Understanding tropical biology is important for solving complex problems such as climate change, biodiversity loss, and zoonotic pandemics, but biology curricula view research mostly via a ...temperate-zone lens. Integrating tropical research into biology education is urgently needed to tackle these issues.
Introducing undergraduate students to major human diseases is a key focus of many parasitology courses. Here I present a multifaceted active learning technique that familiarizes students with major ...human parasitic diseases while simultaneously exposing students to a range of important medical, biological, and ecological concepts. This approach involves a combination of reading and analysis of primary literature, oral presentations and in-class discussions, films, and microscopy skills and could be modified for a range of different courses and teaching styles.
The role of streams and rivers in the global carbon (C) cycle remains unconstrained, especially in headwater streams where CO
2
evasion (F
CO2
) to the atmosphere is high. Stream C cycling is ...understudied in the tropics compared to temperate streams, and tropical streams may have among the highest F
CO2
due to higher temperatures, continuous organic matter inputs, and high respiration rates both in-stream and in surrounding soils. In this paper, we present paired in-stream O
2
and CO
2
sensor data from a headwater stream in a lowland rainforest in Costa Rica to explore temporal variability in gas concentrations and ecosystem processes. Further, we estimate groundwater CO
2
inputs (GW
CO2
) from riparian well CO
2
measurements. Paired O
2
–CO
2
data reveal stream CO
2
supersaturation driven by groundwater CO
2
inputs and large in-stream production of CO
2
. At short time scales, CO
2
was diluted during storm events, but increased at longer seasonal scales. Areal fluxes in our study reach show that F
CO2
is supported by greater in-stream metabolism compared to GW
CO2
. Our results underscore the importance of tropical headwater streams as large contributors of carbon dioxide to the atmosphere and show evaded C can be derived from both in-stream and terrestrial sources.
Disturbances can alter the structure and function of ecosystems. In stream ecosystems, changes in discharge and physicochemistry at short, intermediate, and long recurrence intervals can affect food ...webs and ecosystem processes. In this paper, we compare pH regimes in streams at La Selva Biological Station, Costa Rica, where episodic acidification frequency across the stream network varies widely due to buffering from inputs of bicarbonate‐rich interbasin groundwater. To examine the effects of acidification on ecosystem structure and function, we experimentally increased the buffering capacity of a headwater stream reach and compared it to an unbuffered upstream reach. We compared these reaches to a naturally buffered and unbuffered reaches of a second headwater stream. We quantified ecosystem structural (macroinvertebrate assemblages on leaf litter and coarse woody debris) and functional responses (leaf litter and coarse woody debris decomposition rates, and growth rates of a focal insect taxon Diptera: Chironomidae). Non‐metric multidimensional scaling and analysis of similarity revealed that macroinvertebrate assemblages were relatively homogenous across the four study reaches, although the naturally buffered reach was the most dissimilar. Ecosystem function, as measured by chironomid growth rates, was greater in the naturally buffered reach, while decomposition rates did not differ across the four reaches. Our results indicate that biological assemblages are adapted to pH regimes of frequently acidified stream reaches. Our experiment informs the effects on structure and function at short time scales in streams that experience moderate acidification, but larger magnitude acidification events in response to hydroclimatic change, as projected under climate change scenarios, may induce stronger responses in streams.
Tree cavities are a critical resource for many animals, especially as nesting sites for birds. Patterns of cavity distribution in temperate forests are well studied, yet little is known of cavities ...in tropical forests, despite a hypothesized decrease in cavity availability with decreasing latitude. We studied cavity density and distribution in a wet lowland tropical forest in Costa Rica and compared our results with estimates from forests around the world. Cavities at our site were common, occurred frequently in living trees, and were often formed by damage or decay rather than by woodpeckers. Most cavities had small openings, and woodpecker-created cavities were nonrandomly oriented. Contrary to prediction, cavity density appears to increase from the poles to the tropics. We suggest potential mechanisms to explain these patterns.
Girdling insects produce a circular groove around a stem or petiole typically before ovipositing or feeding on the distal section. We documented that seven of the 11 species of notodontid ...caterpillars that we studied, including members of five genera in two subfamilies, chewed girdles in seven families of trees including species of birch, hickory, oak, elm, cherry, willow, and maple. The frequency of girdling varied with notodontid species, tree species, month, and year. Free-ranging final instar larvae of
Schizura leptinoides
on pecan (
Carya illinoensis
) spent 4–11 % of their time cutting and reinspecting girdles over 5-h and 12-h observation periods. Feeding occurred proximal as well as distal to girdles, a result not expected by most hypotheses for the function of girdling. Histological examination of
S. leptinoides
girdles on river birch (
Betula nigra)
revealed that only the xylem remained intact; however, on pecan, both the xylem and phloem remained mostly uncut by the girdle.
S. leptinoides
larvae often rubbed their mouthparts over the surface of finished girdles, anointing them with fluid from the labial salivary glands or possibly the ventral eversible gland. After feeding,
S. leptinoides
and other notodontids sometimes severed the petiole even when the leaf was only partially eaten; these leaf-clipping larvae were similarly observed rubbing their mouthparts over the severed petiole stub. We propose that notodontids cut girdles and clip leaves at least in part to introduce secretions or their enzymatic products into the vascular system to suppress host defenses and/or enhance nutrition.
Understanding tropical biology is important for solving complex problems such as climate change, biodiversity loss, and zoonotic pandemics, but biology curricula view research mostly via a ...temperate-zone lens. Integrating tropical research into biology education is urgently needed to tackle these issues.
Geothermally modified ground water (GMG) in tectonically active areas can be an important source of stream nutrients, and the relative importance of GMG inflows is likely to change with shifts in ...precipitation that are predicted to occur in response to climate change. However, few studies have quantified the influence of GMG inflows on export of biologically important solutes from watersheds across years differing in precipitation. We quantified N, soluble reactive P (SRP), and dissolved organic C (DOC) export during a year with high precipitation (6550 mm rain) and a year with average precipitation (4033 mm rain) in 2 gauged tropical streams at La Selva Biological Station in lowland Costa Rica. One stream receives extensive inputs of regional GMG, whereas the other is fed entirely by local runoff. In the stream fed only by local runoff, a 62% increase in precipitation from the dry year to the wet year led to a 68% increase in stream discharge, a 67% increase in export of SRP, DOC, dissolved organic N (DON), and NH4
+, and a 91% increase in NO3
– export. In contrast, in an adjacent stream where >⅓ of discharge consists of GMG, the same increase in precipitation from dry year to wet year led to a 14% increase in discharge, a 14 to 31% increase in export of NO3
–, NH4
+, DON, and DOC, and only a 2% increase in SRP export. We are unaware of an SRP export rate from a natural system that is higher than the export from the stream receiving interbasin flow of GMG (19 kg ha–1 y–1). Our results illustrate that regional ground water, geothermally modified or not, can stabilize stream export of biologically relevant solutes and water across a varying precipitation regime.
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