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71.
E. L. García Diez J. L. Labajo Salazar F. de Pablo Dávila 《International journal of biometeorology》1993,37(4):194-199
The present paper offers data on the effect of certain meteorological parameters on the outbreak of forest fires in Galicia (Spain). In a day-to-day analysis, the values of the stability of the air column and the saturation deficit at the lower levels are related to the number of fires occurring in the following 24 h. 相似文献
72.
Several aspects of a diel vertical migration (DVM) of adultEudiaptomus gracilis in Lake Maarsseveen (The Netherlands) are described. The period of DVM lasted from the end of May until the middle of August. On May 21, 1989, the population was found divided into a deep dwelling part and a part in the upper five meter. Large shoals of juvenile perch were observed in the open water for the first time. On June 7, the whole population was down below 10 m and concentrated in a zone of high chlorphyll-a concentrations. One week later, a regular DVM was performed. The amplitude of this migration gradually decreased towards the end of the migration period. The ascent in the evening and the descent in the morning took place after sunset and before sunrise, respectively. The movements coincided with high relative changes in light intensity. Population size increased rapidly during the period of DVM but decreased again before the end of this period. 相似文献
73.
74.
A. S. Davydov 《Journal of biological physics》1991,18(2):111-125
The lifetime of Davydov solitons in a one-dimensional system is studied theoretically. The process of thermalization and the properties of solitons at finite temperature are investigated and the processes of soliton creation and disintegration are discussed. 相似文献
75.
Long-term assessments of species assemblages are valuable tools for detecting species ecological preferences and their dispersal
tracks, as well as for assessing the possible effects of alien species on native communities. Here we report a 50-year-long
study on population dynamics of the four species of land flatworms (Platyhelminthes, Tricladida, Terricola) that have colonized
or become extinct in a 70-year-old Atlantic Forest regrowth remnant through the period 1955–2006. On the one hand, the two
initially most abundant species, which are native to the study site, Notogynaphallia
ernesti and Geoplana multicolor have declined over decades and at present do not exist in the forest remnant. The extinction of these species is most likely
related with their preference for open vegetation areas, which presently do not exist in the forest remnant. On the other
hand, the neotropical Geoplaninae 1 and the exotic Endeavouria septemlineata were detected in the forest only very recently. The long-term study allowed us to conclude that Geoplaninae 1 was introduced
into the study area, although it is only known from the study site. Endeavouria septemlineata, an active predator of the exotic giant African snail, is originally known from Hawaii. This land flatworm species was observed
repeatedly in Brazilian anthropogenic areas, and this is the first report of the species in relatively well preserved native
forest, which may be evidence of an ongoing adaptive process. Monitoring of its geographic spread and its ecological role
would be a good practice for preventing potential damaging effects, since it also feeds on native mollusk fauna, as we observed
in lab conditions.
Júlio Pedroni: Granted by CNPQ–Brazil. 相似文献
76.
77.
78.
V. I. Monchenko 《Hydrobiologia》2000,417(1):101-107
The problem of cryptic species in Diacyclops bicuspidatus was examined using interpopulation crosses of four populations collected from a: (1) permanent flood lake in Kiev, Ukraine, (2) temporary pool in Kiev, (3) permanent pond in St. Petersburg, Russia (1200 km to north from Kiev) and (4) lake in Crimea (1100 km south of Kiev). The only interpopulation crosses to exhibit fertility were those between the St. Petersburg population and each of the two Kiev populations. The crosses between the Kiev and Crimea populations, between the St. Petersburg and Crimea populations, and between the two Kiev populations were sterile, as evidenced by either nonviable eggs, empty egg membranes or incomplete copulations. The F1 hybrids resulting from the St. Petersburg permanent pond X Kiev flood lake cross were fertile and produced mature F2 offspring. Some data on development times of parental and hybrid lines are presented. The St. Petersburg parental line showed development times almost twice as long as those of the Kiev flood lake population when reared at 10 °C and 20 °C in the laboratory. The F1 offspring of the cross between St. Petersburg females and Kiev floodlake males showed similar development times to females of the St. Petersburg parental lines at both temperatures. The F2 hybrids also showed development times that approximated those of the St. Petersburg parental line. These crossbreeding studies suggest the presence of cryptic species in the D. bicuspidatus inhabiting ecologically different populations in many parts of its large holarctic range. 相似文献
79.
80.
Proenkephalin encodes a group of small peptides with opiate-like activity, the endogenous opioids, known to function as neurohormones, neuromodulators, and neurotransmitters. Recently, we have demonstrated that in addition to its abundance in fetal brain tissue, proenkephalin is highly expressed in nondifferentiated mesodermal cells of developing fetuses. We identified the skeletal tissues, bone, and cartilage as major sites of proenkephalin expression. To examine the possibility that proenkephalin is involved in bone development we have studied the expression of this gene in bone-derived cells, its modulation by bone active hormones, and the effects of enkephalin-derived peptides on osteoblastic phenotype. Our studies revealed that osteoblastic cells synthesize high levels of proenkephalin mRNA which are translated, and the derived peptides are secreted. Reciprocal interrelationships between osteoblast maturation and proenkephalin expression were established. These results together with our observations demonstrating inhibitory effects of proenkephalin-derived peptides on osteoblastic alkaline phosphatase activity, strongly support the notion that proenkephalin is involved in bone development. A different direction of research by other investigators has established the capability of the opioid system in the periphery to participate in the control of pain. On the basis of these two lines of observation, we would like to present the following hypothesis: The potential of embryonic skeletal tissue to synthesize proenkephalin-derived peptides is retained in the adult in small defined undifferentiated cell populations. This potential is realized in certain situations requiring rapid growth, such as remodeling or fracture repair. We suggest that in these processes, similarly to the situation in the embryo, the undifferentiated dividing cells produce the endogenous opioids. In the adult these peptides may have a dual function, namely participating in the control of tissue regeneration and in the control of pain. © 1994 Wiley-Liss, Inc. 相似文献