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Habitat Utilization (habitat + utilization)
Selected AbstractsEffects of herbivore species richness on the niche dynamics and distribution of blue sheep in the Trans-HimalayaDIVERSITY AND DISTRIBUTIONS, Issue 6 2009Tsewang Namgail Abstract Aim, To understand the community structure of mountain ungulates by exploring their niche dynamics in response to sympatric species richness. Location, Ladakh and Spiti Regions of the Western Indian Trans-Himalaya. Methods, We used the blue sheep Pseudois nayaur, a relatively widely distributed mountain ungulate, as a model species to address the issue. We selected three discrete valleys in three protected areas with similar environmental features but varying wild ungulate species richness, and studied blue sheep's diet and habitat utilization in them. Habitat variables such as slope angle, distance to cliff and elevation at blue sheep locations were recorded to determine the habitat width of the species. Faecal pellets were collected and microhistological faecal analysis was carried out to determine the diet width of blue sheep in the three areas with different ungulate species richness. Blue sheep's niche width in terms of habitat and diet was determined using the Shannon's Index. Results, The habitat width of blue sheep had a negative relationship with the number of sympatric species. However, contrary to our expectation, there was a hump-shaped relationship between blue sheep's diet width and the sympatric species richness, with the diet width being narrower in areas of allopatry as well as in areas with high herbivore species richness, and the greatest in areas with moderate species richness. Main conclusions, We suspect that the narrow diet width in allopatry is out of choice, whereas it is out of necessity in areas with high herbivore species richness because of resource partitioning that enables coexistence. We suggest that interactions with sympatric species lead to niche adjustment of mountain ungulates, implying that competition may play a role in structuring Trans-Himalayan mountain ungulate assemblages. Given these results, we underscore the importance of including biotic interactions in species distribution models, which have often been neglected. [source] Topographic spatial characterisation of grey seal Halichoerus grypus breeding habitat at a sub-seal size spatial grainECOGRAPHY, Issue 3 2001S. D. Twiss Expansion within breeding colonies may critically depend upon the availability of suitable breeding habitat. Here we use topographic modelling in a GIS to characterise suitable pupping habitat and accurately predict the pattern of colonisation in an expanding grey seal breeding colony-the Isle of May (Scotland), We use high resolution images from large format aerial photographs of the colony to generate sub-metre accurate Digital Terrain Models (DTMs), GIS modelling with these DTMs provides topographic measures of elevation, slope and ease of access to sea and freshwater pools at a 2 m grid cell size. Seal locations during the 1994 breeding season, with sex-age class, were also digitised from the same images. We examine how the physical attributes of cells (locations) with and without pups differ and identify areas suitable for pupping but remaining unoccupied during 1994. We predict patterns of future colonisation by characterising areas differentiated by the densities of pups within 5 m grid cells and identifying areas, both occupied or unoccupied, with a potential for increased future pupping densities. Our predictions were tested by examining pup distributions observed in the 1998 breeding season. Occupied sites were significantly closer to freshwater pools and access to the sea (p < 0.001) than unoccupied sites suggesting that proximity to water may restrict colony expansion before all areas of suitably flat terrain are occupied. All pup density classes occurred in sites with similar slope values and distance to pools. However, higher pupping densities occurred closer to access points (p = 0.014). Pup densities observed in 1998 revealed that our 1994 predictions were accurate (p < 0.0001). Only 12% of 466 grid cells had higher densities in 1998 than predicted, of which 88% differed by only 1 pup. These incorrectly classified cells occurred at the expanding edge of the colony (in a more topographically homogenous area) and at the main access points from the sea (major traffic zones). These results demonstrate the value of the accurate quantification of topographic parameters at the appropriate spatial grain (in this case below the size of the individual) for use in habitat classification and predictions of habitat utilization. [source] Vertical habitat utilization by large pelagic animals: a quantitative framework and numerical method for use with pop-up satellite tag dataFISHERIES OCEANOGRAPHY, Issue 3 2006JIANGANG LUO Abstract A quantitative framework and numerical methodology were developed to characterize vertical habitat utilization by large pelagic animals and to estimate the probability of their capture by certain types of fishing gear. Described are the steps involved to build ,vertical habitat envelopes' from data recovered from an electronically tagged blue marlin (Makaira nigricans) as well as from a longline fishing gear experiment employing temperature,depth recording devices. The resulting vertical habitat envelopes, which integrate depth and temperature preferences of tagged fish, are conducive for comparative studies of animal behavior and for calculation (and visualization) of degrees of overlap , be it among individuals, species or fishing gear. Results of a computer simulation evaluation indicated our numerical procedure to be reliable for estimating vertical habitat use from data summaries. The approach appears to have utility for examining pelagic longline fishing impacts on both target and non-target species and could point to ways of reducing bycatch via modification of fishing strategy or gear configuration. [source] Feeding ecology of wild migratory tunas revealed by archival tag records of visceral warmingJOURNAL OF ANIMAL ECOLOGY, Issue 6 2008Sophie Bestley Summary 1Seasonal long-distance migrations are often expected to be related to resource distribution, and foraging theory predicts that animals should spend more time in areas with relatively richer resources. Yet for highly migratory marine species, data on feeding success are difficult to obtain. We analysed the temporal feeding patterns of wild juvenile southern bluefin tuna from visceral warming patterns recorded by archival tags implanted within the body cavity. 2Data collected during 1998,2000 totalled 6221 days, with individual time series (n = 19) varying from 141 to 496 days. These data span an annual migration circuit including a coastal summer residency within Australian waters and subsequent migration into the temperate south Indian Ocean. 3Individual fish recommenced feeding between 5 and 38 days after tagging, and feeding events (n = 5194) were subsequently identified on 76·3 ± 5·8% of days giving a mean estimated daily intake of 0·75 ± 0·05 kg. 4The number of feeding events varied significantly with time of day with the greatest number occurring around dawn (58·2 ± 8·0%). Night feeding, although rare (5·7 ± 1·3%), was linked to the full moon quarter. Southern bluefin tuna foraged in ambient water temperatures ranging from 4·9 °C to 22·9 °C and depths ranging from the surface to 672 m, with different targeting strategies evident between seasons. 5No clear relationship was found between feeding success and time spent within an area. This was primarily due to high individual variability, with both positive and negative relationships observed at all spatial scales examined (grid ranges of 2 × 2° to 10 × 10°). Assuming feeding success is proportional to forage density, our data do not support the hypothesis that these predators concentrate their activity in areas of higher resource availability. 6Multiple-day fasting periods were recorded by most individuals. The majority of these (87·8%) occurred during periods of apparent residency within warmer waters (sea surface temperature > 15 °C) at the northern edge of the observed migratory range. These previously undocumented nonfeeding periods may indicate alternative motivations for residency. 7Our results demonstrate the importance of obtaining information on feeding when interpreting habitat utilization from individual animal tracks. [source] The effect of habitat management on home-range size and survival of rural Norway rat populationsJOURNAL OF APPLIED ECOLOGY, Issue 6 2008M. S. Lambert Summary 1Norway rat Rattus norvegicus populations are usually controlled with toxic baits, but this approach is increasingly recognized as having negative welfare and environmental impacts. An integrated strategy that relies less on rodenticides is therefore required. Here we investigate the possibility of using a resource-based approach to rat population management. 2Structurally complex habitats provide rat populations with nest sites and opportunities to avoid predators; modifying habitats to reduce structural complexity might reduce their potential to support rat populations. As part of an integrated approach, this could be more sustainable than relying exclusively on lethal control. However, in order to target habitat management efforts most effectively with minimum impact on other species, an understanding of habitat utilization by Norway rats is required. 3In this study, rat populations on farms in the north-east of England were monitored by radio-tracking and population counts before and after a single phase of habitat modification. Rats living near farm buildings utilized areas with high levels of cover; habitat modification reduced the survival rate and size of these rat populations. Rats living in field margins also preferred areas with high levels of cover, but they had significantly bigger home ranges than rats living near farm buildings and were largely unaffected by small-scale habitat management. 4Synthesis and applications. Our results indicate that habitat management near farm buildings has the potential to reduce the size of rat populations. As part of an integrated approach, this technique offers a way of reducing reliance on rodenticides. Habitat use by rats within the wider farm landscape suggests that land management practices have the potential to influence the size and distribution of rat populations; many game-rearing practices and environmental policies designed to create habitats for ,desirable' farm wildlife, inadvertently create desirable habitats for rats. [source] Spatial and temporal scaling in habitat utilization by klipspringers (Oreotragus oreotragus) determined using giving-up densitiesAUSTRAL ECOLOGY, Issue 5 2009DAVE J. DRUCE Abstract An animal's pattern of habitat use can reveal how different parts of its environment vary in quality based on the costs (such as predation risk) and benefits (such as food intake) of using each habitat. We studied klipspringer habitat use in Augrabies Falls National Park, South Africa using giving-up densities (GUDs; the amount of food remaining in a resource patch following exploitation) in experimental food patches. We tested hypotheses related to how salient habitat variables might influence klipspringers' perceptions of foraging costs. At small spatial scales (3,4 m), klipspringer GUDs did not vary with cover and open microhabitats, or with the four cardinal aspects (shading) around shrubs. Adding water adjacent to food patches did not influence GUDs, showing that water is not a limiting complementary resource to food. Generally, klipspringers do not appear to be physiologically constrained. There was no difference in GUDs between four daily time periods, or between summer and winter; however, a significant interaction effect of time-of-day with season resulted from GUDs during the midday time period in winter being significantly higher (perceived value lower) than during the same time period in summer. At moderate spatial scales (10,60 m), klipspringer GUDs increased with distance from rocks because of increased predation risk. Based on GUDs collected at the largest scale (two 4.41-ha grids), klipspringers preferred foraging at greater distances from drainage lines and on pebble and cobble substrates. Overall, this study has shown the efficacy of measuring GUDs to determine klipspringers' habitat utilization while foraging. [source] The influence of increasing population size and vegetation productivity on elephant distribution in the Kruger National ParkAUSTRAL ECOLOGY, Issue 3 2009KIM D. YOUNG Abstract Decisions to reduce the impacts of large herbivores on biodiversity in protected areas are often based on controlling their numbers. However, numbers per se may not be the foremost consideration when managing impacts. This is because density-related changes in distribution can also affect habitat utilization and hence, impact. In this study we tested whether changes in the distribution of African elephants are associated with increasing population size. We used spatially explicit count data collected during the dry seasons from 1998 to 2004 in South Africa's Kruger National Park. We did this at five spatial scales and in landscapes defined by vegetation, geology, climate and soils. We then investigated whether observed distributions and grid-cell-specific densities were associated with the remotely sensed Normalized Difference Vegetation Index (NDVI) as a measure of productivity and therefore food resource availability at the landscape scale. Consistent with density mediated changes, we found that elephant grid-cell occupancy increased with population size, while grid-cell-specific density became less variable. In addition, the combined distribution of bull groups and breeding herds became less clumped with increasing population size. We further found that within landscapes elephants were present on grid-cells with higher NDVI values, but that the influence of NDVI during the dry season on densities among landscapes may be weak. These results suggest that NDVI was more indicative of structural habitat choices such as woody vegetation than food availability per se. Our study highlights the need to consider factors other than population size alone when formulating management decisions to reduce large herbivore impacts on biodiversity in protected areas. [source] | ||||||||||