Monteverde Institute: Tropical Ecology and Conservation

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  Anthropogenic impacts upon neotropical mammal communities, November 2004

  Holle Harjer

  Human fragmentation of tropical rainforests greatly affects animal populations and ecosystem composition. In this study the effects of fragmented secondary forests upon mammal diversity and species richness and continuous secondary forests were examined. Track records and visual observations were made for three habitats including the interior secondary forest, forest edge and disturbed areas. Results showed a higher diversity in the more connected Monteverde habitats than in the fragmented San Luis area. Greatest diversity was exhibited in forest edge habitats for both Monteverde (H = 2.71) and San Luis (H = 1.91). Species overlap and community similarity was also greater in the Monteverde region (Cs > 0.60).

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  A protozoan parasite in wild and captive monarch butterfly populations near Monteverde, Costa Rica, November 2004

  Joanna Hsu

  Although the protozoan parasite Ophyrocystis elektroscirrha was first recovered from Danaus plexippus (Nymphalidae: Danainae) and Danaus gilippus populations in Florida in 1966 and has since been found in many other monarch and queen populations worldwide, no previous studies have shown that this parasite infects butterflies in Costa Rica. This study is the first to do so, documenting the occurrence of Ophryocystis elektroscirrha in a wild and butterfly garden population of D. plexippus near Monteverde, Costa Rica. Although only a few infected individuals were found in both populations, there was a stark contrast in the number of parasites per individual between the two populations. Infected individuals in the captive population had much higher parasite spore loads, 679 and 944, compared to the spore loads of seven and three found in the two infected individuals in the wild population. This finding is significant because only monarchs with high parasite loads suffer decreased fitness and increased mortality. This study raises the possibility that captive monarch populations can serve as a source of disease to wild monarch populations that are healthy. However, simple measures can be taken to ensure that butterfly garden monarchs are free from heavy O. elektroscirrha infections, which ensures the health of the captive population and safeguards that of the local wild population.

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  Butterfly proboscis length and pollen load, November 2004

  Charles McCanna

  Pollination mutualisms between plants and pollinators facilitate increases in genetic variability for plants while providing rewards for pollinators. Specialization of pollinators on specific plants has occurred to maximize benefits of these pollination mutualisms. With this specialization, pollination syndromes have evolved that increase a flower’s chance of eliciting visitation of a specific pollinator. For example, “butterfly flowers” have evolved bright colors, short to medium corollas, and strong scents that tend to attract butterflies. However, some of these flowers have evolved long corollas to specialize on long proboscis butterflies. The purpose of this study was to examine the effect of corolla length on degree of pollen specificity in butterfly pollinated flowers. This was completed by observing proboscis length of butterflies and the corolla lengths of flowers visited. A total of 54 butterflies of 29 different species were collected from a fragmented Lower Montane Moist Forest in Cañitas, Costa Rica. Following removal and measurement, proboscises were observed under a microscope for pollen grains of 24 different species of flowering plants. Proboscises of lengths less than 10 mm were defined as short proboscises. Butterflies with proboscises greater than 17 mm were defined as long proboscis butterflies. Butterflies with long proboscises had a greater pollen species richness, often twice that of small proboscis butterflies. Pollen from long corolla and short corolla flowers was found on all lengths of proboscises. Pollen loads on proboscises suggest that pollination by butterflies is not specific in this community. This non-specificity of butterflies on flowers has ecological and evolutionary effects on community composition and stability.

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  Changes in avian communities in the San Luis Valley, Costa Rica, November 2004

  Nicholas Kovacs

  In this experiment, avifauna of the transformed Costa Rican premontane moist forest was censused using fixedradius point counts within three habitats. Species abundance for all observed birds was calculated based on these observations. Study sites included pasture and fragmented secondary forest. Species abundance was compared to previous values known for the area from a 1993 study. For the 51 species observed in the area, 31 showed frequency changes. Twenty-six of the 31 were negative declines, and five showed positive increases in population. Four species declined from common to rare, three species declined from fairly common to rare and two new species were added that were not in the previous study. Almost all birds that declined relied on forest habitat. The species that showed positive increases generally were not habitat specific. Local and global changes help to explain differences depending on habitat requirements, altitudinal ranges and migratory status.

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  Comparison of protist communities in native and exotic bromeliad species, November 2004

  Michelle L. Rhoney

  In this experiment, I compared protist community and composition found in the tanks, or phytotelmata, of a native bromeliad species, Vriesea werckleana, and an unidentified exotic species. This study was conducted in Monteverde, Costa Rica, near the Estación Biológica Monteverde, between October 22 and November 11, 2004. Samples were taken from 20 individuals of each native and exotic species. The protist species composition and abundance were determined for each individual bromeliad. Local, regional, and metacommunity composition were evaluated and compared. Local (alpha) richness was the average of the protist communities, whereas regional (gamma) richness (or metacommunity) was the sum of all species and diversity indices across all 20 tanks, either native or exotic. The results showed no significant difference between the local composition and diversity of protist communities in the native and exotic species of bromeliads: The average number of protist species (S), number of individuals (N), Shannon-Wiener Diversity Index (H’), and two other diversity indices were the same in both bromeliad species. On the contrary, the metacommunities of protists in the two bromeliad species were different in that the total number of individual protists, H’, Evenness (E) and two other diversity indices were higher for the exotic species. Therefore, exotic bromeliads have greater regional richness and can support larger, more diverse communities. One reason as to why exotic bromeliads harbor greater regional richness may be due to the exotics being closer to one another. The Unified Theory of Biodiversity (Hubbell) asserts that systems of communities are bi-directionally connected via immigration and emigration. Therefore, local communities affect each other and create metacommunities with connectivity. It is important, however, to further explore interactions between protist communities within native and introduced bromeliads because exotic protist species may disrupt native protist species interactions if they are dispersed to native protist communities.

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  Discharge and drift of benthic macroinvertebrates in a tropical montane stream, November 2004

  Megan Moore

  Several studies in temperate regions have observed an active behavioral response of stream invertebrates to environmental factors. However, few of these studies have been conducted in the tropics and the behavior of tropical stream invertebrates is unknown. In an attempt to improve the knowledge on tropical stream ecology, this study observed indirect behavioral responses to discharge within the drift as well as the benthic macroinvertebrate community. Drift, benthic, and discharge samples were taken at 11 sites along the Quebrada Máquina from October 28-November 13 of 2004. The drift community richness and diversity and discharge resulted in a non-significant, negative trend. However, the benthic community richness and diversity and discharge resulted in a significant positive correlation. Further analysis showed that drift and benthic communities were similar in composition, implying that the drift community arises directly from the benthic community. The positive correlation of the benthic community to discharge suggests that, similar to temperate macroinvertebrates, tropical macroinvertebrates actively respond to discharge.

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  Effects of coffee agroecosystems on moth diversity in San Luis, Costa Rica, November 2004

  Nathaniel Talbot

  The majority of Costa Rica’s primary forests have been fragmented and converted to agricultural landscape. Fragmentation studies based on Island Biogeography Theory and Hubble Unified Theory typically view the degraded area surrounding forests as uninhabitable, however, most agroecosystems actually serve as viable habitat to a subset of natural communities as well as a number of colonizing species. As a follow up to Rickets et al (2000) who studied moths in a tropical, agricultural landscape, this study focuses on how moth diversity is affected by coffee plantations in San Luis, Costa Rica. Moths were collected from three sites: a forest, a sun-grown coffee farm and a coffee farm grown shaded banana trees. The samples were then divided into morphospecies and many were identified to family. Shannon-Weiner diversity indices found species diversity to be highest in forest (H'=4.256), lowest in shade-grown coffee (H'=3.413) and intermediate in sun-grown coffee (H'=3.863). Multiple comparisons determined all three sites significantly different in diversity. Beta diversity was highest between forest and shade-grown coffee(0.309), intermediate between forest and sun-grown coffee(0.358), and lowest between the two coffee farms (0.418). The forest also had a larger representation at the family level along with rarer species. These results give many implications as to how effectively agroecosystems harbor biodiversity and whether this is due to structural or geographical dynamics.

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  Effects of competition on copulatory behaviors in Pseudoxychila tarsalis (Coleoptera: Cicindelidae), November 2004

  Hilary Wilson

  This study examines the effects of competition on copulatory behaviors of the tiger beetle Pseudoxychila tarsalis. I tested the hypothesis that copulatory behavior of a P. tarsalis mating pair in the presence of an additional male would induce significant behavioral changes, including longer amplexus time and increased frequency of a variety of copulatory behaviors. Trials were conducted with either one male and one female, or two males and one female, and the behaviors of one copulatory amplexus recorded per trial. No statistical differences were found for the male behaviors of time until mount, amplexus duration, or number of intromissions, but means tended to decline in each for the two-male trials. Rocking and tapping behaviors in males decreased significantly in the presence of a second male, indicating a response to competition. The general downward trend in the two-male trials may be explained by interruption of copulatory behaviors by the non-copulating male. Female batting showed a slight but not significant increase in the presence of a second male, which may be intended as a deterrent so that she may gain access to the second male.

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  Effects of fragmentation and human disturbance on mammal communities in San Luis and Monteverde, Costa Rica, November 2004

  Lindsay Crawford

  Mammals occupy important roles in tropical ecosystems and can often be keystone species, controlling the composition of their communities. This study compared mammal communities in Monteverde and San Luis, Costa Rica, two regions that differ in their current and historical patterns of fragmentation. Three habitats per region, representing a disturbance gradient, were surveyed using scent stations. Prints as well as visual observations were recorded. No significant differences were found in species richness across zones or across habitats. However, overall diversity was consistently higher in Monteverde and locally highest in edge habitats in both regions. Local richness patterns (across habitats) follow the Intermediate Disturbance Hypothesis and show that edge habitat acts as an area of overlap between disturbed and intact habitats. San Luis’s reduced diversity is attributed to a skewed composition and distribution of species due to fragmentation and increased pressure exerted by the largely agricultural community. This study points to the conservation benefits of large, continuous reserves and reports on the current and future threats of fragmentation and disturbance to mammal communities.

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  Epiphytic lichen communities on Ficus spp. microhabitats in relation to canopy density, November 2004

  Tom McFarland

  The purpose of this study was to determine if and how much forest canopy density affects the richness and composition of epiphytic lichen communities in Tropical Premontane Moist Forest. Lichen communities on the trunk and in the canopy on nine Ficus trees were examined. Friedman’s test was used to assess differences in lichen richness along a vertical gradient on trees, and Spearman rank test was used to look for a correlation between canopy density and lichen richness. Average habitat breadth between zones and between trees was also calculated. The results showed that there are significant differences in lichen richness across zones (Freidman test, P = 0.01, N = 7), but no significant correlations were found between canopy density and any individual zone or canopy density and total lichen richness on trees. Lichens were found to have similar average habitat breadth within (average habitat breadth = 2.24) and between trees (average habitat breadth = 2.42).

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  Evidence for floral mimicry in Epidendrum radicans (Orchidaceae) with Asclepias curassavica (Apocynaceae) and Lantana camara (Verbenaceae), November 2004

  Sarah Dupre

  Floral mimicry may occur between plant species with geographic overlap, similar flowering times and a shared set of pollinators. To demonstrate mimicry in such species, visitors must enhance fitness of individual flowering plants. This study focuses on potential floral mimicry for a Neotropical roadside weed, Epidendrum radicans (Orchidaceae), which produces no nectar but resembles nectar-producing, sympatric and phenologically similar plant species, Asclepias curassavica (Apocynaceae) and Lantana camara (Verbenaceae). Twenty pollinia of E. radicans were placed in four different groups. One containing the orchid alone, the second consisting of the orchid and A. curassavica, the third consisting of the orchid and L. camara and the fourth group containing all three species. Proximity to L. camara increased butterfly visitation in E. radicans nearly four-fold and more than doubled visitation when near A. curassavica (Friedman Test, Chi-squared = 22.23, df = 3, p = 0.0001; MCN Test, q = 5.962, df = ∞, p < 0.05). Likewise, pollinia removal increased as a result of proximity to both A. curassavica and L. camara (Friedman Test, Chi-squared = 24.825, df = 3, p = 0.0001; MCN Test, q = 6.261, df = ∞, p < 0.05). Simply doubling E. radicans flowers in monospecific groups to the same total flower number as mixed patches had no effect on visitation nor pollinia removal. Hence, the experiments presented here support the case for floral mimicry in E. radicans, though its impact on wild populations remains in doubt.

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  Foraging patterns of male Tiaris olivacea (Yellow-Faced Grassquits) in different flock sizes, November 2004

  Chai Blair-Stahn

  Flock sizes can have both positive and negative consequences on foraging time of birds. It has been shown that increased flock size decreases any given bird’s time spent scanning for predators and will allow them to increase their foraging time. In this paper I study male Tiaris olivacea (Yellow-faced Grassquits) in different flock sizes in the San Luis Valley, Puntarenas, Costa Rica. A total of 21 groups of T. olivacea were recorded in sizes of 1-50. No significant correlation was found between group size and time spent foraging by males when all data points were analyzed (p = 0.0553, R squared= 0.18), but when an outlier point was removed (group size = 50), a significant positive correlation was found (p = 0.0045, R squared = 0.3685). It appears that an increase in group size benefits male T. olivacea because it reduces the time they must spend scanning for predators and increases foraging time.

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  Fungal community diversity and composition on logs in relation to log size and penetrability, November 2004

  Janaki Patel

  Very little is known about how macrofungal communities on logs vary depending on different log characteristics. This study tested whether macrofungal communities on logs in premontane wet secondary forest in Monteverde, Costa Rica, vary significantly with changes in log size and penetrability. Additionally, this study determined the regional species diversity and turnover of macrofungal communities on logs, and determined whether there were trends between groups of macrofungal species growing on logs of different degrees of penetrability. One hundred logs with macrofungi were sampled randomly and measured for size and penetrability. The fungi on each were recorded according to morphospecies. A total of 57 morphospecies were found, with the shelf fungus Hexagonia papyracea being the most common. There were no significant relationships between the number of species per log and log penetrability, or between the occurrence of H. papyracea and log penetrability. However, H. papyracea occurred on logs with smaller diameters, and the number of species per log increased as a function of log diameter. There were also trends indicating higher species turnover with higher penetrability. The results suggest possible community succession and host specificity among macrofungi that colonize logs, but further research is necessary to determine which log characteristics are important to host-specific macrofungi.

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  High variation in impact in point source pollution on water quality and macroinvertebrate communities in a tropical highland stream, November 2004

  Sarah A. Gruber

  This study measured the water quality around four different point sources of pollution along the Río Guacimal in Monteverde, Costa Rica. To get a complete view of the water quality both biotic and abiotic factors were measured: by collecting macroinvertebrates and testing for seven different biochemical properties. The macroinvertebrate community makeup of the Río Guacimal was dominated by flatworms and commonly included segmented worms, which are absent in pristine streams of the Monteverde area (Moore 2004). A Family biotic index (FBI) (Resh et al. 1996) was used to determine the health of the water according to the macroinvertebrate composition. The FBI indicated that water quality varied from site to site, but was typically good at sites that were spatially distant from point sources of pollution. All sites below point sources of pollution had lower water quality with the farthest downstream site having the worst. Nitrate, phosphate, ammonia, dissolved oxygen, pH, and turbidity levels were measured for abiotic factors along with water temperature. Of the abiotic factors tested, dissolved oxygen, turbidity, and water temperature significantly differed (Friedman, tied p-value < 0.05) between sites. The results of the abiotic factors paralleled the marcroinvertebrate results, with the site that had the greatest distance from point source pollution consistently having healthier values and the farthest downstream site having less healthy values. It is believed that there is thermal pollution which is increasing temperature in the lower site and consequently is decreasing the dissolved oxygen values. Increased turbidity is believed to be from inputs carrying particulate matter. The stream biochemical properties suggest that the river is capable of recovering fairly quickly from point sources, thus giving it greater resilience. The FBI values show that the biotic community also has resilience, although it is more sensitive to perturbations.

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  Host tree dispersal method and community composition of vascular epiphytes, November 2004

  Kathleen White

  The pattern of epiphyte distribution along host trees is a function of many variables. This study examined how the dispersal syndrome of the host tree affected the composition of epiphyte dispersal syndromes in that tree. It was expected that a host tree species bearing bird-dispersed fruits would harbor more epiphytes exhibiting the bird-dispersal syndrome than a tree that has fruits eaten by terrestrial mammals. Two species of host trees were surveyed, Inga sierrae, a tree with terrestrial-mammal dispersed fruits, and Sapium glandulosum, a tree with fruits that are bird-dispersed. Nine of each tree species were sampled. The tree with terrestrial mammal-dispersed fruits contained significantly higher numbers of epiphytes whose fruits are dispersed by birds, while there was no significant difference in numbers of epiphytes with wind- dispersed seeds between the two species. This unexpected result may be due to the differing architecture between the two tree species studied.

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  Ithomiinae visitation to a source of Pyrrolizidine Alkaloids (Ageratum cf. reedii) and proximity to mating leks, November 2004

  Katrina Welch

  Ithomiinae butterflies are protected from predation by pyrrolizidine alkaloids. These compounds are acquired as adults primarily from nectars, and, in the case of females from males via spermatophores. Nectar sources are most common outside of the forest, where Ithomiine collect in large aggregations, called leks, where mating occurs. In these leks males also use PA’s as precursors for mating pheromones. Visits to floral sources of protective compounds by Ithomiinae butterflies is 90-99% male (Drummond 1976). Three hypotheses explain this phenomenon. 1) females are constrained to obtain these pyrrolizidine alkaloids (PA’s) from males via spermatophores passed while mating, 2) females prefer to remain in forested mating aggregations (leks) rather than visit open areas where most nectar sources occur and predation risk is likely greater, and 3) males must visit floral sources more often, as they use PA’s as precursors for mating pheromones and then pass them to females in mating. To test these hypotheses, floral baits known to contain PA’s (Ageratum cf. reedii, Asteraceae) were placed in the center of a mating lek, at varying distances away from the lek in two directions, towards pasture or primary forest. Female Ithomiines were only found within the mating lek, possibly as a result of higher risk aversion there. Male Ithomiinae were more abundant on the A. cf. reedii than females, perhaps due to their dual use of pyrrolizidine alkaloids for both defense and mating. Abundance was highest in the center of the lek and gradually decreased as geographical distance increased. This pattern was only offset in an outlier site approximately 1600m away from the general area of study. Although abundant, species richness in site eight was particularly low. This may suggest that species found in the outlier site were from a different population.

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  Macroinvertebrate communities and streambed substrates of a dammed stream in Monteverde, Costa Rica, November 2004

  John Robert Rancourt

  The purpose of this study was to determine how the dam placed in the Quebrada Máquina, Monteverde, Costa Rica, affects the abundance, richness, and diversity of benthic macroinvertebrate communities. Samples were collected from 20 sites, 50m upstream and downstream of the dam. The relative percentage of streambed substrate composition was also documented at all test sites. There were significant decreases in Order richness and diversity as absolute distance from the dam decreased. In addition, the substrate composition was found to be homogeneous for sand directly upstream of the dam. This leads to the conclusion that the dam has created a buildup of sand, thereby decreasing richness and diversity, by means of destroying suitable habitat.

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  Mucuna urens dispersal by agoutis (Dasyprocta punctata) in the Monteverde area of Costa Rica, November 2004

  Melissa Senf

  Mucuna urens (Papilionaceae) is a large-seeded liana that is largely dispersed by scatterhoarding mammals. Agoutis (Dasyprocta punctata) are one of the most common scatterhoarding dispersers in Costa Rica and are a known disperser of M. urens. D. punctata in two locations in Monteverde, Costa Rica, were presented with 203 flagged M. urens seeds, in groups of twenty, over a period of 16 days. The seeds were recovered after the D. punctata had cached them or the flags were collected for those eaten. There was no significant difference between the number of seeds eaten and the number of seeds cached (p = 0.385 Scheffee). The weight of the cached seeds did not significantly change during the caching process, indicating that no consumption occurred before caching (Paired t-test, p = 0.0550). D. punctata did not preferentially choose bigger or smaller seeds for hoarding or consumption (ANOVA, p = 0.5765). The D. punctata cached most of the seeds within 20 m of the site (x = 5.49) in a contagious or clumped pattern. Although D. punctata did not disperse seeds a great distance from the site, they did cache viable seeds away from the parent tree and may play an important part in seed dispersal.

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  Soil microfungi in the forest-agricultural landscape of San Luis, Costa Rica, November 2004

  Ellyn Yakowenko

  Soil microfungi are known to play key roles in ecosystem function and are often the first indicators of a breakdown in stability (Volk 2001). This study compares soil microfungal abundance and diversity across a tropical human land use gradient in the San Luis valley of Costa Rica. Microfungi were cultured from soil samples collected from primary forest, secondary forest, pasture, and coffee farm sites using the Soil Dilution Plate Technique (Christensen 2001). Thirty-six soil samples yielded a total of 17,321 isolates of 41 different morphological species. Each habitat type was characterized by the dominance of a few abundant species while the rest of the community was comprised of an extensive number of ‘rare’ species. Differences in species richness and diversity across habitats were found to be statistically significant: secondary forest sites were found to be the most diverse (H’= 2.213, S = 33), followed by coffee farm (H’= 1.113, S = 24), pasture (H’= 0.506, S = 21), and primary forest sites (H’= 0.314, S = 26), respectively. In contrast to previous studies on microfungal diversity (Cabello and Arambarri 2002), this study determined that intermediate to high levels of soil disturbance caused by human land use actually may facilitate microfungal diversity in the tropics, instead of hindering it.

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  Stream site selection of Hyalinobatrachium fleischmanni (Centrolenidae), November 2004

  Alicia Ward

  Census work and habitat analysis for the glass frog species Hyalinobatrachium fleischmanni was performed on four streams in Cañitas and Monteverde, Costa Rica. At each of six sites, the habitat occupied by H. fleischmanni was contrasted with a nearby, paired site where individuals were absent. Seven habitat parameters were investigated: water quality based on dissolved oxygen and phosphate content; water speed; discharge; distance from human development; extent of canopy cover; and presence or absence of common monocots (Zingiberaceae: Hedychium coronarium, Costaceae: Costus spp., Musaceae: Musa acuminata). No statistically significant differences were found between Occupied and Unoccupied locations though patterns suggested a preference for sites with faster water speed, greater discharge, and higher levels of dissolved oxygen. No gradients in group size based on habitat characteristics were observed. Population densities found in this study compared to densities reported by other sources and past studies showed an increase in density. This is especially significant in light of drastic frog population declines in past years in the Monteverde area.

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  The effects of edge and pollution on lichen richness, abundance, and distribution in Cañitas, Costa Rica, November 2004

  Jenny Bedell-Stiles

  Lichens are commonly known to be biological indicators of pollution and edge effects. Their use as indicators in temperate regions is well documented, however, less is known about their function as a bioindicator in the tropics. There is also debate over the consequences of edge effects, such as increased temperature, and less moisture and wind, on lichen richness and abundance. In this study lichen communities on tree trunks in three habitat sites (primary forest, pasture, and roadside) were examined. In total 88 trees were censused in order to determine lichen richness, abundance, and similarity. Overall 68 species of lichen were observed. The pasture site demonstrated the highest total number of species (42), average number of species (5.97), and average abundance (28% coverage). In contrast, the road showed the lowest total number of species (16), average number of species (2.39), and average abundance (.37%). It was speculated that these trends were due to the strong effects of edge and air pollution, however, these factors were not directly measured. The moist primary forest site appeared to have moss competing with lichen for area on the tree trunk, possibly limiting the number of species and abundance of lichen in that site. The highest similarity between sites was observed between the pasture and roadside, most likely due to the similarity of these two environments. Both were subject to edge effects, however the road had the additional pressures of air pollution and dust.

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  Trail fidelity in Atta cephalotes, November 2004

  Amy Romer

  Trail fidelity in Atta cephalotes was tested through marking experiments by comparing the movement of 500 marked workers that were removed but replaced on the same trail with the movement of a separate group of 500 marked workers that were displaced to a new trail. Trail fidelity was very high for replaced workers: 94% of workers observed at a census 24 hours after marking remained on the original trail. Trail fidelity was such a strong force in displaced ant behavior that by 24 hours after marking 74% had returned to their original trail. This indicates that worker ants are orientated to a specific trail within the colony, most likely due to orientation cues such as trail specific pheromones. Rate of disappearance of workers from their original trail was compared between replaced and displaced moved workers to illustrate that once displaced, ants return to their original trail, exhibiting similar trail movement behavior to the replaced ants. Lastly, the distance from the original trail to the new trail was significantly correlated with the proportion of switched ants returning to their original trail by 24 hours. (Spearman rank correlation, Rho = -0.8982, P = 0.0024, n = 8). This may suggest that orientation cues for specific trails are weaker with increased distance from the trail opening, reducing the number of ants able to return to their original trail.

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  Vertical stratification of hummingbird pollinated plants in relation to corolla length, November 2004

  Eleanor Gordon

  For members of feeding guilds to co-exist in the same community, species must partition niches to avoid competition. In Tropical Lower Montane Wet Forest, hummingbirds are an important and numerous pollinators, suggesting a large number of niche partitioning mechanisms. Hummingbirds are often tightly co-evolved with the plants they pollinate, having bill lengths corresponding to the length of the flower they pollinate. It is proposed in this study that there is a relationship between heights of hummingbird pollinated plant and length of flower corolla. It is hypothesized that short corolla flowers will exist in some strata and long corolla flowers in other strata. This would indicate vertical microhabitat partitioning of hummingbird resources. This study measured vertical height and flower corolla length of 18 hummingbird pollinated plant species in the Monteverde Cloud Forest Preserve (MVCFP) and Biological Station forest in Costa Rica, covering ~ 40,000m squared. Simple linear and polynomial regressions of plant height and corolla length showed no significant correlation. This suggests that vertical microhabitat partitioning is not affecting hummingbird-pollinated plants and that other mechanisms for niche partitioning in hummingbirds, such as differences in foraging behavior, account for the ability to co-exist. This study also examined flowering phenology of hummingbird-pollinated plants in the MVCFP. The number of flowers in bloom on each species was recorded for the 28th of October and 7th and 15th of November in ~16,000m squared area. This data was compared to October and November flowering phenology data from 1981-2 (Linhart et al. 1987).

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  Worker size, load mass, speed, and foraging efficiency in Atta cephalotes, November 2004

  Zaynab Rezania

  Optimal foraging models have been utilized extensively in the analysis of foraging behavior. Applied to the leaf-cutter ants, Atta cephalotes, these models may identify variables that affect individual and colony foraging efficiency. One colony of A. cephalotes in Cañitas, Costa Rica, was studied to determine the relationships between ant size, load mass, foraging speed, and efficiency. Head width, foraging speed, and load mass were measured for 150 individuals, and efficiency and load/ant size ratio were calculated. The relationships between these variables were analyzed using linear and logarithmic regressions. Ant head width and load mass showed a positive relationship (p < 0.0001), as did head width and foraging speed (p < 0.0001). There was no significant relationship between load mass and speed when individuals of all head sizes were included in a linear regression, however, when separated into small, medium, and large head size groups, linear regressions showed a significant relationship for the small (p < 0.0001) and medium size groups ( p = 0.0007). There were positive correlations between ant head size and efficiency (p < 0.0001), as well as between load mass and efficiency (p < 0.0001). Ant head size and the load/ant size ratio also showed a positive relationship (p < 0.0001). These results indicate that larger ants achieve greater foraging efficiency than smaller ants. In addition, it may be more efficient to transport heavier loads, despite their negative effect on foraging speed. There are many compromises involved in optimal foraging models, as increasing one aspect of efficiency may reduce another.