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21.
22.
Seasonal trends in the gonad index (GI) of two widely separated populations of black teatfish, Holothuria whitmaei (formerly included in Holothuria nobilis), were investigated between Pacific (Great Barrier Reef) and Indian Ocean (Ningaloo Reef) coral reefs of Australia. Reproductive
activity followed a similar annual trend, with the GI of both populations peaking typically between April and June. Macroscopic
and histological analysis of Ningaloo Reef specimens revealed that large germinal tubules, positioned centrally on the gonad
basis, progressed through four maturity stages: growing (II); mature (III); partly spawned (IV); and spent (V). Growing tubules
dominated the central region of the gonad basis between January and March, followed by an increase in the number of mature
tubules throughout the GI peak (April–June). The progressive appearance of partly spawned and spent tubules between June and
October suggests that spawning in H. whitmaei continues intermittently over an extended period throughout the austral winter. The examination of the gonad structure of
sexually mature male and female specimens identified five tubule size classes in total (C1 to C5), each of differing physical and gametogenic status. In females, smaller C1 tubules located at the anterior edge of the gonad basis contained pre- to early vitellogenic oocytes. Larger C2 and C3 tubule cohorts, positioned centrally on the gonad basis, contained mid- to late-stage vitellogenic oocytes. Smaller C4 and C5 tubules, located at the posterior edge, contained only relict oocytes. Similar physical and gametogenic differences were
apparent between tubule cohorts in male specimens. We propose that these results, together with evidence of incomplete gonad
resorption over the austral summer, indicate that gonad development in H. whitmaei conforms to the predictions of the Tubule Recruitment Model (TRM). The TRM is reported rarely among tropical aspidochirotes,
and results presented here (1) provide the first direct evidence of this model in H. whitmaei, and (2) confirm that this species is one of the few winter-spawning tropical invertebrates. 相似文献
23.
Adrian Vallin Sven Jakobsson Christer Wiklund 《Behavioral ecology and sociobiology》2007,61(9):1419-1424
Large eyespots on the wings of butterflies and moths have been ascribed generally intimidating qualities by creating a frightening
image of a bird or mammal much larger than the insect bearing the eyespots. However, evidence for this anti-predator adaptation
has been largely anecdotal and only recently were peacock butterflies, Inachis io, shown to effectively thwart attacks from blue tits, Parus caeruleus. Here, we test whether large eyespots on lepidopterans are generally effective in preventing attacks from small passerines
and whether the size of insect or bird can influence the outcome of interactions. We staged experiments between the larger
eyed hawkmoths, Smerinthus ocellatus, and the smaller peacock butterflies, I. io, and the larger great tits, Parus major, and the smaller blue tits, P. caeruleus. Survival differed substantially between the insect species with 21 of 24 peacock butterflies, but only 6 of 27 eyed hawkmoths,
surviving attacks from the birds. Thus, surprisingly, the smaller prey survived to a higher extent, suggesting that factors
other than insect size may be important. However, great tits were less easily intimidated by the insects’ eyespots and deimatic
behaviour and consumed 16 of 26, but the blue tits only 8 of 25, of the butterflies and hawkmoths. Our results demonstrate
that eyespots per se do not guarantee survival and that these two insects bearing equally large eyespots are not equally well
protected against predation. 相似文献
24.
The model of spatial distribution of main forest soil groups in Croatia was developed as a function of basic pedogenetic factors: lithological substratum, macroclimate and relief. Used data about soil group, lithological substratum, terrain slope and aspect were collected on 1881 soil profiles. Macroclimatic data were estimated for each soil profile by spatial interpolation between meteorological stations. Feedforward neural networks were used as modelling tool. The final model has total classification correctness of 63.5% for training data set and 62.3% for independent test data set. The best result (86.4%) was achieved for fluvisols which are strongly spatially correlated with alluvial sediment in a flood plains. The worst result was achieved for luvisol (14.2%) which mainly comprised very old soils, probably developed under pedogenetic factors different from actual. The model was applied on entire Croatian territory aiming at construction of potential spatial distribution of main forest soils (without human impact), which was compared by the potential spatial distribution of major forest types modelled independently. 相似文献
25.
Bird mortality is heavily affected by birds of prey. Under attack, take-off is crucial for survival and even minor mistakes in initial escape response can have devastating consequences. Birds may respond differently depending on the character of the predator's attack and these split-second decisions were studied using a model merlin (Falco columbarius) that attacked feeding blue tits (Parus caeruleus) from two different attack angles in two different speeds. When attacked from a low attack angle they took off more steeply than when attacked from a high angle. This is the first study to show that escape behaviour also depends on predator attack speed. The blue tits responded to a high-speed attack by dodging sideways more often than when attacked at a low speed. Escape speed was not significantly affected by the different treatments. Although they have only a split-second before escaping an attack, blue tits do adjust their escape strategy to the prevailing attack conditions. 相似文献
26.
Wittgren HB Castensson R Gipperth L Joelsson A Jonasson L Pettersson A Thunvik R Torstensson G 《Ambio》2005,34(3):237-247
Despite political efforts, diffuse pollution from agriculture continues to be the single largest source of nitrogen (N) emissions into the aquatic environment in many countries and regions. This fact, and the recent enactment of a new Swedish environmental code, led to the design of a study targeted at the evaluation of new N pollution abatement strategies. An actor game was chosen as the key component of the study, with a focus on four major goals: to test the implementability of legally binding environmental quality standards for nitrate concentration in groundwater and N transport to the sea, to find sets of agriculturally feasible and cost-effective measures to decrease N loads, to investigate the possibilities for collective action through negotiated and institutionalized actor cooperation, and to investigate the role of mathematical modeling in environmental N management. Characteristics from the agriculturally dominated catchment of Genevads?n (224 km2) on the southwest coast of Sweden served as the playing field for the actor game. The most noteworthy result from the study was that it appeared to be possible to meet ambitious environmental N standards with less economically drastic measures than anticipated by most of the participants. The actor game was shown to be a good method for learning about the new Swedish environmental code and its application and for gaining deeper insight into the issues of N management. In addition, the actor game functioned as an arena for gaining a more thorough understanding of the views of different stakeholders. 相似文献
27.
Nimmermark SA Jacobson LD Schmidt DR Gay SW 《Journal of the Air & Waste Management Association (1995)》2005,55(9):1306-1314
A comparison between predicted and observed odor intensities at 20 neighborhood residences in the vicinity of seven various livestock farms in five different Minnesota counties was made to evaluate the Odor From Feedlots, Setback Estimation Tool (OFFSET) developed by the University of Minnesota. Observations by neighborhood monitors suggest that the OFFSET-predicted separation distances for annoyance-free frequencies of 99, 98, and 97% are large enough. The observations additionally indicate that predicted distances to obtain 94 and 91% annoyance-free frequencies may be large enough for some farms, but for other farms, greater distances may be needed. For two farms in the study, no significant difference between all of the observed and predicted intensities could be found. At four sites, a significant difference was found, and at three of these the difference was considerable. Odor emission rates used in the OFFSET model seem to describe the average emission fairly well for many odor sources, but improvement may be needed for some types of sources. Possible reasons for observations of annoying odor when not predicted include fluctuations in the odor emissions, wind speed fluctuations, topographic variation between sites, sensitivity differences by neighborhood monitors, and background emissions from other sources. 相似文献
28.
Callaghan TV Björn LO Chernov Y Chapin T Christensen TR Huntley B Ims RA Johansson M Jolly D Jonasson S Matveyeva N Panikov N Oechel W Shaver G Schaphoff S Sitch S Zöckler C 《Ambio》2004,33(7):469-473
An assessment of impacts on Arctic terrestrial ecosystems has emphasized geographical variability in responses of species and ecosystems to environmental change. This variability is usually associated with north-south gradients in climate, biodiversity, vegetation zones, and ecosystem structure and function. It is clear, however, that significant east-west variability in environment, ecosystem structure and function, environmental history, and recent climate variability is also important. Some areas have cooled while others have become warmer. Also, east-west differences between geographical barriers of oceans, archipelagos and mountains have contributed significantly in the past to the ability of species and vegetation zones to relocate in response to climate changes, and they have created the isolation necessary for genetic differentiation of populations and biodiversity hot-spots to occur. These barriers will also affect the ability of species to relocate during projected future warming. To include this east-west variability and also to strike a balance between overgeneralization and overspecialization, the ACIA identified four major sub regions based on large-scale differences in weather and climate-shaping factors. Drawing on information, mostly model output that can be related to the four ACIA subregions, it is evident that geographical barriers to species re-location, particularly the distribution of landmasses and separation by seas, will affect the northwards shift in vegetation zones. The geographical constraints--or facilitation--of northward movement of vegetation zones will affect the future storage and release of carbon, and the exchange of energy and water between biosphere and atmosphere. In addition, differences in the ability of vegetation zones to re-locate will affect the biodiversity associated with each zone while the number of species threatened by climate change varies greatly between subregions with a significant hot-spot in Beringia. Overall, the subregional synthesis demonstrates the difficulty of generalizing projections of responses of ecosystem structure and function, species loss, and biospheric feedbacks to the climate system for the whole Arctic region and implies a need for a far greater understanding of the spatial variability in the responses of terrestrial arctic ecosystems to climate change. 相似文献
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