Study On The Food Web Base On Community Assembly And Key Food Chain Functions

Trophic niches condition the energetic performance of species within food webs providing a vital link between food web assembly,species diversity and functioning of ecosystems.Our understanding of this important link is however limited by the lack of empirical tools that can be easily applied to compare entire food webs at regional scales.Benthic macroinvertebrates play key roles in shallow aquatic ecosystems and can contribute substantially to aquatic food webs.However,how macroinvertebrates with different behaviors（for example,pertaining to locomotion,foraging and burrowing）impact water quality and primary producers has not been fully explored.Because of the special properties of lakes in the middle and lower reaches of the Yangtze River,benthivory are used in the niche determination,it complements trophic position as a synthetic metric of a species’resource utilization.Then,by comparison with different a priori synthetic models defined according to specific assembly rules（i.e.,purely random,limiting similarity,and niche filtering）,we demonstrate a set of food web properties（trophic richness,evenness,and divergence）are controlled by ecological processes.We further demonstrate that although both limiting similarity and niche filtering are statistically significant assembly processes shaping our studied lake food webs,their relative importance is richness-dependent,and contextual to the specific food web property under consideration.In order to explore the influence of benthic animals with different behaviors on shallow water ecosystem,two different microcosm experiments were set up,taking Bellamya aeruginosa and Macrobrachium nipponense as experimental objects,to test the Food chain function of significant benthic communities and species.The results showed that presence of snails significantly increased the biomass of filamentous green algae and decreased the biomass of periphyton and water turbidity.In contrast,presence of shrimp significantly decreased the biomass of filamentous green algae and increased the biomass of periphyton and water turbidity.No interactive effects of snail and shrimp presence were found.This could be attributed to different mobility and food preferences by the two consumers,with snail is a low mobility grazer and can filter suspended particles preferring periphyton（mainly diatoms）,and shrimp is a high mobility shredder with burrows,which can strongly disturb sediment,preferring filamentous green algae.In addition,the effects of shrimp were biomass dependent,which showed a hump-shaped response to shrimp biomass with a peak at 24.2 g m^-2.Filamentous green algae disappeared when shrimp biomass reached 9.8 g m^-2.The decrease in water disturbance at high shrimp biomass might be due to food limitation,thus reducing burrowing and foraging activities.Neither snail nor shrimp affected the biomass of H.verticillata,while the biomass of V.spinulosa increased with shrimp biomass.The reason for this could be that shrimp increased nutrient availability and decreased the growth of filamentous green algae that compete with macrophytes.Our results have both important theoretical and practical implications.Theoretically,the observed richness-dependent variation on food web properties contradicts the common criticism on food web theory that food web properties are roughly scale-invariant.Practically,these properties can help avoiding spurious conclusions,while providing useful information for multiple-food web niche space supporting the ecosystem functioning.Our study also demonstrated that different macroinvertebrates have complementary functions in benthic habitats;thus,maintaining macroinvertebrate diversity is important for shallow aquatic ecosystems.Furthermore,the freshwater shrimp M.nipponense could be a potential consumer to control filamentous green algal blooms in its native range,but their biomass should be taken into consideration.