排序方式: 共有2条查询结果,搜索用时 15 毫秒
1
1.
Ulf Sperens 《Oecologia》1997,109(3):368-373
Variation in fruit production and pre-dispersal seed predation by Argyresthia conjugella was studied in␣four populations of Sorbus aucuparia in northern Sweden.␣The number of infructescences, fruits per infructescence, consumed seeds and developed unattacked seeds
per fruit were scored in marked trees from 1984 to 1990. The results showed that the number of fruits produced in each population
determined the number of seed predators occurring in the host population, as the yearly number of seed predators was significantly
and positively correlated with yearly number of fruits, in all but one population. The seed predators showed a delay in response
to variation in number of fruits produced. This lag in response resulted in a large proportion of fruits being attacked and
seeds consumed in a bad fruiting year that followed a good fruiting year, and vice versa. The proportion of fruits attacked
and seeds consumed was largest in the population showing the greatest between-year variation in fruit production and lowest
in the population showing the lowest between-year variation in fruit production. Furthermore, the individuals within the former
population were synchronised, while they were not in the latter population. These results contradict one of the possible explanations
of mast-seeding, where large synchronised between-year variation is supposed to reduce pre-dispersal seed predation. Instead,
differences in attraction of the seed predator to differences in fruit crop size could explain the observed difference in
seed predation between the two populations with opposite fruiting patterns. Within each population, irrespective of year,
the proportion of fruits attacked and seeds consumed was independent of a tree's fruiting display. Therefore, trees with high
fruit production, despite harbouring the largest number of seed predators, produced the largest number of developed seeds
in absolute numbers, compared to trees that produced few fruits.
Received: 25 February 1996 / Accepted: 30 November 1996 相似文献
2.
John S. Donaldson 《Oecologia》1993,94(2):262-271
Mast-seeding behaviour was monitored in 18 populations of eight species of the African cycad genus Encephalartos between 1988 and 1991. The coefficient of variation (V) in annual cone production for each population ranged between 88 and 200, indicating large fluctuations in reproductive effort between years. Data were collected to determine whether mast-seeding reduced levels of predispersal seed predation by satiating seed predators in mast years and whether it resulted in a reproductive advantage over plants which reproduced more frequently. Masting intensity was greatest in those populations in which individual plants suffered the highest levels of predispersal seed predation in years when only a few plants produced seeds. The principal seed predators were two congeneric weevil species, Antliarhinus zamiae and A. signatus, which develop exclusively on cycad seeds. The lowest intensity of mast-seeding was recorded for cycad populations with low levels of seed predation and in which A. zamiae and A. signatus occurred only in low numbers or were entirely absent. Larger seed crops appeared to result in lower levels of seed predation by A. zamiae and A. signatus in four populations of E. altensteinii, and differences in seed crop size accounted for 48–66% of variation in levels of seed predation in populations of five cycad species. In one population of E. altensteinii, lower levels of seed predation in plants reproducing periodically resulted in a reproductive advantage over plants reproducing more frequently. These results are consistent with the predator satiation hypothesis. However, in most cycad populations, numbers of seed predators did not appear to decrease significantly after a period of 2–8 years between reproductive episodes and, in two of three populations examined, periodic reproduction did not increase the number of seeds surviving to dispersal over a 4-year period. These results are interpreted to mean that periodic reproduction has not evolved in response to selection imposed by seed predators, but that selection may favour those plants which experience lower levels of seed predation by coning in synchrony with the majority of plants in the population. 相似文献
1