ISSN:0012-9658    

DOI:10.2307/1941628

出版商:Ecological Society of America    

年代:1988

数据来源: WILEY

摘要:

Aircraft sampling of the planetary boundary layer can be used to measure trace gas distributions and fluxes directly on regional scales. Laser—based detection and in situ atmospheric sampling can be used for fast—response, accurate measurements of gas concentrations in a column of air over time. Lidar (light detection and ranging) techniques provide a unique method for determining the structure and dynamics of the boundary layer over time. Under stable atmospheric conditions, the combination of these techniques allows estimates of gas exchange between the biosphere and atmosphere.

ISSN:0012-9658    

DOI:10.2307/1941629

出版商:Ecological Society of America    

年代:1988

数据来源: WILEY

摘要:

Extending the ecological knowledge base to larger scales will require new measurement tools. Long—path Fourier—Transform Infrared Spectroscopy (FTIR) is a promising technology because of its ability to measure the concentration of multiple trace gases simultaneously over spatial scales up to 1 km. Detection limits reaching 1μL/KL for numerous gases make this a powerful method with the potential to study spatial patterning of biological processes, fluxes between ecosystems, important processing pathways within terrestrial and aquatic ecosystems, and scale—dependent processing phenomena. Repeated measurements down to the second range add excellent temporal capabilities. This analytical tool, drawing on the latest developments in analytical chemistry, expands the temporal and spatial scales over which ecosystem nutrient cycling energy flow, and biospheric/atmospheric interactions can be studied.

ISSN:0012-9658    

DOI:10.2307/1941630

出版商:Ecological Society of America    

年代:1988

数据来源: WILEY

摘要:

Ecologists are expected to play an important role in future studies of the biosphere/atmosphere exchange of materials associated with the major biogeochemical cycles and climate. Most studies of material exchange reported in the ecological literature have relied on chamber techniques. Micrometeorological techniques provide an alternative means of measuring these exchange rates and are expected to be used more often in future ecological studies, since they have many advantages over the chamber techniques. In this article we will provide an overview of micrometeorological theory and the different micrometeorological techniques available to make flux measurements.

ISSN:0012-9658    

DOI:10.2307/1941631

出版商:Ecological Society of America    

年代:1988

数据来源: WILEY

摘要:

Fishes moving onto the surface of a tidal freshwater marsh from an adjacent stream were sampled with flume nets in spring through autumn for 2 yr. Significantly higher numbers were found at sites adjacent to shallow—sloped depositional banks than at sites adjacent to deeper, steeper sloped erosional banks of the stream. Marsh surface features appeared similar, so explanations for this apparent habitat selection were sought in the subtidal portion of the stream. To determine whether the relative abundance of benthic invertebrate prey differed in the two environments, litter bags were placed in the subtidal for 4 wk. Despite higher numbers of invertebrates in erosional zones, both the wet biomass per sample and the mean wet biomass per organism were significantly greater in depositional sites. To test the hypothesis that invertebrate food is more available to fishes in the depositional subtidal, banded killifish (Fundulus diaphanus) were placed in feeding enclosures in both depositional and erosional subtidal habitats in two streams. These fish obtained significantly more food in the shallow depositional subtidal. To test the hypothesis that predation pressure differs with subtidal geomorphology, mummichogs (Fundulus heteroclitus) were tethered on the first half of the rising tide in both depositional and erosional environments in three creeks. Significantly more mummichogs disappeared from tethers and were presumed taken on erosional banks. We conclude that two mechanisms operate in the stream subtidal to give rise to the greater fish abundance at marsh surface sites adjacent to depositional areas. At low tide, when small fishes are confined to creek channels, they select shallow depositional habitats where (1) the availability of benthic invertebrate prey is greatest and (2) predator pressure is less. As the tide rises and inundates the marsh surface, these small fishes seek shelter on the marsh surface adjacent to their preferred low—tide refuge.

ISSN:0012-9658    

DOI:10.2307/1941632

出版商:Ecological Society of America    

年代:1988

数据来源: WILEY

摘要:

The bluegill sunfish (Lepomis macrochirus) undergoes several habitat shifts between the littoral and pelagic zones of small lakes during its life history. After hatching in the littoral zone, bluegill fry migrate to the pelagic zone to feed on zooplankton. In this study the fry then returned to the littoral zone in four different lakes at a relatively constant size of °12.5 mm standard length. Several years are spent feeding in the littoral zone vegetation before the bluegill again shifts to feeding on zooplankton, first in the water column above littoral vegetation and subsequently in the true pelagic zone. This shift to feeding on zooplankton occurred at a specific body size within a lake, but the size ranged from 50 to 83 mm among five different lakes. The size at which the shift occurred was directly correlated with the density of the major predator of the bluegill in these lakes, the largemouth bass (Micropterus salmoides). We demonstrate that the bluegill is faced with a growth (or feeding) rate—predation risk trade—off in making these habitat shifts. Analysis of stomach contents, the growth of small fish caged in the pelagic zone, and predictions of foraging rates in both habitats all indicate that the pelagic zone is the more profitable habitat for all size classes of the bluegill. Through a series of pond experiments we further show that risk of predation by largemouth bass was 40—80 times as great for small bluegills in the open water as for those in the vegetation. We interpret the patterns of habitat use by the bluegill in terms of a model that explicitly weights the costs (predation) and benefits (growth) of making a size—specific habitat shift to the pelagic. Finally, we discussed evidence that the bluegill can facultatively respond to changes in feeding rates and predation risk, and the consequences of such ontogenetic habitat shifts to community dynamics.

ISSN:0012-9658    

DOI:10.2307/1941633

出版商:Ecological Society of America    

年代:1988

数据来源: WILEY

摘要:

Algal—herbivore (fish and sea urchin) interactions in shallow (95% mortality. On the shallow reef, erect and filamentous algae and fish grazing intensity increased substantially following urchin death, while crustose corallines declined. Conversely, Diadema mortality had little effect on the deeper reef. Algal responses were similar to those observed in the urchin exclusion experiments. The erect species that increased most after mortality are resistant to fishes via chemical defenses. These findings demonstrate that herbivory is largely responsible for the algal distribution pattern on the reef. The results suggest that Diadema plays a major role in structuring the shallow community, but only a minor role relative to fishes in structuring the deeper community. They also indicate that different herbivores can have a differential effect on erect macroalgal composition.

ISSN:0012-9658    

DOI:10.2307/1941634

出版商:Ecological Society of America    

年代:1988

数据来源: WILEY

摘要:

A whole—stream enrichment experiment of phosphorus and, further down—stream, of phosphorus and nitrogen, allowed us to examine the growth and density responses of the tube—building larval chironomid Orthocladius rivulorum to nutrient enrichment of the Kuparuk River in arctic Alaska, and to evaluate nutrient effects on the tube microbial community. The larva feeds by grazing a diatom monoculture of Hannaea arcus from the tube exterior, thus direct nutrient effects on the tube microbiota may translate into indirect nutrient effects on the larva. Electron microscopy indicated that tube silk was formed into a sheet, with a filamentous substructure that repeated at 50—nm intervals. Bacterial micro—colonies occurred at the points where the erect diatoms were attached to the silk. Microbial activity of Orthocladius tubes in the P—fertilized section was 2—3 times that of the control section of the river, and total microbial biomass in the P—fertilized section was 3—4 times that of the control section. Chlorophyll a was also higher on Orthocladius tubes downstream of both P and N + P fertilization sites. However, the rate of biomass accumulation on tubes was more rapid downstream of N + P addition, suggesting primary P and secondary N limitation of the rate of primary production in the river. Chlorophyll a was higher on tubes than on rocks or experimental tiles, which indicated that tubes were a more favorable algal habitat for Hannaea. Pupal tubes had less chlorophyll a than larval tubes, suggesting that larval activity may have contributed to the higher algal biomass on tubes. Orthocladius benefitted from the enhanced tube flora; larvae grew larger in the fertilized sections of the stream than in the upstream sections. The results suggest that Orthocladius with its tube and associated biota function as microcommunities that respond directly and indirectly to the surrounding nutrient regime, but have considerable trophic independence from surrounding portions of the epilithon. They may constitute 12—43% of total epilithic algal biomass.

ISSN:0012-9658    

DOI:10.2307/1941635

出版商:Ecological Society of America    

年代:1988

数据来源: WILEY

摘要:

The effects of body size, depth, and sampling scale on spatial heterogeneity were examined in the zooplankton community of a small lake. Analyses were performed by regression analysis of 27 sets (3 scales ° 3 depths ° 3 dates) of replicate (n = 4) samples of the natural zooplankton (cladocerans, copepods, rotifers) community of Lake Cromwell, Quebec, Canada. Spatial heterogeneity was measured as the variance among the four randomly arranged replicate samples of taxa taken at each scale—depth—date combination. The spatial distribution of populations of zooplankton in this community was found to be typical of the spatial heterogeneity encountered in other freshwater and marine ecosystems. The effect of population density on spatial heterogeneity was comparable to that found for other flora and fauna. Small animals were more heterogeneous than large ones, and populations sampled on large spatial scales or at greater depths showed greatest spatial variability. These effects were stable over the season. Few taxa or life stages diverged significantly from these trends.

ISSN:0012-9658    

DOI:10.2307/1941636

出版商:Ecological Society of America    

年代:1988

数据来源: WILEY

摘要:

Replicated experiments in artificial ponds demonstrated that an assemblage of aquatic insects competed with tadpoles of the frogs Hyla andersonii and Bufo woodhousei fowleri. We independently manipulated the presence or absence of aquatic insects, and the abundance of an anuran competitor (O or 150 Bufo w. fowleri per experimental pond), using a completely crossed design for two—factor variance analysis, and observed the responses of initially similar cohorts of Hyla andersonii tadpoles to neither, either, or both insect and anuran competitors. Insects and Bufo significantly depressed the mean individual mass at metamorphosis of Hyla froglets and the cumulative biomass of anurans leaving the ponds at metamorphosis. Neither insects nor Bufo affected the survival or larval period of Hyla. Insects also significantly reduced the mean mass of Bufo, showing that both anurans responded to competition from insects. The intensity of competition between natural densities of insects and Hyla tadpoles was comparable to the intensity of competition between Bufo and Hyla, as a density of 150 Bufo/1000 L.

ISSN:0012-9658    

DOI:10.2307/1941637

出版商:Ecological Society of America    

年代:1988

数据来源: WILEY