Resources are usually considered to be limited in caves and underground habitats. Therefore, lower metabolic rates of ectotherms in these environments should be advantageous. The standard metabolic rate (SMR) of the common harvestman Pachylus paessleri Roewer, 1913 (Arachnida, Opiliones) is determined at two ambient temperatures. Repeatability of SMR is estimated by two methods: (i) product -moment correlation on residuals of body mass and (ii) variance components. Estimations of the thermal sensitivity of metabolic rate (individual Q 10 ). SMR of P. paessleri at 20 °C show a mean of 19.01 ± 6.04 and 14.99 ± 3.64 L CO 2 h -1 for males and females, respectively. Thermal sensitivity of SMR is 2.11 ± 0.23 with a substantial coefficient of variation of 26.7%. In males, residuals of CO 2 release are significantly repeatable ( r p ϭ 0.61) between measurements realized 5 months apart, which reflects the consistency of this trait over time. As typical soil inhabitants, the harvestman P. paessleri present a lower metabolic rate in comparison with arthropods of similar body mass ( e.g. arachnids). Although the coefficient of thermal sensitivity is within of the range reported for arthropods inhabiting Mediterranean zones, it is lower than expected for an organism with such a low SMR. This appears to be the first report of repeatability of metabolic rate in a harvestman species.
Summary
The native continental ichthyofauna of Chile has a low richness in species and marked endemism in comparison to the rest of South America. Since the end of the 19th century 26 fish species have been introduced into the Chilean systems. The study covers the trophic ecology of three native and two exotic fish species from the Chillán River. Stomach contents were analyzed and prey items identified at the family level, then compared with the environmental availability by sampling the benthos and using Ivlev’s Electivity Index to determine the degree of election. The relative importance of each prey item was determined and the Morisita Index applied to determine the level of overlap. The results indicate a greater trophic spectrum for introduced rather than for native species. The Relative Importance Index identified Chironomidae as the most important prey item for all species studied. An elevated overlap was observed between the diets of the five species, being greater within the native and introduced species (> 0.9) than between the two groups (< 0.8). These results do not reveal competition, but allow the authors to infer the negative effects of the introduced species to the conservation of native fish.
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