The investigation of metabolic rate variation, and the gas exchange patterns that support it, are among the most venerable pursuits in environmental physiology. Yet, at least in insects, there is much that remains controversial. In particular, the scaling exponents of metabolic rate during rest, pedestrian locomotion, and flight are not well resolved. It is not known whether the intraspecific and interspecific exponents differ consistently, nor whether phylogenetic non-independence has a large effect on the latter. Likewise, it is not entirely clear why insects at rest show discontinuous gas exchange, nor whether characteristics of the DGC, or for that matter metabolic rates, always show high repeatability. What is clear, though, is that a sound comprehension of metabolic rate variation is essential for understanding the ecology and evolution of insects. Metabolic rate variation not only influences the abundance and distribution of insects (Chown and Gaston 1999), but it probably also determines their likely success in colonizing new environments (Vermeij and Dudley 2000), and might also be instrumental in determining global variation in species richness (Allen et al. 2002). The surprising conclusion, therefore, is that from an ecological point of view, despite a century of careful work, many of the most fundamental questions in insect respiratory physiology remain poorly resolved.
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