2014 @Biotropica Award for Excellence in Tropical Biology & Conservation
Each year the Editorial Board of Biotropica proudly announces the winner of the Biotropica Award for Excellence in Tropical Biology and Conservation. This award recognizes the outstanding paper published in the previous calendar year based on original research conducted in tropical regions. Criteria for selection include clarity of presentation, strong basis in natural history, well-planned experimental and/or sampling design, and novel insights gained into critical processes that influence the structure and functioning of tropical biological systems.
This year we had an outstanding suite of articles nominated for consideration, and for the first time in the history of the award the Editorial Board has decided to recognize two articles and research teams for their contributions:
- Alexandra Pardow and Michael Lakatos. 2013. Desiccation Tolerance and Global Change: Implications for Tropical Bryophytes in Lowland Forests. Biotropica 45(1):27-36.
- Gaston E. Small, Pedro J. Torres, Lauren M. Schweizer, John H. Duff, and Catherine M. Pringle. 2013. Importance of Terrestrial Arthropods as Subsidies in Lowland Neotropical Rain Forest Stream Ecosystems. Biotropica. 45(1): 80-87.
Below we present essays by (1) the Subject Editors that supervised the review of these papers in which they describe why thought they were important and (2) the authors in which they relate what inspired their work.
Congratulations to our 2014 Award recipients!
Alexandra Pardow and Michael Lakatos. 2013. Desiccation Tolerance and Global Change: Implications for Tropical Bryophytes in Lowland Forests. Biotropica 45(1):27-36.
Increased temperatures and droughts associated with climate change can trigger species distribution shifts. However, the impact of these environmental conditions on diversity could vary depending on species tolerance to higher temperatures and desiccation. Bryophytes are important components of tropical forests, can play important roles in nutrient cycling, and offer microhabitats and resources for other species. Bryophytes are particularly dependent on the abiotic environment, and changes in temperature and humidity could be especially risky for these organisms. Considering these physiological traits, during the last years bryophytes have been regarded as sensitive indicators for a variety of environmental conditions such as pollution or climate change.
With this in mind, Alexandra Pardow and Michael Lakatos analysed the desiccation tolerance of 21 epiphytic bryophytes from contrasting microsites at the tropical lowland forest in French Guiana. The authors tested desiccation tolerance for short and long desiccation events, different desiccation intensities, and recovery by rehydration with water vapour. Interestingly, while canopy species were well adapted to desiccation events, understorey species were sensitive to low humid conditions. This study also shows that the photosystem of the studied bryophytes was reactivated efficiently in equilibration with only water vapour only – a previously overlooked trait in bryophytes.
Using a desiccation tolerance index,the authors compared desiccation tolerance of tropical and temperate bryophytes, and their results showed that species from humid sites of the tropical lowland forest understory were very desiccation sensitive and that their desiccation tolerance was similar to that of species from the ever-moist elfin forest. On the other hand, desiccation tolerances of lowland canopy species approached those from xeric temperate habitats. The results of this outstanding study suggest that decreasing humidity caused by climate change and forest degradation could be a concerning threat for understory species of tropical bryophytes. I acknowledge Alexandra Pardow and Michael Lakatos for drawing our attention to this interesting group of organisms, and for their contribution to understanding the complex relationships between physiology of bryophytes, ecology and conservation biology.
Subject Editor, Biotropica
Ever since I first stepped into the forest in Panama during my early studies in biology I got hooked with tropical rainforests. In 2007 I started working which Michael Lakatos, who supervised my graduation thesis on edge effects on epiphytic lichens in the understorey of an Atlantic Rainforest. His enthusiasm for these small organisms and their great physiological potential ultimately fixed my devotion for cryptogams. What I especially liked — and still do — is the fact that when considering bryophytes you have to re-think of what you knew about plant ecology. It is the down-scaling, the shift in the importance of gravity, the change from climatic to microclimatic considerations, and of course the beauty of the organisms that only reveals itself when you have a closer look, when you have a look inside “the forest in the forest”.
I was more than lucky that during my Ph.D. I was able to combine all of my interests with my unappeasable curiosity for what had until then been inaccessible: the forest canopy. Continuing to work with Michael and now collaborating with the group of Robbert Gradstein, we wanted to explore the importance of different water sources for epiphytic bryophytes in French Guiana and how these affect the structural composition of epiphytic bryophytes. French Guiana was the ideal study site because local recurrent fog events allowed comparing the usage of different water sources.
During our work in French Guiana, I had to climb up and down trees countless times collecting samples or installing elaborate equipment and experimental platforms in the canopy. I noticed the role – perhaps small but nonetheless important – that bryophytes play in the forest ecosystem. I saw bugs camouflaged in them, ants and larvae underneath moss samples, and saw seedlings of epiphyte emerging through bryophytes mats. All this made me think the opposite direction of what I was currently concerned with: What happens if environmental conditions become drier? How vulnerable are tropical lowland bryophytes in light of climate predictions and forest degradation? From species surveys it has been assumed that some understory bryophytes might disappear when intact forest became too disturbed. However, there was no ecophysiological data on bryophytes from tropical lowland forests that could help drawing inferences about their vulnerability.
We therefore decided that data on their desiccation tolerance was urgently needed. We conducted a large screening of elaborate desiccation toleranceexperiments on site with the great support of Lena Reibelt, who was integrating these data as part of her master thesis. We developed a global desiccation tolerance index that helped us compare tolerances with the extensive data on bryophytes from other biomes. Indeed, we found that the ability of bryophytes in the forest understory to withstand desiccation was extremely low, leaving them at a high risk when environmental conditions become drier. Furthermore, we found that high humidity conditions – as seen in the forest understory – might be important in the recovery from desiccation events. This further underscores the risks for plants of forest degradation and resulting drier microclimatic conditions. The inner and northern Amazon has been recognized as the center of diversity for forest bryophytes in the Neotropics, yet new species are still being discovered. We hope that our study could point out that we need areas of intact forest for conserving bryophytes, and we hope that it will inspire more studies on the ecophysiology of tropical bryophytes to help assess the risks of global change.
Department of Plant Ecology and Systematics, University of Kaiserslautern
Gaston E. Small, Pedro J. Torres, Lauren M. Schweizer, John H. Duff, and Catherine M. Pringle. 2013. Importance of Terrestrial Arthropods as Subsidies in Lowland Neotropical Rain Forest Stream Ecosystems. Biotropica. 45(1): 80-87.
This innovative study by Small, Torres, Schweizer, Duff and Pringle quantifies terrestrial-aquatic linkages in a tropical forest in Cost Rica. Tropical rainforests support enormous biomass despite typically impoverished soils due tight cycling and retention of nutrients. This paper enhances our knowledge because it shows how forested tropical headwater streams depend on nutrient inputs from the forest yet despite generally fast flows, they too exhibit only small losses of terrestrially derived N and P. Although it is well known that food webs in tropical headwater stream rely on leaf litter from the riparian vegetation because shading impedes instream productivity, Small et al. demonstrate that riparian vegetation also significantly subsidizes aquatic food webs via terrestrial invertebrates falling from the forest canopy that are eaten by insectivorous fish.
Although the importance of terrestrial subsidies has previously been documented for temperate streams, this is the first study to quantify the contribution of arthropods from the forest canopy in the tropics using a variety of field experiments. The results show that arthropods that fall into the streams account for up to half the diet of insectivorous fish that effectively retain and recycle these nutrients within short reaches of the streams. It was found that most insects were consumed by fish within 5 m, and nutrients excreted by these fish were taken up within 150 m (N) or 50 m (P), effectively retaining the nutrients within the forest. Unlike in temperate streams where insect inputs decrease in winter, these subsidies are aseasonal, providing year round nutrients and so they may be of even greater significance in the tropics.
This study highlights the importance of the interrelationships between forests and streams for nutrient cycling which have implications with respect to conservation and management. Loss of riparian vegetation will result in a significant decline in fish, while loss of fish will result in export of the nutrients contained in terrestrial arthropods that fall into the water. Elimination of terrestrial invertebrate subsidies to tropical streams clearly has the potential to cause trophic cascades through aquatic food webs. Where deforestation is inevitable or where reforestation is being considered, maintenance of riparian vegetation is of vital importance to both the forests and the streams.
School of Science, Monash University
First, a confession: I don’t consider myself a tropical ecologist, not by a long shot. But I have had the good fortune of having studied stream ecosystems at La Selva Biological Station, Costa Rica for nearly a decade. One of the great benefits of working at a place like La Selva is that I’ve had the opportunity to interact with researchers (real tropical ecologists!) who study a wide variety of organisms, and my understanding of how streams fit within the larger rainforest ecosystem has undoubtedly been influenced by conversations around the dinner table.
The study that we published in Biotropica — I considered it to be the “fun” chapter of my dissertation. In a tiny headwater stream in which we had been working I was surprised by the large numbers of the poeciliid fish Priapicthys annectens. These fish are insectivores, and in examining the guts of a few individuals I noticed a high proportion of ants. My dissertation research focused on nutrients in the stream food web, and I began to wonder what role these terrestrial insects might play. I started to imagine a “rain” of ants from the canopy into the stream, getting consumed by these fish as soon as they hit the water, and ultimately digested and excreted by the fish, where these ant-derived nutrients then fertilize the microbes and algae that form the base of the stream food web. Wouldn’t it be neat, I thought, if we could measure each step in this chain?
For me, science is the most exciting when you are asking a question that can’t be answered using standard methodology, and instead you are forced to come up with creative approaches. This was one of those questions. Over the next two years, I worked on this project with the help of undergraduate researchers Pedro Torres and Lauren Schweizer. Pedro (now a senior Ph.D. student at the University of Georgia) focused on quantifying the input of terrestrial insects to streams using pan traps, which he deployed along streams throughout La Selva. Lauren (now an attorney) focused on measuring the efficiency with which insects are consumed once they hit the water. My favorite part of this study involved adapting an approach that we typically use for measuring nutrient uptake in streams to instead measure “ant uptake”. We collected ants from the lab at La Selva (the ubiquitous Paratrechina longicornis) and released 100 ants at a time at the top of a stream reach, along with 100 ant-sized squares of waterproof paper to serve as a “conservative tracer”. We blocked off the top and bottom of the reach with nets to prevent movement of fish, and we had drift nets set up at the bottom of the reach to collect ants and paper squares that reached the bottom. We repeated this on several different stream reaches, including on where we had removed all of the fish to test the efficacy of our approach. We also measured fish density, biomass, diet (using gut contents and stable isotopes), body nutrient composition, and fish excretion rates. Then, with help from colleague John Duff from the U.S. Geological Survey, we measured the uptake rate of dissolved ammonia and phosphate in the streams. This allowed us to quantify the “supply chain” of N and P moving from the canopy (as ants) through the stream food web.
It turns out that the ants aren’t all that important as a nutrient flux. While insects represent more concentrated “packets” of nutrients entering the stream, compared to, say, leaves, the input of leaves is several orders of magnitude higher. But, these terrestrial insects certainly are an important subsidy to the stream food web, supporting high densities of fish, and the fish are very efficient in capturing any ant that hits the surface of the stream. And, in these phosphorus limited streams, every atom of P counts, so the relatively small amount of P coming into the streams as ants is efficiently transformed into new algae or microbes within tens of meters.
These back-of-the-envelope calculations for a handful of streams in Costa Rica represent just a small step towards understanding how terrestrial and aquatic ecosystems are connected. My hope is that other researchers will improve our approach and apply it on other locations. Land use changes throughout the tropics are dramatically altering these linkages, and such studies are needed to better understand their consequences.
Gaston E. Small
Biology Department, University of St. Thomas
St. Paul, USA