Patterns of Resource Use and Age Structure Among Species of Desert Scorpion

Abstract

(1) The niche patterns of four species of desert scorpion were analysed from 1975 to 1983 in the Coachella Valley, California. There is a marked skew in the relative abundance of the four species with one (Paruroctonus mesaensis) always constituting >95% of all individuals and three other species (Hadrurus arizonensis, Paruroctonus luteolus and Vaejovis confusus) being relatively rare. (2) The size ranking of animals at both birth and maturity is the same with H. arizonensis (adults = 5.5 g) > P. mesaensis (1-5-2.0 g) > P. luteolus (0-2 g) > V. confusus (0.1-0.2 g). However, because newborn animals require 2-4 years to reach maturity, the size relationship among these species is complex with an array of either 3 or 4 year classes per species each interacting with other year classes of their own and other species. (3) These scorpions prey on a variety of insects and arachnids. Average overlap in prey size (0-67) is considerably higher than the overlap in prey taxa (0-43). Different year classes of the same species use substantially different prey from each other and differ in the degree that they overlap with adults of other species. As predicted by the ecomorphological hypothesis, prey use is a general function of scorpion size; scorpions more different in size are less similar in prey size but not prey taxa. (4) There are significant differences among species in temporal patterns and habitat (=substrate) use. In general, P. mesaensis (especially the adults) occur during times (spring; late summer to early fall) and in the habitat (sand) characterized by the highest availability of prey. Only the temporal patterns of P. mesaensis adults were significantly correlated with prey abundance and the feeding rate of P. mesaensis is significantly greater than that of the other species. (5) The success of P. mesaensis is partially due to the fact that it is the only one of these species fully adapted to sand. However, it is also an aggressive species that frequently eats other scorpions and thus possibly restricts the distribution and abundance of the other three species.