The effects of serotiny and rainfall-cued dispersal on fitness: bet-hedging in the threatened cactus <Emphasis Type="Italic">Mammillaria pectinifera</Emphasis> |
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Authors: | Edward M Peters Carlos Martorell Exequiel Ezcurra |
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Institution: | 1.Dirección General de Investigación de Ordenamiento Ecológico y Conservación de los Ecosistemas,Instituto Nacional de Ecología-SEMARNAT,Mexico, D.F.,Mexico;2.Departamento de Ecología y Recursos Naturales, Facultad de Ciencias,Universidad Nacional Autónoma de México,Mexico, D.F.,Mexico;3.Department of Botany and Plant Sciences,University of California-Riverside,Riverside,USA |
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Abstract: | Serotiny—the retention of seeds in the mother plant for over a year—in unpredictable environments may increase the probability
that at least some seeds are dispersed during favorable periods. Propagules may be expelled when environmental cues announcing
favorable conditions occur, or be gradually released into the environment. This could be a bet-hedging strategy increasing
the long-term fitness by reducing interannual variability in reproduction. However, the impact of seed retention on the population
dynamics of serotinous species and its contribution to fitness has been barely explored under field conditions. We assessed
these issues in the threatened Mammillaria pectinifera, a small globose cactus that gets established only in exceptionally rainy years. This species expels some seeds actively
during unusually rainy periods, while dispersing others passively over several years. Dynamics of the seeds in the mother
plant over two very contrasting years in terms of precipitation was incorporated into a stochastic matrix model. Seed retention
was found to increase significantly the probability that some of the seeds retained in any given year are dispersed within
a subsequent rainy period. Active seed-expulsion raises this probability even further. As expected in bet hedgers, seed retention
increased fitness in the presence of temporal variability. Active fruit expulsion did not affect fitness, but reduced demographic
stochasticity. The incomplete serotiny and fruit expulsion observed is the evolutionary outcome expected for the environment
and life-history attributes of the species. |
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Keywords: | Bradyspory El Niño-La Niña Environmental stochasticity Hygrochasy Seed bank Stochastic population models |
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