Capture efficiencies of web‐building jumping spiders (Araneae, Salticidae): Is the jack‐of‐all‐trades the master of none?

Abstract

According to the ‘Jack‐of‐all‐trades hypothesis’, a specialist predator that uses relatively few discrete predatory behaviours is expected to be highly effective on the few types of prey on which it specializes. A versatile predator, that specializes on these plus additional prey, is expected to be less effective than the specialist predator on the prey they have in common. However, few studies have clearly addressed this hypothesis, especially with respect to behavioural specialization. Portia is a behaviourally complex and aberrant genus of salticid spiders, all studied species of which are cursorial spiders and web‐builders and specialized web‐invading predators that use vibratory aggressive mimicry and feed on the spiders which they deceive. Interspecific and, within P. fimbriata, interpopulational variation occurs in predatory behaviour. ‘Cryptic stalking’, a specialized manner of stalking and capturing other salticids, is unique to P. fimbriata from Queensland, a habitat in which cursorial salticids are superabundant. Otherwise, each studied species and population of Portia uses qualitatively the same repertoire of predatory behaviours (including the same set of vibratory behaviours). Queensland P. fimbriata, having each of the prey‐specific behaviours (‘trades’) of the other Portia plus one more, is more of a jack‐of‐all‐trades. If the postulated trade‐off occurs, then Queensland P. fimbriata would be expected to be less effective than other Portia at using the shared prey‐specific behaviours. Against insect‐prey away from webs, Queensland P. fimbriata had lower capture efficiency than other Portia, apparently supporting the jack‐of‐all‐trades hypothesis; but Queensland P. fimbriata was more, instead of less, efficient as a predator of web spiders, counter to prediction from the hypothesis. Although the jack‐of‐all‐trades hypothesis cannot be viewed as falsified simply on the basis of these findings, the validity of this hypothesis is at least suspect.