Acorn selection by Mexican jays: a test of a tri-trophic symbiotic relationship hypothesis

Abstract

By caching acorns, jays serve as important dispersal agents for oak (Quercus) species. Yet little is known about which acorn characteristics affect selection by jays. In the traditional model of jay/oak symbiosis, large, brown, ripe acorns free of invertebrate parasites (e.g., Curculio acorn weevils) are selected by jays. Recently, it has been suggested that a tri-trophic relationship between oaks, jays, and weevils may have evolved to counter the negative dietary effects of acorn tannins. Under the tri-trophic model, jays would preferentially select acorns containing weevil larvae. We tested the assumptions that (1) acorns containing curculionid larvae exist in sufficient quantities to support jay populations and (2) jays can detect, and preferentially select, acorns containing weevil larvae, and investigated the cues by which jays select acorns. Captive Mexican jays (Aphelocomaultramarina) were presented Emory oak (Quercusemoryi) acorns in aviary feeding trials. Large, dense, viable acorns free of curculionid larvae were preferentially selected. Contrary to results of previous research, color did not affect selection. Acorn viability increased and curculionid larval occupancy decreased in adjacent savannas and isolated stands relative to existing oak woodland, perhaps favoring oak recruitment into adjacent lower-elevation grasslands. Our results compel us to reject the tri-trophic model for this system, and are consistent with the traditional jay/oak symbiosis model. Relatively long-distance dispersal of viable acorns favors Emory oak replacement, and spatial patterns of acorn viability and curculionid parasitism suggest expansion of Emory oak into adjacent low-elevation semi-arid grasslands.

Holm-oak (Quercus ilex subsp. Ballota) acorns infestation by insects in Mediterranean dehesas and shrublands

“…However, the differences among sites were moderate with a 30% mean infestation rate in the highest infested site (site SHR5) and a 10% mean infestation rate in the lowest infested site (site SHR6). Several studies have shown significant differences in acorn infestation rate among forest stands (Hubbard and McPherson, 1997;Branco et al, 2002). In Quercus liaotugensis dominated forests in northern China, differences among forest stands in acorn infestation rate were related to local differences in slope direction and topographic characteristics (Yu et al, 2003).…”

Facilitation of Conspecific Seedling Recruitment and Shifts in Temperate Savanna Ecotones

“…Acorns are not substantially dispersed by wind, water, or seed morphology (Jensen and Neilsen 1986). Instead, acorns are usually dispersed by vertebrates that drop them during transport or fail to relocate acorn caches (, Hubbard and McPherson 1997). At a nearby Q. emoryi savanna site, vertebrate acorn predators included Mexican Jays ( Aphelocoma ultramarina ), Acorn Woodpeckers ( Melanerpes formicivorus ), White‐winged Doves ( Zenaida asiatica ), Peccaries ( Dicotyles xacu ), Coati ( Nasua nasua ), and Sonora white‐tailed deer ( Odocoileus virginianus couesi ) (Hubbard and McPherson, in press ).…”

Edge type effect on germination of oak tree species in the Highlands of Chiapas, Mexico

“…There is evidence that insectattacked acorns have higher (near 90%) germination rates (Branco et al, 2002), however seedlings resulting from these acorns exhibited lower survival, slower growth rates and lower dry mass production than non-attacked seedlings (Branco et al, 2002). Several multi-trophic interactions have been documented between oaks, insects and jays (Hubbard and McPherson, 1997) and between oaks, insects and small mammals (Crawley and Long, 1995;Steele et al, 1996).…”