La Selva REU Mentors 2019
Marcelo Araya-Salas, Ph.D.
Cornell University/Universidad de Costa Rica
Hummingbird vocalizations and behavior
Project 1: Costs and benefits of vocal coordination strategies in lekking hermit hummingbirds. We have documented coordinated singing in long-billed hermits. In this behavior, simultaneously singing males modify the timing of their songs to achieve synchronization. The type of coordination is dependent on the distance between individuals: non-overlapping singing is more common in close proximity while overlapping singing is mostly used when singing at farther distances. We hypothesize that, by overlapping their songs birds may amplify their combined signals and communicate across greater distances, but this benefit is diminished in close proximity, where the ability of bystanders (i.e. females) to locate singers decreases when songs are overlapped by nearby singers. A feasible project would involve measuring the response to overlapping songs emitted by speakers at both close and far distances, expecting that the ability of an individual to find a “singing intruder” (a speaker) will be affected by the distance between the speakers and the type of coordination. This project would require playback experiments and documentation of behavioral responses in lekking hermit hummingbirds.
Project 2: Amplitude modulation in songs and its role as an aggressive signal in a lekking species. This project would be related to the use of amplitude modulation in songs (i.e. singing louder) by lekking hermits during territorial intrusions. Hermit hummingbirds sing from fixed perches at intermediate heights, which allows positioning microphones right underneath singing males and at a consistent distance. This experimental design would allow to test the use of amplitude modulation in aggressive interactions (by simulating singing intruders) and to investigate the morphological correlates of song amplitude.
Christina Baer, Ph.D.
University of Connecticut
Thermal tolerances and preferences of terrestrial invertebrates
Project 1: Can maximum heat tolerance reliably predict invertebrates’ temperature preferences?
Project 2: Is community structure determined by temperature in a heating experiment?
My research tackles a pressing question in ecology: how will tropical species and communities respond to climate change? One way to answer this is to conduct field heating experiments to predict how animals will be affected by a warmer future. Students working with me will perform a field warming experiment on invertebrates using newly developed field heaters. These heaters warm invertebrate communities found in the rolled leaves of heliconias and other banana relatives. Students will have the opportunity to work with everything from beetles and caterpillars to ants and katydids. By comparing the invertebrates found in heated leaves to those found in unheated leaves, students will develop and test hypotheses relating invertebrates’ maximum heat tolerance and temperature preferences to their potential climate change responses. These traits, especially temperature tolerance, are widely used to predict which species will be most vulnerable to climate change, but whether they can correctly identify the most vulnerable species has rarely been tested.
One student will test whether invertebrates’ maximum heat tolerance can accurately predict their temperature preferences. The second student will test whether invertebrate communities found in ambient and heated leaves have different temperature preferences and tolerances. Each student will use different laboratory and statistical methods to tackle these questions but will work together to implement the field heating experiment. They will gain experience in experimental design, tropical field work, and mechanical skills. Students will have the opportunity to publish a research article based on these projects.
North Carolina State University
Ecosystem processes in tropical streams; snail sensitivity to stream chemistry in tropical streams
Project 1: Comparing seasonal effects of experimental stream pH elevation on leaf litter decomposition. In this proposed project, the student will expand on previous studies that quantify the rate of leaf litter decomposition across the range of stream pH in streams at La Selva. Stream pH decreases naturally in response to precipitation events. However, low elevation streams exhibit greater buffering capacity due to inputs of carbonate rich groundwater and acidification events are lower in magnitude. During these acidification events, stream heterotrophs (microbes, macroinvertebrates) decomposition of allochthonous organic material in the stream is inhibited, suggesting acidification events alter ecosystem function within La Selva. This project would examine the response of stream pH to the addition of inorganic carbon, increasing the buffering capacity and preventing acidification events. If utilization of organic matter by heterotrophs is negatively affected during acidification, our hypothesis would conversely state heterotrophic decomposition would be unaffected or positively affected through stabilization of stream pH regime. We plan to answer these questions by conducting leaf litter decomposition experiments using available leaf litter from La Selva in 2 reaches in the Carapa stream: one reference reach with naturally variable stream pH and a second reach downstream of an injection of dissolved inorganic carbon, which will increase the buffering capacity and prevent pH reduction. This experiment will be part of a 2-part study outside the REU program, with one part during the dry season (January-April) and the REU component during the wet season (May-December). This study permits discussion of the effect of season on leaf litter decomposition and stream pH regime.
Project 2: Gastropod distribution and response to stream pH across Neotropical groundwater gradient. In this project, the student would conduct experiments on physiological responses of aquatic macroinvertebrates to episodic acidification frequent in low-solute streams. Previous studies have shown strong macroinvertebrate behavioral response to acidification, but little is known about physiological responses, particularly in sessile macroinvertebrates. Gastropods are a useful model organism to study the effect of acidification on physiology. Gastropods require a range of pH for shell strength and to prevent dissolution of the calcium carbonate matrix and require calcium from the environment to build and maintain shells. This project will take 2 parts: 1) surveys across several streams at La Selva to determine snail presence, abundance, and assemblage; and 2) growth and reciprocal transplant growth studies. Snail surveys will follow developed techniques in previously studied streams to map and identify the gastropod assemblage at La Selva. Growth studies will take place in low elevation and high elevation streams, spanning the groundwater gradient at La Selva. Dominant species of snails will be confined in mesh bags in the stream, and measured before, during, and after deployment in the stream for up to 6 weeks. Pre-growth experiment physiological metrics (dry mass, ash-free dry mass, shell mass) will be taken and used to compare snail allocation of resources and physiological tolerance to the range of stream conditions. We predict snail growth metrics and shell strength will be greatest in low elevation streams where pH is more alkaline and calcium more available, whereas pH in high elevation streams is more acidic and calcium more limiting.
University of Texas at Austin
Passiflora plant-insect interactions
Project 1: Variable susceptibility to predation on different Passiflora species. Predation from natural enemies contributes to the evolution of dietary specialization on specific plant species. It remains unclear if specialist herbivorous insects eating different plants vary in their susceptibility to predators across the suite of plants they can eat. Does the plant that an insect eats predict whether they survive attack by predators? The student that accepts this project will investigate this question by raising Passiflora specialist caterpillars and beetles on different Passiflora species and then present those insects to predatory ants. Survival against ant colonies will be observed in experimental arenas that we will establish at the beginning of the field season. The student will use R to analyze variation in survival between Passiflora species.
Project 2: Influence of herbivory on Passiflora leaf chemistry. Leaf chemistry varies considerably between species, individuals, even between day and night. Evidence exists demonstrating that leaf herbivory also affects this variation by inducing the release of chemicals that deter herbivory. We know that many Passiflora species possess substantial chemical variation between individual plants. However, we do not know whether herbivory affects this variation. Do specialist insects cause Passiflora leaf chemistry to change? The student that accepts this project will explore this question by measuring leaf hydrogen cyanide concentrations (HCN) of leaves not experiencing herbivory and leaves being eaten by caterpillars or beetles. The student will use R to explore whether Passiflora HCN concentrations change when leaves undergo herbivory.
Utah State University
Canopy soil carbon cycling
Project 1: The temperature sensitivity of canopy soil decomposition. Canopy soils form from decaying tree and epiphyte material on rainforest tree branches and play an important role in forest nutrient cycling and rainfall interception. Because canopy soils consist entirely of organic matter, warmer temperatures under climate change may pose a direct threat to these soils by accelerating decomposition. However, the true sensitivity of canopy soil decomposition to temperature, or Q10, is unknown. Assessing the Q10 of canopy soil would allow us to infer the vulnerability of canopy soils to climate change. I propose that we determine the Q10 of canopy soils and compare them to terrestrial soils. We will incubate canopy soils and terrestrial soils under different temperatures in the laboratory and measure decomposition by quantifying CO2 flux with a portable chamber. For each sample, CO2 fluxes at different temperatures will be used to calculate Q10.
Project 2: Nutrients limiting decomposition of canopy soil. Climate change may affect canopy soils indirectly by shifting epiphyte community composition and altering N and P content of their litter inputs. Canopy soil microbes may be nutrient limited, such that increases in epiphyte nutrient input would enhance microbial decomposition of canopy soil. We will test which nutrients (N vs. P) limit canopy soil decomposition by adding these nutrients to canopy soil samples in the laboratory, then measuring CO2 fluxes with a portable chamber.
For either project, students will help analyze results and author a manuscript summarizing the findings of our work. These experiments will contribute to a larger project investigating the vulnerability of canopy soils to climate change.
Kelsey Reider, Ph.D.
Florida International University
Distribution and biodiversity of peccary wallows
My research is focused on understanding patterns of reptile and amphibian diversity and abundance and ecosystem-level effects of large mammals. I will assist REU mentees to develop research questions related to the ecosystem engineering effects of collared peccaries (Pecari tajacu) in lowland tropical forests. As seed dispersers, peccaries have an important role in shaping the structure and diversity of tropical forests. Peccaries also play an important but less understood role in engineering crucial habitat for other organisms.
Project 1: Spatial analysis of peccary wallows. The REU researcher will conduct systematic surveys of small aquatic habitats, also called wallows, created by collared peccaries throughout La Selva. They will use GIS to investigate spatial patterns of wallow density and distribution (e.g., forest type, proximity to trails).
Project 2: Peccary wallows as novel habitat. The REU researcher will conduct a survey of biodiversity of organisms (e.g., amphibians, reptiles, and aquatic invertebrates) using peccary wallows and evaluate ecological hypotheses related to community assembly.
These are labor-intensive projects that require extensive field work. To get the most out of working with me, applicants should be physically and mentally prepared to work long hours in the forest, frequently alone and under difficult conditions.
Ulli Seibt, Ph.D.
University of California, Los Angeles
Soil respiration in response to rain; soil fluxes in wind-created forest gaps
Students will work on measuring soil carbon and water fluxes with a new type of soil flux chamber based on low-cost sensors. The new chambers make it possible to obtain field data across multiple places at a fraction of the cost of a conventional soil flux system.
The chambers consist of a rigid enclosure with flexible skirt to provide a seal with the soil surface. Sensors for CO2 concentration, temperature and humidity of the air inside the chamber provide data that is used to calculate soil carbon and water fluxes. Four chambers will be installed and operated, together with a conventional (LI-COR) soil flux chamber. Since this research involves some technical components, the two students will work together on operating the chambers and analyzing the data. The students can then define their independent projects by
their respective research questions. For guidance, I will provide several options at the start: Do soil fluxes vary along the soil micro-topography? How fast do fluxes change when it rains? Are soil fluxes systematically different in forest gaps (left by the recent storm disturbance)? Ideally the students will also come up with their own questions. The students will then collect preliminary data for about a week to explore these options, and decide on their projects based on what they find. Since data on soil fluxes in tropical rainforests is very limited, any of these projects will provide new insights that will be highly valuable for the flux research community.
Wu Sun, Ph.D.
University of California, Los Angeles
Leaf photosynthetic characteristics
The La Selva station is a hotspot of ecosystem productivity and diversity. The variety of species and leaf traits and the complexity of canopy environment create an ideal natural laboratory to study the photosynthesis of tropical plant species. The proposed projects will focus on the variability of leaf photosynthetic characteristics among different species and canopy environments. Students will use a Portable Chlorophyll Fluorometer (Walz PAM-2500) to collect leaf active fluorescence data on different species and use statistical methods to analyze the controlling factors of leaf photosynthetic parameters.
Project 1: Variability of leaf photosynthetic characteristics among species. The La Selva forest hosts a diversity of plant species and they differ in their photosynthetic capacity. Understanding of interspecies difference of photosynthetic parameters is important to the interpretation of ecosystem scale changes in photosynthetic CO2 uptake. In this project, the student will collect active fluorescence data from a variety of species, derive the photosynthetic parameters from statistical analysis, and explore factors that determine the interspecies differences.
Project 2: Light adaptation of leaf photosynthetic characteristics. The complex light conditions in a canopy can lead to contrasting acclimations of leaf photosynthesis even for the same species. Understanding of such acclimation would provide knowledge on the distribution of photosynthesis within a canopy. The student will collect leaf active fluorescence data from sunlit and shaded leaves from the same species (e.g., Pentaclethra spp.) for a cohort of dominant species in the forest. The student will analyze the data to see how light adaptation of photosynthesis differ between overstory and understory (perennially shaded) species.
Las Cruces REU Mentors 2019
Lindsey Swierk, Ph.D
Binghamton University. State University of New York
Behavioral ecology: social structure and local adaptation in a semi-aquatic lizard
Project 1: Water anole home range and microhabitat use. Understanding how individuals distribute themselves in space is a fundamental problem in ecology. In collaboration with Dr. Bree Putman, this project will explore the social structure of water anole populations and their relationship to the microhabitat. Little is known about this unusual lizard’s home range and social behavior. The student conducting this research will study water anole home range sizes and shapes to address natural history questions regarding sex- and age-related habitat use, territoriality, and density.
Project 2: Social signaling in courtship and aggressive encounters. How animals use signals to communicate with others of their species is an essential component of their behavioral ecology. This project will test how water anoles use behavioral and morphological cues during staged inter- and intra-sexual encounters. Several conspicuous morphological cues are of interest, namely dewlaps (large and colorful “chin-flaps” of skin) in males and the highly changeable body coloration of both sexes. Behaviorally, both males and females perform dramatic displays of aggression, and males actively court females with head-bobs and a suite of stereotyped behaviors. Notably, these morphological and behavioral traits have never been quantified in relation to mating success or contest outcome in water anoles. Specific hypotheses can be generated in consultation with the student researcher, but some options include examining a) the relationship of male body coloration or dewlap characteristics to female mate choice, b) the effect of color change on the outcome of antagonistic encounters, or c) male courtship investment in relation to perceived female reproductive value.
Johana Goyes, Ph.D
University of Kansas
Emerald Glass Frog (Espadarana prosoblepon)
Project 1: Is there any parental care in Espadarana prosoblepon? Early studies of the natural history of this species report little or no parental care. Jacobson (1985, Herpetologica 41:396–404) observed females near the eggs for a few minutes after oviposition but later deserted the clutch. Since then, no studies have further explored the existence of parental care in this species. Using enclosures in the field, the student will make careful observations of mating pairs of E. prosoblepon, to determine if there is an adult frog brooding the eggs, which sex provides care, and for how long the adult remains with the clutch. In addition, through daily monitoring of egg clutches, the student will evaluate the benefits (if any) of the parental care behavior of this species. Elucidating the natural history of poorly studied Centrolenid species, will aid in the understanding of the evolution of parental care in this family.
Project 2: Estimating abundance of Espadarana prosobleponin Las Cruces. With the current amphibian declines it is imperative that we determine abundance parameters of Espadarana prosobleponin Las Cruces. This will provide a baseline for future studies of the population dynamic of this species, and will allow for comparative studies throughout the species range. Using mark-recapture methods, the student will estimate abundance of E. prosobleponin Las Cruces. In this location, E. prosoblepon is a common species, however, to the best of my knowledge, studies estimating local abundance and population size of this species have not been undertaken. Estimating abundance will aid in the understanding of the population dynamic of this species while at the same time will provide a baseline for comparisons with other populations pre and post-arrival of the amphibian chytrid fungus.
Patricia Esquete Garrote, Ph.D
Universidade de Aveiro
Ecology and biology of aquatic invertebrates
Project 1: Microhabitat preferences of benthic invertebrates in tropical streams. Benthic environments in tropical streams host a variety of organisms of different life strategies, ranging from soft bodied, infaunal plathelmints to insects with aquatic larvae or macrocrustaceans. The REU student will develop a project that examines the factors affecting the aquatic invertebrates’ preferences for certain microhabitats, their abundances or species composition across a tropical stream. For this purpose, they will use different field capture techniques, animal manipulation methods and habitat characterization, as well as laboratory methods including the use of microscopes and identification tools. If more than one student is interested, two projects could be carried out on this subject.
Project 2: Predation-prey relationships of semi-aquatic spiders. Semi-aquatic spiders are fascinating animals that live in rocks and crevices in the vicinity of water bodies, preying on insects, frogs, tadpoles, and other organisms including small fish. Two species of the non-web genus Trechalea are abundant in the rainforest’s streams of Costa Rica, where they play an important ecological role by controlling other species’ populations. However, little is known about their behaviour and the factors affecting their hunting/resting activities. This study aims to investigate their predation strategy and activity rhythms; The REU student can expect searching rivers for big spiders during different times of the day, observing activity patterns, and mapping their movements. If more than one student is interested, two projects could be carried out on this subject.
Breanna (Bree) J. Putman, Ph.D
University of California – Los Angeles
Behavior and ecology of water anoles (Anolis aquaticus) at sites differentially impacted by human disturbance.
Project 1: Water anole personality and spatial ecology. Understanding whether consistent individual differences in one or more personality traits associates with movements and home range size.
Project 2: Water anole boldness and predation risk. Understanding whether bolder individuals experience more risk in terms of tail loss rates, and/or are exposed to more risk in terms of amount of time spent defending territories.
University of Toronto
Impact of disturbance and ecological succession on two tropical mutualisms: the legume-rhizobia mutualism and the ant-plant mutualism.
Project 1: Tropical legume – rhizobia mutualisms across various stages of succession. Nutrient availability is low in early-succession communities compared to late-succession communities. Thus, mutualisms that provide additional nutrients are expected to be more important in recently disturbed communities. The student will test this prediction in a legume-rhizobia mutualism across successional plots of increasing age at Las Cruces. Rhizobia form nodules on plant roots in which plants and rhizobia exchange nutrients (fixed nitrogen and carbon). The student will assess whether the most abundant legume species in recently disturbed plots have higher nodulation (nodule number, nodule size, nodule colour) compared to plants in established communities, indicating that plants in recently disturbed plots are more dependent on mutualist-provided resources.
Project 2: Extrafloral nectary production in tropical plant communities. Herbivores are more common in late-succession communities than in early-succession communities. Therefore, defense mutualisms are expected to be more important for plants growing in late-succession communities, where herbivore populations have recovered from disturbance. The student will test this prediction in an ant-plant mutualism, a common mutualism in tropical ecosystems in which ants protect plants from herbivores in exchange for a food reward (nectar) plants produce in structures called extrafloral nectaries. To assess whether plants in recently disturbed communities invest less in attracting ant bodyguards, the student will measure the food rewards in extrafloral nectaries (sugar concentration, nectar volume) on the most abundant nectar producing plant species across various succession plots at Las Cruces.
Project 3: Multiple mutualist common garden experiment in the tropics. Mutualisms that occur over a large geographic range are exposed to a wide diversity of partners. Therefore, we might expect widespread mutualists to be adapted to their local partner. The students will test this prediction in a multiple mutualist system: rhizobia, legumes, and ants bodyguards. Rhizobia form nodules on plant roots and provide fixed nitrogen to the legume in exchange for carbon. Ants protect the legume against herbivores in exchange for sugar from plant extrafloral nectaries. The students will plant legume seeds (Chamaecrista nictitans) collected from temperate, sub-tropical, and tropical locations at a field site at Las Cruces. The student will measure seed production, nodule number, and extrafloral nectar concentrations to test local adaptation.
José-Cristian Martínez, Ph.D.
Insect biodiversity; Insect ecology; Forest restoration
Project 1: Tropical restoration and its effect on the insect community. Students can assess what impact tropical forest restoration have on the insect community across the transitional grasslands, secondary forest, and primary forest at Las Cruses biological station. An additional question such as does selective logging change the leaf-litter habitat compared to the uncut primary forest, can also be addressed.
Project 2: Impact of tropical woodland restoration on leaf litter decomposition dynamics and insect activity density Students can assess how restoration activities at Las Cruses impact the ground leaf-litter habitat, and what members of the detrital insect community are most affected by changes in leaf litter structure. This question can be assessed by documenting the leaf litter characteristics and by using pitfall traps to gauge activity density of major ground active insects such as spiders and beetles.
Justin Montemarano, Ph.D
Armstrong State University
Community-level effects on decomposition dynamics in aquatic systems.
Project 1: Investigating the longitudinal distribution of fish communities in Las Cruces. Previous surveys of fish communities at Las Cruces have suggested low richness (four species), but a possible elevational range extension of at least one fish species. I would like to continue monitoring fish community composition, and extend the monitoring along the Rio Java river.
Project 2: Controllers of freshwater crab behavior and implications for decomposition dynamics. We have found two species freshwater crab (Pseudothelphusidae) associated with stream systems at Las Cruces. Previous projects show that (1) the distribution of the crabs within and outside of streams is highly variable, and (2) that the crabs contribute to the decomposition of leaf matter through shredding. I would like to explore factors controlling crab behavior, densities, and leaf processing rates. For example, crab species and parasite load (trematode metacercariae were discovered in both crab species) may impact activity.