Abstract
Small and peripheral populations are typically vulnerable to local extinction processes but important for the metapopulation dynamics of species. The Slender-billed gull (Chroicocephalus genei) is a long-lived species breeding in unstable ephemeral coastal habitats. Their Western Mediterranean populations are relatively small and represent the edge of their global geographical distribution. At a local scale, using long-term data (14 years) on annual breeding success and capture-resights of marked individuals, we estimated and compared the vital rates and evaluated the connectivity of two Spanish populations (Ebro Delta and Doñana) varying in their local environmental conditions. At a metapopulation scale, we analyzed 22 years of data on breeding numbers to predict their future prospects by means of population demographic models. Local survival and breeding success of gulls from the Ebro Delta was lower than those from Doñana, which is likely the result of higher permanent emigration and/or winter mortality in the former. Gulls from the Ebro Delta wintered mostly in Mediterranean areas whereas those from Doñana did so in Atlantic coasts, where food availability is higher. Whereas adult local survival was constant, juvenile local survival showed temporal parallel variations between colonies, probably related to natal dispersal to other breeding colonies. Our results suggested that dispersal was higher at the Ebro Delta and gulls emigrating from their natal colonies settled preferentially in close patches. We found large fluctuations in breeding numbers among local populations probably related to the fact that the Slender-billed gull is a species adapted to unstable and unpredictable habitats with high abilities to disperse between suitable patches depending on environmental stochastic conditions during breeding.
Highlights
Survival, reproduction an dispersal processes drive local population dynamics and metapopulation functioning [1,2]
The specific objectives of our study were: I) to estimate and compare breeding success and local survival of Slender-billed gulls born at the Ebro Delta and Donana areas, II) to evaluate the effects of environmental conditions during breeding on local survival, III) to study the extent of wintering and breeding spatial movements of individuals marked at the two studied populations; and IV) to evaluate the breeding population trends, population numbers and future population prospects at both local and regional scale over the last two decades
Modeling resighting probabilities at Ebro Delta (survival was modeled as a(1,2, $3).t)
Summary
Reproduction an dispersal processes drive local population dynamics and metapopulation functioning [1,2]. Species breeding in unstable and ephemeral habitats typically show large fluctuations in population numbers and productivity linked to temporal environmental variation in habitat quality [5,6]. Small and peripheral populations may be more likely to go extinct due to demographic and environmental stochasticity [4,8] and dispersal processes will become essential for the maintenance of metapopulations [1]. Given the current scenarios of global change, the study of demographic dynamics at multiple populations including marginal or peripheral populations is of special interest for evolutionary and conservation biologists [3,9,10,11,12]. Peripheral populations are often genetically different from central populations and may be major contributors to evolutionary changes in the response to environmental changes, such as the global warming or habitat fragmentation [9]
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