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1.
Ecol Lett ; 23(1): 160-171, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31698546

RESUMO

Among the local processes that determine species diversity in ecological communities, fluctuation-dependent mechanisms that are mediated by temporal variability in the abundances of species populations have received significant attention. Higher temporal variability in the abundances of species populations can increase the strength of temporal niche partitioning but can also increase the risk of species extinctions, such that the net effect on species coexistence is not clear. We quantified this temporal population variability for tree species in 21 large forest plots and found much greater variability for higher latitude plots with fewer tree species. A fitted mechanistic model showed that among the forest plots, the net effect of temporal population variability on tree species coexistence was usually negative, but sometimes positive or negligible. Therefore, our results suggest that temporal variability in the abundances of species populations has no clear negative or positive contribution to the latitudinal gradient in tree species richness.


Assuntos
Biodiversidade , Árvores , Biota , Características de Residência
2.
Nat Ecol Evol ; 2(9): 1436-1442, 2018 09.
Artigo em Inglês | MEDLINE | ID: mdl-30104751

RESUMO

Survival rates of large trees determine forest biomass dynamics. Survival rates of small trees have been linked to mechanisms that maintain biodiversity across tropical forests. How species survival rates change with size offers insight into the links between biodiversity and ecosystem function across tropical forests. We tested patterns of size-dependent tree survival across the tropics using data from 1,781 species and over 2 million individuals to assess whether tropical forests can be characterized by size-dependent life-history survival strategies. We found that species were classifiable into four 'survival modes' that explain life-history variation that shapes carbon cycling and the relative abundance within forests. Frequently collected functional traits, such as wood density, leaf mass per area and seed mass, were not generally predictive of the survival modes of species. Mean annual temperature and cumulative water deficit predicted the proportion of biomass of survival modes, indicating important links between evolutionary strategies, climate and carbon cycling. The application of survival modes in demographic simulations predicted biomass change across forest sites. Our results reveal globally identifiable size-dependent survival strategies that differ across diverse systems in a consistent way. The abundance of survival modes and interaction with climate ultimately determine forest structure, carbon storage in biomass and future forest trajectories.


Assuntos
Árvores , Clima Tropical , Biomassa , Carbono , Folhas de Planta , Sementes , Temperatura Ambiente , Água
3.
Science ; 360(6391)2018 05 25.
Artigo em Inglês | MEDLINE | ID: mdl-29798853

RESUMO

Hülsmann and Hartig suggest that ecological mechanisms other than specialized natural enemies or intraspecific competition contribute to our estimates of conspecific negative density dependence (CNDD). To address their concern, we show that our results are not the result of a methodological artifact and present a null-model analysis that demonstrates that our original findings-(i) stronger CNDD at tropical relative to temperate latitudes and (ii) a latitudinal shift in the relationship between CNDD and species abundance-persist even after controlling for other processes that might influence spatial relationships between adults and recruits.


Assuntos
Biodiversidade , Árvores , Densidade Demográfica , Plântula
4.
Science ; 360(6391)2018 05 25.
Artigo em Inglês | MEDLINE | ID: mdl-29798855

RESUMO

Chisholm and Fung claim that our method of estimating conspecific negative density dependence (CNDD) in recruitment is systematically biased, and present an alternative method that shows no latitudinal pattern in CNDD. We demonstrate that their approach produces strongly biased estimates of CNDD, explaining why they do not detect a latitudinal pattern. We also address their methodological concerns using an alternative distance-weighted approach, which supports our original findings of a latitudinal gradient in CNDD and a latitudinal shift in the relationship between CNDD and species abundance.


Assuntos
Biodiversidade , Árvores , Ecossistema , Plântula
5.
R Soc Open Sci ; 5(9): 181168, 2018 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-30839691

RESUMO

The relationship between ß-diversity and latitude still remains to be a core question in ecology because of the lack of consensus between studies. One hypothesis for the lack of consensus between studies is that spatial scale changes the relationship between latitude and ß-diversity. Here, we test this hypothesis using tree data from 15 large-scale forest plots (greater than or equal to 15 ha, diameter at breast height ≥ 1 cm) across a latitudinal gradient (3-30o) in the Asia-Pacific region. We found that the observed ß-diversity decreased with increasing latitude when sampling local tree communities at small spatial scale (grain size ≤0.1 ha), but the observed ß-diversity did not change with latitude when sampling at large spatial scales (greater than or equal to 0.25 ha). Differences in latitudinal ß-diversity gradients across spatial scales were caused by pooled species richness (γ-diversity), which influenced observed ß-diversity values at small spatial scales, but not at large spatial scales. Therefore, spatial scale changes the relationship between ß-diversity, γ-diversity and latitude, and improving sample representativeness avoids the γ-dependence of ß-diversity.

6.
Science ; 356(6345): 1389-1392, 2017 06 30.
Artigo em Inglês | MEDLINE | ID: mdl-28663501

RESUMO

Theory predicts that higher biodiversity in the tropics is maintained by specialized interactions among plants and their natural enemies that result in conspecific negative density dependence (CNDD). By using more than 3000 species and nearly 2.4 million trees across 24 forest plots worldwide, we show that global patterns in tree species diversity reflect not only stronger CNDD at tropical versus temperate latitudes but also a latitudinal shift in the relationship between CNDD and species abundance. CNDD was stronger for rare species at tropical versus temperate latitudes, potentially causing the persistence of greater numbers of rare species in the tropics. Our study reveals fundamental differences in the nature of local-scale biotic interactions that contribute to the maintenance of species diversity across temperate and tropical communities.


Assuntos
Biodiversidade , Árvores/classificação , Antibiose , Ecossistema , Florestas , Geografia , Modelos Biológicos , Árvores/fisiologia , Clima Tropical
7.
Ecol Lett ; 17(7): 855-65, 2014 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-24805976

RESUMO

Long-term surveys of entire communities of species are needed to measure fluctuations in natural populations and elucidate the mechanisms driving population dynamics and community assembly. We analysed changes in abundance of over 4000 tree species in 12 forests across the world over periods of 6-28 years. Abundance fluctuations in all forests are large and consistent with population dynamics models in which temporal environmental variance plays a central role. At some sites we identify clear environmental drivers, such as fire and drought, that could underlie these patterns, but at other sites there is a need for further research to identify drivers. In addition, cross-site comparisons showed that abundance fluctuations were smaller at species-rich sites, consistent with the idea that stable environmental conditions promote higher diversity. Much community ecology theory emphasises demographic variance and niche stabilisation; we encourage the development of theory in which temporal environmental variance plays a central role.


Assuntos
Modelos Biológicos , Árvores/fisiologia , Meio Ambiente , Dinâmica Populacional , Fatores de Tempo
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