Spatial and temporal dynamics of fucoid populations (Ascophyllum nodosum and Fucus serratus): A comparison between central and range edge populations

Persistence of populations at range edges relies on local population dynamics and fitness, in the case of geographically isolated populations of species with low dispersal potential. Focusing on spatial variations in demography helps to predict the long-term capability for persistence of populations across the geographical range of species' distribution. The demography of two ecological and phylogenetically close macroalgal species with different life history characteristics was investigated by using stochastic, stage-based matrix models. Populations of Ascophyllum nodosum and Fucus serratus were sampled for up to 4 years at central locations in France and at their southern range limits in Portugal. The stochastic population growth rate (lambda(s)) of A. nodosum was lower and more variable in central than in southern sites whilst for F. serratus this trend was reversed with lambda(s) much lower and more variable in southern than in central populations. Individuals were larger in central than in southern populations for both species, which was reflected in the lower transition probabilities of individuals to larger size classes and higher probability of shrinkage in the southern populations. In both central and southern populations elasticity analysis (proportional sensitivity) of population growth rate showed that fertility elements had a small contribution to lambda(s) that was more sensitive to changes in matrix transitions corresponding to survival. The highest elasticities were found for loop transitions in A. nodosum and for growth to larger size classes in F. serratus. Sensitivity analysis showed high selective pressure on individual growth for both species at both locations. The results of this study highlight the deterministic role of species-specific life-history traits in population demography across the geographical range of species. Additionally, this study demonstrates that individuals' life-transitions differ in vulnerability to environmental variability and shows the importance of vegetative compared to reproductive stages for the long-term persistence of populations.Portuguese Foundation for Science and Technology (FCT) [SFRH/BPD/75843/2011]; European Regional Development Fund (ERDF) through the COMPETE - Operational Competitiveness Programme; FCT [Pest-CIMAR LA 0015/2013, EXCL/AAG-GLO/0661/2012

Challenging Europe:technology, environment and the quest for resource security

Since the nineteenth century, access to and the development of natural resources became an important element of national and international politics. Resource security emerged as an issue vital to national security; and resource competition and crises gave rise to international tensions as well as to technological innovation and new modes of transnational cooperation

Elasticity of the population growth rate to changes in matrix elements summed over different regions (growth, loop, shrinkage and fertility) for southern (Portugal) and central (France) <i>A. nodosum</i> and <i>F. serratus</i> populations.

<p>Elasticity of the population growth rate to changes in matrix elements summed over different regions (growth, loop, shrinkage and fertility) for southern (Portugal) and central (France) <i>A. nodosum</i> and <i>F. serratus</i> populations.</p

Life cycle graph for <i>A. nodosum</i> and <i>F. serratus</i> showing the different stage classes and all possible transitions.

<p>Individuals in a size class (2–6) that survive can grow (G), shrink (S) or stay in the same size class (L). Class 1 includes new recruits that, if survive, enter class 2. Individuals in class 3–6 are reproductive.</p

Stable distribution of the mean matrix for southern (Portugal) and central (France) <i>A. nodosum</i> and <i>F. serratus</i> populations.

<p>Stable distribution of the mean matrix for southern (Portugal) and central (France) <i>A. nodosum</i> and <i>F. serratus</i> populations.</p

Sensitivity of the population growth rate to changes in matrix elements expressed as relative contributions and summed over different regions (growth, loop, shrinkage and fertility) in southern (Portugal) and central (France) <i>A. nodosum</i> and <i>F. serratus</i> populations.

<p>Sensitivity of the population growth rate to changes in matrix elements expressed as relative contributions and summed over different regions (growth, loop, shrinkage and fertility) in southern (Portugal) and central (France) <i>A. nodosum</i> and <i>F. serratus</i> populations.</p

Mean (±SD), minimum (*) and maximum (#) stochastic growth rates (λ_s) for southern (Portugal) and central (France) <i>A. nodosum</i> and <i>F. serratus</i> populations.

<p>Mean (±SD), minimum (*) and maximum (#) stochastic growth rates (λ_s) for southern (Portugal) and central (France) <i>A. nodosum</i> and <i>F. serratus</i> populations.</p

Sensitivity of the population growth rate to changes in the survival transitions for each stage class in southern (Portugal) and central (France) <i>A. nodosum</i> and <i>F. serratus</i> populations.

<p>Sensitivity of the population growth rate to changes in the survival transitions for each stage class in southern (Portugal) and central (France) <i>A. nodosum</i> and <i>F. serratus</i> populations.</p

Mean matrices from stochastic simulations of the <i>A. nodosum</i> and <i>F. serratus</i> populations in France and Portugal.

<p>The transition codes are represented in all matrices to make easier the interpretation of the table. F: Fertility; G: Growth to larger size classes; S: Shrinkage; L: Loop.</p