Importance of predation and germination on losses from the seed bank of calden (Prosopis caldenia).

Abstract

Calden (Prosopis caldenia) seeds not dispersed by animals sometimes constitute a considerable number of seeds to the seed bank which may contribute to the species' dissemination. The monthly change in the number of viable non-animal dispersed seeds was evaluated over a one-year period. We determined the percentage germination of seeds and the amount of predation by bruchid beetles to learn how these factors influence seed longevity. Forty eight bags containing 10 fruits were placed in 4 sites below calden tree canopies at the time of shedding (March). To monitor seed losses we randomly removed 1 bag per site every 25-35 days during a year. At the time of shedding, fruits contained 29 seeds, 73 +/- 5.0% which were viable and 9 +/- 2.2% attacked by bruchids. Viability decreased to 33 +/- 22.3% one year later. Loss of viability was described by a polynomial quadratic (y = 70.12 + 0.0238 t-0.0004 t2 (r2= 0.62)). Bags with germinated seeds were observed beginning in November. Percentage germinated seed increased 4.8 +/- 3.7% in the last month of sampling. Consumption of seeds by bruchids also increased in November, but the effect was highly variable. In the last month of sampling (March in the following year), 35 +/- 18.0% of seeds were affected by bruchids. A predictive seed longevity model was developed considering climatic variables, but data were well described only until January (y = 81.50-0.097 time-3.94 precipitation (r2= 0.66)). Undispersed seeds had a high rate of decay and low germination. Longevity was strongly affected by bruchid attack.