TIELEMAN, B.I. *; WILLIAMS, J.B.; VISSER, G.H.; University of Groningen, The Netherlands; Ohio State University, Columbus; University of Groningen, The Netherlands: The physiology-life history nexus in larks along an aridity gradient

We compared physiological, demographic and ecological variables of larks to gain insights into life history variation along an aridity gradient. Quantifying field metabolic rate (FMR) and water influx rate (WIR) of parents feeding nestlings as measures of parental effort, we found that parental FMR and WIR were lower in larks from arid environments compared with species from mesic areas. Water and energy requirements of 6-8 day old nestlings were reduced in desert species. Nestling growth rate, clutch size and number of clutches decreased with increasing aridity, and nest predation rates increased with increasing aridity. We combined FMR and WIR of parents and chicks, energy and water accumulated during growth, and brood size to establish energy and water budgets of parent-brood units. Our results support the hypothesis that decreasing food and water availability favor lower energy and water requirements of parents and young, reduced growth rates, and smaller clutch sizes with increasing aridity. The decrease in parental effort with increasing aridity might reflect a lower fitness value of a single brood for arid-zone species than for larks from mesic habitats, suggesting that the probability of adult survival is higher in arid than in mesic areas.