Mestre L., Garcia N., Barrientos J.A., Espadaler X., Piñol J. (2013) Bird predation affects diurnal and nocturnal web-building spiders in a Mediterranean citrus grove. Acta Oecologica. 47: 74-80.EnlaceDoi: 10.1016/j.actao.2013.01.001
Spiders and birds can greatly decrease insect populations, but birds also limit spider densities in some habitats. Bird predation is thought to be one of the causes behind nocturnal activity in spiders, so night-active spiders that hide in retreats during the day should be less affected by bird foraging than day-active spiders. However, this hypothesis has not yet been tested. We investigated the importance of bird predation on the spider community of a Mediterranean organic citrus grove. We excluded birds by placing net cages over the trees and we conducted visual searches in the canopies to sample web-building spiders. As there are many nocturnal species in the family Araneidae, we conducted searches both by day and by night to compare the abundance of active araneids in these two time periods. We sampled the tree trunks with cardboard bands to collect hunting spiders. In bird-excluded canopies there were more spiders of the families Araneidae and Theridiidae. There were higher numbers of active Araneidae at night, but these were just as negatively affected by bird predation as day-active Araneidae, so there was no evidence of nocturnal activity serving as an anti-predator strategy. We did not find any negative impact of birds on hunting spiders. Our results contrast with other studies reporting a negative effect of birds on hunting but not on web-building spiders. © 2013.
Martínez-Vilalta J, Aguadé D, Banqué M, Barba J, Curiel Yuste J, Galiano L, Garcia N, Gómez M, Heres; AM, López BC, Lloret F, Poyatos R, Retana J, Sus O, Vayreda J, Vilà-Cabrera A (2012) Las poblaciones ibéricas de pino albar ante el cambio climático: con la muerte en los talones. Ecosistemas 21: 15-21.
Martínez-Vilalta J, Aguadé D, Banqué M, Barba J, Yuste JC, Galiano L, Garcia N, Gómez M, Hereş AM, López BC, Lloret F, Poyatos R, Retana J, Sus O, Vayreda J, Vilà-Cabrera A (2012) Las poblaciones ibéricas de pino albar ante el cambio climático: con la muerte en los talones. Revista Ecosistemas 21: 15–21.
Sol D., Garcia N., Iwaniuk A., Davis K., Meade A., Boyle W.A., Székely T. (2010) Evolutionary divergence in brain size between migratory and resident birds. PLoS ONE. 5: 0-0.EnlaceDoi: 10.1371/journal.pone.0009617
Despite important recent progress in our understanding of brain evolution, controversy remains regarding the evolutionary forces that have driven its enormous diversification in size. Here, we report that in passerine birds, migratory species tend to have brains that are substantially smaller (relative to body size) than those of resident species, confirming and generalizing previous studies. Phylogenetic reconstructions based on Bayesian Markov chain methods suggest an evolutionary scenario in which some large brained tropical passerines that invaded more seasonal regions evolved migratory behavior and migration itself selected for smaller brain size. Selection for smaller brains in migratory birds may arise from the energetic and developmental costs associated with a highly mobile life cycle, a possibility that is supported by a path analysis. Nevertheless, an important fraction (over 68%) of the correlation between brain mass and migratory distance comes from a direct effect of migration on brain size, perhaps reflecting costs associated with cognitive functions that have become less necessary in migratory species. Overall, our results highlight the importance of retrospective analyses in identifying selective pressures that have shaped brain evolution, and indicate that when it comes to the brain, larger is not always better. © 2010 Sol et al.
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