The Shape of the Trade-Off Function Between Reproduction and Future Performance in \u3cem\u3ePlantago major\u3c/em\u3e and \u3cem\u3ePlantago rugelii\u3c/em\u3e

There is a paucity of data describing the nature of the trade-off function between reproduction and future performance. Most studies implicitly assume it is a linear function such that allocation of resources to reproduction results in a proportional decline in future survival and reproduction. We reanalyse data from a field experiment with halfsib families of Plantago major L. that suggests this relationship is in fact curvilinear. Low levels of reproductive investment had relatively little impact on future performance and higher levels of investment had a larger impact. To explain this curvilinear pattern, we conducted an experiment to examine the effect of incremental increases in reproductive investment on rates of resource uptake in P. major and Plantago rugelii Decne. Results suggest that, because of differences in the resource requirements of vegetative versus reproductive tissues, reproduction will have little effect on growth, providing that the limiting resources are required in greater quantities for vegetative as compared with reproductive tissues. These results are in accord with a curvilinear trade-off function between reproduction and future performance and provide an explanation for the maintenance of sexual reproduction in species where seed production may contribute minimally to fitness in the short term

Impact of Flower Harvesting on the Salt Marsh Plant \u3cem\u3eLimonium carolinianum\u3c/em\u3e

Because of the potentially detrimental effects of seed production on adult survivorship and growth, moderate flower harvesting may have little negative impact on population growth of long-lived perennial plants such as Limonium carolinianum (Walter) Britton. We examined this by collecting data on survivorship, growth, and fecundity of an unharvested population over a period of 5 years and conducted a controlled experiment to examine the effect of harvesting on adult survivorship and growth over a 3-year period. Data were summarized in the form of a stage structured matrix population model with a stochastic element that incorporated year-to-year variation in transition probabilities. Contrary to our original hypothesis, we found that preventing seed set through removal of flowers did not increase adult survivorship or growth. By determining the harvest level that reduced population growth rate to 1.0, we estimated the maximum sustainable harvest level to be 16%, a value that is approximately half that of reported harvest levels on accessible marshes in the study area. In spite of this, the reported harvest levels are unlikely to drive local populations to extinction in the foreseeable future. Providing the adult population size is \u3e100 and harvest levels are \u3c90%, time to local extinction will exceed 100 years. This is a function of the very high survivorship of adults in this species and the fact that harvesting has no negative impact on adult survivorship or growth. However, because of the long preadult phase in this species (8–9 years) and the fact that fecundity of young adults is low, recovery from overharvesting is extremely slow. Adult population size can be reduced to 25% of its original value in 7 years at high harvest levels, but it will take 34 years on average to recover once harvesting is terminated

The shape of the trade-off function between reproduction and future performance

Abstract: There is a paucity of data describing the nature of the trade-off function between reproduction and future performance. Most studies implicitly assume it is a linear function such that allocation of resources to reproduction results in a proportional decline in future survival and reproduction. We reanalyse data from a field experiment with halfsib families of Plantago major L. that suggests this relationship is in fact curvilinear. Low levels of reproductive investment had relatively little impact on future performance and higher levels of investment had a larger impact. To explain this curvilinear pattern, we conducted an experiment to examine the effect of incremental increases in reproductive investment on rates of resource uptake in P. major and Plantago rugelii Decne. Results suggest that, because of differences in the resource requirements of vegetative versus reproductive tissues, reproduction will have little effect on growth, providing that the limiting resources are required in greater quantities for vegetative as compared with reproductive tissues. These results are in accord with a curvilinear trade-off function between reproduction and future performance and provide an explanation for the maintenance of sexual reproduction in species where seed production may contribute minimally to fitness in the short term. Key words: reproductive cost, resource allocation, life-history theory, nitrogen uptake, reproductive photosynthesis, Plantago major, Plantago rugelii. Résumé : Il y a peu de données décrivant la fonction d'échange entre la reproduction et la performance future. La plupart des études assument implicitement qu'il s'agit d'une fonction linéaire faisant en sortes que l'allocation des ressources à la reproduction résulte en un déclin proportionnel de la survie et de la reproduction futures. Les auteurs ont réexaminé les données d'une expérience sur le terrain impliquant des familles de demi-frères du Plantago major L., suggérant que cette relation est en fait curvilinéaire. De faibles niveaux d'investissement reproducteur ont relativement peu d'impact sur la performance future, et des niveaux plus élevés d'investissement ont des impacts plus marqués. Pour expliquer ce patron curvilinéaire, les auteurs ont conduit une expérience afin d'examiner l'effet d'augmentations graduelles de l'investissement reproducteur sur les taux d'accumulation des ressources chez le P. major et le Plantago rugelii Decne. Les résultats suggèrent que, compte tenu des différences de besoins en ressources des tissus végétatifs versus les tissus reproducteurs, le reproduction aurait peu d'effet sur la croissance, pourvu que les ressources limitantes soient nécessaires en quantités plus élevées pour les tissus végétatifs que pour les tissus reproducteurs. Ces résultats concordent avec la fonction d'échange curvilinéaire entre la reproduction et la performance future et fournit une explication pour le maintient de la reproduction sexuelle chez les espèces où la production de graines peut contribuer minimalement à l'adaptation à court terme