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121.
1. Completion of a large interbasin water transfer system in northern Texas (U.S.A.) provided the opportunity to test the effects of pre-planned, experimental increases (≈×30) in flow on the fish fauna of a small, low-gradient, natural stream that was included as part of the conveyance system. Water from Lake Texoma (Red River basin) was pumped via a 16-km pipeline to the headwaters of Sister Grove Creek (Trinity River basin), which then carried the donor water 50 km downstream to Lake Lavon.
2. Baseline (pre-transfer) data on the composition of fish assemblages at seven stations on the creek or at its confluence with the receiving reservoir were collected monthly for 3 years, and similar data were collected for 2 years during and after trial flows of Lake Texoma water to Sister Grove Creek. We also documented fish abundance at five creek stations immediately before and after three trial flow periods of 10–14 days each in summer and autumn.
3. Multivariate analysis of all routine monthly samples over the 5-year pre- and post-transfer period showed moderate changes in the fish fauna of the creek after initiation of the trial flows. Samples taken within a week before and after the artificial high flows showed little overall change in abundance of individual fish species, but at some stations the quantitative or qualitative change in composition of the local assemblage was substantial.
4. The trial flows lasted 2 weeks or less. Long-term effects of water transfer on the fish fauna of Sister Grove Creek can only be determined after the conveyance system goes into normal operation, with periods of artificial flow of longer duration. 相似文献
2. Baseline (pre-transfer) data on the composition of fish assemblages at seven stations on the creek or at its confluence with the receiving reservoir were collected monthly for 3 years, and similar data were collected for 2 years during and after trial flows of Lake Texoma water to Sister Grove Creek. We also documented fish abundance at five creek stations immediately before and after three trial flow periods of 10–14 days each in summer and autumn.
3. Multivariate analysis of all routine monthly samples over the 5-year pre- and post-transfer period showed moderate changes in the fish fauna of the creek after initiation of the trial flows. Samples taken within a week before and after the artificial high flows showed little overall change in abundance of individual fish species, but at some stations the quantitative or qualitative change in composition of the local assemblage was substantial.
4. The trial flows lasted 2 weeks or less. Long-term effects of water transfer on the fish fauna of Sister Grove Creek can only be determined after the conveyance system goes into normal operation, with periods of artificial flow of longer duration. 相似文献
122.
123.
GABRIELA A. PINTO‐JUMA JOSÉ A. QUARTAU MICHAEL W. BRUFORD 《Zoological Journal of the Linnean Society》2009,155(2):266-288
Cicadas are widely distributed in the Mediterranean area and are mainly distinguished by male acoustic signals, which act as specific mate recognition systems. Within the genus Cicada L. several species have diverged in their calling songs without showing external morphological differences, so acoustic recordings and genetic studies are particularly useful for systematic, biogeography and evolutionary studies. This study assesses sequence variation in closely related species of Cicada from the Mediterranean area, using domain III of the 12S rRNA mitochondrial gene in order to determine the phylogenetic relationships and the evolutionary history of this group, as well as the population structure of the two most common species, C. orni and C. barbara. Five distinct haplogroups were identified, C. orni, C. barbara, C. mordoganensis, C. cretensis and C. lodosi, each corresponding to a distinct evolutionary group. C. barbara was the most divergent species within this group, while C. orni and C. mordoganensis were the most similar. The population structure and demographic parameters of the species were not completely resolved. However, there is evidence for the separation of the C. orni Greek populations from the rest of Europe and also for demographic expansions probably related to Pleistocene climate changes. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 155 , 266–288. 相似文献
124.
MICHAEL ANTHONY CARTER JEREMY MILES 《Biological journal of the Linnean Society. Linnean Society of London》1989,36(1-2):129-155
Sexual Actinia equina have been maintained in the laboratory. Monthly biopsies show that these animals have annual gametogenic cycles. Regular samples from several natural populations suggest that animals in the wild show similar gametogenic periodicity. In the laboratory, males release sperm, but females brood young, at least for a few weeks. Members of these broods are released sporadically, usually after a water change. Males and non-sexual adults kept in isolation for over a year release a few juveniles during and at the end of that time. These young are likely to be asexually reproduced. There appears to be geographical variation of anemone size and in the frequency of sexual individuals in populations round the British Coast, so that modes of reproduction may vary. 相似文献
125.
126.
The rate of oxygen consumption increased in maturing Xenopus oocytes within 2 hr after progesterone addition, well before GVBD. This suggested an early requirement for energy metabolism during maturation, similar to the situation in sea urchin eggs during fertilization. Yet, the absence of similar increases in glucose-6-phosphate levels, glucose-6-phosphate dehydrogenase activity, glucose conversion to CO2, and the conversion of NAD(H) to NADP(H), indicated that carbohydrate metabolism was not being stimulated in Xenopus oocytes during maturation. The oxidation of other energy yielding substrates is discussed which might account for the finding that, within 5 min of progesterone addition, both reduced forms of the pyridine nucleotides increased 20% over control levels. This was later followed by a drop in NADH levels and a rise in NAD relative to controls. The significance of these changes in pyridine nucleotide levels and their relationship to a number of maturation events are discussed. 相似文献
127.
128.
Abstract. 1. Colonisation of ephemeral aquatic habitats via oviposition by invertebrates may be influenced by a variety of factors, such as the quality of aquatic habitat and the characteristics of the surrounding terrestrial environment. The water-holding bracts of Heliconia caribaea , a subtropical herb that produces ephemeral aquatic habitats, are colonised by a variety of aquatic invertebrates. To date, no experiments have been conducted to identify the cues that affect colonisation patterns via oviposition selection in Heliconia .
2. Artificial bracts were used to assess the influence of two types of resources found in bracts (plant produced carbohydrates and terrestrial snail faeces) on oviposition site-selection by invertebrate taxa via a replicated factorial design at four locations in the Luquillo Experimental Forest of Puerto Rico, U.S.A. Eleven microsite characteristics thought to affect oviposition were measured for each experimental container.
3. Most taxa responded in a minor way to microsite characteristics, whereas site selection by the most numerically dominant groups (e.g. Syrphidae) were influenced principally by resources within artificial bracts. Overall, the greatest response by particular taxa was to the presence of snail faeces. At the community level, total abundance, richness, and evenness of invertebrates increased with increasing biomass of faeces. Variation in sugar produced a more complex response.
4. In general, the terrestrial matrix surrounding these aquatic habitats was only a secondary determinant of population and community attributes; the principal factor affecting site selection was the quality of the aquatic habitat. 相似文献
2. Artificial bracts were used to assess the influence of two types of resources found in bracts (plant produced carbohydrates and terrestrial snail faeces) on oviposition site-selection by invertebrate taxa via a replicated factorial design at four locations in the Luquillo Experimental Forest of Puerto Rico, U.S.A. Eleven microsite characteristics thought to affect oviposition were measured for each experimental container.
3. Most taxa responded in a minor way to microsite characteristics, whereas site selection by the most numerically dominant groups (e.g. Syrphidae) were influenced principally by resources within artificial bracts. Overall, the greatest response by particular taxa was to the presence of snail faeces. At the community level, total abundance, richness, and evenness of invertebrates increased with increasing biomass of faeces. Variation in sugar produced a more complex response.
4. In general, the terrestrial matrix surrounding these aquatic habitats was only a secondary determinant of population and community attributes; the principal factor affecting site selection was the quality of the aquatic habitat. 相似文献
129.
MICHAEL B. ASHCROFT LAURIE A. CHISHOLM KRISTINE O. FRENCH† 《Global Change Biology》2009,15(3):656-667
Current predictions of how species will respond to climate change are based on coarse‐grained climate surfaces or idealized scenarios of uniform warming. These predictions may erroneously estimate the risk of extinction because they neglect to consider spatially heterogenous warming at the landscape scale or identify refugia where species can persist despite unfavourable regional climate. To address this issue, we investigated the heterogeneity in warming that has occurred in a 10 km × 10 km area from 1972 to 2007. We developed estimates by combining long‐term daily observations from a limited number of weather stations with a more spatially comprehensive dataset (40 sites) obtained during 2005–2006. We found that the spatial distribution of warming was greater inland, at lower elevations, away from streams, and at sites exposed to the northwest (NW). These differences corresponded with changes in weather patterns, such as an increasing frequency of hot, dry NW winds. As plant species were biased in the topographic and geographic locations they occupied, these differences meant that some species experienced more warming than others, and are at greater risk from climate change. This species bias could not be detected at coarser scales. The uneven seasonal nature of warming (e.g. more warming in winter, minimums increased more than maximums) means that climate change predictions will vary according to which predictors are selected in species distribution models. Models based on a limited set of predictors will produce erroneous predictions when the correct limiting factor is not selected, and this is difficult to avoid when temperature predictors are correlated because they are produced using elevation‐sensitive interpolations. The results reinforce the importance of downscaling coarse‐grained (∼50 km) temperature surfaces, and suggest that the accuracy of this process could be improved by considering regional weather patterns (wind speed, direction, humidity) and topographic exposure to key wind directions. 相似文献
130.
MICHAEL N. MAUTNER 《Bioethics》2009,23(8):433-440
In the future, human destiny may depend on our ethics. In particular, biotechnology and expansion in space can transform life, raising profound questions. Guidance may be found in Life‐centered ethics, as biotic ethics that value the basic patterns of organic gene/protein life, and as panbiotic ethics that always seek to expand life. These life‐centered principles can be based on scientific insights into the unique place of life in nature, and the biological unity of all life. Belonging to life then implies a human purpose: to safeguard and propagate life. Expansion in space will advance this purpose but will also raise basic questions. Should we expand all life or only intelligent life? Should we aim to create populations of trillions? Should we seed other solar systems? How far can we change but still preserve the human species, and life itself? The future of all life may be in our hands, and it can depend on our guiding ethics whether life will fulfil its full potentials. Given such profound powers, life‐centered ethics can best secure future generations. Our descendants may then understand nature more deeply, and seek to extend life indefinitely. In that future, our human existence can find a cosmic purpose. 相似文献