Food and reproduction of Trichomycterus itacarambiensis, cave catfish from south-eastern Brazil

Trichomycterus itacarambiensis is a troglobitic (cave-restricted) catfish found in the Olhos ďÁgua Cave, Itacarambi Co., Minas Gerais, south-eastern Brazil. The cave is subject to a pronounced seasonality, and is flooded during part of the rainy season. The pigmentation degree is variable in T. itacarambiensis , a third of the population being true albinos; the eyes vary from normal to externally invisible. As expected for a cave-dwelling fish, T. itacarambiensis is a carnivorous generalist, which preys mainly on autochthonous insects and earthworms. It is a chemically oriented predator of bottom and surface animals, using foraging tactics also used by other cave catfishes, such as the pimelodids Pimelodella kronei and Imparfinis sp. However, bottom feeding seems to be more important for T. itacarambiensis than for the latter. There is a severe feeding stress during the dry season, when few individuals are able to get food. Reproduction is seasonal, with increased reproductive activity at the end of the rainy period, as recorded for Imparfinis sp., also a species living in a semi-arid region with a well-defined dry season. It is estimated that up to 50% of the female T. itacarambiensis can reproduce every year, a high proportion for a troglobitic fish species. At least during the study period, pigmented individuals reproduced more frequently than the albinos.     

Fish habitat preferences in large streams of southern France

1. Relationships between fish and their habitat over whole geographic regions, which are evident from studies of many streams and species, can improve understanding of lotic communities and provide reliable management tools. Nevertheless, most habitat preference studies have been based on single sites, and confined to small streams and to game species.
2. Regional habitat preference models, based on local velocity, depth and roughness, were developed for twenty-four species and their size classes commonly found in large European streams. Fish surveys were conducted in six large streams in southern France over an 8-year period. To limit the influences of habitat variables other than those studied, we estimated fish preferences within each survey and averaged this information across surveys. Preferences were fitted with confidence intervals and their sensitivity to field uncertainty was evaluated.
3. Most species and size classes had significant preferences for local habitat conditions which were consistent across the region. Habitat preferences predominant in the region overall were not always observed at any one site, but habitat conditions preferred on average in the region were never actually avoided locally. These results support the use of regional preference models for fish and the development of similar models for other lotic groups whose sensitivity to local habitat conditions has been reported elsewhere.     

Habitat preferences of the Andean bear (Tremarctos ornatus) in the Bolivian Andes

Habitat preferences of the Andean bear Tremarctos ornatus were studied within two adjacent protected areas in the north-western Bolivian Andes. Standard transects measuring habitat variables and bear sign frequency were used spanning seven different vegetation types. Andean bears were present at 28 of 33 sampled sites and actively preferred high-elevation elfin forest and upper montane humid forests, and used high-elevation humid 'páramo' grasslands and middle montane humid forests according to their availability. Bears were absent from dry montane and Andean foothill forests and relative abundance was low in lower montane humid forests. Elevation and basal area of food items were the variables most closely related to the relative abundance.     

Effects of riparian canopy cover on salmonid diet and prey selectivity in low nutrient streams

This study focuses on stream sections within a relatively low nutrient catchment in south‐east Ireland in an attempt to characterize the probable effects of riparian canopy on salmonid diet and prey selectivity within two size classes of nursery stream. Sampling found that brown trout Salmo trutta diet changed significantly in response to riparian canopy regardless of stream size. The observation that S. trutta within unshaded stream sites did not feed on drifting terrestrial prey items to the same extent as those within shaded streams was not due to a lack of availability of this food source. There was no evidence to suggest that S. trutta selectively choose particular prey items.     

Static habitat partitioning and dynamic selection by sympatric young Atlantic salmon and brown trout in south-west England streams

Direct underwater observation of micro‐habitat use by 1838 young Atlantic salmon Salmo salar [mean L_T 7·9 ± 3.1(s.d.) cm, range 3·19] and 1227 brown trout Salmo trutta (L_T 10·9 ± 5·0 cm, range 3·56) showed both species were selective in habitat use, with differences between species and fish size. Atlantic salmon and brown trout selected relatively narrow ranges for the two micro‐habitat variables snout water velocity and height above bottom, but with differences between size‐classes. The smaller fishes <7 cm held positions in slower water closer to the bottom. On a larger scale, the Atlantic salmon more often used shallower stream areas, compared with brown trout. The larger parr preferred the deeper stream areas. Atlantic salmon used higher and slightly more variable mean water velocities than brown trout. Substrata used by the two species were similar. Finer substrata, although variable, were selected at the snout position, and differences were pronounced between size‐classes. On a meso‐habitat scale, brown trout were more frequently observed in slow pool‐glide habitats, while young Atlantic salmon favoured the faster high‐gradient meso‐habitats. Small juveniles <7 cm of both species were observed most frequently in riffle‐chute habitats. Atlantic salmon and brown trout segregated with respect to use of habitat, but considerable niche overlap between species indicated competitive interactions. In particular, for small fishes <7 cm of the two species, there was almost complete niche overlap for use of water depth, while they segregated with respect to water velocity. Habitat suitability indices developed for both species for mean water velocity and water depth, tended to have their optimum at lower values compared with previous studies in larger streams, with Atlantic salmon parr in the small streams occupying the same habitat as favoured by brown trout in larger streams. The data indicate both species may be flexible in their habitat selection depending on habitat availability. Species‐specific habitat overlap between streams may be complete. However, between‐species habitat partitioning remains similar.     

Leaf-Litter Arthropods in Restored Forests in the Colombian Andes: A Comparison Between Secondary Forest and Tree Plantations

Tree monocultures of native and exotic species are frequently used as tools to catalyze forest recovery throughout the tropics. Although plantations may rapidly develop a canopy cover, they need to be evaluated as habitat for other organisms. We compared samples of leaf‐litter arthropods from two elevations in restored forest in the Colombian Andes. At the upper elevation (2,430 m), we compared native Andean alder (Alnus acuminata) plantation and secondary forest, and at the lower elevation (1,900 m) exotic Chinese ash (Fraxinus chinensis) plantation and secondary forest. Samples were obtained in two periods, March–April and September 1995. Species richness and abundance of arthropods were highest in secondary forest at the lower elevation. There were no differences in richness between both plantations and high‐elevation forest. Arthropod richness and abundance increased in the second sampling period in both secondary forest types and the ash plantation but not in the alder plantation, reflecting population recovery after the dry season. Alder leaf litter apparently buffered seasonal variations in arthropod richness and abundance. Composition of morphospecies was different among forest types. Although arthropod richness was lower in ash plantations compared to secondary forest, plantations still provided habitat for these organisms. On the other hand, the alder plantation was not different from secondary forest at the same elevation. At our site, plantations are embedded in a forested landscape. Whether our results apply to different landscape configurations and at different spatial scales needs to be established. The use of plantations as a restoration tool depends on the objectives of the project and on local conditions of forest cover and soils.     

Simple predictions of instream habitat model outputs for fish habitat guilds in large streams

1. In the context of a generalised modification of hydraulic conditions in medium to large streams, modelling the impacts of stream regulation on fish communities in multiple streams is an important challenge for basic and applied freshwater ecology. Conventional instream habitat models such as PHABSIM link a hydraulic model with preference curves for various species to estimate habitat value changes with discharge in stream reaches. Despite world‐wide applications, they have been scarcely used in multiple sites with multiple species. 2. We assigned 21 size classes of European fish species to four habitat guilds (cluster analysis grouping size classes with comparable microhabitat preference curves). Then, we ran a conventional instream habitat model on 28 French stream reaches belonging to the `barbel zone', to estimate habitat values versus discharge curves for the 21 size classes. We summarised the outputs as mean habitat values for guilds, and tested if they were predictable from average characteristics of reaches (discharge, depth, width, particle size). 3. As was obtained elsewhere for populations, habitat values for guilds were strongly related to average, dimensionless characteristics of reaches. The Reynolds number of reaches, equivalent to a discharge per width unit, reflected most of the discharge‐dependent changes in habitat values (within reaches). In particular, habitat values of species preferring bank (respectively midstream) microhabitats decreased (respectively increased) with increasing Reynolds number. The Froude number at median discharge was the major predictor of reach‐dependent but discharge‐independent variations in habitat values. Habitat values of species preferring riffle versus pool or bank microhabitats were higher in reaches with high Froude numbers. These relationships were consistent with existing knowledge on the different species. 4. Such results suggest that the input variables required to estimate habitat values for fish communities can be greatly simplified, as illustrated by a general estimation of the sensitivity of species preferring midstream habitats to discharge changes in any reach. Cost‐efficient alternatives to conventional instream habitat models should facilitate their validation in multiple sites, a point that remains critical in instream habitat modelling of fish communities.     

Historical distribution,habitat requirements and feeding ecology of the genus Equus (Perissodactyla)

相似文献   

Summer habitat relationships of barbels in south‐west Spain

An analysis was made of the associations with local habitat features of barbels ( Barbus sp.) of a Mediterranean river basin. The analysis was based on the presence data from sampling the upper, middle, and lower reaches of 31 rivers in the middle Guadiana River basin (south‐west Spain). Numerous local habitat variables were determined, including the river's size and substratum, physicochemical variables of water, and the aquatic and riparian vegetation. For each species, a univariate analysis was performed using preference indices, and logistic regression was used to construct a parsimonious multivariate model and Gaussian response models with the most influential variables, quantifying the species' limits of tolerance. Distinct habitat associations for every species were obtained, mainly relating Barbus comiza to the larger habitats and higher water levels, Barbus microcephalus to the maintenance of lotic conditions and Barbus sclateri to more fluctuating rivers. Barbus steindachneri showed a different habitat relationship from that of the genetically almost identical B. comiza . Cover played a significant role in all but B. comiza .     

Skull shape variation in extant and extinct Testudinata and its relation to habitat and feeding ecology

Turtles (Testudinata) are a diverse group of reptiles that conquered a broad set of habitats and feeding ecologies over the course of their well‐documented evolutionary history. We here investigate the cranial shape of 171 representatives of the turtle lineage and the relationship of shape to different habitat and diet preferences using two‐dimensional geometric morphometrics. The skull shape of extant turtles correlates with both ecological proxies, but is more affected by habitat than diet. However, the application of these correlations to extinct turtles produces mostly flawed results, as least when compared to external data such as sedimentary environment, highlighting that the morphospace held by extant turtles is not necessarily the optimal location in tree space for a particular ecology. The inability of this study to correctly predict the ecology of extinct turtles is likely related to the fact that the shape of turtle skulls is dominated by the emarginations and jaw closure mechanisms, two shape features unrelated to habitat or feeding ecology. This indicates that various specializations that are apparent in the skull only contribute little to overall shape.