Energetics and consumption rates of alpine grasshoppers (Orthoptera: Acrididae) in New Zealand.

An energy budget, based entirely on field data, has been constructed for a community of three New Zealand alpine grasshopper species, Paprides nitidus Hutton, Sigaus australis (Hutton) and Brachaspis nivalis (Hutton) (Acrididae). The consumption results are compared with a previous gravimetric ingestion rate study of the same field populations. Jointly, the two studies demonstrate some very specific adaptations between grasshopper energetics and feeding behaviour.Several features of the present study are: 1) the derivations of ingestion energy and respiration energy are believed to be new, using field relationships between assimilation efficiencies, egestion energy and (in the case of respiration) production energy; 2) energy differences between instars, sexes and species are shown to be associated in some cases with absolute body weight and in other cases with developmental rate criteria; 3) a wide range of energetic efficiencies is demonstrated in the course of a single life cycle, and is shown to reflect a progression of adaptations during the development of the individual; 4) major energetic differences between overwintering and non-overwintering population members are demonstrated but do not fit commonly held predictions because of alpine adaptations for depressed respiration and low ingestion energy; 5) it is suggested that the balance of low respiration and low ingestion energy necessitates a diet composition of high percent dry weight, and that it may also serve as a mechanism to govern altitudinal zonation in these grasshoppers. It is concluded from survey data that New Zealand alpine grasshoppers are rarely likely to consume more than 6% of annual primary production, and that in the majority of grasslands, their consumption is unlikely to exceed 1-2%. However, percent consumption is shown to be an inadequate measure of their impact on grasslands.