discovered that the tarantulas prefer the chemically protected larvae of Danaus plexippus over the palatable larvae of Archeoprepona sp. Additional observations led me to the conclusion that prey preference of M. mesomelas is dependent on a combination of ideal factors, including not only abundance, but also texture and speed.
Lycosids, or Wolf spiders, are widespread in many habitats and are important predators on leaf litter arthropods. They are highly territorial yet roam to forage. When they encounter another wolf spider they may fight, flee or court them. To determine whether Wolf spider size or sex determined agonistic or courting behavior, thirty spiders were captured and placed in pairs of male-male, female-female, and male-female for a short period of time. Size was not found to be a determining factor. However, female-female interactions elicited significantly more aggression than either male-female or male-male encounters. Additionally, avoidance was seen as the primary response of the spiders across all pairs. A close second was aggression. This study concluded that same sex spider pairs were more likely to avoid one another than fight and different sex pairs were either more likely to be aggressive or display courting behavior.
Species composition and abundance of bark beetles (Curculionidae Scolytinae) in Cecropia petioles across three life zones in Monteverde, Costa Rica
Cecropia petioles are an ideal habitat for beetle development because the plants are found in various habitats and shed their petioles almost daily. This study was done in order to determine the effects of elevation on the number of bark beetles and species richness found in Cecropia petioles. Petioles were collected from five elevations in Monteverde, Costa Rica from three life zones on the Pacific slope; beetle number and species richness was compared. Elevation was positively correlated with number of beetles and species richness. Also, the larger the petioles had the most beetles and higher species richness. Three distinct species were found: Scolytoides atratus, Scolytoides caudatus and Scolytoides acuminatus. These results suggest a difference in the range of the different species and an intricate system of interaction between the species.
Valerie R. Milici
Forest regeneration will play an important role in the future of tropical biodiversity, as much has been lost to deforestation and continues to be degraded. Terrestrial arthropod composition in a community could be an indicator of succession level as arthropods are a highly diverse phylum and their short generation periods allow communities to adapt to changes much faster than plants or animals. This study tests the changes in community composition of terrestrial arthropods along a successional gradient. Pitfall traps were placed in four sites of varying regeneration, from farmland to old growth. It was found that abundance, species richness, and diversity increased as site age increased. Old growth had higher abundance of Arachnida and Coleoptera, 15-year had higher abundance of Orthoptera and moderate abundance of all other orders, 5-year had overall low abundance, and farmland had high abundance of Hymenoptera coupled with low abundance in every other category. Through this, it was determined that terrestrial arthropod composition does change along a successional gradient and that terrestrial arthropod community composition can be used as a tool to assess succession level.
The adaptive function of leaf fenestrations in Monstera spp (Araceae) a look at water, wind, and herbivory
A very important component of biodiversity in tropical forests is the vast variation in leaf morphology among different plant species. Leaf morphology is often a result of adaptations to the specific environmental conditions of a particular ecosystem or habitat. The Monstera genus of tropical plants in the Araceae family has very unique morphological leaf characteristics; it has large, deeply incised leaves with holes along the primary veins. There are many hypothesized adaptive functions of these holes, but no direct experimental studies have been completed to determine the functions they actually serve. This study directly tests the functional significance of the holes in Monstera deliciosa leaves in Monteverde, Costa Rica for three of the most generally accepted hypotheses: water uptake, wind damage reduction, and herbivory deterrence. The difference between normal Monstera leaves and control leaves with no holes were measured in three different treatments, one for each of the hypothesized important factors. Monstera leaves with holes were found to have a significantly higher amount of water capture by the roots of the plant than the leaves without holes. Holes in Monstera leaves were not found to have a very large impact on the degree of wind damage that a plant endures, and the presence of holes was found to actually increase the level of herbivory on a given leaf. These findings confirm that the holes in Monstera leaves are an adaptive function for increasing water uptake efficiency, but contradict the general consensus that the leaves are also adapted to decrease damage from water and herbivory pressures.
The interactions of herbivory, ant species and Mullerian body production in Cecropia obtusifolia (Cecropiaceae)
Mutualisms are prevalent in every ecosystem. The Cecropia-Azteca interaction is an example of a well-studied and prominent mutualism in the neotropics. Azteca ants act as biotic defenders by attacking herbivores and vines that assault the tree. In return, they receive nutrients from the Cecropia in the form of protein rich Müllerian bodies (MBs) and a place to live in the hollow stem of the tree. It is not a specialist mutualism, and while species show some preference to environmental conditions, multiple species of ants are able to live in one species of Cecropia. Different species of ants have different behaviors which elicit responses from the tree. This study examined how herbivory and rate of MB production of C. obtusifolia varied with ant presence and species. Forty C. obtusifolia in the Monteverde region of Costa Rica were sampled. When ants were present they were collected and identified. Herbivory was calculated for each tree as was rate of MB production. When ants were present, there was about 60% less herbivory than when ants were not present. Herbivory did not differ between species and was not related to MB production, suggesting that the presence of ants deters herbivores but one species is not a better defender than another. There were differences in MB production according to species. C. obtusifolia inhabited by A. xanthochroa produced significantly fewer MBs than when no ants were present on the tree and fewer than other trees with different ant species. I attribute this to the prediction that phloem-feeding coccids that Azteca farm on the inside of the Cecropia, which require the tree to invest more energy in repair and less in MB production, are more abundant in trees inhabited by A. xanthochroa. Cecropia obtusifolia without ants produced more MBs than trees with ants, which could also be due to trees trying to recruit ant colonies for biotic defense. The Cecropia-ant relationship is not as simple as the presence or absence of ants; tree responses vary according to ant species and their behavior.
Katherine M. Johnson
In Monteverde the practice of using non-native garden ornamentals is widespread. This practice could be economically and ecologically costly in the future if these non-native species escape gardens. Because many non-native invasive fruits are dispersed by birds, this study assesses non-native and native fruit species and tropical birds as non-native and native fruit dispersers. To determine whether fruits from an introduced species or a native species were preferred by dispersers and more frequently visited by birds, fruits from, Rubus rosifolius, a common roadside non-native, and Acnistus arborescens a common native garden ornamental were monitored for presence or absence and levels and proportion of ripeness, and number of bird visits. Fruit observations show that the introduced fruits took longer to ripen than the native fruits, they provided a smaller proportion of ripe fruits, but they were taken sooner than the native fruits. Bird visit observations show a significantly higher number of bird visits to the native A. arborescens than the introduced R. rosifolius. This difference can be explained by mammal dispersal agents and depredation by insects. Potential invasive species in Monteverde should be monitored for a better understanding of invasion mechanisms.
Air pollution can affect productivity, communities of organisms, and important biogeochemical cycling in terrestrial ecosystems. Lichens are used as bioindicators to monitor levels of air pollution in the temperate zone, and may be useful in the tropics as well. This study investigated the possibility of using lichen as bioindicators for air pollution in the tropics. Transects were performed to identify lichen community diversity at different sites exposed to low and high pollution from local traffic in the Monteverde area, Costa Rica. Lichen communities at low pollution sites still had higher diversity than high pollution sites (P< 0.0001) due to greater species evenness at low pollution sites. These results suggest using lichen diversity may be an excellent method to assess air pollution in the tropics as lichen diversity is negatively affected by air pollution.
Absence of polarity in trail pheromones and use of sun-compass orientation in leafcutter ants Atta cephalotes
Marc A. Bliss
The complex social system of leafcutter ants, Atta cephalotes (Formicidae) requires a high degree of organization and efficiency to ensure the survival of the colony. This suggests that communication between individuals is both common and intricate, especially during the complicated foraging process. Chemical signaling is employed by returning, laden ants along foraging trails. This study tested for the presence of polar properties within these trail pheromones to convey orientation cues to workers. Using manipulated foraging trails of a single colony in San Luis, Costa Rica, I observed individual ant behavior at different times of day. Rather than finding a correlation between ant direction and pheromone direction, A.cephalotes demonstrated a compass-like ability to navigate in vectors to their colony using the sun for navigation. These results indicate that a complicated navigation system in leafcutter ants, A. cephalotes has developed using light to determine relative position in space.
Abundance and species richness of seedlings in proximity to forest in windbreaks of Cañitas, Costa Rica
Windbreaks are important to agricultural landscapes as well as biodiversity. They may preserve crops and livestock, harbor a diverse seed bank, as well as serve as corridors for forest animals. I examined species richness and density of seedlings within the understory of windbreaks connected to a forest. It was expected that closer proximity to forests would have higher species richness and seedling densities. A total of 220 seedlings were observed spanning across 35 different species and 23 families. The plant families of Lauraceae, Myrtaceae, and Solanaceae were found to have the greatest number of species diversity. Viburnum costaricanum, family Caprifoliaceae, and Conostegia xalapensis, family Melastomataceae, were found to have the two highest abundances of individual species. It was also observed that bird dispersed species, and medium growth tree species were the most abundant. Linear regressions confirmed that species richness increases with closer proximity to the forest, as well as abundance with closer proximity to the forest. This study suggests that attaching windbreaks to forest increases seedling diversity and abundance on the agricultural landscape. The study also proposes that there may be a limit to the distance that animals travel into the windbreaks, which forms a gradient of seedling growth. Therefore, the location of windbreaks is of vital importance.
Air pollution and light exposure: lichen species richness, abundance, and diversity in San Luis, Costa Rica
Lichens are a unique and diverse group of organisms that can be bioindicators of atmospheric pollution. In this study, the effects of atmospheric pollution on lichen abundance, richness, and diversity were determined for lichens growing on rocks and fence posts in San Luis, Costa Rica. Lichens growing on rocks from a secondary forest were subjected to large amounts of ATV exhaust, and the effects of the exhaust on the lichens were observed over 22 days. Lichen species richness and abundance were quantified on fence posts along two sections of dirt road: one with high vehicle traffic and one low. Additionally, canopy cover was determined for these fence posts in order to observe the effects of light exposure on lichen species richness, diversity, and abundance. Atmospheric pollution from vehicle exhaust and/or dust negatively impacted lichen species richness, diversity, and abundance. The mean Simpson Diversity Index was 0.33 +/- 0.28 for posts along the main road with more traffic and 0.48 +/- 0.21 for the side road. Mean percent total lichen cover and species richness were also higher for the side road than the main road. In addition, Lichen species richness, diversity, and abundance decreased as sun exposure increased. Four lichen species were correctly identified on the fence posts, and Heterodermia species 1 and Coccocarpia species 1 had the biggest percent area difference between main and side road fence posts (both 160% higher on the side road), and are therefore better bioindicators of atmospheric pollution than the other two species. These results suggest important implications for determining the sensitivity of specific lichen species to air pollution so that they can one day be used to determine the air quality of a specific region and current air quality monitoring techniques can be improved.
Samuel C. Somerville
The functional properties of buttresses are still debated, but hypotheses include they may be a response to mechanical strain and a method to increase the surface area of the tree base; the increased surface area may provide increased structural support and a larger area of surface soil which may give a competitive advantage for nutrient uptake. The effects of the latter “nutrient hypothesis” and whether it supports a rich community of leaf-litter fauna has not been well-studied. A more abundant and species rich macroinvertebrate community in buttresses could be indicative of a more nutrient rich microhabitat. In this study I sampled buttressed trees on hillslopes in the cloud forest of Monteverde, Costa Rica to determine if the buttress microhabitat supports a greater species richness and abundance of leaf-litter macroinvertebrates. Leaf litter was collected from three zones around each tree: upslope buttresses, downslope buttresses, and an adjacent plot. Both macroinvertebrate species richness and abundance are higher in up and downslope buttress plots than in adjacent plots, although only upslope and adjacent differed significantly. Also, a significantly higher number of larvae were found in the buttress plots. Together, the increased abundance and richness of both adult and larval macroinvertebrates in buttress plots suggest that tree buttresses provide preferable habitat for these leaf-litter fauna.
Change in biodiversity in the inflorescence of Xanthosoma robustum (Araceae) during the flowering period
Sabrina Elizabeth Duncan
Inflorescences of the species Xanthosoma robustum (Araceae) create various microhabitats during the flowering period. This thermogenic plant heats its inflorescence for the purposes of pollination and many organisms such as scarab beetles, mites, and flies come to the flowers to mate and feed during the heating process. Most of these organisms stay in the inflorescence for two days and then fly to the next inflorescence. The purpose of this study is to see if species diversity changes during the three day flowering period and to investigate the relationship between pollinating beetles Cyclocephala (Scarabaeidae) and mites (Acari) that visit these plants. Inflorescences were collected the first and second days following heating, and for one day after heating was complete, for a total of three groups of inflorescences. Species diversity was recorded for each inflorescence day. Results showed that day two inflorescences had the greatest species diversity. There was a higher abundance of both Cyclocephala beetles and mites on day one than day three inflorescences. There was a positive correlation between beetle abundance and mite abundance. These results show that species partition the inflorescence and inflorescence day in different ways. They use different parts of the inflorescence for feeding and mating. This study shows species interactions and niche differentiation in small habitats such as phytotelmata.
Development of cane toad (Chaunus marinus) tadpoles in the presence of intraspecific and interspecific competition under resource limiting conditions
Stefan K. Wheat
Increased competition between and within species of amphibians, resulting from reduced volume breeding pools, represents one facet of climate change’s impact on ecosystem dynamics that remains relatively unstudied. This study examines the effect of competition on the development of larval cane toads (Chaunus marinus) at varying levels of intraspecific and interspecific competition using Lithobates forreri as the competitor. While intraspecific competition was shown to be a significant factor affecting C. marinus growth, the effect was not significant for interspecific competition. However, survivorship was shown to be significantly lower in the presence of high interspecific competition as compared with low competition. These results demonstrate an antagonistic relationship between C. marinus and L. forreri, and suggest that high intraspecific competition—potentially resulting from reduced pond volume—can result in a different and potentially detrimental growth pattern in anuran larvae.
Differences in Atta cephalotes foraging rate and amount of substrate harvested following the introduction of an antifungal agent
Optimal foraging theory dictates animals will behave in the most energetic favorable fashion, maximizing energy gained while minimizing energy lost. However, exceptions do exist, such as mating behaviors and predator avoidance. I show that oat flakes contaminated with antifungal powder, simulating secondary compounds, are selected less and at a lower rate by a colony of Atta cephalotes. This demonstrates the ability of the colony to recognize and discriminate against the contaminant to protect their symbiotic fungus. It also suggests that leafcutters, to an extent, can detect the amount or toxicity of the secondary compound. The willingness of the ants to take the antifungal flakes suggests cleaning is involved, possibly with minims, providing support for the hitchhiking cleaning process. Finally, the harvesting of sub-optimal resources might represent an attempt to sustain yields over an extended period of time. These conclusions suggest that we need to reconsider our current models of Atta cephalotes foraging behaviors for they might be more complex than we currently assume.
Ecotourism is an increasingly popular way to promote and conserve biodiversity. Ecotourism provides a source of income, allowing reserves to promote education and afford protection. The downside to ecotourism is increased human activity, which can have negative impacts on local flora and fauna. I sampled mammal diversity at two sites in the Monteverde Cloud Forest Reserve; one site that is commonly visited by tourists, and one site that is never visited by tourists, using track plots and transects. Mammal abundance and densities were slightly higher on trails frequently used by tourists. However, using the Shannon-Weiner diversity index, I found a significant difference in diversity of mammals between the two trails. The lower impacted trail had a higher diversity (H’=1.689) than the moderately impacted trail (H”=0.254). I concluded that confining ecotourism to limited areas of activity is probably the ideal compromise and is necessary in order to protect the rest of the reserve. The benefits of ecotourism and education in the Monteverde Cloud Forest Reserve are probably worth the negative impacts, so long as the negative impacts are confined to small areas and are managed appropriately.
Su Mei Lai
When risks are present, animals consider the costs and benefits of foraging. This study investigates the preferred feeder positions when potential risks are involved in feeding hummingbirds. Two experiments were conducted in this study in order to have a better understanding of animal risk assessment. The first experiment examined whether there was a preference for high or low feeders in hummingbirds. Results showed that hummingbirds had a preference for higher feeders. Results also showed that hummingbirds have a greater preference to feed from feeders that are closer to trees (outer) than feeders farther away (inner) from trees. The second experiment showed no significant difference in the number of visits of hummingbirds when artificial predators were present versus when they were absent. This indicates that hummingbirds prefer to feed on feeders with the minimal potential risk, which suggests that hummingbirds are able to perceive risk. However, risk presented in this study might not be significant enough to have an impact. This study provides an understanding of foraging behavior in hummingbirds and insights for future studies.
Influence of microhabitat conditions on the abundance of American Leaf Spot Disease (Mycena citricolor) on Coffea arabica
Coffea arabica (Rubiaceae) is extremely important to the agriculture, economy, and culture of Costa Rica. The primary production of coffee centers on the use of ‘shade-grown’ cultivation methods; even though this method yields high amounts of coffee, it also fosters conditions that are optimal for the growth of diseases, such as Mycena citricolor. This study aimed to determine which microhabitat conditions favor the growth of the disease. In addition to proximity to forest, the orientation of fungi spots, placement of the disease on the branches, and presence of an agricultural crop near the plant was recorded. It was determined that there was a greater M. citricolor abundance on C. arabica when plants were located closer to the forest, closer to an agricultural crop, and when it resided on the middle branches of the plant. The study also concluded that the disease prefers westerly facing slopes. On a whole, topographical and environmental factors that produce low-light conditions have a significant effect on the development of M. citricolor; in understanding the impact of these characteristics, farmers are better informed on what microhabitats are most suitable for high coffee production and low disease transmission yields.
Several species of leaf-cutter ants, including Atta cephalotes, exhibit an interesting behavior of hitchhiking minima. Minima are the smallest of the polymorphic castes of leaf-cutter ants and the function and origin of this hitchhiking behavior is not completely understood. There are several hypotheses for this behavior, and the most popular include defense against parasites and cleaning the leaf fragment of contaminants. Studies have investigated some patterns of hitchhiking behavior including different frequencies during day and night and distance from colony. This study examined the relationship between head width, leaf area and the number of hitchhiking minima in A. cephalotes. Ants were collected from a single colony in Bajo del Tigre, Monteverde, Costa Rica. The number of minima, head width, and leaf fragment area were recorded. Ants with mimina present had significantly higher mean head width and carried leaf fragments with greater mean area than those without. This implies that larger ants could require more defenses from parasites or larger leaf fragments contain more contaminants.
Cecropia obtusifolia (Cecropiaceae) has a facultative mutualism with Azteca ants to minimize herbivory. In this study, Müllerian Bodies (MBs), glycoprotein bodies the plant produces to feed its mutualist ants, were systematically removed, from C. obtusifolia. A second study tested at what rate the tree would decrease its production of MB if the ants were restricted from removing them. It was found that removal of the MBs did result in an increase in MB production for two of the five trees in the treatment group. The C. obtusifolia where the ants were restricted from removing the MB, in all but one tree, showed a rapid decrease in MB production in the first few days. The results were also looked at in terms percent canopy cover and herbivory. It was found that plants without ants suffered significantly higher herbivore damage (Mann Whitney U-test, df=1, 2 = 5.51, p<.05). A trend between an increase in percent canopy cover and a decrease in MB production was noted but was not statistically significant. It seems that MB production is a costly process for C. obtusifolia and worth the trade off when they receive the protection from the Azteca ants but when ants are not present they will quickly divert that energy elsewhere.
Cebus capucinus monkeys search for licorice-scented Pipers to use as an insect repellent (Brown 1996). Bioassays measuring mosquito larvicidal activity of six Piper plants were completed in Monteverde, Costa Rica to see if scent is a reliable cue. Overall, there was no relationship between strength of scent and larvicidal activity (Linear Regression F=0.064, P<0.05). The species in the study that exhibited the highest larvicidal activity was Piper auritum, a species that contains the essential oil safrole and has a strong licorice odor. Piper auritum and Piper marginatum (the only species C. capucinus is reported to use) both had a licorice-like scent and together had significantly higher larvicidal activity than the four species tested that lacked the licorice-like scent (Independent Samples T-test t=2.74, DF=15, P<0.05). Altogether these data show that the quality of Piper scent can indicate insect repellent ability but strength cannot. Thus, it makes sense that C. capucinus use scent cues to find effective plant repellents as specific scents can indicate larvicidal essential oils.
Pit-trap construction decisions by wormlions (Diptera Vermileonidae) effects of substrate moisture and larval density
James H. Muldoon
During their sessile larval stage, wormlions (Diptera vermileonidae) provide a unique insight into the importance of habitat selection because their local conditions greatly influence their growth and survivorship. Like their ecological relatives, antlions (Neuroptera myrmeleontidae), wormlion larvae are a sit-and-wait predators that construct conical pits to capture their prey. In this study, I demonstrate effects of moisture on larval pit-trap construction to explain the presence of and potential problems with wormlion aggregations. I found that larvae prefer drier soil conditions, for pit presence and size was negatively affected by large amounts of water. Results suggest larvae lack the strength to manipulate the compact, more water-saturated soil and must wait until soil conditions improved to construct their pits. Because dry spaces are limited in rainforests, wormlion larvae are likely to live in dense aggregations. To determine the effects of varying densities on larval aggregations, I compared the number of pits constructed within high concentrations to that observed in the field. As wormlion density increased, pit establishment decreased. Lower pit success in higher densities may be attributed to both direct and indirect competitive interference.
Tropical forests are being degraded by human activity, leading to the fragmentation and isolation of forest regions. Anthropogenic fragmentation may influence community structure in a variety of ways. This study utilized three variously sized fragments of <2ha, 27ha, and a continuous forest, to determine the differences in species richness, species numbers, and additionally the weight in Peromyscus mexicanus (Cricetidae). Fifty seven individuals comprised of five species of rodents were trapped throughout the study. The results indicate that a larger fragment will contain a greater number of individuals than a fragment with less area. However, fragment size does not seem to affect species richness in any clear pattern. Average specimen weights, although not significant, show some trends between sites and between sexes.
The quality, quantity, timing, and placement of nectar can impact pollinator behavior. Here, I investigate the impact of the distribution of nectar in a patch: random, regular and clumped treatment. A 5 x 5 spatial grid was setup using wooden stands and Lantana camara inflorescences in the Monteverde butterfly garden. Nectar was added to 6 flowers in 8 of 25 stands, resulting in 8 stands with and 17 without nectar. Butterflies visited nectar and non-nectar stands equally in all three patterns. However, when comparing non-nectar stands across all treatments, the regular treatment decreased total butterfly visits to non-nectar stands (151visits) and the random treatment increased total butterfly visits to non-nectar stands (215 visits) (chi-square=11.24, df=5, p=0.0468 ). Also, non-nectar stands had a higher average number of flowers visited per stand (5.95 ± 0.306) than those with nectar (5.08 ± 0.361 visits ). Moreover, the rank of visit length (1-5) was longer on nectar stands (1.92 ± 0.091) than non-nectar stands (1.62 ± 0.083). Distance moved within the grid (regular 1.5 ± 0.092, clumped 1.6 ± 0.086, random 1.5 ± 0.078) and off the grid was not impacted by pattern type. In brief, Heliconius butterflies do not demonstrate strong preferences between nectar and non-nectar flowers in a closely spaced, high density pattern. The distribution of nectar in small patches has little impact on pollinator behavior, perhaps because inflorescences are so closely spaces that there is no benefit to differentiate between them.