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Adaptabilidad de anfibios a la transformacin del hbitat y el efecto de las precipitaciones en su patrn de actividad durante la estacin seca
Amphibian adaptability to habitat transformation and the effect of rainfall during the dry season on their activity pattern
Amphibians are being forced to change their habits and lifestyles to adapt to human transformations. Some species of amphibians are becoming dependent on man-made ecosystems to carry out their life cycles. Also, climate change is affecting the seasonality by changing the amount of precipitation and the phenology of amphibians. This study was conducted in San Luis Costa Rica in an area characterized by a pre-montane wet forest during the dry season (April 2011). Pitfall traps and drift fences were set up in a forest location and in a man-made pond location to compare the number species within each location. Rainfall was also measured, and amphibian activity was found to be positively correlated. B. marinus and Rana vaillanti were most abundant at the man-made pond site and were found to have significant difference when compared to other amphibian species inhabiting the same area and mammal species. The change of seasonality and land transformation initiated by humans could have devastating consequences on amphibian species.
Los anfibios se han visto forzados a cambiar sus hbitats y modos de vida para adaptarse a las transformaciones humanas. Algunas especies de anfibios se estn volviendo dependientes de los ecosistemas modificados por el ser humano para desarrollar sus ciclos de vida. Adems el cambio climtico est afectando la estacionalidad mediante el cambio de la cantidad de precipitacin y la fenologa de los anfibios. Este estudio se condujo en San Luis, Costa Rica en un rea caracterizada por un bosque hmedo premontano durante la poca seca (abril 2011).Trampas de cada y cercas de deriva se ubicaron en el bosque y en un lago artificial para comparar el nmero de especies en cada lugar. La precipitacin se midi tambin, y la actividad de anfibios esta correlacionada positivamente. Bufo marinus y Rana Vaillanti fueron ms abundantes en el lago artificial y hay una diferencia significativa en comparacin con otras especies de anfibios que habitan en el rea y especies de mamferos. El cambio en la estacionalidad y la transformacin de la tierra iniciada por los humanos puede tener consecuencias devastadoras en las especies de anfibios.
Text in English.
Costa Rica--Puntarenas--Monteverde Zone--San Luis
Costa Rica--Puntarenas--Zona de Monteverde--San Luis
Tropical Ecology Spring 2011
Amphibians--Effect of human beings on
Ecologa Tropical Primavera 2011
Anfibios--Efecto de los seres humanos en
t Monteverde Institute : Tropical Ecology
Amphibian adaptability to habitat transformation and the effect of rainfall during the dry season on their activity pattern Amber Brossard Department of Biology and Environmental Studies, Gustavus Adolphus College Abstract Amphibians are being forced to change their habits and lifestyles to adapt to human transformations. Some species of amphibian are becoming dependent on man made ecosystems to carry out their lifecycles. Also, climate change is affecting the seasonality by changing the amount of precipitation and the phenology of amphibians. This study was conducted in San Luis Costa Rica in an area characterized by a premontane wet forest during the dry season (April 2011). Pitfall traps and drift fences were set up in a forest location and in a man made pond location to compare the number species within each location. Rainfall was also measured, and amphibian activity was found to be positively correlated. B. marinus and Rana vaillanti was most abundant at the man made p ond site and was found to have significant difference when compared to other amphibian species inhabiting the same area and mammal species. The change of seasonality and land transformation initiated by humans could have devastating consequences on amphib ian species. Resumen Los anfibios se han visto forzdos a cambiar sus hbitats y modos de vida para adaptarse a las transformaciones humanas. Algunas especies de anfibios se estn volviendo dependientes de ecosistemas modificados por el humano para desarro llar sus ciclos de vida. Adems, el cambio climtico est afectando la estacionalidad cambiando la cantidad de precipitacin y la fenologa de anfibios. Este estudio se condujo en San Luis, Costa Rica en un rea caracterizada por un bosque hmedo premont ano durante la poca seca (abril 2011). Trampas de cada y cercas de deriva se ubicaron en el bosque y en un lago artificial para comparar el nmero de especies en cada locacin. La precipitacin se midi tambin, y la actividad de anfibios est correlac ionada positivamente. Bufo marinus y Rana vaillanti fueron ms abundantes en el lago artificial y hay una diferencia significativa en comparacin con otras especies de anfibios que habitan el rea y especies de mamferos. El cambio en la estacionalidad y la transformacin de la tierra iniciada por los humanos puede tener consecuencias devastadoras en las especies de anfibios. Introduction Deforestation has been an every growing concern especially in the tropics and within Costa Rica. turned into secondary forest (FAO 2005). In the case of biodiversity as the forest composition changes so do the species thriving within it (Hamer & McDonnell, 2008). Much of the deforested land is transformed into an urban setting A complex array of interacting biotic and abiotic factors impact amphibians in urban and u rbanizing landscapes (Hamer & McDonnell, 2008).
Urbanization and habitat transformation currently threaten over 30 percent of amphibians species. Most empirical studies on the effects of urbanization on amphibians reported a decrease in species richness, and individual species presence and abundance, with increases in the degree of urbanization (Hamer & McDonnell, 2008). Also, i n a study conducted by Gibbs (1993) it was determined that habitat transformation may lead to population declines of a mphibians i f critical aquatic or terrestrial habitats are destroyed. However, s pecies of amphibian can have different reactions to habitat transformation including potentially benefitting Maes et. al, ( 2008 ) found that species of Rana ( Rana esculenta ) was found to be dependent on roadside man made bodies of water Several highly adaptable species of amphibian are Bufo marinus (Bufonidae) and Rana vaillanti (Ranidae) B. marinus natural habitat consists of forest clearings, either natural or man made, and they are ra rely found in undisturbed habitats (Savage 2002). As humans continue to remove forested areas, the ideal habitat of B. marinus is thought to increase This study took place in a premontane wet forest with the mean annual rainfall being between 2000 4000 mm per year (Haber 2000). For amphibians this is very adequate amount of rainfall to carry out their complex lifecycles Not only do their life cycles often require the use of an aquatic ecosystem but also they are highly at risk of desiccation (Stebbins & Cohen 1995) Their activity is often limited by the amount of moisture available (Stebbins & Cohen 1995) Foraging and other activities must take place within reachable distance of a water source for many amphibians such as Rana spp The furth er an amphibian travels from a water source the higher the risk of desiccation. However, if there is an abundance of moisture in the air due to precipitation amphibians may have the capacity to travel further and therefore be more active. A study conducted by Pounds et. al (1999) showed that the average amount of precipitation in the dry season is declining leading to more dry days. This could be devastating to many species of amphibian. The aim of this study was to determine the effect of two factors tha t impact amphibian distribution: seasonal variation and adaptability to habitat transformation. I compared the frequency of amphibians caught in a man made habitat and a forest clearing in San Luis, Costa Rica. Also, the seasonal variation for the dry seaso n was take n using the amount of precipitation. Methods Study S ite s This study took place in San Luis, Costa Rica in a premontane wet forest life zone. Two separate locations were used: a man made forest edge pond, and a forest clearing in a secondary forest The secondary forest location was surrounded by cattle pastures but would be considered an ideal habitat of B ufo marinus and other amphibian that adapt well to disturbances T here was no livestock disturbance within the forest clearing chosen The s tudy site was located near the forest edge but far away from direct human influence including lights and noises. The second site was a transformed and disrupted man made pond located on the property of The University of Georgia Station Costa Rica Campus. T he pond is frequently used as a watering location for cattle but was not being put to use at the time of this study It is located in a cattle pasture near the forest edge.
Trapping methods Drift nets and pitfall traps were set up in the locations as prev iously described. The drift fences were constructed of silt fence netting. The drift fen ces were 30cm in height and 5 meters long. On either end of the drift fence a 20 liter bucket was placed below ground to act as the pitfall trap. The pitfall traps cont ained a wet sponge to prevent the specimens caught from desiccation. The buckets also had holes drilled in the bottom to prevent the collection of water and, therefore, eliminate the danger of specimens drowning. The drift fence was set up to fo r m a perpendicular angle with two and a half meters of silt fence on either side of the center point The silt fence net was dug into the ground slightly to prevent specimens from crawling under the fence. The traps remained open Sunday Thursday nights. Da ys following the nights when the traps were open, traps were checked in the morning. The number of organisms was recorded and they were immediately released. The traps were then closed and remained closed until sunset. Rainfall The amount of rain and t he t emperature for each day was taken. The daily minimum and maximum temperature was recorded each day the traps were open. The amount of precipitation was co llected with a rain gage that was emptied at the b eginning of each day and every night that data was c ollected from the pitfall traps. Results Species UGA Trap Forest trap Total Sphenomorphus cherrei 0 1 1 Rana vaillanti 10 0 10 Bufo marinus 29 1 30 Oryzomys talamancae 1 1 2 Cryptotis nigrecens 0 3 3 I caught a total of 46 individuals from 5 different species over 12 days 40 of those 46 were amphibians ( fig 1). Amphibians were more often caught at the site near the pond. B. marinus was caught most frequently than any other species. R. vaillanti was the next most frequently caught amphibian. Cryptotis nigrecens and Oryzomys talamancae were the only species of mamm al caught. One species of reptile ( Sphenomorphus cherrei) was caught in the forest trap but only once. Figure 1. The number of each species caught at the two different sites using pitfall traps and drift fences over a 12 day time period
FIGURE 2 Relative abundance of organisms caught near a man made pond at the forest edge and inside the forest in San Luis Costa Rica using drift fen ces Composition of organism present varied between habitats ( X2; p<0.0001 ). Habitat type There was a difference in the composition of organism caught in the 2 different habitats (X 2 = 30.15, df = 3, p<0.0001 Fig. 2) B. marinus predominantly caught in the pond, while R. vaillati was only caught in this habitat. The number of mammals caught in the forest clearing site more than doubled when compared to the man made pond site. Shrews ( Cryptotis nigrecens ) were only caught in the f orest site. Rainfall There was a significant positive relationship between the number of amphib ians caught and rainfall (F = 9.59, df = 1, p = 0.0113 ; Fig. 3 ). For every millimeter of rain the amount of a mphibians caught increases by approximately one in dividual. 0 5 10 15 20 25 30 35 forest UGA Individuals R. vaillanti O.talamancae c. nigrecens B. marinus
Discussion Habitat transformation and its effect on amphibians and other terrestrial vertebrates This study found that B. marinus is the most abundant species in the disturbed, man made pond site suggesting that they are more adaptable to habitat transformation B. marinus has been known to inhabit areas disturbed by humans (Savage 2002) The forest clearing site was similar to a natural undisturbed habitat as described by Savage (2002) but there we re still more B. marinus found and the site directly impacted by humans and livestock. The next most abundant species was the R. vaillanti but there were none in the forest suggesting an even bigger dependence on human disturbance. As Maes et. al, ( 2008 ) found, many amphibians are becoming dependent on man made sites as thei r natural habitats disappears. My study corresponds with Maes et. al in that R. vaillanti and B. marinus are becoming dependent on man made sites. The future of these species is become reliant on human transformed areas. Human transformed areas are often greatly associated with air and water pollution (Hamer & McDonnell, 2008) This pond pollution will often cause limb deformities and mortality (Taylor et. al 2005). Rainfall This study suggests that the amount of rainfall has an impact on the activity level of amphibians. Past studies have concluded that amphibians are very dependable on the moisture in the atmosphere and on bodies of water due to their permeable skin (Stebbins & Cohen 1995) The fact that amphibians are more active as a response to rainfall could simply be explained by their requirement to remain in moist environments. The rainfall will provide excess moisture and could greatly lower the risk of desiccation allowing tra vel further from a water source. Foraging must still take place even on the dry days although there is a higher risk of desiccation. If climate change creates dryer days as suggested in Pounds et. al (1999) then I suspect that the amphibian y = 1.1367x + 2.2377 R = 0.4895 0 2 4 6 8 10 0 2 4 6 8 Individuals Rainfall (mm) FIGURE 3 The relationship of rainfall and the number of amphibians caught in drift fence, April 2011 (Dry season) The fences were set up in a forest clearing and near a man made pond on the forest edge in San Luis, Costa Rica. Each point represents a different night ( 12 nights total).
population will greatly decrease. Also, the number of permanent bodies of water is likely to decrease limiting amphibians in potential breeding locations. Acknowledgements I would like to thank UGA Costa Rica and the Leiton family for allowing me to use their land as my study site. Also, I would like to thank Alan Masters, Pablo Alan, Moncho Calder n, Gisella Fernandez for all their help and advice. There were many people who helped me set up my traps throughout the project including: Randy and Eduardo Leiton, Katie B. L Dogg, Hannah C., and Drew. Thanks friends! Citations G IBBS J. P. 1993. Importance of small wetlands for the persistence of local populations of wetland associated animals. Wetlands: 25 31. H ABER W.H 2000. Amphibians and Reptiles Oxford University Press: 39 43 H AMER A.J., M C D ONNELL M.J 2008. Amphibian ecology and conservation in the urbanising world: A review. Biological Conservation. 141: 2432 2449. M AES J., M USTERS C.J., and D E S NOO G. R. 2008. The effect of agri environment schemes on amphibian divers ity and abundance. Biological Conservation. 141: 635 645 P OUNDS A.J., F OGDEN P.L., and C AMPBELL J.H 1999. Biological response to climate change on a tropical mountain Nature. 398:611 615. S AVAGE J 2002. The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago, USA. S TEBBINS R. C., and C OHEN N.W. 1995 A Natural History of Amphibians Princeton University Press: 3 15. T AYLOR B., S KELLY D., D EMARCHIS L.K., S LADE M. D., G ALUSHA D ., and R ABINOWIT P.M 2005. Proximity to Pollution Sources and Risk of Amphibian Limb Malformation. Environmental Health Perspect. 113: 1497 1501