ABSTRACT
Reductions in bird numbers could hamper ecosystem services such as pollination, but experimental proof is lacking. We show that functional extinction of bird pollinators has reduced pollination, seed production, and plant density in the shrub Rhabdothamnus solandri (Gesneriaceae) on the North Island (“mainland”) of New Zealand but not on three nearby island bird sanctuaries where birds remain abundant. Pollen limitation of fruit set is strong (Pollen Limitation Index = 0.69) and significant on the mainland but small (PLI = 0.15) and nonsignificant on islands. Seed production per flower on the mainland is reduced 84%. Mainland sites have similar adult densities, but 55% fewer juvenile plants per adult, than island sites. Seed addition experiments near adult R. solandri plants on the mainland found strong seed limitation 5 years after sowing for R. solandri but not for two other co-occurring woody species. This demonstrates a terrestrial trophic cascade.
Es demostra l’efecte d’amenaça als mutualismes
Rhabdothamnus solandri (Font: www.forestflora.nz)
Acaba de donar-se a conèixer on line, l’article següent, aparegut a Science (a través de onlineEarly through ScienceExpress)
- Anderson et al. 2011. Cascading Effects of Bird Functional Extinction Reduce Pollination and Plant Density, in press.
És generalment admès que l’extinció dels mutualistes animals (pol·linitzadors, dispersadors de llavors) pot amenaçar les espècies vegetals, però hi ha poques demostracions empíriques. Anderson et al. mostren aquest efecte comparant indrets infestats/no infestats amb rates a Nova Zelanda, que comporten la desaparició d’ocells pol·linitzadors i, a la fi, l’efecte sobre la reproducció de Rhabdothamnus solandri (Gesneriaceae)