Trophic Level Structure Research Articles

Impacts of Spartina alterniflora invasion on the benthic food web in the Yellow River Delta during autumn

Spartina alterniflora was introduced into the Yellow River Delta (YRD) in 1990 with the purpose of shore protection and siltation accretion. However, it spread rapidly and became a severe threat to the local coastal wetland ecosystem. To assess the impacts of S. alterniflora invasion on the benthic food web, we sampled the potential food sources of macrobenthos in November 2020, analyzed the trophic level and the benthic food web structure based on stable isotope technique. Results showed that the average δ13C values of macrobenthic food sources followed an order: sediment organic matter (SOM) > S. alterniflora > benthic microalgae > particulate organic matter (POM) > Suaeda salsa. The average δ15N values significantly differed among food sources, ranging from 1.24‰ to 9.03‰. The trophic levels of different macrobenthos ranged from 1.73 to 4.19, of which the bivalve species was the lowest one. S. alterniflora and the decayed debris were the most important food sources for macrobenthos, but without any impact on the trophic level structure of macro-benthos. In conclusion, Spartina alterniflora invasion distinctly changed the composition of food sources of macrobenthos through a "bottom-up" effect, which would probably impact the local food web structure in the YRD wetland.

Trophic isotopic carbon variation increases with pond\u2019s hydroperiod: Evidence from an Austral ephemeral ecosystem

Trophic variation in food web structure occurs among and within ecosystems. The magnitude of variation, however, differs from system to system. In ephemeral pond ecosystems, temporal dynamics are relatively more important than in many systems given that hydroperiod is the ultimate factor determining the presence of an aquatic state. Here, using stable isotopes we tested for changes in trophic chain length and shape over time in these dynamic aquatic ecosystems. We found that lower and intermediate trophic level structure increased over time. We discuss these findings within the context of temporal environmental stability. The dynamic nature of these ephemeral systems seems to be conducive to greater levels of intermediate and lower trophic level diversity, with omnivorous traits likely being advantageous.

Changes in trophic-level structure of the main fish species caught by China and their relationship with fishing method

Changes in trophic-level structure of the main fish species caught by China and their relationship with fishing method

Trophic dilution of cyclic volatile methylsiloxanes (cVMS) in the pelagic marine food web of Tokyo Bay, Japan

Bioaccumulation and trophic transfer of cyclic volatile methylsiloxanes (cVMS), specifically octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6), were evaluated in the pelagic marine food web of Tokyo Bay, Japan. Polychlorinated biphenyl (PCB) congeners that are “legacy” chemicals known to bioaccumulate in aquatic organisms and biomagnify across aquatic food webs were used as a benchmark chemical (CB-180) to calibrate the sampled food web and as a reference chemical (CB-153) to validate the results. Trophic magnification factors (TMFs) were calculated from slopes of ordinary least-squares (OLS) regression models and slopes of bootstrap regression models, which were used as robust alternatives to the OLS models. Various regression models were developed that incorporated benchmarking to control bias associated with experimental design, food web dynamics, and trophic level structure. There was no evidence from any of the regression models to suggest biomagnification of cVMS in Tokyo Bay. Rather, the regression models indicated that trophic dilution of cVMS, not trophic magnification, occurred across the sampled food web. Comparison of results for Tokyo Bay to results from other studies indicated that bioaccumulation of cVMS was not related to type of food web (pelagic vs demersal), environment (marine vs freshwater), species composition, or location. Rather, results suggested that differences between study areas was likely related to food web dynamics and variable conditions of exposure resulting from non-uniform patterns of organism movement across spatial concentration gradients.

Emergence of complexity in evolving niche-model food webs

We have analysed mechanisms that promote the emergence of complex structures in evolving model food webs. The niche model is used to determine predator–prey relationships. Complexity is measured by species richness as well as trophic level structure and link density. Adaptive dynamics that allow predators to concentrate on the prey species they are best adapted to lead to a strong increase in species number but have only a small effect on the number and relative occupancy of trophic levels. The density of active links also remains small but a high number of potential links allows the network to adjust to changes in the species composition (emergence and extinction of species). Incorporating effects of body size on individual metabolism leads to a more complex trophic level structure: both the maximum and the average trophic level increase. So does the density of active links. Taking body size effects into consideration does not have a measurable influence on species richness. If species are allowed to adjust their foraging behaviour, the complexity of the evolving networks can also be influenced by the size of the external resources. The larger the resources, the larger and more complex is the food web it can sustain. Body size effects and increasing resources do not change size and the simple structure of the evolving networks if adaptive foraging is prohibited. This leads to the conclusion that in the framework of the niche model adaptive foraging is a necessary but not sufficient condition for the emergence of complex networks. It is found that despite the stabilising effect of foraging adaptation the system displays elements of self-organised critical behaviour.

Relation between complexity and stability in food webs with adaptive behavior

We investigate the influence of functional responses (Lotka–Volterra or Holling type), initial topological web structure (randomly connected or niche model), adaptive behavior (adaptive foraging and predator avoidance) and the type of constraints on the adaptive behavior (linear or nonlinear) on the stability and structure of food webs. Two kinds of stability are considered: one is the network robustness (i.e., the proportion of species surviving after population dynamics) and the other is the species deletion stability. When evaluating the network structure, we consider link density as well as the trophic level structure. We show that the types of functional responses and initial web structure do not have a large effect on the stability of food webs, but foraging behavior has a large stabilizing effect. It leads to a positive complexity–stability relationship whenever higher “complexity” implies more potential prey per species. The other type of adaptive behavior, predator avoidance behavior, makes food webs only slightly more stable. The observed link density after population dynamics depends strongly on the presence or absence of adaptive foraging, and on the type of constraints used. We also show that the trophic level structure is preserved under population dynamics with adaptive foraging.

Effects of solar UV radiation on aquatic ecosystems and interactions with climate change

Recent results continue to show the general consensus that ozone-related increases in UV-B radiation can negatively influence many aquatic species and aquatic ecosystems (e.g., lakes, rivers, marshes, oceans). Solar UV radiation penetrates to ecological significant depths in aquatic systems and can affect both marine and freshwater systems from major biomass producers (phytoplankton) to consumers (e.g., zooplankton, fish, etc.) higher in the food web. Many factors influence the depth of penetration of radiation into natural waters including dissolved organic compounds whose concentration and chemical composition are likely to be influenced by future climate and UV radiation variability. There is also considerable evidence that aquatic species utilize many mechanisms for photoprotection against excessive radiation. Often, these protective mechanisms pose conflicting selection pressures on species making UV radiation an additional stressor on the organism. It is at the ecosystem level where assessments of anthropogenic climate change and UV-related effects are interrelated and where much recent research has been directed. Several studies suggest that the influence of UV-B at the ecosystem level may be more pronounced on community and trophic level structure, and hence on subsequent biogeochemical cycles, than on biomass levels per se.

Species composition, feeding specificity and larval trophic level of flower-visiting insects in fragmented versus continuous heathlands in Denmark

Heathlands of Northwest Europe, which once covered extensive areas, are now reduced to small and large fragments in an agricultural landscape. In this study, we investigate the effect of fragmentation on the flower-visiting insect fauna in relation to species composition, level of specialization/generalization at the adult and larval stages, and larval trophic level. Two study sites were used: a large continuous tract of heathland, and a fragmented mosaic area. The assemblages of entomophilous plants at the two sites were similar. However, of a total of 256 species of flower-visiting insects observed, only 108 were shared between the two sites. The fragmented heath supported a taxonomically and ecologically more diverse assemblage of flower-visitors, compared to the extensive heath. At both sites, the majority of adult flower-visiting insect species were generalists, consuming floral resources from a variety of flowers. Larval types encompassed both specialists and generalists, represented by a spectrum of trophic groups, feeding classes and substrates. Species presence was dependent on the availability of larval resources and habitats rather than the requirements of imagines. No difference in level of specialization of adults or larvae was found between sites. Fragmentation affected trophic-level structure among larval specialists, significantly more high trophic-level species being found at the continuous heath tract, compared to the fragmented area. In contrast, no effect was observed among larval generalists, supporting the trophic-level hypothesis of island biogeography. Thus, although species richness is not negatively affected, composition and trophic structure is markedly changed by fragmentation of heathlands.

Long-Term Development of Biological Communities

I shall define biological community as the species comprising a temporally and spatially localized assemblage. Although members of a community may interact, I do not wish to imply that the community behaves as a functional unit or that interactions among members determine its structure. When discussing community structure in this paper, I refer exclusively to the diversity of species because of the general availability of comparative data and because most of community theory makes predictions concerning number of coexisting species. Other important community attributes, such as relative abundance patterns, trophic level structure, food web organization, resistance to and recovery from perturbation, and physical architecture, will not be considered.

On Biomass and Trophic Structure of the Central Amazonian Rain Forest Ecosystem

The importance of litter in the total energy flow dynamics of a central Amazonian rain forest near Manaus, Brazil, is discussed. The study area is located in the hinterland of Manaus between the Rio Negro and the Amazon. Its substrate is Tertiary sediment. The area receives 1771 mm rainfall per year, and the soil is classified as yellow latosol. The forest comprises 93,780 dicotyledonous trees and palms per hectare reaching 38.10 meters in height. Over 500 species of palms and dicotyledonous trees above 1.5 m. in height are identified for a 2000 sq. m. plot. The estimate for fresh living dicotyledonous tree and palm biomass is 939.5 metric tons per hectare consisting of 1.9% leaves, 49.7% stems, 21.3% branches and twigs, and 27.1% roots. Lianas, vascular epiphytes, and parasites are estimated to comprise 46.2 mt/hectare in the fresh state. At the soil surface there are 59 mt/hectare of fresh litter. Living animal biomass is about 200 kg/hectare of which half is soil fauna. The high proportion of soil fauna, the type of humus, the decomposition of litter, the apparent dependence of soil fauna on fungi, and the low nutrient content of litter are all factors which strongly support a consumer food chain based almost entirely on dead organic matter. The fungi play a decisive role in concentrating the otherwise limited nutrient resources. ECOLOGICAL STUDIES carried out in the Amazon region (Fittkau et al. 1969) raised further questions concerning the richness of the Amazonian ecosystems, the distribution of their biomass, and importance of overall as well as trophic-level structure. Additional experience obtained through later fieldwork in Amazonia and the results of our studies in hydrobiology, ecology, landscape ecology, pedology, and terrestrial production indicated the importance of finding out what the relationship of all these factors is in the entire central Amazonian' rain forest where the predominant soil type is latosol. Also considered must be the geochemical structure of that region, the division of the area as demonstrated by Fittkau (1969, 1970a, 1970b, 1971a, 1971b; fig. 1), and its influence on the nutrient supply available to the biomass in terrestrial and aquatic environments. A discussion of the bioenergetics of a tropical rain forest is difficult because few studies have been conducted either on the basis of the specific trophic levels involved or on the basis of the whole biomass. As a consequence, a discussion of available nutrients for specific species at various trophic levels is even more difficult. However, comparisons of litter-fall with the soil complex have been published, and the results are interesting enough to investigate the problem further. In a study by Klinge and Rodrigues (1968), the litter-fall of a central Amazonian tropical lowland rain forest was determined for 1963 and 1964. The average litter-fall for this period shows that 7.3 metric tons (mt) of dry matter per hectare (h) per year are returned to the soil. Dry matter per hectare is made up of 5.6 mt of leaves, or 76.6 percent of the total dry matter; the remainder is composed of flowers, small fruits, and twigs. It is interesting to note that this amount of litter is smaller than the litter-fall reported for tropical rain forests in Africa and Asia (Bray and Gorham 1964). Klinge and Rodrigues (1968) showed hat Amazonian litter is poorer in nutrients when compared with litter from other tropical forests. Results from our chemical analyses indicated that the following raw elements occur in the litter returned to the soil in central Amazonia (kg per hectare per year): 2.2 P, 12.7 K, 5.0 Na, 18.4 Ca, 12.6 Mg, and 105.6 N. In 1970, estimates were made of the amount of woody material involved in litter-fall of the central Amazonian rain forest (Klinge, unpublished). The results of the analyses show that one mt of stems (stem-part of plant between soil surface and first ramification), two mt of branches (ramifications without leaves), and 1.35 mt of twigs (ramifications bearing leaves), bark, etc. are involved. Because the 1963-1964 litter-fall experiment was not suitable for the measurement of the total fruit-fall, we calculated roughly the amount of fruits involved in annual litter-fall by kind, weight, and number of fruits in a 2000 m2 forest plot. Thus, we determined amounts of 0.35 mt of small fruits (up to 5 g in weight) and 0.5-1.0 mt of larger fruits (over approximately 5 g in weight). We 1 In this paper, 'central Amazonia' and 'central Amazonian' refer only to the ecological unit of Amazonia defined by Fittkau (1963) and illustrated in figure 1. 2 BIOTROPICA 5(1): 2-14 1973 This content downloaded from 157.55.39.243 on Wed, 05 Oct 2016 04:36:47 UTC All use subject to http://about.jstor.org/terms