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Gap-Crossing Decisions by the Red Squirrel, a Forest-Dependent Small Mammal   总被引:3,自引:0,他引:3  
Abstract:  Forest-associated species in fragmented landscapes must traverse potentially inhospitable gaps to move between habitat patches. Although conservation biologists advocate connecting patches with corridors or improving the matrix to make it suitable for movement, little is known about the factors influencing gap-crossing decisions for most species. We investigated gap crossing by the red squirrel ( Tamiasciurus hudsonicus ) in logged landscapes in southeastern Alaska, where the species avoids microhabitats associated with gaps created by clearcutting. We released individuals across clearcuts and determined the routes they took home with tracking spools and radio telemetry. Of 36 adult red squirrels translocated across six clearcuts, 14 crossed clearcuts to reach home. Squirrels were more likely to cross clearcuts if the detour efficiency (distance to home crossing gap divided by distance of forested detour) was low, indicating an ability to compare distances along alternate routes and travel costs or risks in different habitats. No other landscape metrics, such as gap size or crossing distance, predicted crossing behavior. Red squirrels of low body mass were more likely to cross clearcuts, where the probability of encountering conspecifics is low. Distance predicted route choice for squirrels detouring around clearcuts. Indirect evidence suggests that perceived predation risk, energetic costs, or both are higher in clearcuts. Detour efficiency reportedly influences the gap-crossing decisions of some forest-associated birds, but this is the first demonstration of its role in gap-crossing decisions by a mammal.  相似文献   

3.
A monitoring programme during 4 years (1993-1996) was established in four eutrophic marine basins along the Mediterranean coast of Alexandria (Egypt) to follow the occurrence of a newly recorded dinoflagellate Gymnodinium catenatum and ambient environmental conditions. the species achieved its massive occurrence in warm seasons at low salinity, density stratified water column and different nutrient concentrations. A simple statistical approach showed temperature and phosphate to effect its distribution. Apparently no cases of toxic effect have accompanied the occurrence of G. catenatum. the regular occurrence of the species during the 4 year survey mean the existence of its benthic resting cysts, which certainly have important implications for its distribution dynamics.  相似文献   

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Summary Seventeen red squirrels (Tamiasciurus hudsonicus) were displaced and released about 600 or 2000 m from their home site, and the routes they followed during several hours after release were recorded. The analysis of these routes shows that, in their first attempts to leave the release site area, the squirrels' orientation is non-random with respect to the home direction (Fig. 2a). However, after a few hundred meters in this initial direction, the animals tend to go back to the release site area, and then to perform a series of radial forays centered on the latter.The results suggest that, in the conditions of the experiment, the squirrels have some information on the direction, but not on the distance to the home site. Their behavior appears to be governed by two complementary (but occasionally conflicting) strategies, one being to use the directional information available, the other not to proceed further than a distance which corresponds to the distance normally covered in spontaneous exploratory trips. It is argued that this double strategy is appropriate for spontaneous homing trips consecutive to an exploratory foray.  相似文献   

6.
In the field of tourism, where environmental resources are the primary attraction, ecotourism is one of the sustainable approaches now considered as an alternative when considering today's increasing environmental problems. Indeed, according to the World Tourism Organisation, ecotourism is the fastest growing market within the tourist industry. The purpose of this study is to determine tourism activities sensitive to the environment, to help tourism in Turkey and neighbouring countries, and to help spread ecotourism by protecting biological species. The Kazdagi (Mt. Ida) area in Turkey is used as an example and case study.  相似文献   

7.
Approximately 22 species of sea anemones and 20 species of alcyonarians were found on the reef fringing the shallow water at Eilat (Gulf of Aqaba) and other localities along the Red Sea coast of the Sinai Peninsula. Investigations showed that these 2 groups of non-scleractinian coelenterates from (on different substrates) well identified colonies, part of them inhabiting sandy bottoms, other groups growing on the reef surface. Observations lead to the conclusion that several of the sea anemones and alcyonarians can act, under certain conditions, as factors limiting the development of hermatypic corals. In some areas, several species of the 2 groups of animals are found together with their symbiotic partners, such as fishes and crustaceans.This research has been sponsored partly by a grant from the Smithsonian Institution, No. SFC-7-0074 to L. B. Slobodkin (N. Y.) and L. Fishelson (T.-A.).  相似文献   

8.
Growth and age of Chaetodon larvatus were studied using growth bands in otoliths and length-frequency analyses. Otoliths of 180 C. larvatus were extracted and measured. Polished sections of sagittae revealed alternating opaque and translucent bands corresponding with a seasonal growth pattern. Both mass and size of the otoliths continue to grow steadily throughout life. Length-at-age data revealed very fast growth during the first year. Growth proceeded at a decreasing rate during the second and the third year; fishes older than 3 years did not grow noticeably. No difference in growth patterns between males and females could be detected. The growth parameters obtained for the whole population are: the asymptotic length (L )=10.64 cm, growth constant (K)=1.14 year−1 and the theoretical age at length zero (t 0)=−0.30 year. The maximum age recorded was 14 years. Length frequency data collected at a recruitment site confirmed the fast growth of juveniles.  相似文献   

9.
研究了不同母质来源的红壤剖面层中稀土元素结合形态的变化以及可溶态稀土元素含量的变化,结果表明,红壤中稀土元素的有效性较其他类型土壤为高,可溶态稀土元素在土壤稀土总量中所占的比例可达6%~7%左右,稀土的有效性主要与土壤中粘土矿物及有机质等组分对稀土的吸附有关。  相似文献   

10.
The distribution of the main herbivorous fishes (Acanthuridae, Scaridae, Siganidae) was studied across a coral reef of the Jordanian coast in the Gulf of Aqaba (Red Sea). Visual counts were realized by diving along transects (200 m long and 5 m wide), parallel to the shore, at 10 stations located from the lagoon to 40 m deep on the outer reef slope. Herbivorous reef fishes reach their highest abundance on the reef front, where 234 fishes were counted per 1,000 m2. Their density decreases on the reef flat, with an average of 150 fish 1,000 m-2, and is lowest on the outer reef slope (69 fish 1,000 m-2). Surgeonfishes form 63% of the herbivorous ichthyofauna, parrotfishes 35%, and rabbitfishes 2%. Families and species display different distributions according to biota. The Acanthuridae dominate on the reef flat, whereas the Scaridae are more numerous on the outer reef slope. The evolution of the social structure of the main species was observed: the adults generally school in the lagoon and on the reef flat, but are mainly solitary on the reef slope. The distribution of juvenile individuals is more restricted: they are concentrated on the reef front and on the upper part of the reef slope.This study is part of a cooperation programme between the University of Nice (France) and the University of Jordan, to study the ecology of the coral reefs and the surrounding waters of the Jordanian coast (Gulf of Aqaba, Red Sea)  相似文献   

11.
A total of 12 feeding experiments were conducted in the northern Gulf of Aqaba during spring (March/April) and autumn (September/October) 2002 at the Marine Science Station (MSS) in Aqaba. Females of three species of clausocalanids were selected: Clausocalanus farrani, C. furcatus and Ctenocalanus vanus. Natural occurring particle (NOP) larger than 5 μm were investigated as food source. The ambient chlorophyll a concentration at sampling depth (∼70 m) ranged between 0.15 and 1.00 μg chl a l−1 and NOP concentrations ranged between 1.78 and 14.0 × 103 cells l−1 during the sampling periods. The division of particles into five size classes (5–10, 10–20, 20–50, 50–100 and >100 μm) revealed that most of the particles were found in the size classes below 50 μm (81–98%), while most of the natural occurring carbon (NOC) was concentrated in the size classes larger than 20 μm (70–95%). Ingestion rates were food density dependent rather than size dependent ranging between 0.02 and 1.65 × 103 NOP ind−1 day−1 and 0.01 and 0.41 μg NOC ind−1 day−1, respectively, equivalent to a body carbon (BC) uptake between 0.4 and 51.8% BC day−1. The share of the size classes to the total ingestion resembled in most cases the size class composition of the natural particle community.  相似文献   

12.
絮凝剂P(AM-DMC)对染料活性艳红K-2BP具有很好的脱色及去除CODCr性能,脱色率和CODCr去除率分别为97.18%、75.7%。脱色效果受絮凝剂用量、电荷密度、特性粘度、外加盐浓度及溶液pH值影响。红外光谱、可见吸收光谱及电荷量分析表明,P(AM-DMC)对活性艳红K-2BP的絮凝脱色过程中电荷中和起着重要作用,絮凝剂分子中的—N+(CH3)结构与染料分子中的-SO3-发生化学反应,同时也有分子间氢键形成,从而使水中染料分子聚集沉降。  相似文献   

13.
Molluscan assemblages were studied on fringing reefs (reef flats, Millepora-fringing reefs, fringing reefs with massive corals) and fore-reef hard substrata (coral patches, coral carpets and small patch reefs) in the Gulf of Aqaba at water depths ranging from the intertidal to 26 m. A total of 1,665 molluscan individuals from 51 taxa was counted on 44 transects, which covered 220 m2 at eight diving sites. The most important molluscs in the assemblage were the parasitic gastropod Coralliophila neritoidea, the encrusting gastropod Dendropoma maxima and the coral-associated bivalve Pedum spondyloideum. The dead assemblage, in contrast, was dominated by encrusting bivalves (Ostreoidea, Chamoidea, Spondylidae) and the coral-predating gastropod Drupella cornus. Distinct molluscan assemblages inhabit each of the three fringing reef-habitats and most of the important depth-related community changes occurred within the uppermost 5 m. In contrast, the three deeper fore-reef habitats are characterized by a more uniform molluscan composition. Molluscan assemblages were more dependent on substrata and their coral associations than on water depth. Comparisons with other published studies indicate that reefoidal hard substrata in the northern Red Sea are largely characterized by similar species-abundance patterns. The minor differences to other Red Sea studies probably reflect the northern, isolated position of the Gulf of Aqaba, the lack of certain molluscan habitats, and the differential impact of anthropogenic influences. Strong differences between living and dead assemblages in Aqaba are similar to those observed in other regions and are due to distinct biases in the dead assemblage. Molluscs closely associated with living corals (mostly bivalves and Dendropoma) can easily be overgrown after death and are thus undetectable in visual censuses. Some gastropod taxa are preferentially transported into surrounding soft-substrata postmortem or redistributed by hermit crabs. Such complex relationships between ecology and taphonomy are crucial in evaluating the quality of the molluscan fossil record in coral reef environments. The comparison of our results with literature data documents an increase in coral predators during the last two decades in the northern Red Sea. Due to the greater mollusc biodiversity in the shallower Aqaba reef habitats, damage to this coral reef zone would have the greatest impact on the overall mollusc community.  相似文献   

14.
Chambers and canal system in the shells of Operculina ammonoides (Gronovius) and Heterostegina depressa d'Orbigny contain different protoplasm. The connections between the two main parts of the protoplasmic body are much smaller than the connections from chamber to chamber by the stolo system. The connections between chamber and canal system are located in the marginal sulcus and at the base of the chamber. The chamber protoplast (including the stolo system) is protected by a relatively thick, lamellar, mucopolysaccharide membrane — called organic lining — which represents also the template for the mineralization of the shell. Together, organic lining and shell form the cell wall. Over the pore holes in the lateral chamber walls, the organic lining thins out, but is not perforated. The plasma membrane below the organic lining seems to be differentiated by a bossy surface with comparatively coarse granules. The symbionts are concentrated below the lateral wall of the chambers, nestling against 2 or 3 pore-hole depressions. The differentiation of the organic lining, the plasma membrane below the pore holes, and the position of the symbionts in the chamber plasma point to a physiologic relationship between pores and symbionts. The cell organelles in the chamber protoplasm indicate the mainly metabolic function of the chamber protoplast. The protoplasm in the canal system is covered only by the plasma membrane, and is particularly rich in microtubuli similar to ordinary foraminiferal rhizopods. The canal system is, therefore, interpreted as consisting of a system of invaginations of the cell wall determining the morphology of proximal parts of the pseudopods.  相似文献   

15.
The sponge Latrunculia magnifica was found to be toxic for fish. A toxin has been isolated from this sponge by organic extraction-column chromatography and thin-layer chromatography. Several chemical properties of the toxin were determined by spectroscopic analysis. Toxicity tests were performed on the fish Gambusia affinis. In vitro experiments showed the toxin to be a cholinesterase inhibitor.  相似文献   

16.
The food of 3 feather-stars, Lamprometra klunzingeri Hartlaub, 1890), Heterometra savignii (J. Müller, 1841) and Capillaster multiradiatus (Linnaeus, 1758), from the shallow water of Eilat (Red Sea) was found to be composed of planktonic and semi-benthalic organisms with a strong dominance of zooplankton. Monthly analyses of stomach contents showed seasonal changes in the participation of various systematic units in the diet. Food-comprising organisms were found to be selected according to size, and those measuring up to 400 formed 90% of the diet.This research has been sponsored partly by the Oceanic Biology Branch, Office of Naval Research, U.S.A. under contract N 62558-4556 and contract F 671052 67C 0043 between the Office of N.R. and the Tel-Aviv University. It represents part of the M.Sc. thesis of the first named author (in the framework of Red Sea investigations headed by Dr. L. Fishelson).  相似文献   

17.
The early ontogeny of Peraclis reticulata, Limacina inflata, L. trochiformis, Styliola subula, Clio convexa, Cl. cuspidata, Hyalocylis striata, Creseis acicula, Cr. virgula, Cuvierina columnella, Diacria quadridentata, D. trispinosa, Cavolinia uncinata, C. longirostris, and C. inflexa is described. Their larval development is characterized, and strategies of ontogeny of pteropods are viewed in the context of their biology and taxonomic position. The reconstruction of the juvenile shell into the voluminous adult shell in Diacria spp. and Cavolinia spp. is described in detail. The general features of the early ontogeny of Thecosomata does not deviate from those of other marine gastropods in essential ways as has been proposed by some authors, but postmetamorphic retainment of the sinistral coiling of the shell as well as reshaping of the juvenile shell in Diacria spp. and Cavolinia spp. are unique features of the euthecosomatous pteropods.  相似文献   

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金城山植物群落优势种群的种间关系   总被引:1,自引:1,他引:1  
采用2×2列联表的χ2检验、Ochiai关联度指数、Pearson 相关系数和Spearman秩相关系数检验,研究了南充金城山植被24个优势种群共276个种对的种间关联(或相关).结果表明: 1) χ2检验有15个种对呈正相关, 3个种对呈负相关,正负关联比为5.0,其余258种对联结程度不显著; Pearson相关系数检验23个种对正相关, 1个种对呈负相关,正负关联比为23.0,其余252种对联结程度不显著; Spearman秩相关系数检验24个种对呈正相关, 5个种对呈负相关,正负关联比为4.8,其余247种对联结程度不显著; 2)χ2检验只能反映出种对间联结性显著与否,经χ2检验不显著的种对并不意味着其间没有联结性,故只有与Ochiai关联度指数结合,结论才比较合理; 3)与Pearson相关系数检验相比, Spearman相关系数检验具有较高的灵敏度; 4) 按照对环境的适应方式和主导生态因素,24个优势种可划分为4个生态种组,同一生态种组内,各种间具有较强的正联结,表明其资源利用方式和生态要求相似,而不同组间联结较为松散,主要是由于它们具有不同的生物学特性,对生境具有不同的生态适应性和相互分离的生态位所致.桤木、千筋树、插田泡、乌蔹莓和小叶菝葜等呈独立分布.图4表4参19  相似文献   

20.
In order to provide a background picture of the water quality of the Egyptian Red Sea a number of hydrological and chemical parameters have been measured bimonthly in 2000. Few data are available on this area, which is apparently subjected to an increasing human impact due to recreational (swimming and diving), industrial (mainly phosphate shipping and industry) and fishing/harbor activities. The results of the present study indicate that changes in the salinity and pH were not significant with highly oxygenated seawaters. The levels of suspended solids (as total suspended matter, TSM) and chlorophyll-a (Chl-a) were generally low and showed an homogeneous distribution in the study region. The ratio of chlorophyll-a to total suspended matter concentrations increased between November and March and decreased from May to September. Chlorophyll-a was significantly correlated with transparency and total suspended matter concentrations in July, September and November. Nitrogen, phosphorus and reactive silicate concentrations were generally low, and allowed classifying the Egyptian Red Sea coastal water as oligotrophic to mesotrophic. The middle region of the study area, which was located between Safaga and Qusair displayed relatively high phosphate contents when compared with other coastal areas. The high values of N:P ratios indicate that PO 4 -P is the limiting factor for phytoplankton growth in the Red Sea coastal waters, with the possible exception of the middle region. Significant relationships were found between chlorophyll-a concentrations and nutrient levels in different sampling periods. Spatial distribution patterns of the studied variables revealed that productivity of the Red Sea coastal waters is mostly controlled by phosphate concentrations, salinity, temperature and dissolved oxygen.  相似文献   

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