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In population ecology, there has been a fundamental controversy about the relative importance of competition-driven (density-dependent) population regulation vs. abiotic influences such as temperature and precipitation. The same issue arises at the community level; are population sizes driven primarily by changes in the abundances of cooccurring competitors (i.e., compensatory dynamics), or do most species have a common response to environmental factors? Competitive interactions have had a central place in ecological theory, dating back to Gleason, Volterra, Hutchison and MacArthur, and, more recently, Hubbell's influential unified neutral theory of biodiversity and biogeography. If competitive interactions are important in driving year-to-year fluctuations in abundance, then changes in the abundance of one species should generally be accompanied by compensatory changes in the abundances of others. Thus, one necessary consequence of strong compensatory forces is that, on average, species within communities will covary negatively. Here we use measures of community covariance to assess the prevalence of negative covariance in 41 natural communities comprising different taxa at a range of spatial scales. We found that species in natural communities tended to covary positively rather than negatively, the opposite of what would be expected if compensatory dynamics were important. These findings suggest that abiotic factors such as temperature and precipitation are more important than competitive interactions in driving year-to-year fluctuations in species abundance within communities. [ABSTRACT FROM AUTHOR]

"Effective non-bicarbonate" buffering capacity (or buffer value) was measured in white muscle of yellow perch (Perca flavescens) by titrations with mineral acid and base in a carbon-dioxide free, closed system. Yellow perch were collected at three month intervals throughout 1983 from an acidic lake (pH ∼ 4.6) and two alkaline lakes (pH ∼ 7.8) in northern Wisconsin. "Buffering capacity" was also determined for white muscle of perch kept in the laboratory under different regimes of temperature and ration. The mean "buffering capacity" of white muscle from yellow perch taken directly from natural environments ranged from 40.7 ± 3.1 (SD) slykes in March of 1983 to 53.7 ± 2.8 (SD) slykes in July of that year. These changes in "buffering capacity" were strongly correlated with water temperature. Egg production and thirty-day laboratory starvation produced significant decreases in "buffering capacity" and increases in the water content of yellow perch muscle. Fed perch in the laboratory had a temperature dependent "buffering capacity" similar to "field caught" fish. "Buffering capacity" of white muscle did not differ between yellow perch from acidic and alkaline lakes. Investigators using "buffering capacity" as a gauge of species differences in metabolic potential, should be wary of seasonal and reproductive factors that might alter their conclusions.

Gaseous respiration by central mudminnows (Umbra limi), particularly their use of bubbles composed of gas mixtures other than air, may have evolved as an adaptation to the oxygen-depleted, carbon dioxide-rich water of winterkill lakes. Under simulated winterkill conditions, mudminnows frequently engulfed gaseous bubbles. Use of bubbles was not related to varying methane or nitrogen content (0 to 80 percent) when all bubbles contained 20 percent oxygen. When the oxygen content of bubbles varied (0 to 20 percent), fish visited bubbles randomly but remained longer and took fewer "breaths" at bubbles with high oxygen content. High temperature (16 degrees to 34 degrees C) and low pH (6.8 to 4.5) did not stimulate increased air-breathing when dissolved oxygen was sufficient.

Behavioural thermoregulation and locomotory activity of green sunfish were examined in a temporal temperature-gradient apparatus. Green sunfish actively avoided temperatures exceeding 30.3 degrees C and below 26.5 degrees C and had a median preferred temperature of 28.2 degrees C. Temperature preference did not vary significantly during the diel period even though locomotory activity patterns were markedly crepuscular. Activity was stimulated by the change in illumination levels at dawn and dusk.

Electronic equipment allows fishes, by their spatial movements, to regulate the temperature in experimental tanks. Swimming into warmer water causes the temperature of the entire tank to increase; conversely, swimming into cooler water causes the temperature to decrease. The technique may be adapted for studying simultaneous behavioral regulation of temperature and nonthermal factors.