Feeding ecology of polymorphic larval barred tiger salamanders in playas of the Southern Great Plains

Abstract

In playas of the Southern Great Plains, larval barred tiger salamanders ( Ambystoma tigrinum mavortium Baird, 1850) (= Ambystoma mavortium mavortium ) are present as polymorphic populations. Typical and cannibal morphs have been previously investigated but intermediate forms have received little attention and their role in playa food web structure is unknown. We investigated the diet composition of these three morphotypes and compared diet preferences of typical versus nontypical morphs. Typical and intermediate morphs had similar body morphology (snout to vent length and stomach content mass), but cannibal morphs had larger stomach content mass than the other morphotypes. However, the intermediate morph had a distinctive diet composition from cannibal and typical individuals as determined by diet composition rankings, diet overlap and similarity indices, and diet diversity. By comparing prey availability versus consumption, we determined that nontypical morphs preferred larger invertebrates such as tadpole shrimps (Triopsidae) and fairy shrimps (Streptocephalidae), whereas typical morphs preferred smaller prey taxa like ostracods (Cyprididae) and water boatmen (Corixidae). Several prey taxa were avoided by all larvae suggesting that feeding in A. t. mavortium in playas is not opportunistic. Our study demonstrates that larval A. t. mavortium are present not only as dimorphic but also as polymorphic populations in playas and indicates that identifying these morphs is essential for the proper understanding of aquatic food webs.