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161.
The franciscana dolphin Pontoporia blainvillei is the most endangered small endemic cetacean species of the southwestern South Atlantic Ocean. We assessed intra-specific variation in the diet of franciscana regarding biological parameters (sex, total body length, age class and sexual maturity) and between distinct environments (open marine area vs. an area adjacent to an estuary) from the Buenos Aires coast, Argentina, using both stable isotopes and stomach content analysis. We found a significant isotopic enrichment in 15N in neonates and nursing calves, representative of the lactation period. We found differences in the diet of franciscana between dolphins from the open marine area and dolphins living in waters influenced by the estuary, by both diet estimating methods. The lower δ15N values in dolphins living in waters adjacent to the estuary could be associated with a higher consumption of small sizes of the striped weakfish (Cynoscion guatucupa), which has lower isotope values than the larger sizes consumed in the open marine area. This trophic differentiation between locations is in agreement with the existence of two genetically distinct populations recently found in the study area. This study reveals geographical variations in the diet of franciscana dolphin, supporting the new delineation of distinct franciscana populations in Argentine waters. Considering the small home range and the limited movement pattern of the species, the population living near the estuary would likely need protection due to its low level of genetic diversity and feeding preferences. Therefore, the preservation and conservation of the mentioned habitat is recommended to ensure population viability of franciscana in the region. 相似文献
162.
Dhiya Shafiqah Ridzuan Che Salmah Md. Rawi Suhaila Abdul Hamid Salman Abdo Al-Shami 《农业工程》2017,37(2):97-104
Stable isotope analysis has been extensively used as an effective tool in determination of trophic relationship in ecosystems. In freshwater ecosystem, aquatic invertebrates represent main component of a river food web. This study was carried out to determine potential food sources of freshwater organism together with pattern of trophic position along the river food web. In this study, rivers of Belum-Temengor Forest Complex (BTFC) has been selected as sampling site as it is a pristine area that contains high diversity and abundance of organisms and can be a benchmark for other rivers in Malaysia. Stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) were applied to estimate trophic position and food web paradigm. Analysis of stable isotopes based on organic material collected from the study area revealed that the highest δ13C value was reported from filamentous algae (? 22.68 ± 0.1260/00) and the lowest δ13C was in allocthonous leaf packs (? 31.58 ± 0.1870/00). Meanwhile the highest δ15N value was in fish (8.45 ± 0.1770/00) and the lowest value of δ15N was in autochthonous aquatic macrophyte (2.00 ± 1.2340/00). Based on the δ15N results, there are three trophic levels in the study river and it is suggested that the trophic chain begins with organic matter followed by group of insects and ends with fish (organic matter < insects < fish). 相似文献
163.
Trophic adaptability is a term used to describe feeding flexibility in fishes. Though a useful conceptual starting point,
fishes often face constraints on their ability to switch prey that could limit feeding success even when prey switching is
observed. We compared striped bass diet compositions summarized from previously published studies in California’s Sacramento-San
Joaquin Delta during two time periods (1963–1964 and 2001–2003), which allowed us to evaluate trophic adaptability in San
Francisco Estuary striped bass at multiple time scales, ranging from intra-annual to multidecadal. The Delta is the landward
region of the San Francisco Estuary; over time between the study periods, the Delta underwent substantial changes in potential
prey availability for striped bass. We found evidence for trophic adaptability in San Francisco Estuary (SFE) striped bass
at all temporal scales examined. Despite this ability to adapt to changes in prey availability, the relative abundance and
carrying capacity of young striped bass have declined. This decline has previously been associated with substantial declines
in their dominant historical prey—mysid shrimp. Our results, coupled with these previous findings, indicate that trophic adaptability
may have limited usefulness as a conceptual model to predict foraging success when other food web constraints are not considered.
We speculate that this is particularly true in highly invaded ecosystems like the San Francisco Estuary because invading species
often introduce substantial and permanent changes into food webs, decreasing the likelihood that a predator will find prey
assemblages that fully replace historical prey assemblages. 相似文献
164.
Nubbins of the coral Acropora aspera were artificially bleached and nitrogen fixation (acetylene reduction) rates were measured on the developing epilithic communities.
Seasonal comparisons were made between corals that died in summer of heat stress and corals that died in winter from natural
cold stress. Rates of acetylene reduction from artificially bleached corals peaked at 26.66 nmol cm−2 h−1 2 weeks after summer mortality, while rates from natural winter mortality peaked at 18.07 nmol cm−2 h−1 12 days after coral death. Comparative rates of acetylene reduction taken from live corals and coral rubble ranged between
0.56 and 1.16 nmol cm−2 h−1, and 0.15 and 12.77 nmol cm−2 h−1, respectively. N2-fixation rates from dead corals were up to 30 times greater than those measured on live corals. The observed increase in
N2-fixation from dead corals may increase the availability of nitrogen for use in trophic processes within the reef for an extended
period following the initial mortality event. If the spatial scale over which coral mortality has occurred in past thermal
bleaching events is considered the ramifications of such an increase may be substantial. 相似文献
165.
André Andrian Padial Sidinei Magela Thomaz Angelo Antonio Agostinho 《Hydrobiologia》2009,624(1):161-170
Macrophytes have a fundamental structuring role in aquatic environments. Several authors have suggested that trophic interactions
are particularly mediated by aquatic plants. In the current article, we evaluated the effects of the structural heterogeneity
provided by Eichhornia azurea (Kunth) roots on predation and habitat use by the small fish Moenkhausia sanctaefilomenae (Steindachner). We tested the hypotheses that (i) high structural heterogeneity protects macroinvertebrates against predation
by M. sanctaefilomenae; (ii) distinct prey types are differently protected by the refuge provided by roots; and (iii) the behavior of M. sanctaefilomenae is affected by the structural heterogeneity provided by macrophyte roots. To test these hypotheses, we performed an experiment
in 20 l aquaria in which macroinvertebrates (Cypricercus sp. and Chironomus sp.) were exposed to M. sanctaefilomenae predation for 4 h under three structural heterogeneities, represented by different root densities. High structural heterogeneity
protected macroinvertebrates against predation. Additionally, E. azurea roots similarly protected different prey species. The macrophyte spatial structure substantially changed the habitat use
of M. sanctaefilomenae. In general, our results corroborated the hypothesis that the structural heterogeneity provided by E. azurea roots significantly affects predation and habitat use by M.
sanctaefilomenae.
Handling editor: S. Declerck 相似文献
166.
Denitrification efficiency for defining critical loads of carbon in shallow coastal ecosystems 总被引:2,自引:2,他引:0
Denitrification efficiency [DE; (N2 − N/(DIN + N2 − N) × 100%)] as an indicator of change associated with nutrient over-enrichment was evaluated for 22 shallow coastal ecosystems
in Australia. The rate of carbon decomposition (which can be considered a proxy for carbon loading) is an important control
on the efficiency with which coastal sediments in depositional mud basins with low water column nitrate concentrations recycle
nitrogen as N2. The relationship between DE and carbon loading is due to changes in carbon and nitrate (NO3) supply associated with sediment biocomplexity. At the DE optimum (500–1,000 μmol m−2 h−1), there is an overlap of aerobic and anaerobic respiration zones (caused primarily by the existence of anaerobic micro-niches
within the oxic zone, and oxidized burrow structures penetrating into the anaerobic zone), which enhances denitrification
by improving both the organic carbon and nitrate supply to denitrifiers. On either side of the DE optimum zone, there is a
reduction in denitrification sites as the sediment loses its three-dimensional complexity. At low organic carbon loadings,
a thick oxic zone with low macrofauna biomass exists, resulting in limited anoxic sites for denitrification, and at high carbon
loadings, there is a thick anoxic zone and a resultant lack of oxygen for nitrification and associated NO3 production. We propose a trophic scheme for defining critical (sustainable) carbon loading rates and possible thresholds
for shallow coastal ecosystems based on the relationship between denitrification efficiency and carbon loading for 17 of the
22 Australian coastal ecosystems. The denitrification efficiency “optimum” occurs between carbon loadings of about 50 and
100 g C m−2 year−1. Coastal managers can use this simple trophic scheme to classify the current state of their shallow coastal ecosystems and
for determining what carbon loading rate is necessary to achieve any future state.
Guest editors: J. H. Andersen & D. J. Conley
Eutrophication in Coastal Ecosystems: Selected papers from the Second International Symposium on Research and Management of
Eutrophication in Coastal Ecosystems, 20–23 June 2006, Nyborg, Denmark 相似文献
167.
Sébastien Personnic Isabelle Domaizon Ursula Dorigo Lyria Berdjeb Stéphan Jacquet 《Hydrobiologia》2009,627(1):99-116
Flow cytometry (FCM) was used to assess microbial community abundances and patterns in three natural, large and deep peri-alpine
hydrosystems, i.e., lakes Annecy (oligotrophic), Bourget, and Geneva (mesotrophic). Picocyanobacteria, small eukaryotic autotrophs,
heterotrophic prokaryotes, and viruses were studied in the 0–50 m surface layers to highlight the impact of both physical
and chemical parameters as well as possible biotic interactions on the functioning of microbial communities. Some specificities
were recorded according to the trophic status of each ecosystem such as the higher number of viruses and heterotrophic bacteria
in mesotrophic environments (i.e., Lakes Geneva and Bourget) or the higher abundance of picocyanobacteria in the oligotrophic
Lake Annecy. However, both seasonal (temperature) and spatial (depth) variations were comparatively more important than the
trophic status in driving the microbial communities’ abundances in these three lakes, as revealed by principal component analysis
(PCA). A strong viral termination of the heterotrophic bacterial blooms could be observed in autumn for each lake, in parallel
to the mixing of the upper lit layers. As virus to bacteria ratio (VBR) was indeed very high at this period with values varying
between 87 and 114, such important relationships between viruses and bacteria were likely. The magnitudes of seasonal variations
in VBR, with the highest values ever reported so far, were largely greater than the magnitude of theoretical variations due
to the trophic status, suggesting also a strong seasonality in virioplankton production associated to prokaryotic dynamics.
FCM analyses allowed discriminating several viral groups. Virus-Like Particles group 1 (VLP1) and group 2 (VLP2) were always
observed and significantly correlated to bacteria for the former and chlorophyll a and picocyanobacteria for the latter, suggesting that most of VLP1 and VLP2 could be bacteriophages and cyanophages, respectively.
On the basis of these results, new ways of investigation emerge concerning the study of relationships between specific picoplanktonic
groups; and overall these results provide new evidence of the necessity to consider further viruses for a better understanding
of lake plankton ecology.
Handling editor: Luigi Naselli-Flores 相似文献
168.
The estimated population of the Tsushima leopard cat Prionailurus bengalensis euptilura is only 80–110 individuals. However, the cause of the population decline is not clear. We investigated temporal changes in
the food habits of the cat and two other species of Carnivora (marten and weasel) inhabiting the Tsushima Islands by measuring
δ13C and δ15N values in hair samples. Hair samples of the cat were collected not only from specimens and furs, but also from feces. The
gathering of hair from cat feces was most efficient when the feces were collected in the spring. The food habit of male cats
seemed to be more diverse and tended to comprise prey of higher trophic levels than the food habits of the females. The δ13C and δ15N measurements suggested that the trophic level of the food sources has been decreasing over the last several decades for
the cat and weasel, but not for the marten. Increased consumption of prey from lower trophic levels in the food habit of the
cat seems to be related to the decline of the cat population because these phenomena occurred simultaneously. 相似文献
169.
Alejandro G. Farji-Brener Ernesto Gianoli Marco A. Molina-Montenegro 《Ecological Research》2009,24(1):139-145
Small-scale disturbances caused by animals often modify soil resource availability and may also affect plant attributes. Changes
in the phenotype of plants growing on disturbed, nutrient-enriched microsites may influence the distribution and abundance
of associated insects. We evaluated how the high nutrient availability generated by leaf-cutting ant nests in a Patagonian
desert steppe may spread along the trophic chain, affecting the phenotype of two thistle species, the abundance of a specialist
aphid and the composition of the associated assemblage of tending ants. Plants of the thistle species Carduus nutans and Onopordum acanthium growing in piles of waste material generated by leaf-cutting ant nests (i.e., refuse dumps) had more leaves, inflorescences
and higher foliar nitrogen content than those in non-nest soils. Overall, plants in refuse dumps showed higher abundance of
aphids than plants in non-nest soils, and aphid colonies were of greater size on O. acanthium plants than on C. nutans plants. However, only C. nutans plants showed an increase in aphid abundance when growing on refuse dumps. This resulted in a similar aphid load in both
thistle species when growing on refuse dumps. Accordingly, only C. nutans showed an increase in the number of ant species attending aphids when growing on refuse dumps. The increase of soil fertility
generated by leaf-cutting ant nests can affect aphid abundance and their tending ant assemblage through its effect on plant
size and quality. However, the propagation of small-scale soil disturbances through the trophic chain may depend on the identity
of the species involved. 相似文献
170.
Organismal performance changes over ontogeny as the musculoskeletal systems underlying animal behavior grow in relative size and shape. As performance is a determinant of feeding ecology, ontogenetic changes in the former can influence the latter. The horn shark Heterodontus francisci consumes hard-shelled benthic invertebrates, which may be problematic for younger animals with lower performance capacities. Scaling of feeding biomechanics was investigated in H. francisci (n=16, 19–59 cm standard length (SL)) to determine the biomechanical basis of allometric changes in feeding performance and whether this performance capacity constrains hard-prey consumption over ontogeny. Positive allometry of anterior (8–163 N) and posterior (15–382 N) theoretical bite force was attributed to positive allometry of cross-sectional area in two jaw adducting muscles and mechanical advantage at the posterior bite point (0.79–1.26). Mechanical advantage for anterior biting scaled isometrically (0.52). Fracture forces for purple sea urchins Strongylocentrotus purpuratus consumed by H. francisci ranged from 24 to 430 N. Comparison of these fracture forces to the bite force of H. francisci suggests that H. francisci is unable to consume hard prey early in its life history, but can consume the majority of S. purpuratus by the time it reaches maximum size. Despite this constraint, positive allometry of biting performance appears to facilitate an earlier entry into the durophagous niche than would an isometric ontogenetic trajectory. The posterior gape of H. francisci is significantly smaller than the urchins capable of being crushed by its posterior bite force. Thus, the high posterior bite forces of H. francisci cannot be fully utilized while consuming prey of similar toughness and size to S. purpuratus, and its potential trophic niche is primarily determined by anterior biting capacity. 相似文献