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Ecology and Physiological Aspects of Reproductive Strategies in Two Lizards
Author(s) -
Derickson W. Kenneth
Publication year - 1976
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1936430
Subject(s) - lizard , biology , ecology , sauria , avian clutch size , foraging , reproductive success , zoology , reproduction , population , demography , sociology
Two lizard species, the northern prairie lizard (Sceloporus undulatus garmani) from Reno County, Kansas and the northern sagebrush lizard (Sceloporus graciosus graciosus) from Washington County, Utah, were used to test four hypotheses and one assumption related to the theory of r— and K—selection. The northern prairie lizard is short—lived, matures early, and has a high reproductive effort (r—strategist) while the northern sagebrush lizard is long—lived, has delayed maturity, and a low reproductive effort (K—strategist). One of the assumptions of the r— and K—selection theory is that competition for food is more intense for K—strategists than for r—strategists. Given this assumption, greater food availability for the prairie lizard was hypothesized to result (1) a higher level of body lipids, (2) a higher rate of lipid utilization, (3) a lower percentage of ingested energy available for metabolism, and (4) and expenditure of less energy per offspring than in the sagebrush lizard. Total lipid levels in the two species collected before and after hibernation indicated that prairie lizards had significantly higher lipid levels than sagebrush lizards during both collection periods. A comparison of the amount of body lipids lost and the amount of egg lipids gained during vitellogensis of the first clutch suggested that more lipids are being utilized for egg production in prairie lizards than in sagebrush lizards. Sagebrush lizards apparently are better adapted physiologically to lower food levels since they had lower rates of lipid utilization during starvation studies and they extracted more energy usable for metabolism from ingested food than prairie lizards. Although both species expended about the same amount of energy on a given clutch of eggs, prairie lizards produced more offspring per clutch and therefore expended less energy per offspring. Prairie lizards produced as many as three clutches per season as compared to two clutches per season for sagebrush lizards, and changes in length—lean weight relationships for the two species over a given season suggested that the additional clutch of eggs produced by prairie lizards may be contributing to the higher mortality observed in this species. Indirect evidence, based on precipitation levels and insect biomass at the two study sites and mouthgapes of the two species, supported the assumption that more food was available to the prairie lizards than the sagebrush lizard. Higher precipitation levels (indicating greater insect biomass) occurred at the prairie lizard collection site and this species had a smaller mouthgape index, indicating greater specification in utilization of prey sites.