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641.
On the Solovetskiye Islands, subtundra forests and forest-tundra crooked forests are considered to be zonal biocenoses, as this region is intersected by the 12°C isotherm for July, which marks the boundary between the northern taiga and forest-tundra zones in northern Europe. The formation of extrazonal tundras on the islands is attributed to the cooling effect of the sea and the prevalence of cold northeasterly winds in the growing period. Herbaceous and herb-bilberry forests similar to their middle-taiga counterparts develop in this region due to a convective heat flow anomaly of high intensity (up to 40–50 W/m2). The phenomenon provides evidence for the existence of an active heat source in the crust under the archipelago. This source is probably a diapir fold involving the upward movement of the mantle. 相似文献
642.
643.
Variation in the reproduction of Varroa jacobsoni mite was studied in relation to the expansion of the range of its parasitism on the honeybee. Geographic differences in the seasonal dynamics of mite reproduction in the nests of bee families were revealed. Variation in the sex ratio of mites and the factors inhibiting their reproduction at the northern boundary of the honeybee range are considered. The forms of parthenogenetic reproduction in V. jacobsoni are discussed. 相似文献
644.
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646.
G. W. Uetz William J. McClintock Douglas Miller Elizabeth I. Smith Kristina K. Cook 《Behavioral ecology and sociobiology》1996,38(4):253-257
Males of the brush-legged wolf spider Schizocosa ocreata (Hentz) have conspicuously decorated forelegs used in courtship and agonistic displays. Approximately one in five juvenile
males has a missing or regenerating foreleg, and regeneration of a leg lost during development usually results in the absence
of a decorative tuft on that leg. The subsequent asymmetry in this male secondary character significantly decreases success
in both courtship of females and male-male agonistic interactions. Experimental removal of tufts from one leg of previously
successful symmetric males produces similar results. As a test for concomitant behavioral effects, female spiders were shown
video images of a courting male with symmetric tufts and the same video image altered to have asymmetric tufts. Female receptivity
to the asymmetric video image was lower. In contrast to fluctuating asymmetry resulting from developmental instability, leg
tuft asymmetry in S. ocreata most likely arises from a single event during ontogeny – possibly leg loss from an aggressive or predator encounter – and
may serve as a quality indicator in female mate choice.
Received: 27 July 1995/ Accepted after revision: 19 November 1995 相似文献
647.
Martin Drechsler Karin Johst Frank W?tzold Michael I Westphal 《Ecological applications》2006,16(5):1959-1966
Flexible conservation management, where measures (e.g., mowing of meadows, removing invasive species) are selected in each decision period depending on the current state of the ecological system, is generally perceived as superior to fixed management, where the same measure is applied in each decision period independent of the current state of the system. In past comparisons of fixed and flexible conservation strategies the additional costs that arise only in flexible strategies have usually been ignored. In this paper, we present a framework to integrate costs of flexible management into the evaluation of flexible conservation strategies. Using the example of an endangered butterfly species we demonstrate that the costs of flexible management may reverse the rank order of flexible and fixed conservation strategies, such that fixed strategies may lead to better ecological results than flexible ones for the same financial budget. 相似文献
648.
Statistical analysis of the combined influence of lake surface area (S), water pH, and total dissolved solids (TDS) on the formation of zooplankton communities in lakes has been made on the basis of available data on the number of species (N sp ) of pelagic zooplankton in 256 lakes of the temperate zone of Europe, Asia, and North America. Graphic analysis and analysis of variance have shown that extremely high or extremely low values of pH and TDS inhibit lake zooplankton. If the value of one of these factors is extremely high, any increase in the other factor is favorable for the inhibited zooplankton, and this second factor determines the value of N sp . 相似文献
649.
Mal'kova M. G. Pal'chekh N. A. Yakimenko V. V. Kuz'min I. V. 《Russian Journal of Ecology》2004,35(1):27-34
The spatial structure of populations has been studied in two rodent species inhabiting the subzone of meadow steppes of the steppe zone of Omsk oblast: the narrow-sculled vole (Microtus gregalis Pall.) and steppe lemming (Lagurus lagurus Pall.). Their populations are represented by combinations of territorial family groups whose structure and spatial distribution vary by season depending on population density, the phase of the population cycle, and the status of their members in the population. In the areas cohabited by M. gregalis and L. lagurus, the pattern of territory use and the rhythm of animal activity during the day depend primarily on their total density: under conditions of low density, the population groups of both species are spatially separated; at increased density, they are distributed with respect to the pattern of daily activity. Both species jointly use part of the territory but at different times of day: M. gregalis, mainly at night and in the morning; L. lagurus, in the daytime. 相似文献
650.
T.I. Khan 《The Environmentalist》1997,17(4):283-287
Director of environmental studies at the Indira Gandhi Centre for Human Ecology, Environmental and Population Studies at the University of Rajasthan. This paper describes the biodiversity in the north-western Indian State of Rajasthan, its relationship with the environment and the existing human and livestock populations. As the biodiversity is depleting in this area due to zoogenic and anthropogenic reasons, certain pragmatic conservation strategies are advocated. The north-western part of India is occupied by a desert ecosystem, the Thar Desert. Animal husbandry is the major livelihood in the region, followed by agriculture. The vegetation, which is predominantly xerophytic and quite sparse, occurs in great variety. Six hundred and eighty-two plant species and 390 animal species have been identified from the Thar Desert. Many plant and animal species have become endangered due to zoogenic and anthropogenic activities. Plants such as Calligonum polygonoides, Tecomella undulata and Prosopis cineraria urgently require conservation. 相似文献