Search tactics of desert lizards: how polarized are they?

Abstract

The patterns of foraging movements of the teiid species Cnemidophorus tigris (western whiptail) and four iguanid species, Gambelia wislizeni (leopard lizard), Uta stansburiana (side-blotched lizard), Phrynosoma platyrhinos (desert horned lizard), and Callisaurus draconoides (zebra-tailed lizard), were investigated between 1978 and 1981. Rates and frequencies of movement while foraging, based on more than 44 000 minutes of observation of over 500 different lizards, were analysed with respect to temporal variation on yearly, seasonal and daily time scales and compared to expectations froma dichotomous view of foraging modes. The notion of polarized foragiing tactics among lizards was partially supported. Among the iguanid species, only Gambelia exhibited rates of foraging movements that were not always significantly less than those of the active forager, Cnemidophorus. Nevertheless, the analyses also revealed temporal variation in the search tactics of iguanid species. Gambelia exhibited a seasonal decline in foraging movements during three out of four years. Phrynosoma, Callisaurus and Uta all exhibited seasonal declines in their foraging movements in some years, but not in others. The foraging movements of all iguanid species increased during the early-season of 1978, corresponding to a marked increase in late winter/early spring rainfall that year. Uta showed diurnal shifts in foraging movements during most years. Such diurnal variation was also apparent in Callisaurus in some years. Despite consistent differences between Cnemidophorus and most iguanid species, the presence of temporal variability in foraging movements of iguanid lizards indicates a capacity for shifts in tactics in these species. Thus, this variability more realistically reflects a continuum of foraging tactics than it does dichotomous strategies.