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1.
Nat Commun ; 11(1): 286, 2020 01 15.
Artigo em Inglês | MEDLINE | ID: mdl-31941904

RESUMO

A prominent tree species coexistence mechanism suggests host-specific natural enemies inhibit seedling recruitment at high conspecific density (negative conspecific density dependence). Natural-enemy-mediated conspecific density dependence affects numerous tree populations, but its strength varies substantially among species. Understanding how conspecific density dependence varies with species' traits and influences the dynamics of whole communities remains a challenge. Using a three-year manipulative community-scale experiment in a temperate forest, we show that plant-associated fungi, and to a lesser extent insect herbivores, reduce seedling recruitment and survival at high adult conspecific density. Plant-associated fungi are primarily responsible for reducing seedling recruitment near conspecific adults in ectomycorrhizal and shade-tolerant species. Insects, in contrast, primarily inhibit seedling recruitment of shade-intolerant species near conspecific adults. Our results suggest that natural enemies drive conspecific density dependence in this temperate forest and that which natural enemies are responsible depends on the mycorrhizal association and shade tolerance of tree species.

2.
Proc Natl Acad Sci U S A ; 115(24): 6237-6242, 2018 06 12.
Artigo em Inglês | MEDLINE | ID: mdl-29848630

RESUMO

The theory of "top-down" ecological regulation predicts that herbivory suppresses plant abundance, biomass, and survival but increases diversity through the disproportionate consumption of dominant species, which inhibits competitive exclusion. To date, these outcomes have been clear in aquatic ecosystems but not on land. We explicate this discrepancy using a meta-analysis of experimental results from 123 native animal exclusions in natural terrestrial ecosystems (623 pairwise comparisons). Consistent with top-down predictions, we found that herbivores significantly reduced plant abundance, biomass, survival, and reproduction (all P < 0.01) and increased species evenness but not richness (P = 0.06 and P = 0.59, respectively). However, when examining patterns in the strength of top-down effects, with few exceptions, we were unable to detect significantly different effect sizes among biomes, based on local site characteristics (climate or productivity) or study characteristics (study duration or exclosure size). The positive effects on diversity were only significant in studies excluding large animals or located in temperate grasslands. The results demonstrate that top-down regulation by herbivores is a pervasive process shaping terrestrial plant communities at the global scale, but its strength is highly site specific and not predicted by basic site conditions. We suggest that including herbivore densities as a covariate in future exclosure studies will facilitate the discovery of unresolved macroecology trends in the strength of herbivore-plant interactions.


Assuntos
Herbivoria/fisiologia , Animais , Biodiversidade , Biomassa , Clima , Ecossistema , Plantas
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