Dispersal is a key process for the population dynamics of spatially structured populations (at local and metapopulation levels), so the understanding of the mechanisms underlying the movement of individuals in space and time is important for evolutionary and ecological studies. Here we analyzed, for the first time, a long‐term (1992–2009) multi‐site capture– recapture database collected at four local populations of a long‐lived seabird, the Audouin’s gull Larus audouinii, covering 90% of its total world population. Those local populations show different ecological and demographic features that allow us to assess the influence of several key factors involved in breeding dispersal patterns at large spatio‐temporal scales. A recently developed analytical tool in mark–recapture modelling, the multi‐event approach, allowed us to obtain separate departure and settlement probabilities and test different biological hypotheses for each step of the dispersal process. Our results revealed that site fidelity was the most common strategy among breeders, and dispersal was only high from the site with the lowest population size and habitat quality. However, departures from the two largest local populations increased over the study period in response to severe ecological perturbations. Dispersers chose different settlement patches depending on their site of origin, with settlement choices determined by the population size of the destination colony rather than by the local reproductive performance, foraging area (a proxy of food availability) or distance to the destination site. Our results indicate that a breeding site is not abandoned by breeders unless a series of cumulative perturbations occur; once dispersing, settlement is directed towards densely populated sites, with dispersers using population size to rapidly assess the quality of the breeding patch.
Summary1. Large-scale seasonal climatic indices, such as the North Atlantic Oscillation (NAO) index or the Southern Oscillation Index (SOI), account for major variations in weather and climate around the world and may influence population dynamics in many organisms. However, assessing the extent of climate impacts on species and their life-history traits requires reliable quantitative statistical approaches. 2. We used a new analytical tool in mark-recapture, the multi-event modelling, to simultaneously assess the influence of climatic variation on multiple demographic parameters (i.e. adult survival, transient probability, reproductive skipping and nest dispersal) at two Mediterranean colonies of the Cory's shearwater Calonectris diomedea, a trans-equatorial migratory long-lived seabird. We also analysed the impact of climate in the breeding success at the two colonies. 3. We found a clear temporal variation of survival for Cory's shearwaters, strongly associated to the large-scale SOI especially in one of the colonies (up to 66% of variance explained). Atlantic hurricane season is modulated by the SOI and coincides with shearwater migration to their wintering areas, directly affecting survival probabilities. However, the SOI was a better predictor of survival probabilities than the frequency of hurricanes; thus, we cannot discard an indirect additive effect of SOI via food availability. Accordingly, the proportion of transients was also correlated with SOI values, indicating higher costs of first reproduction (resulting in either mortality or permanent dispersal) when bad environmental conditions occurred during winter before reproduction. 4. Breeding success was also affected by climatic factors, the NAO explaining c. 41% of variance, probably as a result of its effect in the timing of peak abundance of squid and small pelagics, the main prey for shearwaters. No climatic effect was found either on reproductive skipping or on nest dispersal. 5.Contrarily to what we expect for a long-lived organism, large-scale climatic indexes had a more pronounced effect on survival and transient probabilities than on less sensitive fitness parameters such reproductive skipping or nest dispersal probabilities. The potential increase in hurricane frequency because of global warming may interact with other global change agents (such as incidental bycatch and predation by alien species) nowadays impacting shearwaters, affecting future viability of populations.
Climatic shifts may increase the extinction risk of populations, especially when they are already suffering from other anthropogenic impacts. Our ability to predict the consequences of climate change on endangered species is limited by our scarce knowledge of the effects of climate variability on the population dynamics of most organisms and by the uncertainty of climate projections, which depend strongly on the region of the earth being considered. In this study, we analysed a long-term monitoring programme ) of Hermann's tortoise (Testudo hermanni) aimed at evaluating the consequences of the drastic changes in temperature and precipitation patterns predicted for the Mediterranean region on the demography of a long-lived species with low dispersal capability and already suffering a large number of threats. Capture-recapture modelling of a population in the Ebro Delta (NE Spain) allowed us to assess the effect of climate variability on the survival of tortoises. Winter rainfall was found to be the major driver of juvenile and immature survival, whereas that of adults remained high and constant across the study. Furthermore, local climate series obtained ad hoc from regional climate simulations, for this and 10 additional Mediterranean locations where tortoises occurred, provided us with reliable future climate forecasts, which were used to simulate the fate of these populations under three precipitation scenarios (mean, wet and dry) using stochastic population modelling. We show that a shift to a more arid climate would have negative consequences for population persistence, enhancing juvenile mortality and increasing quasiextinction risk because of a decrease in recruitment. These processes varied depending on the population and the climate scenario we considered, but our results suggest that unless other human-induced causes of mortality are suppressed (e.g. poaching, fire, habitat fragmentation), climate variability will increase extinction risk within most of the species' current range.
1. In recent years, marine protected areas (MPAs) excluding all or some fishing activities have become widely applied as a tool to rebuild marine ecosystems and fisheries, but still, our knowledge of the effects of MPAs on the demography of harvested populations remains scarce, especially in cases where partly protected areas are still supporting some fishing activities. 2. Here, we investigated the influence of partial protectionexcluding fixed gears such as gillnets and traps but still allowing a hook and line fisheryon the demography of Atlantic cod Gadus morhua along the Norwegian Skagerrak coast. To do so, we applied novel multievent models to a 9-year data set containing both live recaptures and dead recoveries of marked fish of different sizes collected before and after the implementation of an MPA, also including several unprotected sites. 3. At the MPA site, the annual proportion of deaths due to fishing decreased from 0Á59 before MPA implementation to 0Á32 after MPA implementation. As a result, annual survival increased by 167% (from 0Á09 to 0Á24) for small (16-44 cm) and 83% (from 0Á23 to 0Á42) for big (45-97 cm) cod, respectively. 4. Average survival was lower in unprotected areas, and annual fishing mortality was higher, representing almost 100% of the total mortality of large-sized cod in some years. 5. Annual emigration rates (i.e. spillover from the MPA) increased in the last years of the study, but no differences in body growth were detected between sites. 6. Closure of the fishery within the MPA would further increase the annual survival of smaller individuals by 100% (from 0Á24 AE 0Á07 to 0Á48 AE 0Á11) and that of larger individuals by 44% (from 0Á42 AE 0Á05 to 0Á60 AE 0Á09). 7. Synthesis and applications. Our study reveals how current marine protected areas (MPAs) function and provides important insights for guiding a future adaptive management process. Given that harvested populations will not be able to sustain annual survival rates consistently below 30%, as found here; our results underscore the urgency of effective management measures such as no-take zones in areas where local populations are particularly reduced or in dire need of demographic rescue.
Summary1. Many species are found today in the form of fragmented populations occupying patches of remnant habitat in human-altered landscapes. The persistence of these population networks requires a balance between extinction and colonization events assumed to be primarily related to patch area and isolation, but the contribution of factors such as the characteristics of patch and matrix habitats, the species' traits (habitat specialization and dispersal capabilities) and variation in climatic conditions have seldom been evaluated simultaneously. 2. The identification of environmental variables associated with patch occupancy and turnover may be especially useful to enhance the persistence of multiple species under current global change. However, for robust inference on occupancy and related parameters, we must account for detection errors, a commonly overlooked problem that leads to biased estimates and misleading conclusions about population dynamics. 3. Here, we provide direct empirical evidence of the effects of different environmental variables on the extinction and colonization rates of a rich butterfly community in the western Mediterranean. The analysis was based on a 17-year data set containing detection/nondetection data on 73 butterfly species for 26 sites in north-eastern Spain. Using multiseason occupancy models, which take into account species' detectability, we were able to obtain robust estimates of local extinction and colonization probabilities for each species and test the potential effects of site covariates such as the area of suitable habitat, topographic variability, landscape permeability around the site and climatic variability in aridity conditions. 4. Results revealed a general pattern across species with local habitat composition and landscape features as stronger predictors of occupancy dynamics compared with topography and local aridity. Increasing area of suitable habitat in a site strongly decreased local extinction risks and, for a number of species, both higher amounts of suitable habitat and more permeable landscapes increased colonization rates. Nevertheless, increased topographic variability decreased the extinction risk of bad dispersers, a group of species with significantly lower colonization rates. 5. Our models predicted higher sensitivity of the butterfly assemblages to deterministic changes in habitat features rather than to stochastic weather patterns, with some relationships being clearly dependent on the species' traits.
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