Energy budgets for populations of long-lived arthropod predators (Chilopoda: Lithobiidae) in an old beech forest

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Abstract
Energy budgets are derived for two chilopod populations—Lithobius mutabilis L. Koch and L. curtipes C.L. Koch (Chilopoda, Lithobiidae)-in a 125-year-old beech stand in the Solling, Northern West Germany. Lithobiids were sampled from February 1972 to July 1975 by monthly quadrat samples (12 samples of 625 cm2 each) which were extracted in an apparatus slightly modified after Kempson (Kempson et al. 1963; Weidemann 1971). Regression equations are set up relating fresh weight to width of the cephalic shield and dry weight to fresh weight. The calorific content is estimated by use of literature data. Oxygen consumption is estimated from laboratory measurements in a Warburg apparatus. The values have been corrected for temperature fluctuations in the field and should be increased by a factor of about 1.75 to account for the higher activity of lithobiids in the field. Energy balances for average individuals of L. mutabilis and L. curtipes are presented. An average individual of L. mutabilis produces in the course of its life about 0.42 kJ, respires 0.92 kJ (laboratory value) or 1.6 kJ when increased activity in the field (f.a.) is taken into account. An average individual of L. curtipes produces about 0.18 kJ and respires 0.40 kJ, or 0.7 kJ (f.a.). Production, respiration, and assimilation of the populations are estimated by multiplying the energetic values obtained for the different instars of the average individual with the number of instars occurring per year (average individual method). Population biomass and respiration is obtained by a “direct method”. By means of regression equations fresh weight, dry weight, energy content, and oxygen consumption of each animal extracted were determined and from this the population energy budget established. The values for the L. mutabilis population are: abundance 55 individuals m-2, biomass 2.9 kJ m-2, production 2.55 kJ m-2, respiration 5.5 kJ m-2 or 9.6 kJ m-2 (f.a.), and assimilation 8.0 kJ m-2 or 12.2 kJ m-2 (f.a.). The values for the L. curtipes population are: abundance 39 individuals m-2, biomass 0.9 kJ m-2, production 1.1 kJ m-2, respiration 2.3 kJ m-2 or 4.0 kJ m-2 (f.a.), assimilation 3.3 kJ m-2 or 5.1 kJ m-2 (f.a.). The fit of the values obtained for production and respiration to the regression equations of McNeill and Lawton (1970), Shorthouse (1971), and Humphreys (1979) is discussed. It is argued that the production values given for two lithobiid populations by Wignarajah (1968), which were used by McNeill and Lawton and Humphreys for their regression equations, are severely underestimated. Regarding the relationship between biomass and production, the values show fairly good agreement with regression equations between production: biomass ratio and life length, but not with equations relating production: biomass ratio and body weight. Both chilopod species together contribute about 17%–27% to total assimilation by predatory macroarthropods in the system studied. Total consumption of the L. mutabilis population is estimated as 35.5 kJ m-2, of the L. curtipes population as 14.8 kJ m-2. This is about 3%–4% of mean annual production of total soil fauna.