Cohort variation, climate effects and population dynamics in a short‐lived lizard

Abstract

Summary1. Demographic theory and empirical studies indicate that cohort variation in demographic traits has substantial effects on population dynamics of long-lived vertebrates but cohort effects have been poorly investigated in short-lived species. 2. Cohort effects were quantified in the common lizard (Zootoca vivipara Jacquin 1787), a shortlived ectothermic vertebrate, for body size, reproductive traits and age-specific survival with mark-recapture data collected from 1989 to 2005 in two wetlands. We assessed cohort variation and covariation in demographic traits, tested the immediate and delayed effects of climate conditions (temperature and rainfall), and predicted consequences for population growth. 3. Most demographic traits exhibited cohort variation, but this variation was stronger for juvenile growth and survival, sub-adult survival and breeding phenology than for other traits. 4. Cohort variation was partly explained by a web of immediate and delayed effects of climate conditions. Rainfall and temperature influenced distinct life-history traits and the periods of gestation and early juvenile life were critical stages for climate effects. 5. Cohort covariation between demographic traits was usually weak, apart from a negative correlation between juvenile and sub-adult body growth suggesting compensatory responses. An agestructured population model shows that cohort variation influences population growth mainly through direct numerical effects of survival variation early in life.6. An understanding of cohort effects is necessary to predict critical life stages and climatic determinants of population dynamics, and therefore demographic responses to future climate warming.

Hormonally mediated maternal effects, individual strategy and global change

“…Furthermore, maternal-age effects, which are manifested in terms of allocation of energy to reproduction and provisioning of antibodies and steroids to the progeny, generate drastic changes in cohort structure and consequently affect population dynamics [196]. This is especially likely if climate change differentially impacts on old versus young cohorts [197]. Key demographic traits, including growth rate and survival exhibited higher variability in younger cohorts, specifically juveniles and subadults, than adults, which was attributable to climatic variation (temperature and rainfall).…”

Consecutive cohort effects driven by density-dependence and climate influence early-life survival in a long-lived bird

“…Several previous studies show that the effects of early-life conditions on fitness components can be important: the harsher the conditions an individual experiences during early life, the higher fitness costs the individual will undergo [1,3,4,6]. However, few studies have attempted to unravel the fitness consequences of early-life conditions in critical periods other than the rearing period, especially in wild populations [3].…”

“…The ability of offspring to compensate for a poor start in life determines whether early-life conditions have short-or long-term fitness consequences [6][7][8]. The former, also known as numerical effects, involve changes in traits such as pre-breeding survival, birth weight, birth date and body growth; the latter, known as delayed quality effects, affect future breeding performance and thus result in changes in the age of first breeding attempts, lifetime reproductive success and adult survival [2][3][4][5][9][10][11][12][13]. Environmental forcing in early life drives complex trade-offs between vital rates, and thus many of the effects noted above are likely to be interrelated [10,14].…”

“…Those conditions are known as cohort or silver-spoon effects, and have been widely explored on a large range of vital rates in many taxa (see electronic supplementary material S1) [2][3][4][5]. Individuals facing harsh early-life conditions are expected to experience higher fitness costs later in life [1].…”

“…Individuals facing harsh early-life conditions are expected to experience higher fitness costs later in life [1]. Harsh conditions include unfavourable climate, high population size, low habitat quality, poor parental quality and low food availability, and their potential interaction (see electronic supplementary material S1) [2][3][4][5]. The ability of offspring to compensate for a poor start in life determines whether early-life conditions have short-or long-term fitness consequences [6][7][8].…”