Evol Ecol Res 6: 397-413 (2004) Full PDF if your library subscribes.
Resource allocation in the dioecious shrub Rhamnus alpinus: the hidden costs of reproduction
María-José Bañuelos* and José-Ramón Obeso
Departamento de Biología de Organismos y Sistemas, Unidad de Ecología, Oviedo University, 33071 Oviedo, Spain
Address all correspondence to María-José Bañuelos, Department of Ecology, Botanical Section, KVL (Royal Veterinary and Agricultural University), Rolighedsvej 21, 1958 Frederiksberg C, Denmark.
We know little about the demographic consequences of reproductive investment in woody plant species, especially dioecious ones. We analysed the sexual dimorphism in the reproductive investment of the dioecious shrub Rhamnus alpinus at different hierarchical levels (shoot, branch, plant, population), and the consequences of such investment for both males and females. We found no short-term reproductive costs at shoot or branch levels for either sex. This lack of costs can be attributed to translocation of resources from other shoots or branches. We found evidence for reproductive costs in female shrubs at the plant and population levels. Dendrochronological analyses showed a connection between the estimated age of first reproduction and a decrease in growth rate of females over time. The annual ring growth of females differed significantly from that of males in periods with low annual precipitation, which could exacerbate the costs of reproduction. Populations with older individuals exhibited male-biased sex ratios, which might be due to higher mortality rates of females because of the cumulative effects of reproductive costs. Evidence for the costs of reproduction at lower modular levels depends on the balance of autonomy and integration of branches at the whole shrub level. Cumulative effects may be seen at the whole shrub and population levels after a number of reproductive episodes.
Keywords: growth rate, hierarchical structure, sex ratio, sexual dimorphism, trade-offs.
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