35 resultados para fixed-point
Resumo:
Surveys on migratory waterbirds and their habitats at Lashihai Lake, China, were conducted from October 1999 to April 2000. Five fixed points, representing different degrees of habitat disturbance and quality, were selected around the lake. We used counts (n = 30) to compare diversity and abundance of waterbirds at each point and evaluate the effects of habitat disturbance. The distribution of waterbirds was affected by disturbance, with snore than one-third of the total species and nearly half of the total individuals occurring at the least disturbed point. Species richness was weakly and abundance was strongly correlated to habitat disturbance, but not to habitat quality. Habitat destruction and use of canoes were prominent at the lake. Naxi ethnic fishermen (n = 37) were interviewed. They caught 570 waterbirds between October 1999 and March 2000 in fishing nets. An estimation of the total number of waterbirds been trapped on the lake is 6164. Diving species were most susceptible. Conservation measures that should implement immediately include the cessation of habitat destruction, better plan for the development of tourism, a reduction in the number of canoes and zoning of the non-fishing area. (C) 2002 Elsevier Science Ltd. All rights reserved.
Resumo:
从9种科鱼类的福尔马林标本中获得了333bp的细胞色素b基因片段的序列。这9个种分别代表科鱼类的8个属。333bp的DNA序列经MUST软件排序后,有101个变异位点,其中有39个信息位点。序列在成对物种间的距离为8~48。平均遗传距离为24%~144%。简约分析产生了最大简约系统树,其步长是162(CI=0735,RI=0494)。在该系统树上,Bagarius是最原始的属,并与所有其他的物种形成姊妹群。其余8个属形成一个单系类群并分为二个姊妹群。尽管在形态上具有13个离征,但在分子系统树上