Mismatch between species distribution and climatic niche optima in relation to functional traits

Background:Forecasts of climate change impacts on biodiversity often assume that the current geographical distributions of species match their niche optima.However,empirical evidence has challenged this assumption,suggesting a mismatch.We examine whether the mismatch is related to functional traits along temperature or precipitation gradients.Methods:The observed distributions of 32 tree species in northeast China were evaluated to test this mismatch.Bayesian models were used to estimate the climatic niche optima,i.e.the habitats where the highest species growth and density can be expected.The mismatch is defined as the difference between the actual species occurrence in an assumed niche optimum and the habitat with the highest probability of species occurrence.Species’functional traits were used to explore the mechanisms that may have caused the mismatches.Results:Contrasting these climatic niche optima with the observed species distributions,we found that the distribution-niche optima mismatch had high variability among species based on temperature and precipitation gradients.However,these mismatches depended on functional traits associated with competition and migration lags only in temperature gradients.Conclusions:We conclude that more relevant research is needed in the future to quantify the mismatch between species distribution and climatic niche optima,which may be crucial for future designs of forested landscapes,species conservation and dynamic forecasting of biodiversity under expected climate change.

Multi-scale analysis on species diversity within a 40-ha old-growth temperate forest

In order to better explore the maintenance mechanisms of biodiversity, data collected from a 40-ha undisturbed Pinus forest were applied to the Individual Species-Area Relationship model(ISAR) to determine distribution patterns for species richness. The ecological processes influencing species abundance distribution patterns were assessed by applying the same data set to five models: a LogNormal Model(LNM), a Broken Stick Model(BSM), a Zipf Model(ZM), a Niche Preemption Model(NPM), and a Neutral Model(NM). Each of the five models was used at six different sampling scales(10 m×10 m, 20 m×20 m, 40 m×40 m, 60 m×60 m, 80 m×80 m, and 100 m×100 m). Model outputs showed that:(1) Accumulators and neutral species strongly influenced species diversity, but the relative importance of the two types of species varied across spatial scales.(2) Distribution patterns of species abundance were best explained by the NPM at small scales(10 m-20 m), whereas the NM was the best fit model at large spatial scales.(3) Species richness and abundance distribution patterns appeared to be driven by similar ecological processes. At small scales, the niche theory could be applied to describe species richness and abundance, while at larger scales the neutral theory was more applicable.

Neutral theory in community ecology

One of the central goals of community ecology is to understand the forces that maintain species diversity within communities.The traditional niche-assembly theory asserts that species live together in a community only when they differ from one another in resource uses.But this theory has some difficulties in explaining the diversity often observed in specie-rich communities such as tropical forests.As an alternative to the niche theory,Hubbell and other ecologists introduced a neutral model.Hubbell argues that the number of species in a community is controlled by species extinction and immigration or speciation of new species.Assuming that all individuals of all species in a trophically similar com-munity are ecologically equivalent,Hubbell’s neutral theory predicts two important statistical distributions.One is the asymptotic log-series distribution for the metacommunities under point mutation speciation,and the other is the zero-sum multinomial distribution for both local communities under dispersal limitation and metacommunities under random fission speciation.Unlike the niche-assembly theory,the neutral theory takes similarity in species and individuals as a starting point for investigating species diversity.Based on the fundamental processes of birth,death,dispersal and spe-ciation,the neutral theory provided the first mechanistic explanation of species abundance distribution commonly observed in natural communities.Since the publication of the neutral theory,there has been much discussion about it,pro and con.In this paper,we summarize recent progress in the assumption,prediction and speciation mode of the neutral theory,including progress in the theory itself,tests about the assumption of the theory,prediction and speciation mode at the metacommunity level.We also suggest that the most important task in the future is to bridge the niche-assembly theory and the neutral theory,and to add species differences to the neutral theory and more stochasticity to the niche theory.

Experimental evidence that soil heterogeneity enhances plant diversity during community assembly

Aims Environmental heterogeneity is a primary mechanism explain-ing species coexistence and extant patterns of diversity.Despite strong theoretical support and ample observational evidence,few experimental studies in plant communities have been able to demonstrate a causal link between environmental heterogene-ity and plant diversity.This lack of experimental evidence sug-gests that either fine-scale heterogeneity has weak effects on plant diversity or previous experiments have been unable to effectively manipulate heterogeneity.Here,we utilize a unique soil manipu-lation to test whether fine-scale soil heterogeneity will increase plant richness through species sorting among experimental patch types.Methods This experiment was conducted in the tallgrass prairie region of south-central Kansas,USA.We utilized the inherent variation found in the vertical soil profile,which varied in both biotic and abiotic characteristics,and redistributed these strata into either homoge-neous or heterogeneous spatial arrangements in 2.4×2.4 m plots.After the soil manipulation,34 native prairie species were sown into all plots.We conducted annual censuses at peak biomass to quantify species composition and plant density by species within the experimental communities.Important Findings After 2 years,species richness was significantly higher in heteroge-neous relative to homogeneous plots and this pattern was independ-ent of total plant density.In the heterogeneous plots,13 species had higher establishment in a specific patch type representing one of the three soil strata.Conversely,no species had greater estab-lishment in the mixed stratum,which comprised the homogene-ous plots,relative to the heterogeneous strata.These species sorting patterns suggest that fine-scale heterogeneity creates opportunities for plant establishment due to niche differences,which translates into increased plant diversity at the plot scale.Species richness was more strongly related to plant density among patches comprising homogenous plots-where fine-scale heterogeneity was minimized,but weak in heterogeneous plots.This pattern is consistent with the idea that richness-density relationships dominate when neutral pro-cesses are important but are weak when niche processes operate.Unlike many previous attempts,our results provide clear,experi-mental evidence that fine-scale soil heterogeneity increases species richness through species sorting during community assembly.