Community Trophic Structure Research Articles

Latitudinal differences in fish community trophic structure, and the role of fish herbivory in a Costa Rican stream

We experimentally manipulated fish grazing pressure to determine whether fish herbivory played an important role in the structure of a Costa Rican stream. Non-planktonic plant matter represented a significant percentage (≥ 25%) of the diet of 77% of the 17 fish species in the community. We prevented fish grazing on macrophytes, tree leaves, and periphyton using fish exclusion cages. Fish grazedPanicum sp., used as a generalized aquatic macrophyte, to the stems after 6 days in control areas, and consumed all or much ofFicus insipida andMonstera sp. leaves when placed in the stream after 48 hours. Plants and leaves experimentally protected by cages remained intact. In periphyton studies, fifty percent more ash free dry weight occurred on 25 × 25 cm floor tiles protected from fish grazing by cages than on tiles in roofless controls exposed to fish grazing for 19 days, suggesting a reduction in periphyton biomass. These results demonstrate that fish herbivory affects macrophyte abundance, and impacts the amount of leaf litter in the stream. Fish herbivory may also have an important effect on overall periphyton biomass. Herbivorous fish species generally represent a larger proportion of the total fish community in tropical compared to temperate streams; thus fish grazing is more likely to have an important influence on plant and animal abundances and distributions in tropical streams.

Fossil communities of the upper Trenton Group (Ordovician) of New York State

During the late Trentonian the New York State region experienced gentle crustal subsidence which preceded the onset of the Hudson Valley phase of the Taconic Orogeny. The lower and middle Steuben Limestone represents several shallow-water facies: a protected shoal, a wave dissipation zone and a shallow shelf. Overlying strata of the upper Steuben and the Hillier limestones represent progressively deeper water facies. After a short period of uplift, which produced a minor unconformity, black shales began to bury the Trenton carbonate platform.Three fossil communities are found in the upper Trenton Group. Each had been present on the Trenton bank since it first formed. The Liospira Community existed on the shallow protected shoal facies of the Steuben Limestone. Its assemblages are dominated by brachiopods, gastropods, bryozoans, and crinoids. The Encrinurus Community was found in the wave dissipation zone and on the shelf facies. This diverse community was dominated by brachiopods, bryozoans, and crinoids. The Trematis Community is found in the deeper shelf deposits of the Hillier Limestone. It was a very heterogeneous community with brachiopods, crinoids, gastropods, trilobites, and conodonts all represented.These communities have now been traced through a minimum of eight million years of their history and it is now possible to evaluate their patterns of community evolution. At the species level these communities were quite changeable. Between 45% and 55% of the species which were present in the lower Trenton Group were replaced by the late Trentonian. Despite this changeover, the communities maintained a remarkably familiar look because there was great stability at higher taxonomic levels and the same proportions of brachiopods, bryozoans, crinoids, etc., were maintained throughout the Trentonian. Community trophic group structure also seems to have been quite stable throughout the Trentonian. If these patterns are representative, then these invertebrate communities appear to be genuinely stable entities. Evolution changes the cast of characters but the play is the same!

Taphonomic Gradients in Shelf Fossil Assemblages: Pliocene Purisima Formation, California

Shell and bone beds in the Pliocene Purisima Formation of central California accumulated through dominantlyphysicalprocesses of concentration in shallow-marine facies and by ecological mechanisms in deep-shelf lithofacies. This trend reflects onshoreoffshore variations in rate of sedimentation, frequency of current reworking, and preservation of bioturbation. The shift from physical to ecological processes tracks a change from high frequency of reworking by currents in shallow water to lower rates ofphysical reworking below storm-wave base. Storm and currentgenerated shell beds decrease in abundance offshore due to decreased current strength andfrequency and to increased bioturbation. Shell deposits in deep shelf settings result from sediment starvation and such ecological processes as aggregation of shelled molluscs, encrustation of pre-existing shell lags, and repeated pulses of larval settlement. Nearshore shell beds preserve considerable information on current direction, types of bottom flows, duration of exposure of shells on the bottom, and flow regime, but little data on community trophic structure or species diversity. Offshore shell deposits, in contrast, preserve community associations and encruster-host relationships (which may be destroyed in the high-energy, nearshore region) as well as information regarding rate of sedimentation and early diagenetic conditions.

Community Structure and Seasonal Changes in Standing Stocks of Fish in a Warm-water Stream

A comprehensive study of the standing stocks of fish species in Glover Creek, Oklahoma, was conducted on a seasonal basis from 1977-1979. Community structure was described by biomass of species and feeding guilds and comparisons were made among seasons. Invertivore and invertivore-piscivore feeding guilds contained 79.9%o of the total fish standing stock. Guild structure differed among riffles and pools and varied less seasonally than between habitat types. The annual average total fish standing stocks were 60 and 90 kg/ha, for riffle and pool sites, respectively. Total standing stocks differed among seasons with the annual average occurring in April-May and October-November, and the maximum occurring during July-August. INTRODUCTION More reliable assessments of habitat impacts on streams could be made using a biological integrity approach rather than indicator species or diversity approaches (Cairns, 1977; Karr, 1981). Karr (1981) recently proposed a method to assess the biological integrity of stream fish communities. However, one of the basic assumptions of Karr's method is that biologists know what the structure of the fish community should be in unmodified habitats, and can then compare the observed community attributes with those expected under unmodified conditions. Although many studies have investigated how fish species richness varies with stream order (Huet, 1959; Sheldon, 1968), flow variability (Horwitz, 1978) and habitat structure (Gorman and Karr, 1978), relatively few investigators have attempted to quantify community trophic structure and seasonal changes in fish biomass in unmodified stream systems. For example, Funk (1975) found only seven studies of streams inhabited by black bass (Micropterus), in which composition of total fish biomass was estimated. Most of the studies reviewed by Funk (1975) suffered from four limitations: (1) smaller fish species were not considered; (2) estimates of total fish biomass were conducted only in pools; (3) population estimates were taken during one season giving no indication of typical seasonal variation, and (4) interpretation was complicated by the large number of species, even when smaller fishes were excluded. Schlosser (1982a) found that trophic structure was stable across both seasons and years in an unmodified stream, yet was seasonally unstable in a modified stream. Furthermore, Schlosser (1982b) attributed spatial variation in community organization to habitat structure and the temporal variability in habitat and food availability. However, few comparable studies assess the generality of Schlosser's findings. The objective of this study was to describe the structure of the fish community in an unmodified stream in relation to season and habitat type. Specifically, we ask: (1) Do fish communities in unmodified streams have a stable trophic structure? (2) Are there general differences in trophic structure between riffle and pool habitats? and (3) Does a typical seasonal pattern in total fish biomass exist? STUDY AREA The study area was located on Glover Creek in SE Oklahoma (Orth and Maughan, I Present address: Department of Fisheries and Wildlife Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061 2 Cooperators are the Oklahoma Department of Wildlife Conservation, Oklahoma State University, and the U.S. Fish and Wildlife Service.

A Comparative Study of Heavy Metal Accumulation in Tissues of the Crested Tern, Sterna Bergii. Breeding Near an Industrial Port Before and After Harbour Dredging and Ocean Dumping.

Eight different tissues taken from crested terns, Sterna bergii, were analysed for the metals cadmium, lead, copper, chromium, manganese, zinc and iron. Birds were taken from a breeding colony before and after the commencement of harbour dredging and ocean dumping operations in nearby Port Kembla Harbour. Levels of chromium and lead were similar in both adult and fledgling terns after dredging began, indicating that chicks acquired these metals from food brought to them by adult birds. However, these metals were found in relatively low concentrations. No conclusive evidence was found of increased assimilation of heavy metals into the trophic structure of communities in waters adjacent to the Five Islands after dredging and ocean dumping operations.

Littoral benthos‐sediment relationships in Manukau Harbour, New Zealand

Abstract Sampling of 57 littoral stations in Manukau Harbour, Auckland, (37° 02’ S, 174° 41’ E) for species composition, distribution, and abundance as part of a base‐line ecological survey of the harbour shows that the community trophic structure is related to the sediment grain size. Deposit feeders such as the bivalves Macomona liliana and Nucula hartvigiana and the gastropod Zeacuman‐lus lutulentus are most abundant in fine sand, whereas suspension feeders such as the bivalves Chione stutchburyi and Paphies australe are most abundant in medium sand. The proportion of deposit feeders in the sample increases with decreasing grain size of the sediment. Most stations conform to this general trend, although when the results are plotted as the percentage of deposit feeders against the median and mean grain sizes of the sediment in which they occur, three groups of stations appear anomalous. These stations, at Waiau Pa, Pollok Beach, and Fosters Bay, may be unstable and undergoing a change in community struc...

Trophic Structure Determination and Equilibrium in an Arthropod Community

Heatwole and Levins (1972) contend that the island recolonization experiment of Simberloff and Wilson (1969) demonstrates a community trophic structure equilibrium determined by species interactions. Data do not support this contention. Heatwole and Levins may have overstated the determinateness and importance of trophic structure for two reasons: (1) they pooled data from separate islands, (2) the statistic with which they characterize trophic structure is strongly dependent on species number. That trophic interactions are important in this system remains unproven; on the other hand, such species characteristics as dispersal ability and microhabitat requirements may be critical to some dominant species.

Role of Allochthonous Detritus in the Trophic Structure of a Woodland Springbrook Community

The community trophic structure of Morgan's Creek, Meade County, Kentucky was analyzed through regular measurement of standing crops of the chief potential sources of plant materials available to the animals (suspended particulate, attached particulate, and allochthonous leaf materials) and an examination of their gut contents. The most important food was allochthonous leaf materials, which occurred as suspended material in the water, as a component of materials attached to the streambed, and as whole leaves and fragments. Diatoms were the only other important source of plant materials and constituted the greatest proportion of the attached organic fraction. Mean standing crop measurements of potential foods for five sampling stations ranged from 0.6 to 1.0 kcal/m3 for suspended particulate organic matter; 12 to 19 kcal/m2 for attached particulate organic matter; and 4.7 to 13 kcal/m2 for allochthonous leaf materials. Comparison of standing crop data with previous findings indicates that the values generally are within the known ranges for flowing waters. Analysis of gut contents and determination of the principal pathways of energy flow in the stream indicate that imported organic matter in the form of allochthonous leaf materials provides the main source of energy for the primary consumers and, indirectly, for the entire benthic community of Morgan's Creek. Of the 37 taxa of animals studied, 24 were herbivores, 5 omnivores, and 8 carnivores. In general, detritus made up from 50 to 100% of all the materials ingested by both the herbivores and omnivores. The total number of benthic animals was comprised of 14% herbivores, 83% omnivores, and 3% carnivores. Gammarus minus was the single most important member of the fauna. It contributed 81% of the total number of invertebrates, and well over 90% of its diet consisted of allochthonous leaf detritus.