Variation of predator satiation and seed abortion as seed defense mechanisms across an altitudinal range

Peguero G., Bonal R., Espelta J.M. (2014) Variation of predator satiation and seed abortion as seed defense mechanisms across an altitudinal range. Basic and Applied Ecology. 15: 269-276.
Enlace
Doi: 10.1016/j.baae.2014.03.006

Resumen:

Predator satiation and seed abortion have been reported as effective mechanisms reducing pre-dispersal seed predation, however, whether they may act simultaneously and whether their contribution to seed defense may spatially vary has been barely addressed. Across the altitudinal range of the dry tropical tree Acacia pennatula we investigated the importance of seed production and seed abortion as defense mechanisms against its pre-dispersal seed predators (Mimosestes spp.). Additionally, we measured the potential relationship between the number of seeds that escaped predation and plant recruitment. Predator satiation was effective since greater fruit production was associated with a lower proportion of predated seeds, while high seed abortion rates were related to increases in larval mortality. Although both mechanisms were present simultaneously, their relative contribution varied considerably across the altitudinal range: predator satiation was favored in the middle parts of the range, where seed production is much higher, whereas seed abortion was particularly relevant at the peripheral sites and especially high at the upper margin. The number of seeds that escaped predation was related to seedling density at plot level, indicating the demographic significance of these defense mechanisms against pre-dispersal seed predation. Overall, these results highlight the importance of considering spatial variability when analyzing seed defense traits and they also suggest considering predator satiation and seed abortion as two complementary mechanisms to reduce seed loss. © 2014 Gesellschaft für Ökologie.

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Endozoochory and Fire as Germination Triggers in Neotropical Dry Forests: An Experimental Test

Peguero G., Espelta J.M. (2014) Endozoochory and Fire as Germination Triggers in Neotropical Dry Forests: An Experimental Test. Biotropica. 46: 83-89.
Enlace
Doi: 10.1111/btp.12076

Resumen:

Endozoochory and fire are crucial ecological factors determining germination success and recruitment in many plant species. Fire is a well-known germination trigger while endozoochory may allow seed dispersal along with an increase in germination. Their interaction has rarely been addressed, however, even though both factors are pervasive in human-transformed ecosystems like most Neotropical Dry Forests (NDF). For three common Mesoamerican tree species (Acacia pennatula, Enterolobium cyclocarpum, and Guazuma ulmifolia), we used feeding trials to assess the preference of cattle, which are their main seed dispersal agent. We also experimentally tested the interaction between gut passage and fire as triggers of germination. The fruits of the three species were eaten by cattle, but the small seeds of G. ulmifolia were ingested 10-fold more than those of the other species. While gut passage did not have any effect on germination, heat-shocks above 90 °C increased the number of germinating seeds by 15 percent. These results suggest that cattle may be a key dispersal vector in NDF, but that fire may be an important germination trigger. Physical dormancy in these species may have been selected for by extinct megaherbivores because it was a key trait ensuring seed survival after gut passage. However, in light of the recent expansion of cattle-ranching and fire occurrence in NDF, it has become a useful exaptation facilitating the colonization of disturbed areas. © 2013 The Association for Tropical Biology and Conservation.

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