Predators are real lowlifes

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IMAGE: Using plasticine caterpillar models like this one at the Smithsonian’s ForestGEO site of Tai Po Kau in Hong Kong, researchers discovered a global pattern of higher predation at low elevations… view more 

Credit: Chung Yun Tak

By deploying green clay caterpillars across six continents, researchers unmasked an important global pattern. Their study will be published in Science on May 19. Their discovery that predation is most intense near sea levelChanges in sea level, globally or locally, due to (i) changes in the shape of the ocean basins, (ii) changes in the total mass and distribution of water and land ice, (iii) changes in water density, and (iv) changes in ocean circulation. Sea level changes induced by changes in water density are ... in the tropics–in places like their study sites at the Smithsonian Tropical Research Institute (STRI) in Panama–provides a foundation for understanding biological processes from crop protection and carbon storageA process consisting of separation of carbon dioxide from industrial and energy-related sources, transport to a storage location, and long-term isolation from the atmosphere. (IPCC)An integrated process in which CO2 is separated from a mixture of gases (e.g. the fl ue gases from a power station ... to the effects of climate changeClimate change is a lasting change in weather patterns over long periods of time. It can be a natural phenomena and and has occurred on Earth even before people inhabited it. Quite different is a current situation that is also referred to as climate change, anthropogenic climate change, or ... on biodiversityThe total diversity of all organisms and ecosystems at various spatial scales (from genes to entire biomes). (IPCC).

Insects drove the trend, not mammals or birds. “As someone who has studied insect biodiversityBiodiversity is the degree of variation of life. This can refer to genetic variation, species variation, or ecosystem variation within an area, biome, or planet. Terrestrial biodiversity tends to be highest near the equator, which seems to be the result of the warm climate and high primary ... in the tropics for most of my life, I wasn’t surprised that insects were responsible for most of the predation observed,” said Yves Basset, leader of the ForestGEO Arthropod Initiative at STRI.

The team put out almost 3,000 model caterpillars for four to 18 days at 31 different sites from Australia to Greenland at different altitudes, from zero to 2,100 meters above sea level. Based on characteristic marks left by predators in the clay, they could tell whether the models were attacked by birds, mammals or insects.

Tropical sites were the most dangerous. In Greenland, the daily chances of a caterpillar model being attacked by a predator were only 13 percent of the odds at the equator. And for every 100 meters of increase in altitude, the chance of being attacked fell by almost 6.6 percent. At the highest forested site, the daily odds of a predator attack was only 24 percent of the odds of attack at sea level.

“Most previous studies that didn’t support the conclusion that predation is more intense in the tropics were pieced together from evidence gathered in different ways by different groups of people,” Basset said. “My colleagues and I were part of a team of people from around the world who all used the same method at different sites, including a few of the ForestGEO sites. We deployed many replicates of fake caterpillars, modeled after a geometrid moth, and analyzed our results together.”

“This seems like a very simple experiment but the results are relevant to the way we understand some of the important processes in nature, like the innovation of defenses and how temperature changes may affect biodiversity,” Basset said. “The results further emphasize the power of citizen science for simple, yet significant experiments.”

“Caterpillars eat plants, therefore causing crop damage and forcing plants to create new chemicals in their leaves to defend themselves,” Basset said. “Caterpillars also defend themselves from predators. Our finding that predation pressure is stronger in the tropics also suggests that insects in the tropics have to be more innovative in order to defend themselves.”

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The authors of this study represented 35 research centers and universities, including STRI; the Swedish University of Agricultural Sciences; the University of Helsinki, Finland; the Institute of Entomology, Czech Academy of Sciences; the University of South Bohemia, Czech Republic; the New Guinea Binatang Research Center; the University of California-Irvine; Eidgenossische Technische Hochshule, Zurich; the University of Texas-Arlington; the University of New England, Australia; the University of Alberta, Edmonton; the University of Iceland; the University of Sao Paolo; the University of Hong Kong; the Natural History Museum of Denmark, Copenhagen; Instituto de Ecología, Xalapa, Mexico; Escuela Politécnica Nacional, Ecuador; the University of Ostrava, Czech Republic; Zoological Society of London, the University of Oxford; the University of Turku, Finland; Chinese Academy of Sciences; the University of Aberdeen; Makerere University, Uganda; Swarthmore College, U.S.; the State Institution of Education, Zditovo, Belarus; Aarhus University, Demark; the University of Tartu, Estonia; the University of Bergen, Norway; the University of Beyruth, Germany; and the University of Lancaster, UK.

The Smithsonian Tropical Research Institute, headquartered in Panama City, Panama, is a part of the Smithsonian Institution. The Institute furthers the understanding of tropical nature and its importance to human welfare, trains students to conduct research in the tropics and promotes conservation by increasing public awareness of the beauty and importance of tropical ecosystemsA system of living organisms interacting with each other and their physical environment. The boundaries of what could be called an ecosystem are somewhat arbitrary, depending on the focus of interest or study. Thus, the extent of an ecosystem may range from very small spatial scales to, .... STRI website: http://www. stri. si. edu.

Roslin. T., Hardwick, B., Novotny, et al. 2017. Higher predation risk for insect prey at low latitudes and elevations. Science.

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