Foraging by the Smooth Newt (Triturus vulgaris) on Zooplankton: Functional Responses and Diet Choice

Publisher Website
Google Scholar
Abstract
(1) This study analyses foraging by the smooth newt (Triturus vulgaris) on different size zooplankton. Adults and three size classes of tadpoles were observed in laboratory aquaria. (2) Foraging efficiency was estimated at different prey densities for monospecific populations of 2.3 mm Daphnia magna and 1.5 mm D. longispina. To evaluate diet choice in experiments with both prey available D. magna and D. longispina were provided at different densities from 1:1 to 1:40. To examine possible effects of newt foraging upon zooplankton communities we allowed newts to feed in 40 l aquaria on zooplankters varying in body size from 0.2 to 4 mm. (3) Functional responses of the predator to prey density were type II (Holling 1966) for both sizes of Daphnia. Tadpoles ate greater numbers of D. longispina than D. magna. Adults in contrast ate more D. magna, but the difference was small. Feeding on D. magna was more profitable than feeding on D. longispina; two-three times for tadpoles and ten times for adults in terms of energy per handling time. (4) In the two-prey experiments newts preferred the larger D. manga over smaller D. longispina. Numbers of D. magna eaten corresponded closely to numbers of D. magna eaten in single-prey experiments. No changes in newts' diet width were observed with increasing abundance of Daphnia in the 1:1 two-prey experiments. (5) When many sizes of prey were available newts affected the size distribution of the zooplankton by feeding more on large prey than on small prey. We postulate that, foraging by newts will alter the size distribution of zooplankton in natural environments inhabited by newts. Along the south coast of Finland rock-pools with newts had fewer large plankton than rock-pools without newts.