Trophic Potential Research Articles

Ornithological study of the special protected area "Benturi" (Balta Ialomiţei Area, Romania)

Ornithological study of the special protected area "Benturi" (Balta Ialomiţei Area, Romania) "Benturi" special protected area (SPA) (Balta Ialomiţei area) is formed of three lakes: Bentul Mare, Bentul Mic and Bentul Mic Cotoi, and is situated in a natural area, without dams, belonging to the Lower Danube Green Corridor. By its position, in the middle of Balta Ialomiţei area, "Benturi" SPA represents one of the few territories which were not subjected to major anthropic influences, being visited by many birds. Avifaunal list includes 76 bird species (after new observations made in 2010) which use this territory for its trophic potential, as a resting and nestling place. Among them, there are 25 bird species of EU community interest, 35 bird species which need special protection and 17 bird species included in the Red Book of Vertebrates from Romania (for their conservation a Special Protected Area is needed). The list of the breeding bird fauna includes 54 breeding species and 11 probably breeding species; we noticed the presence of some rare breeding species in Romania and globally threatened species. Near this surface, there is an important archaeological site: Popina-Borduşani.

Mesenchymal stem cell-based therapies in regenerative medicine: applications in rheumatology

Growing knowledge on the biology of mesenchymal stem cells (MSCs) has provided new insights into their potential clinical applications, particularly for rheumatologic disorders. Historically, their potential to differentiate into cells of the bone and cartilage lineages has led to a variety of experimental strategies to investigate whether MSCs can be used for tissue engineering approaches. Beyond this potential, MSCs also display immunosuppressive properties, which have prompted research on their capacity to suppress local inflammation and tissue damage in a variety of inflammatory autoimmune diseases and, in particular, in rheumatoid arthritis. Currently, an emerging field of research comes from the possibility that these cells, through their trophic/regenerative potential, may also influence the course of chronic degenerative disorders and prevent cartilage degradation in osteoarthritis. This review focuses on these advances, specifically on the biological properties of MSCs, including their immunoregulatory characteristics, differentiation capacity and trophic potential, as well as the relevance of MSC-based therapies for rheumatic diseases.

Linking allometric macrobenthic processes to hypoxia using the Peters mass balance model

Eutrophication alters coastal aquatic food web structure and function through effects of organic enrichment and hypoxia. Macrobenthic communities provide good ecological indicators of impacts on ecosystem function induced by eutrophication. However, effective resource management requires validation of ecological indicators through mechanistic links to specific stressors of concern. Organic enrichment along with subsequent hypoxia typically engenders depauperate macrobenthic communities consisting of small short-lived surface-dwelling organisms. Metabolic ecology theory offers great promise for understanding the role of body size within the context of the trophic dynamics of aquatic ecosystems. Body size is a fundamental ecological trait because it underpins vital rates, which can be scaled up to the ecosystem level through allometric laws. Thus, body size-dependent mechanisms can potentially be used to link macrobenthic indicators to ecosystem consequences of organic enrichment and hypoxia. The Peters mass balance model (PMBM) [Peters, R.H., 1983. The Ecological Implications of Body Size. Cambridge University Press, New York, 329 pp.] provides a platform for projecting stress-induced changes in the distribution of biomass among discrete size classes of organisms. In the PMBM, changes in the distribution of biomass ensue over time from differences between gains due to ingestion and losses due to egestion, respiration, and mortality. Production of biomass results when ingestion exceeds combined losses. In the present study, the PMBM was modified to envisage an inhibitory effect of hypoxia on ingestion by: (1) using unique size-specific mortality coefficients in order to realize target inverted biomass-size distributions during model initialization; (2) linking ingestion rate to the hyperbolic relationship between oxygen consumption rate (OCR) and ambient dissolved oxygen (DO); (3) hypothesizing how oxygen regulation ability follows an allometric scaling rule relative to the supply of DO. If food is unlimited, the most straightforward hypothetical connection between the oxygen consumption rate and ingestion assumes a direct proportional relationship under oxygen limitation. Although small organisms can attain much higher mass-specific rates of oxygen consumption than large ones, previous limited research on oxygen consumption relative to oxygen supply implies that large organisms regulate oxygen intake better than small individuals as ambient DO declines. Counterintuitively, linked ingestion deficits would be accordingly higher for small organisms than large organisms under hypoxia. In pilot simulations incorporating hypothetical ingestion deficits due to oxygen limitation within a modified PMBM, contrasting scenarios emulated continuous DO and water temperature conditions experienced at two shallow subtidal sites for 32 d in summer. Resulting ingestion deficits reduced total biomass and favored large size classes. Effects were stronger under the more hypoxic scenario: total biomass was lower and the biomass-size distribution was more uneven among the size classes. Differences were even more evident in terms of an integrative macrobenthic process indicator, the normalized biomass-size spectrum (NBSS). A realistic hypoxia mass balance model (HMBM) must incorporate various allometric effects that are not necessarily expressed in the same direction relative to body size. A useful resource management tool for anticipating effects of environmental stress on aquatic ecosystem function could be developed from the quantification of trophic transfer potential within a refined PMBM.

Effect of Various Platelet Preparations on Retinal Müller Cells

Peeling of the internal limiting membrane is the treatment of choice for macular holes. Fresh platelet suspension (PS) is used to support wound healing in persistent macular holes. The concentration of growth factors in fresh, frozen, and thrombin-activated PSs were compared, to optimize their trophic potential and examine their capacity to support proliferation, migration, and contraction of human retinal Müller cells. The concentration of various growth factors in frozen PS, thrombin-activated PS, and plasma were evaluated by ELISA. The effect of these preparations on proliferation, migration, and contraction of human Müller cells were evaluated with an ATP-assay, a colony-dispersion assay, and a detached collagen gel contraction assay respectively. Plasma was tested as a control. Frozen and thrombin-activated PSs contained significantly more EGF, TGF-beta1, and PDGF than did plasma. The highest concentrations of EGF and FGF were found in frozen PS. All platelet preparations and plasma supported cell growth significantly better than the control, which was serum-free culture medium. Müller cells migrated better when incubated with thrombin-activated PS than with any other test solution. Contraction was extremely strong after incubation with fresh PS compared with plasma or thrombin-activated or frozen PSs. Frozen and thrombin-activated PSs may be suitable alternatives to fresh PS for persisting macular holes, due to their superior effect on Müller cell migration.

A new Irish wilderness? Trophic status and conservation potential of cutaway peatland lakes in Ireland

A new Irish wilderness? Trophic status and conservation potential of cutaway peatland lakes in Ireland

Some issues in the assessment of eutrophication of river waters as a consequence of the construction of a storage reservoir (on the example of the Bystrzyca River)

The quality and its changes of the Bystrzyca River waters, related to the operation of the reservoir in Zemborzyce (Lublin area), were analysed. In the years 2005–2007, the following eutrophication indicators were analysed in the Bystrzyca River: total nitrogen, total phosphorus, nitrate, and chlorophyll a content. In accordance with the flowing waters criteria of the Polish law, the river waters did not show susceptibility to eutrophication or showed advanced water eutrophication. In the case of the criteria applicable to stagnant waters, the river waters showed high eutrophic potential. When constructing a reservoir on a river, water trophic potential based on the standing water criteria should be taken into account.

Macroinvertebrate 13C variability analysis for the assessment of lake trophic functioning

The aim of this study was to better understand the relationships of within- and among-lake variability of macroinvertebrate carbon stable-isotope ratios with both lake trophic potential and lake trophic functioning. Two approaches based on the macroinvertebrate communities were undertaken on 11 French lakes: the Lake Biotic Index (LBI), a lake biological quality assessment method (Verneaux et al. 2004 a), and the carbon isotopic signatures of macroinvertebrates expressed by metrics of dispersion (standard deviation of the littoral macroinvertebrate mean δ 13 C values and differences between littoral and deep mean δ 13 C values (Δδ 13 C)). The littoral macroinvertebrate mean δ 13 C values obtained ranged from -11.7%o to -38.6‰. This great among-lake variability can be partially explained by different geological substrata on which the lakes are located and, potentially, by the lake organic matter recycling activity. Moreover, the depth-related differences in macroinvertebrate community δ 13 C (Δδ 13 C values) or macroinvertebrate taxa (taxon 13 C depletion: TΔδ 13 C) were highly correlated to the values of a LBI sub-index, which was itself correlated to hypolimnion oxygenation and deep sediment organic matter contents. This result suggests that the studied lakes showed various degrees of deep recycled carbon assimilation. The depth-related macroinvertebrate 13 C depletion may then be considered as describing the result of lake trophic functioning. However, because no correlation was observed between littoral macroinvertebrate δ 13 C variability and lake trophic potential, it seemed difficult to conclude as to the influence of different carbon sources on this potential.

Can functional groups be used to indicate estuarine ecological status?

International legislation demands that statutory bodies report on the health of aquatic ecosystems. Traditionally, ecosystem components have been characterised according to species assemblages but with limited success in predicting health. On the other hand, many studies based upon functional groupings that include trophic relationships and bioturbation potential have shown response to pollution. However, these and other functional group responses have not yet been linked to broad scale physical variables. To date this has hindered the development of a predictive model of function based on abiotic factors. In addition, most functional studies ignore any potential role of body size when assessing the importance of each species to overall functional group measures. By weighting all species that belong to the same guild equally, the investigator risks overestimating the true importance of any one guild to the environment. This study compared the ability of different functional group approaches to discriminate between separate estuarine sites, whilst linking biotic data with abiotic factors. Using data for the Tamar Estuary, we show that no two methods of classifying the biotic data, according to function, produce the same groupings of sites; nor did any method produce groupings that matched clusters based on abiotic factors alone. Instead, results show that not only can choice of functional method alter our perception of site associations but also, can influence the strength of similarity relationships between abiotic and biotic datasets. Both the use of bioturbation measures and weighting species abundance data by body size provided better relationships between biotic and abiotic data than the use of trophic groups. Thus both methods merit further research to produce algorithms for modelling studies.

Uptake and loss of dissolved 109Cd and 75Se in estuarine macroinvertebrates

Semaphore crabs (Heloecius cordiformis), soldier crabs (Mictyris platycheles), ghost shrimps (Trypaea australiensis), pygmy mussels (Xenostrobus securis), and polychaetes (Eunice sp.), key benthic prey items of predatory fish commonly found in estuaries throughout southeastern Australia, were exposed to dissolved (109)Cd and (75)Se for 385 h at 30 k Bq/l (uptake phase), followed by exposure to radionuclide-free water for 189 h (loss phase). The whole body uptake rates of (75)Se by pygmy mussels, semaphore crabs and soldier crabs were 1.9, 2.4 and 4.1 times higher than (109)Cd, respectively. There were no significant (P>0.05) differences between the uptake rates of (75)Se and (109)Cd for ghost shrimps and polychaetes. The uptake rates of (109)Cd and (75)Se were highest in pygmy mussels; about six times higher than in soldier crabs for (109)Cd and in polychaetes for (75)Se - the organisms with the lowest uptake rates. The loss rates of (109)Cd and (75)Se were highest in semaphore crabs; about four times higher than in polychaetes for (109)Cd and nine times higher than in ghost shrimps for (75)Se - the organisms with the lowest loss rates. The loss of (109)Cd and (75)Se in all organisms was best described by a two (i.e. short and a longer-lived) compartment model. In the short-lived, or rapidly exchanging, compartment, the biological half-lives of (75)Se (16-39 h) were about three times greater than those of (109)Cd (5-12h). In contrast, the biological half-lives of (109)Cd in the longer-lived, or slowly exchanging compartment(s), were typically greater (1370-5950 h) than those of (75)Se (161-1500 h). Semaphore crabs had the shortest biological half-lives of both radionuclides in the long-lived compartment, whereas polychaetes had the greatest biological half-life for (109)Cd (5950 h), and ghost shrimps had the greatest biological half-life for (75)Se (1500 h). This study provides the first reported data for the biological half-lives of Se in estuarine decapod crustaceans. Moreover, it emphasises the importance of determining metal(loid) accumulation and loss kinetics in keystone prey items, which consequently influences their trophic transfer potential to higher-order predators.

Biological quality assessment of three French Alpine lakes (Lake Annecy, Lake Crop, Lake Grand Domenon) using the Lake Biotic Index (LBI)

The Lake Biotic Index (VERNEAUX et al. 2004 a), a new lake biological quality assessment method based on the bathymetric distribution of macroinvertebrate assemblages, was applied to three reference French lakes having different geomorphological characteristics (altitude, size, geology, maximum depth). The Lake Biotic Index (LBI) is interpreted through its two sub-indices; one is a littoral quantitative index (littoral biotic index: Bl which considers the littoral taxon richness and the littoral density per m 2 ) related to lake trophic potential, the second (taxon deficit index: Df) is a qualitative index reflecting the relative loss of taxon richness between littoral and deep zones in relation to the lake's ability to transfer available matter up to consumers (trophic functioning). The results show a great impact of the geomorphological characteristics of the lakes on the reference LBI values (from 12/20 to 18.5/20) due only to different littoral macroinvertebrate biodiversities. Lake Annecy, a great lake situated 457 m a. s. on calcareous substratum, showed a much higher Bl value (62.6) than the two other lakes (Lake Crop Bl: 26.2, Lake Grand-Domenon Bl: 26.4) which are small lakes located at high altitudes on siliceous substratum. Concerning the qualitative index Df, no differences were observed between the three lakes which obtained high Df values (Lake Annecy Df: 0.9/1, Lakes Crop and Grand-Domenon Df: 1/1). It can therefore be concluded that the geomorphological factors considered did not affect the efficiency of lake trophic functioning.

Principal component analysis: an appropriate tool for water quality evaluation and management—application to a tropical lake system

An eutrophic lake system characteristic of Ivory Coast provided us with the opportunity to check that the values of all analytical variables are linked to both causes and effects of eutrophication (feedback effect). Therefore, none of these values can accurately describe a trophic state alone. To solve this difficulty we suggest here, that relationships between analytical variables are able to generate better descriptors than variables themselves. We show that principal component analysis (PCA) using coefficients of linear regression is, by construction, an appropriate tool for this purpose. The graphic representations obtained underline that: (i) the first principal component is linked to the trophic potential and the second one to the trophic level; (ii) the graphical locations of the different lakes studied are consistent with their apparent features; (iii) allochthonous inputs have a spreading effect on the graphic representation. Extension of this model to other lakes, located in the same geographical area, was successfully carried out. Furthermore, it has been shown that it is possible to reduce the number of analytical parameters to four (pH, conductivity, UV absorbance at 254 nm and permanganate index for raw water) without notably impairing the quality of the PCA representation. Moreover, these very simple parameters are easier to quantify than classical one (nutrients, chlorophyll-a, etc.) and make their use easier for the water resources management.

Principal component analysis: an appropriate tool for water quality evaluation and management?application to a tropical lake system

An eutrophic lake system characteristic of Ivory Coast provided us with the opportunity to check that the values of all analytical variables are linked to both causes and effects of eutrophication (feedback effect). Therefore, none of these values can accurately describe a trophic state alone. To solve this difficulty we suggest here, that relationships between analytical variables are able to generate better descriptors than variables themselves. We show that principal component analysis (PCA) using coefficients of linear regression is, by construction, an appropriate tool for this purpose. The graphic representations obtained underline that: (i) the first principal component is linked to the trophic potential and the second one to the trophic level; (ii) the graphical locations of the different lakes studied are consistent with their apparent features; (iii) allochthonous inputs have a spreading effect on the graphic representation. Extension of this model to other lakes, located in the same geographical area, was successfully carried out. Furthermore, it has been shown that it is possible to reduce the number of analytical parameters to four (pH, conductivity, UV absorbance at 254 nm and permanganate index for raw water) without notably impairing the quality of the PCA representation. Moreover, these very simple parameters are easier to quantify than classical one (nutrients, chlorophyll-a, etc.) and make their use easier for the water resources management.

Winter and spring mixing depths affect the trophic status and composition of phytoplankton in the northern meromictic basin of Lake Lugano

The trophic state of Lake Lugano is still too high to be acceptable, despite extensive recovery measures undertaken in recent decades which have resulted in a reduction of the external phosphorus load to the deepest of the lake's basins (northern basin; Zmax=286 m) to fairly acceptable values. Since meromixis was established in the middle of last century, the deep hypolimnion of the northern basin (the layer between ca 100 m and the bottom) has contained high quantities of nutrients (especially phosphorus) which are a major potential source of internal load. When there are particularly strong winter mixing events, a portion of this phosphorus reserve is redistributed along the upper water column (0-100 m). The impact of meteo-climatic conditions on the plankton biocenosis were analysed using data collected in the northern basin (Gandria station) during the three-year period 1998-2000. The phytoplankton composition, which is typical of eutrophicated waters, shows marked interannual variations, also depending on the degree of mixing of the waters at the start of the vegetative period. Though there is no steady pattern of typical dominant species / master species in the lake, there is a seasonal succession characterised by a marked development of diatoms in spring, and a predominance of chlorophyceans and cyanobacteria in summer and autumn. Under present conditions, the mechanisms of internal replenishment of nutrients towards the euphotic layer, due to the phenomena of late winter and spring mixing, constitute a significant source of nutrients for the spring and summer growth of phytoplankton. On the other hand, pronounced mixing phenomena, like those occurring in the two-year period 1999-2000, can reduce the hypolimnetic nutrient reserves and cause a decrease in the trophic potential of the basin, contrasting with an increase in algal biomass in the euphotic zone.

The importance of the riparian ecotone and river hydraulics for sustainable basin-scale restoration scenarios

1. The effect of riparian ecotone functional complexity and stream hydraulics on an upland river ecosystem has been analysed. 2. The amount of nutrients retained by bottom sediment was lowest on a sandy substrate (range: 26–104 mg m−2 P-PO4) and highest in wetland bays (range: 558–5368 mg m−2 P-PO4). A stream bed covered by Berula erecta had about three times higher retentive nutrient capacity ( x̄ = 584 mg m−2 day−1) than did a sandy substrate( x̄ = 205 mg m−2 day−1). 3. The amount of allochthonous organic matter (CPOM) deposited on the stream bed decreased with current velocity. The trophic potential of CPOM, measured as total protein, was significantly correlated with the amount of deposited CPOM (r = 0.863; p<0.00001) and depended on stream order. 4. Both invertebrate and fish biomass in the upland river were significantly correlated with calcium/bicarbonate (benthos: r = 0.858; p<0.006; fish: r = 0.918; p<0.001). 5. Fish biomass, diversity and species richness were highest in pools, lower in riffles and lowest in the run/transition zone. 6. Macroinvertebrate biomass was highest at an intermediate riparian ecotone complexity with an adequate supply of organic matter and incident light. Fish biomass followed the same trend, being lowest in heavily shaded areas and in open channels without riparian vegetation (range: 1–4.5 g m−2), but highest in ecotones of intermediate complexity (range: 1.6–92.8 g m−2). The ‘cascading effect’ of invertebrate density depletion, which was inversely related to fish biomass, was observed seasonally. 7. The above results indicate that riparian ecotone structure and the heterogeneity of the stream channel may regulate biodiversity, productivity and nutrient retention in the fluvial corridor. These quantitative data help to create alternative scenarios for sustainable river basin management. © 1998 John Wiley & Sons, Ltd.

Neurotrophin-4/5 selectively protects nigral calbindin-containing neurons in rats with medial forebrain bundle transections.

Three neurotrophic factors associated with the nigrostriatal dopaminergic system were tested for their trophic potential to rescue degenerating substantia nigra dopaminergic neurons in adult rats with transections of the medial forebrain bundle. Axotomy of nigral dopaminergic neurons results in a retrograde degeneration of their cell bodies. Unilateral transections resulted in a partial reduction of the number of dopaminergic neurons as identified by immunocytochemistry for tyrosine hydroxylase to approximately half of the number of neurons present on the intact contralateral substantia nigra. A similar percentage loss was found for the subpopulation of nigral neurons which contain the calcium binding protein calretinin. In contrast, the small subpopulation of neurons which contain calbindin was less sensitive to the lesion and showed only mild loss in the number of cells, which was reduced to 87% of control. Neurotrophin-4/5, transforming growth factor alpha or basic fibroblast growth factor were infused supranigrally for two weeks after transection. None of the trophic factors tested reversed the loss of tyrosine hydroxylase-positive or calretinin-positive cells. In contrast, neurotrophin-4/5, but not transforming growth factor alpha or basic fibroblast growth factor, was found to reverse the axotomy-induced loss of calbindin-positive neurons and indeed increased the number of cells to 45% above control levels. In addition, neurotrophin-4/5 elevated the number of calbindin-containing neurons in intact unlesioned animals to 15% above control. These findings suggest that neurotrophin-4/5 selectively acts on nigral calbindin neurons following medial forebrain bundle transection and prevents these cells from degenerating.

The trophic potential of sewage effluent resulting from various levels of treatment

On Italy's Adriatic coast there are a large number of aerobic sewage treatment plants, the majority of which do not feature high-efficiency tertiary treatment processes. In order to investigate the relationship between these plants and the trophic potential of the water they discharge, we constructed a pilot plant capable of reproducing the sewage treatment process with four different levels of purification on a rising scale of efficiency in terms of the best-known macronutrients (nitrogen and phosphorus). Water samples taken at various points on the plant for each of the four operating modes underwent laboratory assessment to establish their trophic potential in relation to a dinoflagellate alga ( Prorocentum micans). We were thus able to demonstrate that after biological treatment alone the sewage water has a high eutrophication effect; this gradually decreases as the nutrients are removed and virtually disappears when the plant is providing maximum removal at full efficiency.

Motile cryptofauna of a coral reef: abundance, distribution and trophic potential

The major groups of mot~le cryptofauna lnhab~tlng dead coral substrata across several environmental zones of Davies Reef In the central Great Barner Reef, Austral~a, have been quantified In general terms of both numbers and b~omass the main groups of ep~benth~c cryptofauna were harpac- hco~d copepods, gammar~d amph~pods, syll~d polychaetes and gastropod n~olluscs Other crustaceans abundant In some locat~ons were so pods tana~ds and ostracods Copepods compr~sed 55 to 60 % of total number of cryptofauna over all reef locations and up to 28 % of b~omass Polychaetes were usually the dominant biomass component of the fauna Abundance of total cryptofauna vaned wth reef locat~on, being h~ghest on the fore-reef region In terms of both density and biomass Damself~sh terntones were shown to be a refuge for cryptofauna In all locat~ons of the reef Mean density of anlmals ins~de territories was 58 300 m-2 an average of 3 6 tlmes h~gher than on adjacent, well-grazed surfaces Cryptofaunal abundance was closely related to algal abundance and not complex~ty of the coral rock substratum It IS predicted that cryptofauna are s~gn~f~cant consumers of epilithic algae and associated matenal In locations such as damselfish terntones, on coral reefs

Nonspecific adaptation of jejunal amino acid uptake in the rat

Luminal nutrients are a major effector of intestinal adaptation. Amino acids are trophic to the intestine, but their role in regulating amino acid transport is not well documented. The presence of several distinct amino acid transport systems raises the question of whether adaptation is class-specific. Studies were carried out in parenterally nourished rats receiving a 7-day jejunal infusion of a 3% solution of either aminoisobutyric acid, aspartic acid, glutamine, histidine, lysine, or valine. While all amino acids were trophic to the intestine, their effects on the in vitro uptake of 0.1, 1.0 and 10.0 mM aspartic acid, lysine, and valine (representative acid, basic, and neutral amino acids) were variable and nonspecific. Compared to controls receiving either total parenteral nutrition alone or total parenteral nutrition plus luminal saline, prior lysine and aspartic acid infusion significantly increased in vitro uptake of all three amino acids tested, whereas valine had little effect on trarisport. No effect on transport was seen with glutamine (actively metabolized by the intestine as is aspartic acid), aminoisobutyric acid (a nonmetabolizable amino acid congener), or histidine (the most trophic amino acid). In conclusion, while individual amino acids cause an adaptation of amino acid Uptake, the effects are nonspecific and independent of their metabolic or trophic potential.

Sympatric Coevolution of the Trophic Niche of Two Detritivorous Isopods, Asellus aquaticus and Proasellus coxalis

The role of 16 species of microfungi in the potential trophic niche of populations of Asellus aquaticus (L.) and Proasellus coxalis Dolff. collected in both sympatry and allopatry was determined in the laboratory. Animals and fungi were collected in three woodland streams similar as to geographic location and hydrogeologic, physical and chemical features. The fungi were offered as the sole food source to the animals for 50 d. Young animals, born in the laboratory, were tested for their trophic potential. Sympatric A. aquaticus and P. coxalis had a much more differentiated potential trophic niche than allopatric populations. In particular, the sympatric species had a potential overlap in the usc of 25% of the tested fungi, while allopatric species had a potential overlap of 75% of the fungi. The two species from sympatric locations were specialized on fungal species not very common in nature, while more common fungi were used without distinction by both species. The exclusiveness of each fungal species for the isopods living in sympatry increased inversely to its frequency in nature. The results suggest a possible effect of co-occurrence on the character displacement shown by sympatric populations and support the hypothesis of coevolutionary trophic partitioning between them. The results also imply that the importance of the fungi in the co-occurrence of the isopod species is greater than suggested by the small biomass of the fungi.

Trophic structure and species diversity

This paper considers a model of an ecosystem in which interactions between species are described by pathways for energy flow. We introduce a new measure of diversity which incorporates the complexity of interaction between the various populations in the trophic web. This diversity measure which is given in terms of the feedback at various levels of the ecosystem reduces to the classical Shannon-Weaver measure when the flow of energy from the primary producer to the other populations in the community are equal. We also introduce the concept trophic potential of an ecosystem. The trophic potential measures the mean of the contribution of the various populations to the equilibrium species distribution. This concept is related to the diversity measure. Diversity is precisely the product of the net productivity and the mean turnover time when the trophic potential of the ecosystem is zero.