One of my passions is the biological world around us. I grew up watching Steve Irwin explore rainforests and coral reefs all around the world, and have been in love with biology ever since. The Biology Foreign Study Program brings Dartmouth students to the tropics to conduct scientific research in the rainforests of Costa Rica and the coral reefs of the Cayman Islands. It was the most magical experience I have ever had and a dream come true. We have so much to learn from the natural world. Some of the most ingenious ideas have already been invented by nature, and all we as engineers have to do is look around to find them.
Each week, we arrived in a new site and began asking questions about what we saw around us. We came back as a group and narrowed down our questions to a short list of the most interesting potential avenues of research. We then split up into small groups of 2-5 and conducted a week-long research project to try and answer our chosen question.
Each project had about 3 days of data collection in the field, which varied from quiet observation to grueling hypothermic hikes to sample species. After overcoming or sidestepping the inevitable roadblocks, we returned to the lab to analyze our data in JMP and R.
After analyzing the data, we drew conclusions and wrote a full-fledged scientific paper detailing our introductory framework, our methods, our results, and our conclusions. These papers were peer and faculty reviewed, then published in Dartmouth’s Biological Foreign Studies Journal.
The following abstracts are from each of the projects that I was a part of during the trip.
ANTLION CAPTURE EFFICIENCY, PIT MORPHOLOGY, AND SUBSTRATE TYPE
Abstract: There are two main ways that foraging efficiency can be optimized: minimizing time spent foraging or maximizing energy return from foraging. Antlions (Family Myrmeleontidae) are larval lacewings that capture prey in funnel-shaped pits of sand. This unique foraging strategy works to maximize returns from foraging, but it is less clear if it also minimizes energy expenditure. While previous studies suggest that larger body sizes allow antlions to capture larger prey, larger body size should also allow for shorter capture time. Previous studies have shown that antlions have a preference for finer-grained substrates, suggesting that capture time should be affected by substrate type as well. We conducted an observational study that measured and compared pit diameter and antlion body size in the field. We also conducted an experiment that tested the interaction of pit morphology, capture time, antlion size, and substrate type. We found that larger antlions formed pits with greater diameters and had lower capture times irrespective of the slope of the pit or substrate type. Our study raises new questions regarding the factors informing substrate preference and suggests that antlion foraging behavior also minimizes energy expenditure.
ANALYSIS OF RISK IN THE FORAGING STRATEGIES OF HUMMINGBIRDS IN MONTEVERDE CLOUD FOREST
Abstract: Both the mean and variance of energy reward can impact the foraging strategies of organisms. Risk-averse foragers preferentially select food sources that provide a reliable reward in order to consistently meet their daily energy needs. Conversely, risk-prone foragers should preferentially feed on food sources with a variable reward searching for a high payoff. Hummingbirds (family Trochilidae) have one of the highest daily energetic demands of any animal due to their high metabolism. A few studies suggest that hummingbirds have a risk-averse foraging strategy, but this pattern is not well-established. Based on hummingbirds well established preference for red flowers, we predicted that flower color may be a useful visual proxy for nectar variation in flowers. We therefore hypothesized that red flowers should be correlated with a more consistent food reward and that hummingbirds should employ a risk-averse foraging strategy by preferentially feeding from red flowers. We measured the nectar content of three species of red and three species of purple flowers, and investigated hummingbird preference with a reciprocal transplant experiment. We found that red flowers correspond to more consistent nectar rewards whereas purple flowers have a higher variance nectar reward, though this trend was not statistically significant. We also found that, given a choice between red Callistemon spp. (Bottlebrush) and a purple Stachytarpheta frantzii (Porterweed) in the same location, hummingbirds preferentially fed from the red Bottlebrush flowers. Bottlebrush flowers had a significantly lower variation in sugar concentration than the Porterweed flowers. These results imply that hummingbirds may use color cues as a mechanism to employ a risk-averse foraging strategy.
INFLORESCENCE INVESTMENT IN ALNUS ACUMINATA
Abstract: Organisms in the tropical rainforest must allocate resources and energy in order to survive in such a highly competitive, light-limited environment. For pioneer species like the alder tree (Alnus acuminata) the threat of competitive exclusion begins once the environment becomes suitable for more competitive species. As a monecious plant, the alder tree produces both male and female sex organs (inflorescences), with male inflorescences being less energetically costly to produce. Thus, in order to resist displacement in post-pioneer environments, alder may alter its resource allocation to favor male inflorescences in order to conserve energy. We hypothesized that light limitation would prompt a change in resource allocation which would favor the production of male inflorescences. We found that canopy position influenced the sex ratio of inflorescences, with understory trees producing exclusively male inflorescences while canopy trees produced a combination of both sexes. Our data did not explain the variation in the sex ratio among canopy trees, but suggest that light availability is a factor that influences resource allocation in the alder tree.
RISK-AVERSION AND EFFICIENCY ALONG A DISTANCE GRADIENT OF A CENTRAL PLACE FORAGER (ATTA CEPHALOTES)
Abstract: Central place foraging theory seeks to explain the strategies used to maximize energetic gains in organisms that forage and return regularly to a central location. Studies in this field consider the trade-offs in foraging strategies such as tendencies toward either range maximization or risk-aversion. Eusocial insects like leaf-cutter ants (Atta spp.) are often studied in the context of central place foraging theory due to the complexity of their foraging behavior. Our study explored this behavior by examining the interaction between distance from colony and ant foraging efficiency. We determined that ant foraging efficiency increased near the end of a given trail. Between trails, however, efficiency at the end of a trail decreased as total trail length increased. A decrease in efficiency far from the colony suggests that leaf-cutter ants minimize risk by maintaining their most efficient workers nearer to the colony.
PHENOTYPIC PLASTICITY IN PENTAGONIA MONOCAULIS
Abstract: Phenotypic plasticity is a measure of how much an individual’s phenotype can change in various environmental conditions. Light and herbivory in tropical forests drive plant adaptation and can influence phenotypically plastic traits. We studied phenotypic plasticity in Pentagonia monocaulis, a plant whose young leaves express anthocyanin, an anti-herbivory secondary metabolite that fades as the leaves mature. We found that anthocyanin concentration in young leaves is phenotypically plastic in relation to differential light availability, while chlorophyll content, leaf toughness and leaf size in young leaves are all phenotypically plastic traits related to differential herbivory. We also found that plants exposed to greater herbivory rates will produce tougher new leaves that contain higher chlorophyll content, but do not trade-off this investment of energy allocation for red leaf intensity. While phenotypic plasticity as found in the Pentagonia monocaulis could help increase plant fitness by allowing it to adapt rapidly to changes in herbivory or light availability, the relationships and trade-offs surrounding these traits is not fully understood.
OPTIMAL FORAGING STRATEGIES IN A PARASITIC GASTROPOD (CYPHOMA GIBBOSUM)
Abstract: Optimal foraging theory predicts that across unequal resource patches, organisms will aggregate upon higher quality resource patches. Cyphoma gibbosum, the flamingo tongue snail, is an aposematic marine gastropod that may distribute in accordance with optimal foraging theory, but aggregates by mechanisms that remain unclear. This species parasitizes toxic soft corals and sequesters host toxins as a predator defense. Literature suggests a preference for certain host species and a tendency to follow conspecifics, though these behaviors have not been linked to optimal foraging theory. Using host toxicity as a proxy for resource quality, an optimally foraging flamingo tongue snail should maximize the toxins it can sequester. We explored host preference and optimal foraging in flamingo tongue snails on four soft coral species, Plexaura homomalla (black sea rod), Briareum asbestinum (corky sea finger), Eunicea succinea (shelf-knob sea rod), and Gorgonia ventalina (common sea fan), predicting that flamingo tongue snails would prefer more toxic hosts and follow conspecific mucus trails to those hosts. Our study also considered the size of host corals as a proxy for resource quantity and predicted that the flamingo tongue snail would prefer larger hosts. We also predicted that the snails would be larger on the preferred host species. In our field observations, we found that flamingo tongue snails preferentially parasitized and aggregated upon the most toxic P. homomallaover other observed hosts but there was no relationship between abundance of snails and host size. We also found that those individuals on P. homomallahad larger body size. Our experimental results, however, showed no preference for specific host species and suggested that flamingo tongue snails do not use conspecific mucus trails to locate potential hosts. These results indicate that while host toxicity plays a role in foraging behavior, future studies should explore additional factors that influence host selection and the mechanisms behind conspecific attraction.
DISTRIBUTION OF ECHINODERMS AMONG DAYTIME SHELTERS
Abstract: Echinoderms are marine invertebrates that forage at night and seek shelter from predation under rocks during the day. Our study examined two classes of echinoderms, brittle stars (Ophiuroidea) and sea urchins (Echinoidea), and their distribution among daytime shelters across three factors: shelter size, surrounding substrate of shelter, and the relative abundances of the two classes. We found that larger shelters supported more individuals of each class, but the densities of both classes decreased with increasing shelter size independent of their size differences. This result suggests that, for both classes, the amount of available space influences the distribution of echinoderms. Despite known differences in substrate preference for foraging between classes, the substrate surrounding daytime shelters (sand or turtlegrass) did not influence class distribution. Although both classes utilized the same daytime shelters, the relative contribution of each class to echinoderm abundance did not change across shelter size. This result suggests that their competitive abilities to occupy space do not change across shelter sizes. Our results may be applicable to other taxa because the utilization of daytime shelters as a predator avoidance behavior is common among many species of aquatic organisms. Therefore, our results lead to a better understanding of the distribution of nocturnal foragers in daytime shelters and can better inform future studies of the distribution of individuals across spatial resources.