Biol. Rev. (2014), pp. 000 – 000. 1 doi: 10.1111/brv.12106 Elevational trends in life histories: revising the pace-of-life framework Sabine M. Hille 1,∗ and Caren B. Cooper 2 1 Institute of Wildlife Biology and Game Management, Department of Integrative Biology and Biodiversity Research, University of Natural Resources and Life Science, Gregor Mendel-Strasse 33, A-1180 Vienna, Austria 2 Cornell Laboratory of Ornithology, 159 Sapsucker Woods Road, Ithaca, NY 14850, U.S.A. ABSTRACT Life-history traits in birds, such as lifespan, age at maturity, and rate of reproduction, vary across environments and in combinations imposed by trade-offs and limitations of physiological mechanisms. A plethora of studies have described the diversity of traits and hypothesized selection pressures shaping components of the survival–reproduction trade-off. Life-history variation appears to fall along a slow–fast continuum, with slow pace characterized by higher investment in survival over reproduction and fast pace characterized by higher investment in reproduction over survival. The Pace-of-Life Syndrome (POLS) is a framework to describe the slow–fast axis of variation in life-history traits and physiological traits. The POLS corresponds to latitudinal gradients, with tropical birds exhibiting a slow pace of life. We examined four possible ways that the traits of high-elevation birds might correspond to the POLS continuum: (i ) rapid pace, (ii ) tropical slow pace, (iii ) novel elevational pace, or (iv) constrained pace. Recent studies reveal that birds breeding at high elevations in temperate zones exhibit a combination of traits creating a unique elevational pace of life with a central trade-off similar to a slow pace but physiological trade-offs more similar to a fast pace. A paucity of studies prevents consideration of the possibility of a constrained pace of life. We propose extending the POLS framework to include trait variation of elevational clines to help to investigate complexity in global geographic patterns. Key words: life-history theory, altitude, clutch size, avian. CONTENTS I. Introduction ................................................................................................ 2 II. Latitudinal trends: the slow – fast continuum of life-history traits ........................................... 2 (1) Traits comprising slow pace at low latitude ............................................................ 2 (2) Selection pressures for slow pace of life at low latitudes ................................................ 2 III. Predictions given potential selection pressures in alpine environments ..................................... 3 IV. Life histories along elevational gradients ................................................................... 4 (1) Clutch size ............................................................................................. 4 (2) Egg size ................................................................................................ 5 (3) Parental nest attendance ............................................................................... 5 (4) Number of clutches .................................................................................... 5 (5) Development period ................................................................................... 5 (6) Reproductive success ................................................................................... 5 (7) Survival ................................................................................................ 6 (8) Metabolic rate ......................................................................................... 6 V. Discussion .................................................................................................. 6 VI. Directions for future research .............................................................................. 7 VII. Conclusions ................................................................................................ 8 VIII. Acknowledgements ......................................................................................... 8 IX. References .................................................................................................. 8 * Address for correspondence (Tel: +431 47654 4463; E-mail: sabine.hille@boku.ac.at). Biological Reviews (2014) 000 – 000  2014 The Authors. Biological Reviews  2014 Cambridge Philosophical Society