Friday, February 19, 2016

The diversity of Las Cruces Biological Station

The biodiversity of both plant and animal life is astounding in Las Cruces Biological Station. I could spend a lifetime in the botanical garden and surrounding forest and still never come to fully discover and understand the complexity of the dynamics of each ecosystem. During my two-week stay at Las Cruces, every day I had many unexpected visitors at my doorstep. One in particular was the largest grasshopper of Central America, Tropidacris cristata. This insect, as large as a small bird, measured about 10 centimeters in length and had a wingspan of 18 centimeters. The grasshopper was as thick as the handle of a small umbrella and its external wings had a yellow and black coloration with many small indentations. Underneath, it had bright red wings that were folded back against its abdomen like an accordion, and it had a very tough exoskeleton with a wheel-like crest on its thorax and powerful hind legs with large spikes to deter predators. Erika, one of my professors, recounted an old story of a scientist who had mistakenly shot the insect in flight thinking it was a new bird species.
            What makes Las Cruces unique in comparison to other biological stations in Costa Rica is the diversity of non-native plant life that is introduced and preserved in the Wilson Botanical Garden. Species from all over the world, from Africa to Asia, Australia to Madagascar, can be observed and studied in the garden by both students and researchers. Rodolfo, the station director, remarked that researchers who would otherwise have needed to travel to remote parts of the world are able to perform their research in just this single location. These nonnative species are not only interesting from a species perspective. The whole garden has developed its own set of symbiotic relationships through plant-animal interactions. Animal species that are exposed to foreign plants can develop a wide range of interactions with them, ranging from mutualisms which help in the proliferation of both the plant and its animal associate, to herbivory or parasitism, in which the animal exploits the plant and uses its resources, often resulting in the death of the plant. In such cases, human intervention is necessary to sustain the survival of plants that are at risk. Furthermore, nonnative seed dispersal outside of the garden is a large concern. Birds and small mammals such as toucans and agoutis often consume and transport plant seeds into the secondary and primary forest surrounding the area, and plants that use wind dispersal can end up colonizing other locations. In particular, ginger is one of the most successful plants in dispersing into the forest. Rodolfo and the station managers prioritize efforts to hinder its progression, since they do not want to risk the expansion of ginger and the possibility of it becoming invasive, which could bring economic and/or environmental harm through out-competing native species.
            One of the most interesting aspects of Las Cruces for me was crepuscular activity and the transition into nocturnal ecological dynamics. When the sun began to set on my first day in the station, I immediately noticed a transition in activity and presence of organisms. The first indicator of this switch was the appearance of butterflies of the tribe Brassolini, including the genera Caligo and Eryphanis. Known as owl butterflies, these large insects with conspicuous dark eyespots on the undersides of their wings only take flight at dawn and dusk to forage and mate. Because of their impressive crypsis, it is very difficult to spot them resting on vegetation during the day, but in the evening you can spot them flying with iridescent structural blue and purple colors on the dorsal side of their wings. After observing them and realizing nightfall was just beginning, I would often go searching in the forest at night to find and learn about species that were not visible during the day. One night in particular, Mauricio, another of my professors, took me along with the other tropical biology students on a night hike. We found countless amphibians, arachnids, and insects, including a tailless whip scorpion (Amblypygi) with intimidating red chelicerae, scorpions (Centruroides sp.) that fluorescence under ultraviolet light, venomous wandering spiders (Cupiennius sp.), and frogs such as various Leptodactylus sp. and the emerald glass frog, Espadarana prosoblepon. This was my first time encountering a glass frog, and it was unbelievable that the underside of the body was completely transparent. I could see all the organs at work, including its beating heart. Mauricio mentioned that in the past the structure and color of the internal organs have been used for species identification.
            To my surprise, we were not able to see very many nocturnal mammals, although opossums and small rodents are supposedly common in the park. Cats such as jaguars and ocelots, and other large mammals like tapirs are almost never reported in the Las Cruces area, and when they are, the animals are often scouting out new locations to live in or find resources. Rodolfo said that the primary reason this habitat could not support mammals such as these is the limited area and lack of connectivity to other areas of preserved forest. One of the major long-term goals of the Las Cruces Station is to expand westward and connect to the Guayani reserve through reforestation of cleared land and the formation of a biological corridor.
            Corridors allow for migration, the persistence of species with large home ranges, and gene flow to maintain genetic variation and thus greater adaptability in populations. One drawback to this effort is the vulnerability of animals passing through the corridor. Due to the larger amount of edge, hunting and spread of disease could become prevalent in the corridor, and possibly endanger the already intact populations in the two reserves. However, many conservation biologists argue that the formation of the corridor will result in a decreased chance of local extinction and act against the risks of isolation of forest fragments, ultimately preserving and enhancing the viability of neotropical ecosystems.
Christian Perez
Harvard University

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