排序方式： 共有18条查询结果，搜索用时 15 毫秒
1.
Although oaks (Quercus spp.) have historically dominated many forests in eastern North America, forest composition is changing due to anthropogenic impacts on disturbance regimes. Silvicultural practices, such as partial harvesting, are one component of management to promote oak regeneration. From 2007 to 2009 our research examined nest-site selection and nesting success for a guild of five canopy songbirds in upland mixed-oak forests in southeastern Ohio, USA. We monitored >700 nests across three state forests in both open canopy shelterwood stands harvested to approximately 50% stocking, and closed-canopy mature second-growth. Habitat attributes, including topography, canopy structure, and floristics, were measured at nest sites and random plots ?100 m from nests representing microhabitat available within the territory. Canopy songbirds selected specific topographic microclimates: Eastern Wood-pewees (Contopus virens) nested on xeric ridgetops, Blue-gray Gnatcachers (Polioptila caerulea) favored valleys, and Cerulean Warblers (Dendroica cerulea) preferred productive northeast-facing slopes. Nest sites differed among species in terms of concealment, nest support, topographic position on the slope, and basal area of trees >38 cm dbh. Four of the five focal species selected Quercus alba as the nest substrate more than twice as much as available, and three species avoided Quercus rubra. Daily survival rates of nests were negatively associated with basal area of red oak species (both Quercus velutina and Q. rubra) for several species individually and across the canopy-nesting guild. Additional factors related to success included time of season for Eastern Wood-pewees, nest age for Cerulean Warblers, and concealment and size of the support branch for Scarlet Tanagers (Piranga olivacea). In the long-term management for oak regeneration could benefit canopy songbirds, but our results indicate that white oaks, especially Q. alba, may be preferable to red oak species. 相似文献
2.
Gisle K Sverdrup Justin J Meager Anders Fern Jon E Skjraasen Petra Rodewald Anne G V Salvanes Torbjrn Jrvi 《Aquaculture Research》2011,42(10):1539-1548
Studies of contest competition between wild and farmed fish have mostly focused on fish with strongly territorial behaviour. Little is known about species with more plastic social behaviour, such as Atlantic cod (Gadus morhua L.), a species that can either aggressively defend territories or shoal. There is also concern that cod that escape from farms will compete with wild populations. We examined dyadic contest competition between wild and farmed juvenile cod using an intruder–resident experimental set‐up in the laboratory. No prior residency advantage was observed, but the differences between farmed and wild cod were clear. Farmed cod were more submissive than wild cod and fled earlier during contests, which suggests that wild fish often out‐compete farmed intruders. Both fish types initiated aggression earlier against fish of the same background. A multivariate analysis of 11 different behavioural traits indicated that a group of 59% of farmed fish were behaviourally very similar to the 55% most submissive wild fish. These results suggest that wild juvenile cod may be quite robust towards competition for food and shelter from juvenile farmed cod, but further research is needed to verify this pattern. 相似文献
3.
Despite the widely accepted idea that shaded plantations are valuable habitats for Neotropical migrants in disturbed landscapes, little empirical evidence is available in relation to the quality of this habitat for Neotropical-Nearctic migratory birds in the Andes. We evaluated the suitability of shaded plantations for overwintering Neotropical-Nearctic migratory birds by examining diurnal and seasonal variation in body condition of migrants in these agroforests in the Andes. During October to April 2008–2009 and 2009–2010, we mist-netted eight species of Neotropical-Nearctic migrants in shaded plantations in the Colombian Andes. Body condition improved throughout the day for Cerulean Warbler (Setophaga cerulea), Blackburnian Warbler (Setophaga fusca), Tennessee Warbler (Leiothlypis peregrina), and especially Canada Warbler (Cardellina canadensis). Similarly, body condition improved across the season for Tennessee Warbler, Rose-breasted Grosbeak (Pheucticus ludovicianus), and Summer Tanager (Piranga rubra). Our results provided additional evidence that several common Neotropical migrants, including species of conservation concern such as Cerulean Warbler and Canada Warbler, may improve their body condition in shaded plantations. However, about half of the species assessed in this study did not show any significant improvement in their body condition (e.g. Red-eyed Vireo). Furthermore, on average, species were in poor condition (i.e. body condition scores were negative) in these coffee farms. Thus, the extent to which this agricultural system represents high quality habitat should be looked with caution. Overall, our data contribute novel information on daily patterns of body condition improvement for several common migratory birds in Andean shaded plantations. 相似文献
4.
Context
Species distributions are driven by a wide variety of abiotic and biotic factors, including nest placement for breeding individuals. As such, the spatial distribution of nests within a landscape can reflect environmental heterogeneity, habitat preferences, or even interactions with predators and other species.Objectives
We determined the extent to which environmental heterogeneity and predation risk accounted for the observed spatial distribution of nests.Methods
We assessed the spatial distribution of 112 nests of a migratory shorebird, the Hudsonian Godwit (Limosa haemastica), at Beluga River, Alaska, from 2009 to 2012, and explicitly tested for the relative influence of habitat characteristics and predation risk on nest locations. We also evaluated the effect of nest location, distance to conspecific nests, and proximity to roads on nest fate using 64 nests that were monitored through completion.Results
Hudsonian Godwit nests were clustered across the landscape despite a lack of significant spatial autocorrelation (i.e., patchiness) in vegetation characteristics at either the micro- or landscape scale. Nest fate also was not predicted by either the distance to the nearest conspecific neighbor or proximity to roads. Thus, neither habitat characteristics nor predation risk explained the clustering of godwit nests.Conclusions
These results suggest that godwits may select nest locations based more on social cues than underlying heterogeneity in vegetation or predation risk. As such, intra- and inter-specific interactions should be considered when developing management plans for species of conservation concern.5.
6.
A device for the irrigation of soil columns An irrigation device was designed for maintaining a constant water flow in soil columns over a long period of time. The apparatus consists of three construction elements: A balance for the dosage of the water, a sprinkler to distribute the water on the soil surface and an electronic time control to adjust different time steps. The wide range of possible rain intensities is shown. The mean variation of the water pulses and their distribution over the surface are discussed. The apparatus exhibits good results in long duration experiments. 相似文献
7.
Stephen N. Matthews Louis R. IversonAnantha M. Prasad Matthew P. PetersPaul G. Rodewald 《Forest Ecology and Management》2011,262(8):1460-1472
Species distribution models (SDMs) to evaluate trees’ potential responses to climate change are essential for developing appropriate forest management strategies. However, there is a great need to better understand these models’ limitations and evaluate their uncertainties. We have previously developed statistical models of suitable habitat, based on both species’ range and abundance, to better understand potential changes of 134 tree species habitats in the eastern United States (http://www.nrs.fs.fed.us/atlas). Our focus here is to build on these results via a more robust assessment framework called modification factors (ModFacs) that is made up of five components. ModFac 1 addresses nine biological characteristics (e.g., shade tolerance and seedling establishment) that quantify the influence of species life-history traits. ModFac 2 considers 12 disturbance characteristics (e.g., insect pests, drought, and fire topkill) which address the capacity of a species to tolerate and respond to climate-induced changes in habitat. ModFac 3-5 distill the tree SDM results and facilitate communication of model uncertainty; we quantified the variability in projected change for General Circulation Models (GCM) and emissions scenarios (ModFac 3), the extent to which each species’ habitat intersects novel climate conditions (ModFac4), and accounted for long-distance extrapolations beyond a species’ current range (ModFac5). The life-history components of ModFacs 1 and 2 demonstrate the marked variability among species in terms of biological and disturbance characteristics, suggesting diverse abilities to adapt to climate change. ModFacs 3-5 show that the information from the SDMs can be enhanced by quantifying the variability associated with specific GCM/emission scenarios, the emergence of novel climates for particular tree species, and the distances of species habitat shifts with climate change. The ModFacs framework has high interpretive value when considered in conjunction with the outputs of species habitat models for this century. Importantly, the intention of this assessment was not to create a static scoring system, but to broadly assess species characteristics that likely will play an important role in adaptation to climate change. We believe these scores based on biological, disturbance, and model synthesis factors provide an important expansion of interpretive and practical value to habitat model projections. 相似文献
8.
Marja H. Bakermans Amanda D. Rodewald Andrew C. Vitz Carlos Rengifo 《Agroforestry Systems》2012,85(1):85-94
Shade coffee plantations support high numbers of Neotropical migratory birds, but relatively little is known about the structural and floristic attributes used by individual species. From 2005 to 2007, we studied the relationship between habitat characteristics and Neotropical migratory birds in shade coffee plantations in the Venezuelan Andes. Our results indicate that density of migrants was significantly related to both structural and floristic attributes of coffee farms. Specifically, upper canopy foragers were positively associated with number of large trees (>38?cm dbh), tree canopy height, and understory vegetation density. Low canopy and ground foragers were positively associated with numbers of small (8?C23?cm dbh) and medium (23?C38?cm dbh) trees and increased shade cover. Moreover, certain tree species, especially Inga spp., Erythrina spp. and Acnistus arborescens, were important components of habitat for those species that forage in the canopy. For example, our detailed foraging observations showed that Inga trees were used in greater proportion than available throughout plantations by Cerulean Warblers (Dendroica cerulea), a species of high conservation concern. Overall, our research suggests that suitability of coffee plantations for migratory birds may be improved by managing for particular structural and floristic characteristics of plantations. 相似文献
9.
Changes in historical forest composition and structure may have cascading effects throughout the forest community. Perhaps nowhere is there a better example of current forests that carry a legacy from their past than in eastern North America. The Cerulean Warbler (Dendroica cerulea), a declining Neotropical migratory bird of high conservation concern, is one excellent example of a species that seems to be sensitive to both landscape configuration and subtle features of eastern forests of North America. We used the Cerulean Warbler as a model species to demonstrate how an appreciation of fine-scale structural attributes of forests may improve our ability to conserve late-successional forest species. To do this we evaluated the extent to which multiscale habitat features were associated with density, spatial distribution, and nesting success of Cerulean Warblers in 12 mature forest sites in southeast Ohio, 2004–2006. Results suggest that adjacency of regenerating clear-cuts did not influence density or nesting success of Cerulean Warblers in adjacent mature forest. Instead, variation in demographic parameters was best explained by local habitat features. Density and nesting success were positively associated with canopy openness, numbers of large-diameter trees, and number of grapevines—all of which are typical of heterogeneous steady-state phase forests. Thus, improved management for Cerulean Warblers may require creating features (e.g., large canopy gaps) that mimic old-growth forests. Although fragmentation and habitat loss remain important contributors to population declines of many mature forest species, our work provides evidence that subtle changes in forest structure, particularly to features associated with old forests, warrant additional attention from the conservation community. 相似文献
10.
G Bl?dow P Rommel E Kanitz M Kitzig S Rodewald F Schneider 《Archiv fuer experimentelle veterinaermedizin》1990,44(4):599-610
Highly sensitive radio-immuno assay (RIA) was used for 21 days to study the curves of several steroid hormones, progesterone (P), oestradiol 17 beta (E2), and testosterone (T), as well as of luteinizing hormone (LH) in peripheral blood of six heifers to which oestrus had been induced by prostaglandin F2 alpha. The validity of the authors' RIA for P, E2, and T determination in blood plasma was positively verified by two reliability criteria, correctness and accuracy, as well as by comparative determinations, using reference methods. Only four of the six heifers returned to oestrus, within 21 days from first oestrus induction. A typical cycle-related curve of the P concentration in peripheral blood with peak values between the 13th and 17th days of cycle (15-26 nmol/l) was recorded from four animals. The peak values of pre-ovulatory E2 and LH were between 33.0 and 53.2 pmol/l or between 19.5 and 52.5 micrograms/l. Some of the T rises in peripheral blood were in parallel to E2 concentrations. All hormone curves are presented in detail and are discussed in relation to clinico-physiological findings. 相似文献