Population catastrophes are widespread, unpredictable phenomena occurring in natural populations that have important, yet frequently underappreciated, consequences for persistence. As human impacts on ecosystems increase globally, the frequency of catastrophes is likely to rise as increasingly fragmented and depleted populations become more vulnerable. Species with slow life histories are expected to recover slowly from catastrophes because of their longer generation times, and assessing their population recovery requires data spanning long periods. We report results from a long‐term mark–recapture study of snapping turtles (Chelydra serpentina) in Algonquin Provincial Park, Ontario, that experienced a major mortality event from winter predation by river otters. We estimated abundance and survival of nesting females before, during, and 23 yr following the catastrophe. We built multistate mark–recapture models incorporating movement between sites, temporary emigration, and observation effects. We found that during the 3‐yr mortality event, abundance of nesting females declined by 39% overall, and by 49% at our focal nesting area. Apparent survivorship of nesting females during these three years fell from 0.94 before the mortality event to 0.76 at the focal site and 0.86 at adjacent nest sites. Survivorship over the following 23‐yr period averaged 0.972 and 0.940 at the two sampling areas. Despite high post‐catastrophe survivorship and connectivity with other populations, the population failed to recover, displaying consistently reduced abundances across 23 post‐catastrophe years. We discuss the relationship between life‐history attributes and the causes and consequences of local catastrophes and their conservation implications.

The consequences of individual variation in life‐history traits have been well studied due to their importance in evolutionary ecology. However, a trait that has received little empirical attention is the rate of indeterminate growth. In long‐lived ectotherms, subtle variation in growth after maturity could have major effects over the animals’ lifetimes. These effects are difficult to measure due to the challenges involved in reliably estimating individual variation in the face of environmental stochasticity, and the need to account for trade‐offs among growth, reproduction and survival. However, modelling advances have made such analysis possible if long‐term high‐quality datasets are available. We used an integrated state‐space modelling framework to reveal relationships between indeterminate growth, reproduction and survival in a population of North American snapping turtles (Chelydra serpentina) using a 41‐year dataset for 298 adult females. A hierarchical version of the von Bertalanffy model fitted to data on carapace lengths showed substantial individual variation in growth trajectories, and hierarchical models fitted to clutch‐mass data and recapture histories showed that reproductive output and survival probability increased with size. Integration of these models revealed no detectable trade‐offs—i.e., individual growth parameters were not correlated with size‐specific survival or reproduction rates, and individual variation in reproductive output did not affect the size‐specific survival rate. Consequently, individual variation in growth parameters was estimated to result in >2‐fold variation in post‐maturity life expectancy and >4‐fold variation in expected lifetime reproductive output. These results illustrate that indeterminate growth can have major fitness consequences in long‐lived species. We suggest that the individual variation in growth rates reflects variation in environments experienced during development or later life. An understanding of this variation may be essential for predicting the population dynamics of long‐lived species under threat and identifying the most important environments to protect. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13014/suppinfo is available for this article.

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Patterns of sexual size dimorphism (SSD) in turtles are correlated with ecological mode, and it has been hypothesized that mating systems are also shaped by ecological mode. Male combat and coercive mating are competing explanations for male-biased SSD, but are difficult to assess empirically in aquatic species with cryptic behaviour. We quantified SSD and compiled observations of putative combat wounds collected from over 500 captures of Snapping Turtles (Chelydra serpentina (L., 1758)) in Algonquin Provincial Park, Ontario, to test hypotheses of mate competition and coercion. We found that both sex and body size were important predictors of risk of wounding, consistent with the hypothesis that male–male sexual competition is the primary driver of intraspecific aggression. Low wounding rates among females suggests that resource competition and coercive mating are not important causes of injuries. The risk of wounding increased monotonically with body size in adult males but not in adult females, and small males were less likely to be injured, suggesting that they employ a risk-averse strategy by avoiding direct competition for mates. There was no evidence of asymptotic or decreasing wounding probability in the largest males, which is consistent with the hypothesis that large males compete most intensively to monopolize mates.

Habitat fragmentation is a leading cause of reptile declines worldwide. We examined demographic differences between populations of Northern Map Turtles, Graptemys geographica (Le Sueur, 1817), inhabiting intact and fragmented sites along the Trent-Severn Waterway (TSW) in Ontario over two field seasons. We examined population densities, sex ratios, body size, and growth rates in two control sites and two fragmented sites (where the waterway is disrupted by dams). We predicted that population density would be higher in control sites, and that sex ratios would differ among sites. Abundance was greater than expected, but densities could not be compared owing to a lack of recaptures. Sex ratios in control sites were slightly male-biased and were significantly female-biased in fragmented sites. Turtles in fragmented habitats were significantly smaller than those in control habitats. Estimated growth rates of juveniles and males were significantly reduced in fragmented populations compared with controls. We hypothesize that habitat alterations in fragmented sites are differentially affecting demographic classes because of the intersexual niche divergence observed in Map Turtles. We emphasize the need for further research to examine the interactions between habitat alteration and invasive species and the effects they are having on Northern Map Turtle populations.Résumé : La fragmentation des habitats est une des causes principales du déclin des reptiles à l'échelle planétaire. Nous examinons les différences démographiques entre des populations de tortues géographiques boréales, Graptemys geographica (Le Sueur, 1817) habitant des sites intacts et fragmentés du réseau fluvial Trent-Severn (TSW) en Ontario au cours de deux saisons de terrain. Nous mesurons les densités de population, les rapports des sexes, les tailles corporelles et les taux de croissance dans deux sites témoins et deux sites fragmentés (dans lesquels le cours est perturbé par des barrages). Nous avons prédit que la densité de la population serait plus grande aux sites témoins et que le rapport des sexes différerait d'un site à l'autre. L'abondance était plus grande que prévu, mais les densités n'ont pu être comparées par manque de recaptures. Les rapports des sexes favorisaient légèrement les mâles dans les sites témoins et les femelles dans les sites fragmentés. Les tortues dans les sites fragmentés étaient significativement plus petites que dans les habitats témoins. Les taux de croissance estimés des jeunes et des mâles étaient significativement réduits dans les populations fragmentées, par rapport aux populations témoins. Nous émettons l'hypothèse selon laquelle les modifications des habitats dans les sites fragmentés affectent de manière différentielle les diverses classes démographiques à cause de la divergence de niche observée entre les sexes chez les tortues géographiques. Nous soulignons la nécessité de recherches additionnelles pour examiner les interactions entre les modifications des habitats et les espèces envahissantes et les effets qu'ell...