The Life Cycles of Two Sympatric Species of Ichnotropis (Sauria: Lacertidae)

Abstract

The sand-lizards Ichnotropis squamulosa and I. capensis are widespread and common in southern Mrica, although not found south of the Orange River. They often occur together, but one species is invariably represented only by adults and the other only by subadults or juveniles. This phenomenon was analysed by recording the snout-vent length and month of collection for 124 specimens of I. squamulosa and 74 specimens of I. capensis in the Umtali Museum. The material is from Bechuanaland, Rhodesia, Zambia and Mozambique. The size range and mean snout-vent lengths for each month are shown in Table 1 and the growth curves for the two species are plotted in Fig. 1. These data indicate that both lizards have remarkably short life· cycles of less than one year's duration, so there is no overlap between generations, the species surviving in the egg form for a period of three to four months. These life cycles are staggered so that there is never inter-specific competition between lizards of similar size, the two species thus being segregated by size of prey. Competition between sympatric congeneric species of lizards is often reduced by differences in microhabitat (e.g. Platysaurus torquatus and P. imperator, Broadley 1962) or diet (e.g. Pseudocordylus subviridis and P. langi, Broadley 1964). Staggered life cycles can be equally effective for "annual" species. Data on the life spans of lizards are meagre, but tropical forms are relatively short-lived when compared with temperate species which hibernate for nearly half the year. M. Smith (1951) considered the Palearctic species Lacerta agi/is to be full grown when 4 or 5 years old and the same is probably true of Lacerta vivipara. Males of both species may be sexually mature when 22 months old. Most Mrican lacertids probably live for two or three years. With regard to Nucras tessel/ata ornata, Eremias lugubris and Eremias namaquensis, I have examined series which include at least two generations. If factors like predation levels are similar for the local genera oflacertids, one could expect to find an indication of life expectancy in the number of eggs laid. FitzSimons (1943) gives approximate clutch sizes of 10-12 for Ichnotropis squamulosa and 6 for I. capensis, compared with 4-6 for Eremias spp., 4-6 for Meroles spp. and 4 for Nucras spp. It is significant that Ichnotropis squamulosa has both the shortest known life expectancy (8 months) and the largest clutch size, while the species of Nucras, which probably live for 2-3 years, have the lowest average clutch size. There is plenty of scope for research on the ecology of local lizards, and their life cycles may prove to be particularly interesting. REFERENCES BROADLEY, D. G. 1962. On some reptile collections from the northwestern and northeastern districts of Southern Rhodesia 1958-61, with descriptions of four new lizards.