Linking ecosystem services, rehabilitation, and river hydrogeomorphology

This is the publisher's version, which may also be found at: http://www.jstor.org/stable/10.1525/bio.2010.60.issue-

The ecology of freshwater molluscs

This is the publisher's version, which may also be found at: http://www.jstor.org/stable/266420

Effects of Microhabitat Selection on Feeding Rates of Net-Spinning Caddisfly Larvae

Net-spinning caddisfly larvae of the family Hydropsychidae are known to prefer microhabitats with large, stable substrate and high water flow velocity. It is often assumed that net spinners in high-velocity microhabitats have higher feeding or growth rates than larvae in less preferred sites, but there is no direct evidence to support this assumption. We hypothesized that net-spinning caddisflies would select microhabitats that offered the greatest feeding rates. This hypothesis was tested by field experiments in which we determined if net-spinning caddisfly larvae preferred high-velocity sites even when substrate size and type were held constant. We then measured feeding rates of net spinners in microhabitats with different flow characteristics. High-flow positions were selected by 96% of hydropsychid larvae colonizing artificial moss substrates. Artemia nauplii released into the water column were captured by individual larvae in high-flow sites at a rate of 0.016%/m, significantly higher than the capture rate in low-flow sites. Combining this rate of prey capture with mean hydropsychid densities of 1125 individuals/m2, we estimate that hydropsychid larvae in riffles remove drifting invertebrate prey at a rate of «18%/m. Assuming exponential prey removal, a prey item in the drift would travel an average of only 5.5 m before being consumed. This study is one of the first to show that the distribution of a stream filter feeder is related to the feeding rates obtainable in different microhabitats

Effects of crowding on growth rate and symbiosis in green hydra

In order to examine the relationship between crowding and growth rate in green hydra (Hydra viridis), we raised animals at various levels of fixed population densities; all new individuals in excess of the fixed densities were counted and removed every 4 days. A significant inverse relationship between population density and population growth rate exists. In addition, hydras were found to increase or decrease their growth rates in response to rapid changes of density after acclimation to fixed densities. The most dramatic effects were noted when the changes in degrees of crowding were greatest. Investigation of the effects of crowding in hydras on the total quantity of algal endosymbionts and their pigments revealed no significant changes in algal numbers or in carotenoid to chlorophyll-tf ratios at any level of crowding. Data on the presence of a water borne inhibitor of asexual reproduction supported the hypothesis that crowded culture medium contains a substance which depresses growth rates in green hydras

Regulation of Freshwater Community Structure at Multiple Intensities of Dragonfly Predation

We examined the role played by predaceous dragonfly nymphs, Celithemis fasciata (Odonata: Libellulidae), in the regulation of the community structure of a benthic macroinvertebrate assemblage in Par Pond, an 1100-ha reservoir in South Carolina. Effects of predation intensity on species richness, evenness, and density were evaluated by adding zero, two, four, and eight large dragonfly nymphs (antepenultimate and penultimate instars) to previously sieved (0.85-mm mesh) bottom sediment containing benthic macroinvertebrates. Predator and prey assemblages were then placed in individualfieldmicrocosms that consisted of polyethylene trays surrounded by underwater screens (mesh <2 mm diagonally) and suspended 15 cm belowfloatingplatforms. Twelve replicates of each treatment level were run during each of three 6-wk experimental periods: April-May 1980, August-October 1980, and January-February 1981. In addition, colonization of microcosms by invertebrates was quantified, and samples from natural, unenclosed benthic fauna were collected seasonally along a transect for comparison with experimental assemblages. We tested whether predators enhanced, depressed, both increased and decreased, or had no effect on the complexity of the community structure. The dual effect of predation on community structure is predicted by Connell's "intermediate disturbance hypothesis." Results showed that dragonfly nymphs can significantly influence the structure of the benthic community. However, the results did not show that invertebrate predation is the sole or even the primary regulator of community structure. Species richness was significantly greater at intermediate treatment levels (thus supporting Connell's general hypothesis), but the increase was not great (a range of -10%). The mechanisms by which species richness is maximized at intermediate intensities of predation are not entirely evident, but are probably a combination of prey refuges and nonselective predation with patch switching. In contrast, species evenness, as measured by equitability and by Simpson's index, was greatest at the highest predation level (which does not support the intermediate disturbance hypothesis). Dragonflies appeared to exert a greater influence on prey density than on community diversity

Field Experiments on Responses of a Freshwater, Benthic Macroinvertebrate Community to Vertebrate Predators

We examined the seasonal importance of vertebrate predators in potentially regulating the abundance and diversity of the benthic macroinvertebrates in the littoral zone of a soft-bottom reservoir that receives thermal effluent from a nuclear production reactor. Thirty-six predator (fish and turtle) exclusion cages (4 m-') were placed in shallow water at six locations along a thermal gradient in Par Pond, a 1100-ha cooling reservoir on the Savannah River Plant near Aiken, South Carolina, USA. An additional 36 control plots (4 m-) were also set up. Cages were in place during three, 3-mo test periods beginning in September 1977. Estimates of benthic density, taxon richness, and distribution within functional groups (defined by feeding mechanism) were calculated for each test period. Effects of temperature on predator-prey relationships were also determined. Experimental results of this study suggest that vertebrate predation was not the fundamental parameter organizing the benthic macroinvertebrate community in the littoral zone of this reservoir. Neither taxon richness nor density of total macroinvertebrates was conclusively related to predator treatment. Relationships between predator treatment and community response (changes in density and taxon richness) were generally unaffected by either plot locality, temperature fluctuations from thermal effluent, or seasonal changes. When data from caged and control plots were pooled, however, both location and water temperature individually had direct impacts on the benthic community. From our results and other field studies we hypothesize that individual species of "keystone" benthic predators (Paine 1969b) do not occur in the littoral zone of freshwater lentic environments with soft bottoms. This hypothesis is based on the following four arguments. First, environmental heterogeneity should reduce predator efficiency relative to that found in rocky intertidal systems where keystone predation may be present. Second, relative food web complexity should reduce the community importance of an individual predator species. Third, the apparent relatively greater resource partitioning of space and food in the freshwater littoral zone hinders monopolization of ratelimiting environmental resources by a single dominant prey species. Fourth, the effects of predation may not be extensive enough in time or area to provide sufficient resource space (and thus food) for exploitation by fugitive species. Possible regulation by a guild of predators and cases where the general hypothesis might be falsified are discussed

Putting New Life Into Pastures

Many of the old permanent bluegrass pastures in Iowa can almost be made “ to feed two cattle where one fed before.” We found this out from a study of the problem at Mt. Pleasant during the 6 years, 1933 to 1938. In the past 3 years some 250 Iowa farmers in 45 counties have cooperated in demonstrating the possibilities of increasing the returns from permanent pastures by introducing clover into old grass sods and from applying lime and phosphate fertilizer in addition to reseeding

Expression patterns of chondrocyte genes cloned by differential display in tibial dyschondroplasia

AbstractTibial dyschondroplasia (TD) appears to involve a failure of the growth plate chondrocytes within growing long bones to differentiate fully to the hypertrophic stage, resulting in a mass of prehypertrophic chondrocytes which form the avascular TD lesion. Many biochemical and molecular markers of chondrocyte hypertrophy are absent from the lesion, or show reduced expression, but the cause of the disorder remains to be identified. As differentiation to the hypertrophic state is impaired in TD, we hypothesised that chondrocyte genes that are differentially expressed in the growth plate should show altered expression in TD. Using differential display, four genes, B-cadherin, EF2, HT7 and Ex-FABP were cloned from chondrocytes stimulated to differentiate to the hypertrophic stage in vitro, and their differential expression confirmed in vivo. Using semi-quantitative RT-PCR, the expression patterns of these genes were compared in chondrocytes from normal and TD growth plates. Surprisingly, none of these genes showed the pattern of expression that might be expected in TD lesion chondrocytes, and two of them, B-cadherin and Ex-FABP, were upregulated in the lesion. This indicates that the TD phenotype does not merely reflect the absence of hypertrophic marker genes, but may be influenced by more complex developmental mechanisms/defects than previously thought