Details

Autor(en) / Beteiligte

• Ågren, Jon
• Willson, Mary F.

Titel

Cost of Seed Production in the Perennial Herbs Geranium maculatum and G. sylvaticum: An Experimental Field Study

Ist Teil von

• Oikos, 1994-05, Vol.70 (1), p.35-42

Ort / Verlag

Oxford: Munksgaard International Publishers, Ltd

Erscheinungsjahr

1994

Beschreibungen/Notizen

• Life-history models are based on the assumption that there is a trade-off between allocation to reproduction and allocation to other functions. We used a field experiment to ask if seed production reduces subsequent survival, vegetative growth or flowering in two forest populations of Geranium maculatum in Illinois, USA, and in one meadow and one forest population of G. sylvaticum in northern Sweden. In each population, one set of plants was prevented from setting seed (stigmas were excised at flower opening) and a second set of plants was allowed to mature seeds naturally. Reproductive effort in control plants (estimated as the seed-mass to leaf-mass ratio) was 0.06 ± 0.01 (Mean ± SE) and 0.08 ± 0.01 in the two G. maculatum populations, and 0.40 ± 0.04 and 0.06 ± 0.01 in the two G. sylvaticum populations. Seed production was associated with a reduced probability of flowering in the subsequent year in the G. sylvaticum populations, but not in the G. maculatum populations. There were no significant differences between treatments in mortality, in the number of leaves produced in the following year, or in the number of flowers produced by floral plants in the second year in any population. Although the seed-mass to leaf-mass ratio of G. sylvaticum control plants was markedly higher in the meadow than in the forest population, this difference in reproductive effort was apparently not associated with a higher cost of reproduction: The proportion of control plants that flowered in the second year was more than twice as high in the meadow population (0.53 vs 0.23), and the response to the experimental prevention of seed production was not stronger in the meadow than in the forest population. The experimental results demonstrate that the seed-mass to leaf-mass ratio need not be a good indicator of the cost of seed production when different species or conspecific populations in different environments are compared. It is suggested that a greater temporal overlap between reproductive and vegetative growth in G. sylvaticum than in G. maculatum may be important for the difference in reproductive cost between the two species.