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Seasonal variation in aquatic food web structure at Mad Island Marsh, Matagorda Bay, Texas, was examined using dietary information
obtained from the analysis of gut contents from large samples of fish and crustacean specimens. Unique aspects of this study
include the use of large samples of consumer gut contents (n=6,452), long-term sampling (bimonthly surveys over 18 mo), and
standard methods of data collection and analysis facilitating comparisons with other aquatic food webs. Dietary data were
partitioned for analysis into warm (summer) and cold (winter) seasons. Most consumers fed low in the food web, with trophic
levels ranging from about 2 to 3.5 during both summer and winter. Vegetative detritus was more important in macroconsumer
diets than live algae and macrophytes. Low trophic levels of consumers reflected the important role of abundant detritivores
(e.g., striped mulletMugil cephalus, Gulf menhadenBrevortia patronum, and macroinvertebrates) in linking detritus to top predators via short food chains, a finding consistent with many other
estuarine food web studies. Despite changes in community composition and population size structure of certain species, most
food web properties revealed comparatively little seasonal variation. The summer food web had more nodes (86), more links
(562), a higher density of links as indicated by connectance (0.08), and a slightly higher predator: prey ratio (0.51) compared
to the winter food web (75 nodes, 394 links, connectance = 0.07, predator: prey ratio = 0.47). Proportions of top (0.06–0.07),
intermediate (0.75–0.76), and basal (0.19) species did not vary significantly between seasons, but mean trophic level was
higher during summer. Addition of feeding links based on information from the literature increased connectance to 0.13 during
both seasons; other web parameters had values similar to those obtained for our directly estimated food webs. Seasonal variation
in food web structure was influenced by changes in community composition (e.g., influxes of postlarval estuarine-dependent
marine fishes during winter), availability of resources (e.g., more submerged macrophytes and amphipods during summer), and
size structure and ontogenetic diet shifts of dominant consumer taxa. Our findings suggest that some basic properties of estuarine
food web are resilient to seasonal changes in population and community structures and food web architecture. 相似文献