Metabolic Rates of Resting Salticid an D Thomisid Spider S

Rates of metabolism of jumping and crab spiders were evaluated to determine if life-styl e characteristics are associated with rates of energy expenditure in these `sit-and-wait' predators . Resting rates of oxygen consumption were measured under standardized conditions in nine species of salticid and three species of thomisid spiders . These rates and those previously reported ranged from 50–70% of tha t expected for their size in these families . They are similar to those of other families of spiders with similar modes of prey capture, life span, and distribution . No significant differences in this measure were detecte d between the two families . Rates of energy expenditure in spiders exhibit much variation, and it has been my goa l to document and account for this diversity (Anderson 1970; Anderson & Prestwich 1982 ; Anderson 1994) . As in most organisms (Peters 1983), body size is the major source of variation in energy expenditure in spiders (Humphreys 1977; Greenstone & Bennett 1980 ; Anderson & Prestwich 1982) . Nonetheless , considerable variation in this measure remain s after adjustment for size . Most spiders have low rates of metabolism (— 50% of expected for their size) compared to other ectothermi c poikilotherms . This feature is considered an adaptation to an unpredictable food supply (Anderson 1970; Greenstone & Bennett 1980) in these predators . This interpretation is consistent with the observation that those specie s with very low metabolic rates, i .e ., less than 50% of expected for their size, live much longer than one year, often colonize margina l habitats, and are restricted in distribution to lower latitudes (Anderson & Prestwich 1982 ; Anderson 1994) . Conversely, the high rates of metabolism (-100% of expected) found i n orb-weavers and comb-footed spiders are associated with high reproductive rates, rapi d growth, high population densities, and wide spread distribution (Anderson 1994) . The proposed associations between energetics and biology were made by measurement of rates of respiratory gas exchange i n resting spiders . Since spiders are inactive mos t of the time, this measurement represents a sig nificant fraction of their total energy requirement (Andrews & Pough 1985) . Interpretatio n of such comparisons is complicated becaus e any given trait may reflect selection associated with environmental constraints as well as phylogenetic affiliations (Huey 1987 ; Wang & Abe 1994) . Huey (1987) recommends that studies of closely related species most effectively resolves such ambiguities . Conversely , Andrews & Pough (1985) suggested that associations between energy metabolism an d ecology of a species could be evaluated from data obtained on species with similar ecological characteristics but who differ phylogenetically . I selected species in the families Salticida e and Thomisidae as a compromise betwee n these two recommendations . There is little in formation available relating to energetics i n these important taxa . Both families constitut e a large and important component of the spider fauna. They contain 4,000 and 2,000 described species, respectively, out of a tota l 34,000 spiders in this order and are cosmopolitan in distribution (Coddington & Lev i 1991) . Obviously they differ in phylogeny a s they are separated at the familial level . The two families are, however, closely related (Coddington & Levi 1991) . They differ greatly in morphology but are similar in certain particulars: both are diurnally active and d o not use a web to capture prey . Jumping spiders have a better sense of vision and ofte n pursue prey over some distance . Larger spe -