Energy costs of the predation strategy of the web-spinning spider Lepthyphantes zimmermanni bertkau (Linyphiidae)

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Abstract
The energy costs of the predation strategy of the web-spinning spider Lypthyphantes zimmermanni were investigated in the laboratory. The standard respiratory costs associated with the stationary aspect of the strategy were estimated by means of a Gilson respirometer run at the different temperatures prevailing month by month in the beech woodland litter layer which comprises the spider's natural habitat. Respiration rate is related to weight by an exponent with a mean value of 0.7398. The Q 10 of respiration rate is 2.41 between 5°C and 10°C and 1.97 between 10°C and 15°C. The energy costs of producing a web comprise the active respiratory costs associated with the locomotory activity involved in spinning a web together with the energy value of the silk used in the web manufacture. The former were evaluated by allowing a spider to spin a web in a respirometer, subtracting the calculated standard respiratory energy costs for a spider of equivalent weight and multiplying by a correction factor for web size. The relationship between spider weight and area of web produced was established in the laboratory. The respiratory cost of spinning a web is effectively constant with temperature at 724.46·10-3 J for an adult (4 mg) spider. The energy value of spider silk was estimated by means of a bomb calorimeter and found to be 17,435 J g-1. The energy content of the silk of a single adult's web is 1.16 J, giving energy cost of web production of 1.88 J at all temperatures.