Temperature-Induced Shift in Foraging Ability in Two Fish Species, Roach (Rutilus rutilus) and Perch (Perca fluviatilis): Implications for Coexistence between Poikilotherms

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Abstract
(1) The effects of temperature on capture probability, attack coefficient (or instantaneous search rate), handling time, swimming speed and capture rate of two fish species, roach (Rutilus rutilus) and perch (Perca fluviatilis), were studied in the laboratory. (2) The attack coefficient increased exponentially for both species. Handling time decreased asymptotically with temperature for perch and in a sigmoid way for roach. Roach had a longer handling time and lower capture rate than perch at low temperatures (12-18.degree. C), while the reverse was the case at high temperatures (18-21.degree. C). The results suggest a shift in the species having the higest competitive ability at a temperature around 18.degree. C. The increased capture rate and decreased handling time of roach at high temperatures was attributable to an increase in swimming speed and capture success. (3) The temperature region (17-19.degree. C) within which capture rate and handling time intersected for perch and roach in the laboratory study was compared with the vertical distribution of the species in thermally stratified lakes. A high correspondence between the predictions from the laboratory data and the actual field distribution of the species was found. (4) It is argued that including temperature in foraging models will improve both the predictions of prey selection and of resource partitioning in poikilothermic animals. Temperature may also mediate coexistence between poikilotherms in environments in which temperature varies spatially and temporally.