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Fragmentation and destruction of natural habitats is currently considered to be the major threat to wildlife populations.
We here perform a comprehensive analysis of the demographic effects of habitat fragmentation and destruction on 14 populations
of the root vole. The experiment was divided into two consecutive periods. During the first period, we contrasted populations
with the same initial size and structure in continuous and fragmented habitat. During the second period, we fragmented the
continuous habitat into the same configuration as the permanently fragmented habitat so that the effect of habitat destruction
could be evaluated. We estimated survival and fecundity parameters and combined them into population projection matrices to
evaluate their relative impact on population growth. In the first period of the experiment there was no difference in population
growth rate between fragmented and continuous populations, although litter size was significantly higher in the continuous
populations. In the second period, we found higher population growth rates in populations that had experienced habitat destruction.
By applying the transition matrix model to empirical estimates of demographic parameters, we demonstrate that the difference
in population growth rate in the second period of the experiment was the result of a nonsignificant difference in adult survival.
Movements out of the habitat patches were significantly lower in populations that had experienced habitat destruction. We
conclude that predator-caused mortality of animals moving out of the habitat patches was the main determinant of demographic
variation in this system.
Received: January 31, 2002 / Accepted: March 25, 2003 相似文献
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Electron paramagnetic resonance (EPR) and absorption spectroscopy have been used to study the low temperature photochemical behavior of the Photosystem II D-1/D-2/ cytochrome b559 reaction center complex. The reaction center displays large triplet state EPR signals which are attenuated after actinic illumination at low temperatures in the presence of sodium dithionite. Concomitant with the triplet attenuation is the buildup of a structured radical signal with an effective g value of 2.0046 and a peak-to-peak width of 11.9 G. The structure in the signal is suggestive of it being comprised in part of the anion radical of pheophytin a. This assignment is corroborated by low temperature optical absorbance measurements carried out after actinic illumination at the low temperatures which show absorption bleachings at 681 nm, 544 nm and 422 nm and an absorbance buildup at 446 nm indicating the formation of reduced pheophytin.Abbreviations EPR
electron paramagnetic resonance 相似文献
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Harry S. Prihar Steven R. Wanamaker Stephanie J. Duber Edward J. Bethrman 《Carbohydrate research》1977,56(2):315-324
Fusion or β-l-fucopyranose tetraacetate with phosphoric acid for 1 min at 50° gives a 9:1 anomeric mixture of the α-and β-pyranosyl phosphates. Longer fusion times give the α-anomer exclusively. The l-fucofuranose tetraacetates were synthesized for the first time by acetolysis or methyl-2,3,5-tri-O-acetyl-β-l-fucofuranoside. Fusion or the furanose tetraacetates with phosphoric acid gave a mixture or the fucofuranosyl phosphates in which the β-anomer predominated (β/α = 2.4). Anomeric pairs in the fucofuranose series appear to be distinguishable by the chemical shift of the C-6 methyl protons, as already shown by Sinclair and Sleeter in the pyranose series. 相似文献
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