We conducted a study from 1998 to 2001 to determine the efficacy of a benthic trawl designed to increase species detection and reduce the incidence of zero catches of small-bodied fishes. We modified a standard two-seam slingshot balloon trawl by covering the entire trawl with a small-mesh cover. After completing 281 hauls with the modified (Missouri) trawl, we discovered that most fish passed through the body of the standard trawl and were captured in the cover. Logistic regression indicated no noticeable effect of the cover on the catch entering the standard portion of the modified trawl. However, some fishes (e.g., larval sturgeons Scaphirhynchus spp. and pallid sturgeon S. albus) were exclusively captured in the small-mesh cover, while the catch of small-bodied adult fish (e.g., chubs Macrhybopsis spp.) was significantly improved by use of the small-mesh cover design. The Missouri trawl significantly increased the number and species of small-bodied fishes captured over previously used designs and is a useful method for sampling the benthic fish community in moderate-to large-size river systems.

SUMMARY Flying squirrels are well known for their ability to glide between trees at the top of a forest canopy. We present experimental performance and behavioural evidence that flight in flying squirrels may have evolved out of a need to control landing forces. Northern flying squirrels were filmed jumping from a horizontal branch to a much larger vertical pole. These were both slightly compliant (less than 1.9 mm N–1), and instrumented using strain gauges so that forces could be measured. Take-off and landing forces were both positively correlated with horizontal range between 0.5 and 2.5 m (r=0.355 and r=0.811, respectively, P<0.05), but not significantly different to each other at each range tested. Take-off forces ranged from 1 to 10 bodyweights, and landing forces were between 3 and 10 bodyweights. Glide angles increased rapidly with horizontal range, approaching 45° at 3 m, above which they gradually decreased, suggesting that northern flying squirrels are optimised for long distance travel. We show that northern flying squirrels initiate full gliding posture at ranges of less than 1 m, without landing any higher than an equivalent ballistic projectile. However, this gliding posture enables them to pitch upwards, potentially stalling the wing, and spreads the landing reaction force over all four extended limbs. At steeper approach angles of close to 45°, flying squirrels were unable to pitch up sufficiently and landed forelimbs first, consequently sustaining higher impact forces. We investigate four hypotheses to explain the origin of flight in these animals and conclude that the need to reduce landing impact forces was most likely to have stimulated the development of aerial control in flying squirrels.

Large rivers worldwide have been altered by the construction and maintenance of navigation channels, which include extensive bank revetments, wing dikes, and levees. Using 7 years of Long‐Term Resource Monitoring Program (LTRMP) data collected from the unimpounded upper Mississippi River, we investigated assemblages in two main‐channel‐border physical habitats—those with wing dikes and those without wing dikes. Fishes were captured using daytime electrofishing, mini‐fyke netting, large hoop netting, and small hoop netting. Our objectives were to (1) assess associations among fish species richness, physical measurements, and main‐channel‐border physical habitats using stepwise multiple regression and indicator variables; (2) identify abundant adult and young‐of‐year (age‐0) families in both physical habitats to further investigate assemblage composition; and (3) calculate standardized species richness estimates within each physical habitat for adult and age‐0 fishes to provide additional information on community structure. We found species richness was greater at wing dikes for both adult and age‐0 fishes when compared with main channel borders. Stepwise multiple regression revealed significant relationships between adult species richness and passive gear deployment (e.g., hoop nets and mini‐fyke nets), physical habitat type, and river elevation, as well as interactions between physical habitat and passive gears, and physical habitat and transparency (i.e., Secchi depth). This model explained 56% of the variance in adult species richness. Approximately 15% of the variation in age‐0 species richness was explained by the sample period, sample date, transparency, physical habitat, and depth of gear deployment. Long‐term impacts of river modifications on fishes have not been well documented in many large river systems and warrant further study. The findings from this study provide baseline ecological information on fish assemblages using main channel borders in the unimpounded upper Mississippi River, information that will aid managers making channel maintenance decisions in large river systems.

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The roles of climate and competition in relation to the structure of temperate zone lizard communities were investigated. Lizard species richness was positively related to mean January temperature, but negatively related to warm-season precipitation and mean July temperature. Generic groups showed little overlap in morphological factor space but considerable overlap in habitat use. Species that were similar in either morphology or habitat use were dissimilar in the alternative factor space. A canonical correlation analysis revealed a si~ificant relationship between lizard morphology and habitat use. In general, large bulky hzards were associated with extensive vegetative cover while smaller slenderbodied lizards were found in open desert or grassland conditions. No significant relationship was found between community size and measures of niche overlap or species packing in either morphological or ecological space. A comparison of species packing between the fiel~ co~munities and randomly generated null communities revealed no significant ov-erdts~erswn of the natural communities in either habitat use or morphology, thus providing no evtdence to support the limiting-similarity hypothesis.