Biology subjects

Caizergues, A.

Publications and source records attributed to Caizergues, A..

5 recordsLinked to original sources

bioRxiv2026

Is hidden demographic heterogeneity pervasive? Harvested birds as an example

Individual demographic heterogeneity refers to the fact that individuals from a given population exposed to similar environmental conditions express different demographic traits or tactics. This heterogeneity can either be linked to factors/states such as age, sex or body condition, or be due to hidden factors/states not immediately apparent or easily characterized (hereinafter referred to as 'hidden heterogeneity'). Yet accounting for demographic heterogeneity, and more particularly heterogeneity in survival is crucial because it is an important mechanism underlying compensation processes between natural and harvest mortality. In this study, we used capture-mark-recapture-recovery data of 6 hunted species covering a large range of the demographic slow-fast continuum (61,432 individuals ringed from 1953 to 2020 among Common Teal Anas crecca, Mallard A. platyrhynchos, Common Pochard Aythya ferina, Common Snipe Gallinago gallinago, Common quail Coturnix coturnix, and Blackbird Turdus merula), to assess the presence of unexplained heterogeneity in survival with multievent models. We detected hidden survival heterogeneity in most species, even though the differences between the high and low categories of survival were often small. The probability for an individual to display a low vs high survival rate was not related to potentially important individual factors/states such as migration phenology or to morphology. The presence of hidden heterogeneity was pervasive, affecting species distributed along a relatively large spectrum of demographic strategies. This, in our opinion, supports that part of this heterogeneity in survival evidenced in our study is indeed hidden, resulting either from hidden intrinsic (inherent) individual differences of survival among individuals, or hidden extrinsic factors e.g., linked to spatial variations in hunting pressure. Our findings suggest that hidden heterogeneity needs to be explored more thoroughly in huntable species and accounted for in management policies.

ecology↗

bioRxiv2026

Productivity drives demography and sex structure in a declining waterfowl species

Demographic models are crucial for uncovering the mechanisms underlying changing populations trajectories and structure and to identify the drivers of such changes. Common pochard populations of North east/North west Europe have experienced a sharp decline accompanied by an increase in male proportions among adults since the mid-1990. We used a two-sex, two-stage deterministic matrix population model, to perform a prospective perturbation analysis and to explore, through simulations, some plausible causes underlying the observed decline and change in sex structure. We show that Common pochard populations are more sensitive to changing survival than to changes in productivitys components (clutch size, nest survival...). However, due to an environmental variance much higher than that of survival, components of productivity, especially nest survival, would be the main drivers of Common pochard populations growth rate, a finding supported by empirical data. More importantly, we show that although sex-specific changes in survival at any stage of the life cycle are potent drivers of both population growth rate and changing sex ratio, there is no need to resort to them for explaining the increasing proportions of males such as observed in Common pochard. Because adult males display higher survival than adult females (0.74 against 0.64 on average), any factor affecting recruitment (nest or first year survival) increases the weight of adults into the populations and hence the proportion of males. Thus, in species displaying sex-biased mortality, such as many ducks, decreasing recruitment can underly declining population size and changes in sex structure at the same time, emphasising the importance of accounting for males in monitoring schemes and demographic models.

ecology↗

bioRxiv2026

Harvest probabilities of European ducks: the very first estimation based on reward rings

Ringing-recoveries are an overarching element of population dynamic studies that allow estimating mortality causes and hence improve wildlife management. However, possible drawbacks of recovered rings reside in the fact that reporting probability is rarely known, but consistently lower than 100%. Thus, estimating harvest probabilities (mortality probability due to harvesting) of exploited species without knowledge of ring reporting probability by people exploiting these animals is not straightforward. We here provide the first ever reward-ring study carried out to evaluate European reporting probabilities, hence European harvest probabilities, in three species of ducks (Mallard Anas platyrhynchos, Eurasian Teal A. crecca and Common Pochard Aythya ferina). The 70 Euros reward on some rings was considered to yield a total return of the rings, allowing by comparison to evaluate the reporting probability of standard rings. After the initial year of ringing, annual reporting probability was very similar among the three species, at 0.63-0.66, suggesting two-thirds of the found rings are sent back to the ringing centre. This allowed computation of the annual harvest probability, which was up to 0.27 during the first months after ringing in fall but decreased to 0.04-0.10 during later years. Compared to North American results, the present estimates suggest birds are submitted to a heavy hunting mortality during the first months after ringing, but this pressure declines in later years, likely owing to counter selection of vulnerable/exposed individuals and/or learning by the birds.

ecology↗

bioRxiv2024

Delayed dichromatism as a convenient tool to disentangle the effects of survival and productivity on the population dynamics in waterfowl

Monitoring the number of individuals is by far the most popular strategy for studying the environmental factors that determine population dynamics and for measuring the effectiveness of management actions aimed at population recovery, control or eradication. Unfortunately, population size monitoring is inefficient in identifying the mechanisms underlying demographic processes and, in particular, in assessing the extent to which population growth rate is influenced by changes in adult survival rather than variations in reproductive parameters. In many waterfowl species, sexual dichromatism is observed in adults, while immatures of both sexes display a plumage pattern similar to that of adult females. In these species, the apparent proportion of males increases as the female-like immature males gradually take on the plumage of adult males. The difference between the apparent sex ratio before and after the young reach sexual maturity then provides information about the age ratio of a population. Using winter counts that distinguished between female-like and male-like individuals of two non-native populations of Ruddy duck Oxyura jamaicensis, a species that exhibits such a plumage pattern, we present a non- invasive method based on the apparent sex ratio to split population growth rate into adult survival and recruitment rates (the latter also referred to as productivity). This method can correctly detect annual changes in vital rates, supporting the assumption that counts conducted in an appropriate time window reflect the age structure of a population. We exemplify how the respective contributions of survival and productivity to the population growth rate are essential for understanding the processes behind demo- graphic dynamics. Finally, we point out some best practices to correctly apply the "apparent sex ratio" method described here.

ecology↗

bioRxiv2020

Endemic island songbirds as windows into evolution in small effective population sizes

Due to their limited ranges and inherent isolation, island species have long been recognized as crucial systems for tackling a range of evolutionary questions, including in the early study of speciation [1,2]. Such species have been less studied in the understanding of the evolutionary forces driving DNA sequence evolution. Island species usually have lower census population sizes (N) than continental species and, supposedly, lower effective population sizes (Ne). Given that both the rates of change caused by genetic drift and by selection are dependent upon Ne, island species are theoretically expected to exhibit (i) lower genetic diversity, (ii) less effective natural selection against slightly deleterious mutations [3,4], and (iii) a lower rate of adaptive evolution [5-8, see also Note S1]. Here, we have used a large set of newly sequenced and published whole genome sequences of Passerida bird species or subspecies (14 insular and 11 continental) to test these predictions. We empirically confirm that island species exhibit lower census size and Ne, supporting the hypothesis that the smaller area available on islands constrains the upper bound of Ne. In the insular species, we find significantly lower nucleotide diversity in coding regions, higher ratios of non-synonymous to synonymous polymorphisms, and lower adaptive substitution rates. Our results provide robust evidence that the lower Ne experienced by island species has affected both the ability of natural selection to efficiently remove weakly deleterious mutations and also the adaptive potential of island species, therefore providing considerable empirical support for the nearly neutral theory. We discuss the implications for both evolutionary and conservation biology.

evolutionary biology↗