New Publication on Storm Petrels !

Hernández, N., Oro, D and Sanz-Aguilar, A., Environmental conditions, age and senescence differentially influence survival and reproduction in the Storm Petrel. 2017. Journal of Ornithology. Volume 158, pp 113–123. DOI: 10.1007/s10336-016-1367-x

Abstract: Demographic parameters in wild populations are expected to be shaped by individual covariates and environmental variability. Thus, the understanding of the effects of age and/or environmental conditions on variability in vital rates is of special importance in ecological and evolutionary studies. Early age-related improvements in survival and reproduction and later declines due to senescence are expected, above all in long-lived species. Survival in these species is predicted to be a more conservative parameter than reproduction, thereby giving rise to less temporal variability. We studied age-dependent patterns of survival and breeding success in a long-lived seabird, the Mediterranean Storm Petrel Hydrobates pelagicus melitensis, and the additive influence of individual heterogeneity and environmental climatic variables using 22 years of individual-based data (1993–2014). The North Atlantic Oscillation index (NAO) and sea surface temperature (SST) were selected as proxies of environmental conditions in both breeding and wintering areas. Our results show that vital rates improved with age for both survival and breeding success. A slow effect of senescence at older ages was detected for breeding success, whereas models did not disentangle the occurrence or the absence of actuarial senescence. Reproduction was also influenced by the age of first observed reproduction: at the same age, more experienced birds that recruited earlier had a higher breeding success than less experienced ones. Breeding success (but not survival) also showed great temporal variability in accordance with theoretical predictions. Neither the NAO nor the SST explained this variability, probably because petrels feed on lower trophic levels than most pelagic seabirds and other physical features such as river runoffs and winds may be involved, as well as other environmental stressors such as predation by sympatric gulls.

New Publication on Lilford's wall lizard !!

Rotger, A., Smith, J.J., Igual, J.-M. and Tavecchia, G., 2016: Relative role of population density and climatic factors in shaping the body growth rate of Lilford’s Wall Lizard (Podarcis lilfordi). Canadian Journal of Zoology. doi: 10.1139/cjz-2015-0188

 Abstract: The growth rate in small reptiles is modulated by per-capita food resources and recent evidence suggested that this constraint is the mechanism underlying differences between cohorts. Per-capita food resources depend on population size and climatic factors, but their relative role in explaining the variations in growth rate is unclear.

Photo: G. Tavecchia

We used morphological data collected over 6 years to model the body growth of an insular lizard (Lilford’s Wall Lizard, Podarcis lilfordi (Günther, 1874)). We used nonlinear equations to describe the appropriate length-at-age relationship. For each sex, seasonal growth was observed and the oscillatory von Bertalanffy curve was fitted to the data. Three age classes were recognized, and we investigated the relative role of density, spring rainfall, and temperature in explaining the variation of the growth rate in each sex-by-age class. Results showed that the relative role of density and climatic factors varied according to the age considered. While population size and temperature had a negative effect on the growth rate of juveniles, rainfall had a positive influence on the growth of subadults. Adult growth was near zero and constant over time. The different role of density-dependent and climatic factors in explaining age-dependent growth rate provides an important insight in understanding lizard population dynamics and life-history tactics.

New Publication on Scopoli's Shearwater!

Hernandez, N., Genovart, M., Igual, J.-M. and Oro, D., 2015 The influence of environmental conditions on the age pattern in breeding performance in a transequatorial migratory seabird. Forntiers in Ecology and Evolution.http://dx.doi.org/10.3389/fevo.2015.00069

 Abstract: Several studies of marine top predators, above all of seabirds, have analyzed the effects of either individual age or environmental fluctuations on reproduction; nevertheless, little is known about the age patterns in breeding performance in a variable environment.

Photo: Pedro Trejo (c)

To investigate the simultaneous influence of age and environmental conditions on laying dates and egg volumes, we tested different climate and food availability indices in a transequatorial migratory seabird using female data from a 23-year study. Our results show an improvement in breeding parameters with age (i.e., earlier laying dates and greater egg volumes) but no pattern of senescence in older age groups. The best models showed an interaction of time and age in breeding performance, i.e., the age pattern of breeding performance changed each year likely as a result of environmental variability.
Nevertheless, climatic indexes used here explained part of that annual variability: NAO and SOI index accounted for 24 and 20% of deviances in laying dates and egg volume, respectively. Part of that unexplained variability might be related to other processes such as intermittent breeding and the individual quality of breeders, which were not assessed in our study.