Impact of dispersal status on estimates of local population growth rates in a Temminck's stint Calidris temminckii population

Abstract

Due to different costs and benefits associated with dispersal and philopatry, life history traits of immigrants and philopatric individuals may differ. Despite of the apparent effects, dispersal status is only rarely considered in analyses of population dynamics. We analysed whether dispersal status explains variation in life history traits of an endangered Temminck's stint Calidris temminckii population breeding at the Baltic Sea. We also estimated the impact of immigration and dispersal status on the population growth rate (λ) with a population matrix model, in which immigrants and philopatric individuals are separated to their own stages. We found that philopatric individuals had a higher apparent survival than immigrants in both sexes. In reproductive parameters, variation due to dispersal status was not clear. Nests incubated by philopatric individuals survived better than those of immigrants, but this did not translate in hatchling production per breeding attempt. Models described a sink population in which the inclusion of both immigration rate to the population and the dispersal status of individuals into the model increased estimates of λ. When the better success of philopatric individuals was considered, the population growth appeared more stable (λ=0.972). If this was not taken into account, λ implied a strong decline (λ=0.911). The results support the hypothesis that immigrants exhibit lower components of lifetime reproductive success and therefore contribute less to population growth and the gene pool than local recruits. While we cannot distinguish whether this difference reflects higher mortality or permanent emigration, the latter explanation seems more plausible. Our results highlight the importance of considering immigration and dispersal status in population modelling. In the case of the endangered study population, the results implied that management options directed to improve local recruitment would be a profitable option.

Phylogeography of the Temminck’s Stint (Calidris temminckii): historical vicariance but little present genetic structure in a regionally endangered Palearctic wader

“…(2010) revealed that both natal and breeding dispersal seem to be rare at regional scale (5–50 km). Pakanen et al. (2010, 2011) also observed that individuals recruited to the population as immigrants were more likely to change breeding sites between seasons, especially if they had experienced poor breeding success.…”

“…In this case, receiving only very few immigrants might cause inbreeding , although in the Bothnian Bay there is evidence that immigration, even if occurring at a low rate, has likely saved the population from extinction so far (Rönkä et al. , 2008; Pakanen et al. , 2010).…”

“…The Bothnian Bay, Lapland and Yakutsk populations are all marginal populations, located at the edges of the breeding range and might not be well connected through migration to the main breeding population. In this case, receiving only very few immigrants might cause inbreeding , although in the Bothnian Bay there is evidence that immigration, even if occurring at a low rate, has likely saved the population from extinction so far Pakanen et al, 2010).…”

“…Between more distant populations, the kinship coefficients were even negative and no signs of isolation by distance were detected, which suggests that there are two types of behaviour in the Temminck's Stint; either the individuals are philopatric or they disperse over vast geographical distances, keeping even the furthest populations genetically similar. A recent population analysis by Pakanen et al (2010) revealed that both natal and breeding dispersal seem to be rare at regional scale (5-50 km). Pakanen et al (2010Pakanen et al ( , 2011 also observed that individuals recruited to the population as immigrants were more likely to change breeding sites between seasons, especially if they had experienced poor breeding success.…”

“…A recent population analysis by Pakanen et al (2010) revealed that both natal and breeding dispersal seem to be rare at regional scale (5-50 km). Pakanen et al (2010Pakanen et al ( , 2011 also observed that individuals recruited to the population as immigrants were more likely to change breeding sites between seasons, especially if they had experienced poor breeding success. Strong site fidelity combined with longdistance dispersal was suggested to result in bimodal dispersal distance distribution, which obtains support from the results presented here.…”