At rest, insects show a large variety of gas exchange patterns. These range from continuous gas exchange, by diffusion-convection or convection (including active ventilation), with the spiracles held open (Fig. 3.6), to DGCs (Fig. 3.7) where gas exchange is either of the diffusive-convective kind, or where, in the case of active ventilation, ventilation and spiracular opening are highly coordinated (Kaars 1981; Miller 1981; Lighton 1996). Between these extremes, insects show a continuum of patterns, ranging from barely cyclic through to strongly cyclic gas exchange that differs only marginally from DGC (Hadley and Quinlan 1993; Williams and Bradley 1998; Shelton and Appel 2001a) (Fig. 3.8).
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