MAXIMUM DAILY CONSUMPTION AND RESPIRATION RATES AT FOUR TEMPERATURES FOR FIVE SPECIES OF CRAYFISH FROM MISSOURI, U.S.A. (DECAPODA, ORCONECTES SPP.)

We tested for differences in maximum daily consumption ($\text{C}_{\text{max}}$) and respiration (R) rates at four temperatures (18, 22, 26, and 30°C) for crayfishes with varying distributions in Missouri, U.S.A. Five species of crayfish were studied: Orconectes eupunctus (Williams, 1952), found only in the Eleven Point River downstream of Greer Spring, O. hylas (Faxon, 1890), found only in the Black and St. Francis River drainages in the Ozarks, O. luteus (Creaser, 1933) and O. punctimanus (Creaser, 1933), which are widespread through the Ozarks, and O. virilis (Hagen, 1870), which has a broad distribution in Missouri but is most abundant in the northern agricultural region and in the transitional area along the northern and western border of the Ozarks. For species restricted to the Ozarks,$\text{C}_{\text{max}}$increased from 18 to 22°C and stabilized or declined at the two warmest temperatures, while$\text{C}_{\text{max}}$peaked at 26°C for O. virilis before declining at 30°C. Significant interspecific differences in$\text{C}_{\text{max}}$were found at several temperatures.$\text{C}_{\text{max}}$for O. virilis was significantly greater than$\text{C}_{\text{max}}$for one or more Ozark crayfishes at 18, 22, and especially at 26°C. Respiration rates (R) increased with temperature for all species, but few differences in R were observed between species. Results suggest that O. virilis has a potential bioenergetic advantage over Ozark crayfishes, particularly at temperatures near 26°C. Our findings hint that warming of Ozark streams due to changes in climate or land use could yield growth conditions which are more favorable for introduced species such as O. virilis and possibly O. rusticus compared to native species, resulting in increased probability of shifts in crayfish community composition. /// Nous avons testé les différences de consommation journalière maximale ($\text{C}_{\text{max}}$) et de taux de respiration (R) à 4 températures différentes (18, 22, 26 et 30°C) chez des écrevisses à répartitions variables dans le Missouri, U.S.A. Cinq espèces d'écrevisses ont été étudiées: Orconectes eupunctus (Williams, 1952), trouvée uniquement en aval de la rivière Eleven Point, Greer Spring; O. hylas (Faxon, 1890), rencontrée seulement dans les bassins de drainage des rivières Black et St Francis dans les Ozarks, O. luteus (Creaser, 1933) et O. punctimanus (Creaser, 1933), qui sont largement répandus dans les Ozarks, enfin O. virilis (Hagen, 1870), qui a une l