排序方式: 共有27条查询结果,搜索用时 0 毫秒
21.
E. P. Pister 《Journal of fish biology》1990,37(SA):183-187
The habitat degradation and species endangerment that preceded and accompanied the North American environmental movement in the late 1960s and early 1970s found the conservation community ill-prepared. Protective legislation and basic research necessary for structuring recovery efforts did not exist. Desert aquatic communities were among the first to need attention, and an interdisciplinary effort was mounted in an early application of conservation biology. The history and evolution of desert ecosystem preservation are discussed, and case histories are presented that may prove helpful in other parts of the world as habitats are inexorably reduced. The role of the Desert Fishes Council in co-ordinating efforts of research scientists and resource managers to achieve common objectives is emphasized. 相似文献
22.
Synopsis Important differences were observed in the early ontogenies ofLucania parva andLucania goodei. These differences can be explained in terms of the altricial-precocial model of speciation.Lucania parva can be recognized as an altricial form that produces many eggs with relatively little yolk investment, compared to the more precocialL. goodei. Many of the differences observed in embryo, larva and juvenile specimens appear to be related to these differences in gamete investment. Accelerated developmental rates in the precocial form suggest that paedomorphosis is an important proximate mechanism in the bifurcation of alternative life-history styles in this genus. Some morphological characteristics, such as vitelline circulation and body shape, may be transformations associated with the particular environmental conditions in which the animals must develop and survive. Our observations suggest that these two species in the genusLucania have followed different ontogenic trajectories in response to prevailing environmental conditions. 相似文献
23.
We report the characterization of nine new microsatellite markers for a threatened species, the White Sands pupfish (Cyprinodon tularosa), using an enriched library method. These markers show moderate levels of variation (two to five alleles per locus) in the two native populations of this species and reveal substantial divergence between these two populations as indicated by a high percentage of private alleles. These markers will prove very useful in the conservation management of this rare species. 相似文献
24.
Miguel Clavero Francisco Blanco-Garrido José Prenda 《Environmental Biology of Fishes》2007,78(2):173-182
The Andalusian toothcarp, Aphanius baeticus, is a critically endangered cyprinodontid species, with only nine known extant populations. Although not yet studied in the
field, the distribution and abundance of Andalusian toothcarp are thought to be strongly influenced by interspecific interactions.
We analysed the abundance and microhabitat use of Andalusian toothcarp in two water courses, one in which several other fish
species occurred (sympatric site) and one hypersaline stream in which toothcarp was the only species present (allopatric site).
Fish were sampled using plastic minnow traps and results were analysed separately for three size categories. Toothcarps were
clearly more abundant in the allopatric population than in the sympatric one, though the difference was less apparent in the
smallest size category. In coexistence with other species, toothcarp occupied shallower microhabitats, but in both sites in
the absence of shelter fish selected deeper positions than in its absence. While in the sympatric site sheltered microhabitats
were used predominately by small individuals, in the allopatric ones they were used by larger ones. Observed patterns strongly
suggest that predation is the main mechanism involved in the differences in abundance and microhabitat use between sites.
Our results confirm that the presence or absence of coexisting species is an important habitat feature for Andalusian toothcarp
populations. 相似文献
25.
Charles F. Duggins Alvan A. Karlin Kenneth G. Relyea Ralph W. Yerger 《Biochemical Systematics and Ecology》1983,11(3):283-294
Samples representing the three nominal subspecies of Floridichthys carpio were examined electrophoretically. Although the populations in Florida could not be distinguished completely from the populations in Yucatan by morphology, 5 of the 30 electrophoretic characters demonstrated fixed differences between Florida and Yucatan populations. Based on the observed genetic differentiation between Florida and Yucatan populations and the absence of genetic differentiation within those populations, we conclude that the Yucatan population has diverged to the species level. We, therefore, propose to elevate the nominal Yucatan subspecies Floridichthys carpio polyommus to a species status. 相似文献
26.
27.
B. Elvira 《Journal of fish biology》1990,37(SA):231-232