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91.
Field observations of seedlings and saplings of Avicennia marina showed patterns that correlated with salinity, light and sediment. Models that account for these observations were subsequently tested in a series of field experiments. Establishment varied within an estuary under controlled conditions but was not related to salinity or sediment type. Seedling survival was uniform over 3 years regardless of position in estuary and sediment type. Seedling densities and survival under canopies or in canopy gaps were not significantly different. However, seedling growth and density of saplings were greater in canopy gaps. Experiments involving manipulations of canopies showed no differences in seedling survival under canopies or in light gaps, but addition of slow-release fertilizer enhanced growth and survival in canopy gaps and under canopies. Long-term comparison of areas denuded of a canopy and with sediment disturbance showed enhanced establishment and survival when compared with areas with canopy gaps but with undisturbed sediments. Overall there appears to be no restriction to establishment of propagules within mangrove stands other than the supply of propagules and tidal or wave action. In contrast, recruitment to the sapling stage appears to be restricted by light and sediment resources. We suggest that propagules need to establish in a regeneration niche for seedling recruitment to the sapling stage. This differs from the view that seedlings in the under-storey are analogous to a seed pool in the soil. 相似文献
92.
We compared the gastrointestinal parasites of the baboon,Papio cynocephalus ursinus, living in montane (altitude, >1800 m) and coastal lowland (altitude, 100–200 m) habitats in Natal, South Africa, using fecal analysis. While the montane animals harbored a smaller number of species, helminth egg-output rates were higher in them than in the lowland animals. The decrease in parasite diversity with increasing altitude was expected, but the difference in helminth egg output was not. It may be due to a combination of food shortage, which characterizes the montane environment, especially at the end of winter, and the high proportion of soil-contaminated items in the diets of the montane animals. 相似文献
93.
Stable isotopic structure of aquatic ecosystems 总被引:1,自引:0,他引:1
Isotopic, biogeochemical and ecological structure can provide a new dimension for understanding material flows, and the simultaneous
function and structure of an ecosystem. Distributions ofδ
13C andδ
15N for biogenic substances in the Nanakita river estuary involving Gamo lagoon in Japan were investigated to construct isotope
biogeochemical and ecological structure for assessing fate and transfer of organic matter, and food web structure. The isotopic
framework of the ecosystem was successfully described in aδ
15N–δ
13C map. In this estuary the variations of isotope ratios of biogenic substances were clearly explained by the mixing of land-derived
organic matter, and marine-derived organic matter.
A trophic-level effect of15N enrichment was clearly observed. Organisms were classified into three groups depending upon the contribution of land-derived
organic matter in a food chain. Almost all biota except mollusca in the lagoon depend on organic matter of marine origin.
The contributions of both land and marine organic matter were comparable for mollusca in the lagoon. 相似文献
94.
The Value of a hoard: not just energy 总被引:4,自引:2,他引:2
We present a stochastic dynamic programming model of the contributionof stored food to winter survival. Using the acorn woodpecker(Melanerpes formtcivorus) as a model organism, we demonstratethat a hoard of small energetic value can impart considerableimprovement in the probability of surviving the winter and soimprove fitness. With this model we hope to resolve Koenig andMumme's paradox, that acorn woodpeckers expend much time andeffort to create and maintain hoards of acorns which provideno more that 16% of their energetic needs over the period inwhich they are used. We further demonstrate that the contributionof hoarded acorns to survival depends on the variability inforaging outcome, independently of the energetic value of thehoard in absolute terms. We point out that the results applyin principle to all hoarding animals and suggest a number offurther elaborations of the model. 相似文献
95.
The impact of organic nutrients and massive addition of bacteria was followed in lake water mesocosms in a eutrophic lake. Increased DOM initiated a sequence of trophic responses indicated by rapid increases in bacterioplankton, protozoa, and algal biomass. The populations of Keratella cochlearis and Keratella quadrata showed a distinct response by rapid increase in birth rate followed by maxima of production and abundance. This succession clearly reflected the trophic position of these rotifer populations in the food chain. A reverse response was observed in Conochilus unicornis. 相似文献
96.
D. Massicotte F. Péronnet C. Pitre E. Adopo G. R. Brisson C. Hillaire-Marcell 《European journal of applied physiology and occupational physiology》1993,67(5):402-407
The purpose of this study was to test the hypothesis that the well-documented changes in background 13C enrichment of expired CO2 observed in response to exercise and carbohydrate ingestion, in subjects living on a North American diet, are not present in subjects living on a Western European diet. The experimental protocol used by Pirnay et al. in 1977 and by Krzentowski et al. in 1984 in subjects living on a Western European diet (4 h of exercise on a treadmill at 50% VO2max with ingestion of 100 g of glucose in 400 ml of water) was duplicated as closely as possible in six subjects living on a North American diet. The actual amounts of exogenous glucose oxidized, computed with a high artificial 13C enrichment of glucose (+189.7 13C PDB-1) which allows one to neglect the 1–2 changes in 13C background, were [mean (SEM)] 54.7 (5.4) and 84.2 (3.4) g over 2 h and 4 h of exercise, respectively. These values compare well with data computed by Pirnay et al. [56.6 (13.1) and 94.9 (4.2) g] and by Krzentowski et al. [55.0 (6.2) and 88.0 (4.5) g] using a natural enrichment of glucose (–11.21 and –10.63 13C PDB-1, respectively) assuming no change in 13C background in their Western European subjects. Under the same assumption and using a natural enrichment of glucose (–11.30 13C PDB-1) the oxidation of exogenous glucose was overestimated by 30–40% in our North American subjects. This result indicates that because of a lower input of 13C in their diet, the difference between the isotopic composition of carbohydrate and fat stores are smaller, and changes in 13C background are small or absent in response to moderate workload in Western European subjects, when compared to their North American counterparts. 相似文献
97.
Dorothee Hodapp Irene T. Roca Dario Fiorentino Cristina Garilao Kristin Kaschner Kathleen Kesner-Reyes Birgit Schneider Joachim Segschneider Ádám T. Kocsis Wolfgang Kiessling Thomas Brey Rainer Froese 《Global Change Biology》2023,29(12):3304-3317
Driven by climate change, marine biodiversity is undergoing a phase of rapid change that has proven to be even faster than changes observed in terrestrial ecosystems. Understanding how these changes in species composition will affect future marine life is crucial for conservation management, especially due to increasing demands for marine natural resources. Here, we analyse predictions of a multiparameter habitat suitability model covering the global projected ranges of >33,500 marine species from climate model projections under three CO2 emission scenarios (RCP2.6, RCP4.5, RCP8.5) up to the year 2100. Our results show that the core habitat area will decline for many species, resulting in a net loss of 50% of the core habitat area for almost half of all marine species in 2100 under the high-emission scenario RCP8.5. As an additional consequence of the continuing distributional reorganization of marine life, gaps around the equator will appear for 8% (RCP2.6), 24% (RCP4.5), and 88% (RCP8.5) of marine species with cross-equatorial ranges. For many more species, continuous distributional ranges will be disrupted, thus reducing effective population size. In addition, high invasion rates in higher latitudes and polar regions will lead to substantial changes in the ecosystem and food web structure, particularly regarding the introduction of new predators. Overall, our study highlights that the degree of spatial and structural reorganization of marine life with ensued consequences for ecosystem functionality and conservation efforts will critically depend on the realized greenhouse gas emission pathway. 相似文献
98.
稻飞虱卵寄生蜂——缨小蜂资源生态位的研究 总被引:5,自引:1,他引:4
本通过稻飞虱卵寄生蜂——缨小蜂资源生态位的田间调查,测定3种主要缨小蜂(稻虱缨小蜂Anagrus mllaparvalat,长管稻虱缨小蜂Anagrus longllubulosus,拟稻虱缨小蜂Anagrus paranllaparvalac)的生态位宽度,生态位重叠和生态位相似性比例。在生态位测定的基础上,按生态位的理论观点,充分调动了稻飞虱缨小蜂保护问题。 相似文献
99.
ABSTRACT. Gymnodinium sanguineum, Gyrodinium uncatenum , and Ceratium furca are large phototrophic dinoflagellates that commonly form red tides in the mesohaline portion of Chesapeake Bay during the summer. Examination of protargol-stained specimens revealed that these dinoflagellates also feed heterotrophically as indicated by the presence of food vacuoles containing partially digested prey. Ingested prey were generally identified as nanociliates (≥20 μm) belonging to the oligotrich genera Strobilidium and Strombidium ; occasionally other small ciliates (e.g. Balanion sp. and Mesodinium sp.), dinoflagellates, and diatoms were observed in early stages of digestion. the percentage of these mixotrophs that had ingested prey was usually less than 20%, but approached 30% in some samples. Occurrence of food vacuoles in Gymno. sanguineum was positively correlated with ≤20 μm oligotrichous ciliate density; limited data for Gyro. uncatenum suggests a similar relationship, but C. furca feeding was not related to nanociliate densities. 相似文献
100.
Understanding community saturation is fundamental to ecological theory. While investigations of the diversity of evolutionary stable states (ESSs) are widespread, the diversity of communities that have yet to reach an evolutionary endpoint is poorly understood. We use Lotka–Volterra dynamics and trait-based competition to compare the diversity of randomly assembled communities to the diversity of the ESS. We show that, with a large enough founding diversity (whether assembled at once or through sequential invasions), the number of long-time surviving species exceeds that of the ESS. However, the excessive founding diversity required to assemble a saturated community increases rapidly with the dimension of phenotype space. Additionally, traits present in communities resulting from random assembly are more clustered in phenotype space compared to random, although still markedly less ordered than the ESS. By combining theories of random assembly and ESSs we bring a new viewpoint to both the saturation and random assembly literature. 相似文献