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Size does matter, but not only size: Two alternative dispersal strategies for viviparous mangrove propagules

par De Ryck, Dennis ;Robert, Elisabeth Maria Rogier;Schmitz, Nele ;Van Der Stocken, Tom;Di Nitto, Diana ;Dahdouh-Guebas, Farid ;Koedam, Nico
Référence Aquatic botany, 103, page (66-73)
Publication Publié, 2012

Article révisé par les pairs

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Résumé :

We studied the propagules of two widespread mangrove species, Ceriops tagal and Rhizophora mucronata, that are similar in shape but differ in other morpho-anatomical features (average length is 23.1±2.2cm and 44.4±4.3cm, resp., n=180). We hypothesized the propagules of both species to have a different hydrodynamic behavior and establishing capacity, resulting in a different dispersal strategy. More specifically, we hypothesized that C. tagal propagules have a larger dispersal capacity than those of R. mucronata. The dispersal strategies of C. tagal and R. mucronata propagules were elucidated through a combination of a propagule tracking (n=180 per species), predation (n=20 per species) and root-growth experiment (n=120 per species), carried out in the field. C. tagal and R. mucronata adopted two different dispersal strategies. C. tagal releases a large number of propagules and disperses fast, having a slender morphology and low density (average ρ: 985.29±19.02gL -1), as well as a high agility (smaller size) when dispersing through dense root systems. C. tagal propagules have a theoretical advantage to disperse over longer distances over the thicker, longer and denser R. mucronata propagules (average ρ: 1003.92±8.52gL -1; t=8.90, p<0.0001, n=197). C. tagal have, however, lower establishment chances due to slower root-growth, desiccation sensitivity and smaller size. In contrast to Ceriops' tactic of releasing high numbers of propagules and fast dispersal, R. mucronata has adopted a dispersal tactic of survival. Fewer propagules are released, but they are more resistant to predators due to their larger size and they can anchor themselves faster due to quicker root-growth (Mann-Whitney U: p<0.0001, n Ct=59, n Rm=57). Overall, propagule characteristics of both species result in different and alternative dispersal strategies on a local scale, contradicting our initial hypothesis. On a global scale, we hypothesize this might lead to a similar capacity for long-distance dispersal, ending in successful establishment. © 2012 Elsevier B.V.