Resource abundance is one of the primary determinants of animals’ distributions. However, direct assessment of resources may be unreliable if those resources fluctuate or are not easily detected. Individuals under such conditions may instead use indirect cues to assess the quality of potential foraging sites. Naïve or young individuals may be particularly likely to use indirect cues to compensate for their inexperience and to reduce assessment costs. To investigate the cues juvenile crab spiders (Misumenops asperatus) use when selecting foraging sites, we performed individual choice trials in small test chambers. We first examined whether spiderlings’ site preference was influenced by prey abundance, a direct cue of foraging site quality. We next investigated whether juvenile crab spiders assessed potential foraging sites using indirect cues, including flower quality, cues left by conspecifics, or conspecifics themselves. Spiderlings were allowed to choose between the two sides of the test chamber, with both sides generally containing artificial flowers on which the spiderlings could perch; to examine the role flower quality plays in foraging site selection we used real goldenrod flowers (Solidago sp.) instead of the artificial flowers.
Results/Conclusions
The spiderlings did not use prey abundance to assess foraging sites; the number of individuals that chose the side of the test chamber with approximately 30 Drosophila did not differ significantly from the number that settled where there were no potential prey. They did however use indirect cues when choosing where to forage. Spiderlings preferred sites that would be likely to attract larger numbers of their arthropod prey, choosing blooming flowers over both senescing flowers and buds. Hungry spiderlings also used cues left by conspecifics, preferring sites on which a conspecific had previously foraged. Finally, spiderlings avoided sites that contained large numbers of conspecifics, but were attracted to sites with relatively low abundances of conspecifics. This indicates that when these spiderlings choose where to forage, they weigh the possibility of improving their foraging success by joining conspecifics against the potential costs, such as increased competition and the risk of cannibalism, of being in larger groups. We show here that young, relatively inexperienced animals do not always directly assess prey abundance when choosing foraging sites, but instead these individuals are capable of detecting indirect cues and using those cues to evaluate the quality of foraging sites.
