Evidence for insect seed predator dynamics mediated by vertebrate frugivores

Peguero G., Espelta J.M. (2013) Evidence for insect seed predator dynamics mediated by vertebrate frugivores. Revista Chilena de Historia Natural. 86: 161-167.
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Doi: 10.4067/S0716-078X2013000200005

Resum:

Vertebrate frugivores have been suggested to reduce seed predation, indirectly controlling populations of insect seed predators (ISP) by means of consuming many individuals when feeding on fruits. The possibility has not been explored, however, that this 'frugivore predation' may differentially affect ISP according to species-specific differences in larval development time within the fruit. In the dry tropical forest trees Acacia pennatula and Guazuma ulmifolia we compared seed predation and the absolute and relative abundances of bruchid beetle species (Bruchinae) in two sites, one with large frugivores (cattle) and the other cattle-free for a considerable time. In the site with cattle we found a notable overall reduction in the proportion of seeds predated (ca. 15 %) with respect to cattle-free site, and changes in the ISP community as well, in particular a reduced absolute and relative abundance of the bruchid species with the longest larval development time. Our results suggest that the interplay between evolutionary processes (resulting in variation in insect life-histories) and complex ecological interactions (inadvertent consumption by larger animals) may contribute to the coexistence of different insect species feeding upon the same host plant. © Sociedad de Biología de Chile.

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Allelopathic potential of the neotropical dry-forest tree Acacia pennatula Benth.: Inhibition of seedling establishment exceeds facilitation under tree canopies

Peguero G., Lanuza O.R., Savé R., Espelta J.M. (2013) Allelopathic potential of the neotropical dry-forest tree Acacia pennatula Benth.: Inhibition of seedling establishment exceeds facilitation under tree canopies. Plant Ecology. 213: 1945-1953.
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Doi: 10.1007/s11258-011-0014-0

Resum:

Secondary succession after land abandonment in tropical dry forests has been suggested to be favoured by the facilitation effects for seedling establishment exerted by pioneer trees isolated in these savannah-like landscapes. However, it has also been noticed that these pioneer species may sometimes have an encroaching effect and arrest succession for several decades. We investigated in this study whether allelopathy can play a role in limiting seedling establishment of co-occurring tree species under the canopy of Acacia pennatula by means of lab bioassays and field experiments in north-west Nicaragua. Leaf extracts of A. pennatula did not affect seed germination but reduced the general growth and especially the development of the root compartment in seedlings, shifting their biomass allocation model to a reduced root/shoot ratio. Survival of planted seedlings under the canopy of A. pennatula was about 20-30% lower than outside, and this reduction was particularly pronounced as the dry season progressed, despite the milder conditions (e. g. higher soil moisture) being experienced in the inner positions under the canopy. Altogether, our results suggest that, rather than facilitating, A. pennatula may inhibit the establishment of seedlings under its canopy probably by means of an allelopathic interference in the development of the root system with critical negative consequences for young seedlings in terms of overcoming the dry season. This article warns about overemphasizing the nucleation effect that remnant and isolated trees may have to facilitate secondary succession in these highly disturbed savannah-like tropical dry forests. © 2011 Springer Science+Business Media B.V.

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