Aims We aim to quantify the relative importance of various endogenous and exogenous processes influencing the spatial distribution of the individuals of plant species at different temporal and spatial scales in a species-rich and high-cover meadow in the eastern tibetan Plateau.Methods We calculated green’s index of dispersion to infer the spatial dis-tribution patterns of 73 herbaceous species at two scales(0.25 and 1.0 m2).We constructed a series of generalized linear models to test the hypotheses that different species traits such as mean plant stem density,per capita dry biomass,maximum plant height and mean seed mass contribute to their spatial distribution.We used the first principal component of soil C,N and P to explain abundance vari-ation across quadrats and sub-plots.Important Findingsthe individuals of the species studied were highly spatially aggregated.at both spatial scales,biomass and stem density explained the most variation in aggregation,but there was no evidence for an effect of mean seed mass on aggregation intensity.the effects of soil carbon,nitrogen and phosphorus at different depths affected plant abundance mostly at the broader spatial scale.our results demonstrate that self-thinning and habitat heterogeneity all contribute to determine the spatial aggregation patterns of plant individuals in alpine meadow vegetation in the eastern tibetan Plateau.
Aims The neutral theory of biodiversity has been criticized for being fragile with even slight deviations from its basic assumption of equal fitness among species.In response to this criticism,Hubbell((2001)The Unified Neutral Theory of Biodiversity and Biogeography.Princeton,NJ:Princeton University Press)proposed that competitive exclusion can be infinitely delayed by dispersal and recruitment limitation,thus making species effectively neutral.But the theoretical foundation for this claim still remains unclear and controversial,and the effects of dispersal and recruitment limitation are often confounded,especially in field studies.This study aims to provide an affirmative theoretical answer to the question of whether dispersal limitation and recruitment limitation can separately or jointly overwhelm the effects of fitness differences among species and lead to neutral community dynamics.Methods Computer simulations were used to investigate the effects of dispersal and recruitment limitation on delaying competitive exclusion in a homogeneous habitat in a spatially explicit context.Important Findings We found that even a slight competitive asymmetry would require extremely strong dispersal and recruitment limitation for neutrality to emerge.Most importantly,when the effects of dispersal and recruitment limitation were set apart,it is found that recruitment limitation is more effective in delaying competitive exclusion,whereas dispersal limitation tends to have a stronger impact on the general shape of both species abundance distributions and species–area relationships.
Aims The process of facilitation,where a species increases the survival,growth,and fitness of another species,is becoming increasingly recognized as a critical factor in shaping the structure of plant communities.This process is particularly important in stressful environments.Yet few studies have attempted to incorporate positive interactions into community ecological theories such as the neutral theory of biodiversity.Here,we use an equalizing trade-off model as a foundation to study the potential impact of facilitation on species richness and community temporal turnover.Methods Based on a spatially explicit birth–death trade-off model,we assume that the occurrence of facilitation is dependent on the presence of interspecific neighbours.We further propose that the realized birth rate for a given individual subject to facilitation is proportional to the number of interspecific neighbours within its neighbourhood.Thus,in our model,the individuals of rare species will benefit more from the existence of heterospecific individuals than common species.Important Findings As the facilitative coefficient increased,the species richness for simulated communities at the dynamically stochastic equilibrium was also increasing.Simulations also demonstrated that facilitation could increase the replacement of species through time:communities with facilitation become more dissimilar(i.e.have smaller Bray–Curtis similarity values)than communities without or with a lower degree of facilitation after the same time interval.Facilitation from interspecific neighbours on rare species increased their population sizes and consequently made them less prone to extinction,thus enhancing species richness.Meanwhile,in a saturated community,with the increase of species richness,mean population size of entire communities decreased,making species more prone to extinction on average,and thus increased the community temporal turnover.Our results suggest that future experimental work on the effect of facilitation on community-level properties
