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NH-Invertebrate Zoology
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Symbiotic nitrogen (N)-fixing trees can provide large quantities of new N to ecosystems, but only if they are sufficiently abundant. The overall abundance and latitudinal abundance distributions of N-fixing trees are well characterised in the Americas, but less well outside the Americas. Here, we characterised the abundance of N-fixing trees in a network of forest plots spanning five continents, 5,000 tree species and 4 million trees. The majority of the plots (86%) were in America or Asia. In addition, we examined whether the observed pattern of abundance of N-fixing trees was correlated with mean annual temperature and precipitation. Outside the tropics, N-fixing trees were consistently rare in the forest plots we examined. Within the tropics, N-fixing trees were abundant in American but not Asian forest plots ( 7% versus 1% of basal area and stems). This disparity was not explained by mean annual temperature or precipitation. Our finding of low N-fixing tree abundance in the Asian tropics casts some doubt on recent high estimates of N fixation rates in this region, which do not account for disparities in N-fixing tree abundance between the Asian and American tropics. Synthesis. Inputs of nitrogen to forests depend on symbiotic nitrogen fixation, which is constrained by the abundance of N-fixing trees. By analysing a large dataset of 4 million trees, we found that N-fixing trees were consistently rare in the Asian tropics as well as across higher latitudes in Asia, America and Europe. The rarity of N-fixing trees in the Asian tropics compared with the American tropics might stem from lower intrinsic N limitation in Asian tropical forests, although direct support for any mechanism is lacking. The paucity of N-fixing trees throughout Asian forests suggests that N inputs to the Asian tropics might be lower than previously thought.
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NZP
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NMNH
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STRI
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SI-Libraries
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NH-Anthropology
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As threats to migratory birds in the Western Hemisphere, including North America, intensify and bird populations decline, there is a growing interest among zoo biologists in the conservation and management of these taxa. The purpose of this article is to explore the role that Association of Zoos and Aquariums (AZA)-accredited zoos and aquariums either are playing or could play in the conservation and management of migratory birds. Topics explored include: (1) Public education and advocacy; (2) Captive breeding and reintroduction; (3) In situ conservation; (4) Tracking and monitoring; (5) Research/technology development; and (6) Sustainability/green practices; and (7) Partnerships. Zoos and aquariums could play an important role in increasing the public's access to understanding migratory birds and the threats they face, ultimately helping to protect these remarkable species.
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USNM
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USNM
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