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The two semi-aquatic shrew species Neomys fodiens and Neomys anomalus are very similar in their ecology and morphology. Thus, they tend to be strong competitors for resources when they occur syntopically in habitats. We analysed the microhabitat selection of both species based on 14 parameters at two study sites in western Saxony (Germany). At the first study site, the results show segregation into different preferred microhabitats. In comparison to N. fodiens, N. anomalus occurred in low distance to the oxbow lake at places with denser herbal cover. Thus, we verified the hypothesis of Rychlik (Acta Theriologica 42:351-388 1997) who assumed differences in microhabitat niches for both shrew species to avoid competition. Furthermore, there was a spatial segregation within N. fodiens depending on their age. While adults occurred close to the water at areas with sparse herb layer, the juveniles and subadults were predominantly captured in some distance to the stream at denser vegetation. We assume that this is the result of different microhabitat preferences in N. fodiens depending on age and not a result of intraspecific antagonism. Moreover, the possibility to build subsurface burrows (and as an equivalent to this, crevice systems resulting of bank fixation with large stones) seems to be the main limiting factor for the occurrence of N. fodiens at the other surveyed site. At this site, no differences in microhabitats were visible between the age classes of N. fodiens.
A method was proposed for studying population density, microhabitat preference, daily activity and seasonal activity in small rodents. In this method, artificial tunnels (PVC pipes) imitating a natural system of burrows were applied. Their use by rodents was recorded by means of the electronic counters provided with a photoelectric cell. The study was conducted in an alder swamp 110 years old, located in the Kampinos National Park (52°25’N, 20°53’E) during 2003–2005. In this area, the bank vole Clethrionomys glareolus (Schreber, 1780) accounted for 90–99% of the captured rodents. The use of the tunnels by rodents (the number of passages) did not depend on their length within a range of 1–8 m applied in the experiment (P = 0.22). The tunnels were used by day and night, at the highest rate in the evening and at night. The use of tunnels increased when a bait was exposed in the vicinity (P = 0.001). It was positively correlated with population density (estimated with the CMR technique), and varied from season to season (in spring, summer, and autumn). The formula: density = 0.1717 + 0.0304 × mean number of passages per day, enabled the estimation of population density based on the number of passages through the tunnels. It has been found that a single tunnel was typically used by 5 individuals (mean 4.6 individuals, SD = 1.8). The location of tunnels had a significant effect on their use. Tunnels connecting fallen logs or bases of alders (hummocks) were more frequented than those leading to shrubby areas (P <0.000) or to microhabitats covered with herbaceous vegetation (P <0.001). This method enabled a multisided analysis of the behaviour of rodents at a minimum interference in the life of animals. Thanks to the application of electronic counters of passages, it was possible to obtain easily a large number of data. It is proposed to mark rodents with electronic transponders in the future studies to identify the individuals using artificial tunnels. This method could replace the methods used so far in the studies of small rodents, requiring trapping (CMR) or radio-telemetry.
The modes and efficiency of foraging in the terrestrial and aquatic habitats in water shrews Neomys anomalus Cabrera, 1907 and N. fodiens (Pennant, 1771) were compared in order to investigate if these species can avoid competition for food when they occur syntopically. Seven individuals of N. anomalus and five of N. fodiens, caught in the Białowieża Primeval Forest, were tested individually in the terrarium of size 3 x 0.5 m, containing a 0.25-m-wide 'stream' with flowing water of an average depth 25 cm. Six experimental variants, simulating different habitat conditions, were established. Each animal was tested in a given variant during 3 succeeding days for 6 h a day. In total, 738 h of shrews' behaviour were recorded in darkness using 2 infra-red sensitive video-cameras. Results obtained on four N. fodiens tested with similar methods (648 h; Ruthardt 1990) were included for comparison. N. anomalus swam and dived significantly shorter than N. fodiens, and they did not take food under water, even when there was no food on land. N. fodiens found and took food placed under water and foraged quite efficiently here. They found on average 17.7% of food portions placed under water in the most similar to natural conditions and 19.4% when there was no food on land. In both species foraging time on land was much longer than in water. The presence of natural structures increased duration and efficiency of foraging, but this influence was stronger in N. anomalus than in N. fodiens. These results and literature data suggest that in the wild: (1) both species forage in shallow water and in muddy grounds of wet habitats (wading foraging mode), and also in drier terrestrial habitats (epigeal and hypogeal foraging); (2) only N. fodiens forage in deep water (aquatic foraging); (3) the competition for food between N. anomalus and N. fodiens may be very weak, when potential aquatic prey are available.
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