Inferring dispersal dynamics from local population demographic modelling: the case of the slender‐billed gull inFrance

Abstract

Although it is today accepted that population viability analyses are needed at a meta-population level for most species, usually only single populations are monitored in the context of management and conservation programmes. This paper outlines a fairly general and easy-to-implement approach based on counts and capture-recapture data that allow the dynamics of single populations to be assessed even when they are highly connected to other populations. This approach was motivated by a study of the French population of the slender-billed gull Larus genei, which experienced a sharp population increase in the 1980s and 1990s, suggesting that the species was not at risk of extinction. However, several recently raised concerns indicate that the observed population increase is unlikely to have been achieved uniquely by an intrinsic growth rate. We estimated local adult survival probability at 0.81 (0.79-0.83), which is considerably lower than that of other gull species of comparable size. Moreover, local fecundity observed in slender-billed gulls [0.66 (0.47-0.85)] is lower than that observed in similar species. Massive reproduction failures and the low demographic parameters observed could be caused by chick exposure to aerial and terrestrial predation, leading to permanent emigration. Unrealistically high demographic parameter values would be needed to generate the observed local population increase. The results of our study indicate that connections with other neighbouring populations are responsible for the local population dynamics, and that about 10% of the individuals may be immigrants into this local population annually. However, our results suggest that the population of the slender-billed gull may be stable at the west Mediterranean scale. The high annual fluctuations of population size observed at a larger scale also highlight the necessity for coordinated international action to protect a maximum of potential breeding sites in order to protect the species. bs_bs_banner Animal Conservation. Print

The Whiskered Tern Chlidonias hybrida expansion in Poland: the role of immigration

“…The full recruitment is achieved at age 3 (fourth cy). All breeders produce offspring (f) In order to estimate the number of immigrants necessary to enter the population every year to match the observed population growth, in the next step, we added an immigrant class to the matrix, following Doxa et al (2013). The number of immigrants was estimated in an iterative way, and all immigrants were assumed to be adult females, reproducing every year after entering the population.…”

“…Calculations were performed in R 2.11 (R Development Core Team 2013). We used the R code proposed by Doxa et al (2013), modified to reflect the three recruitment classes used in calculations (see ESM 1).…”

“…The growth of an expanding population results from internal production of first colonisers (Pyk et al 2013) and/or from immigration (Oro and Ruxton 2001;Skórka et al 2005;Coulson and Coulson 2008;Doxa et al 2013). While it may be difficult to tell which is more important at times, assessing the support for immigration effect is fairly easy (Pulliam 1988): the observed population size is plotted against the one expected without immigration (i.e.…”

“…In some studies of terns and gulls, however, these parameters are not the ones specified for a given population, but rather are taken from estimates published for other populations (e.g., Gill and Mewaldt 1983;Skórka et al 2005). Far more precise results can be achieved by using demographic parameters from the population of interest (i.e., Peery et al 2006;Altwegg and Anderson 2009;Abadi et al 2010;Szostek and Becker 2012;Doxa et al 2013). Integrated population models (IPMs) represent a novel modelling framework that effectively uses count data (i.e., observed population size) and demographic (productivity and survival) data to achieve deep insights into the population dynamics (reviewed by Abadi 2011, also Kéry and.…”

“…Larids (gulls and terns) are frequently used species in various population-demographic studies (e.g., Nisbet and Cam 2002;Lebreton et al 2003;Cam et al 2004;Coulson and Coulson 2008;Szostek and Becker 2012;Doxa et al 2013), but the marsh terns (the genus Chlidonias) remain poorly studied so far (Shealer 2007;Van der Winden and van Horssen 2008;Ledwoń et al 2013). To fill this gap, in this paper we focus on the pattern of expansion of the Whiskered Tern Chlidonias hybrida, the marsh tern species that has been colonising Polish inland for the last four decades (Tomiałojć and Stawarczyk 2003;Betleja and Stawarczyk 2007).…”