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A MONG MANY OF THE ENDANGERED FISH IN NEW YORK STATE ARE THE SHORT-NOSED STURGEON (PICTURED BELOW) AND THE EASTERN SAND DARTER. THE NOW-EXTINCT BLUE PIKE LOOKS VERY MUCH LIKE THE STILL- ABUNDANT WALLEYE, AND AS RECENTLY AS THE 1970S IT WAS A MAJOR COMMERCIAL FISH. The reason for the concentration of terrestrial diversity in rainforests and their marine equivalent in the coral reefs is one of the great unknowns of ecology. The concentration is actually the result of a more or less continuous increase in diversity encountered while traveling from the poles to the equator, the so-called latitudinal gradient of biodiversity. When biologists say “unknown” in this particular case, they really mean “not known with certainty.” Several hypotheses have been advanced, any one of which—or all of which—could be true to some extent. I am going to take a deep breath and try to impart the most likely explanation from a synthesis of these hypotheses, with due respect to current evidence: B i o l o g i c a l 20 D i v e r s i t y
The tropical zones generally have a more congenial climate for life, providing it with longer growing seasons, an even distribution of solar energy, and freedom from freezing and other extreme, unpredictable, shortterm changes in temperature. The rainforest, moreover, offers a humidity regime and tree structure (that is, prevalence of broad, nearly horizontal branches) favorable to epiphytes such as orchids and bromeliads. This “elevated swampland” with its little pools of water and moist root masses offers vast numbers of additional living sites for animals. The delicate life cycles of the epiphytes and their co-evolved animal populations are pre-eminently tropical. It is unlikely that the organisms could endure the freezes of the Temperate Zone. The stability of the climate and the layering of vegetation allows division of the ecosystem into large numbers of niches and a corresponding number of plant and animal species, many bound together by intricate and finely tuned symbioses. A small shift from one part of a tree to another, or from one species of tree to another, or from one elevation on a mountainside to another, opens an opportunity for the evolution of yet another kind of animal or plant. The entirety of evolution has built the equivalent of a house of cards: vast numbers of species propped and leaning on one another and dependent on a steady environment to avoid collapse. It used to be thought that diversity created stability; in other words, the more species were locked together by co-evolution, the less likely any one of them could be extirpated. This diversity-stability hypothesis has gradually given way to its exact reverse, the stability-diversity hypothesis, wherein external, climatic stability is thought to allow the buildup of biodiversity. In the Temperate Zones, plant and animal species must adapt to a more drastically and unpredictably shifting environment. As a consequence, each Temperate Zone species is, on the average, likely to occur in a greater range of habitats, elevation and so forth than individual tropical species. In short, Temperate Zone species occupy a broader niche. Fewer species can be fitted together, resulting in lower biodiversity in temperate climates. Destructive human activity, including habitat removal, pollution, and excessive exploitation, have reduced large numbers of plant and animal species in the Temperate Zones even though they are “tougher” in the sense of having wider ranges on the B i o l o g i c a l 21 D i v e r s i t y
Page 1: Biological Diversity: T H E O L D E
Page 4 and 5: THE UNIVERSITY OF THE STATE OF NEW
Page 6 and 7: Copyright © 1999 by The New York S
Page 9 and 10: Preface This book is based on a man
Page 11 and 12: Additional information on the activ
Page 13 and 14: Biological Diversity: T H E O L D E
Page 15 and 16: some degree of potency. A much high
Page 17 and 18: Some groups of organisms, such as f
Page 19 and 20: to their environment and to one ano
Page 21 and 22: N EW YORK’S BIODIVERSITY IS THREA
Page 23 and 24: 12 10 Number of Butterflies Observe
Page 25 and 26: It is possible that the next hundre
Page 27 and 28: environment. For almost 3 billion y
Page 29 and 30: W ITH ITS WISPINESS AND LIGHT-AND-D
Page 31: sophisticated microscopic and bioch
Page 35 and 36: average as well as greater ecologic
Page 37 and 38: early extinction within the next 30
Page 39 and 40: perished. As the paleontologist Dav
Page 41 and 42: collected in the stream in 1936 and
Page 43 and 44: Systematics, or taxonomy, is at the
Page 45 and 46: Community ecology addresses the man
Page 47 and 48: Biological field stations from four
Page 49 and 50: Biogeography 1 The scientific study
Page 51 and 52: Dispersal In biology, the way a spe
Page 53 and 54: Global warming An increase in the c
Page 55 and 56: Ozone A form of oxygen (O 3 ) that
Page 57 and 58: Termites A group of insects that is
Page 59 and 60: Grifo, Francesca, and J. Rosenthal
Page 61 and 62: diverse and why the threat to that
Page 63 and 64: Mitchell, Richard S., L. Danaher, a
Page 65 and 66: 9. Is an ecologist the same as a ta
Page 67 and 68: 31. Do you know of a biological res
Page 69 and 70: B i o l o g i c a l 57 D i v e r s
Page 72: THE NEW YORK STATE MUSEUM IS A PROG

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