Niche Preemption Model Research Articles

Species-Abundance Models for the Early Postfire Succession of Subalpine Shrub Grassland

Fire is one of the principal factors influencing subalpine ecosystem succession. Species numbers and plant compositions are used to determine postfire disturbance, vegetation, structural change, and succession. Ecologists also integrate species diversity and mathematical models to enable researchers to obtain increasingly detailed insights into habitats during post-disturbance restoration processes. This study employed five species-abundance models, namely the niche preemption model, the broken-stick model, the log-normal model, the Zipf model, and the Zipf–Mandelbrot model, to perform fitting analysis on the abundance data of postfire species coverage in shrub grasslands near 369 Hut at Xue Mountain in Shei-Pa National Park, Taiwan. We performed the logarithmic transformation on plant-coverage areas for each period of postfire shrub-grassland succession, and then, based on histograms drawn for species–coverage distribution modes, the test results consistently showed normal distributions (p < 0.05). Species-coverage histograms measuring various periods showed that there were comparatively higher numbers of common species during postfire succession and that the numbers of rare species progressively increased. The fitting results of the five species-abundance models showed that although the most suitable abundance models for each period of postfire succession varied, the majority of these periods demonstrated decent fitting with respect to the Zipf–Mandelbrot model. These findings showed that fuel consumption provided nutrients in a manner that facilitated postfire regeneration. Moreover, dominant species, such as Yushania niitakayamensis, and Miscanthus transmorrisonensis, did not fully occupy growing spaces and resource availabilities; consequently, seeded species were able to grow.

Species-Abundance Distribution Patterns of Plant Communities in the Gurbantünggüt Desert, China

It is important to study the species-abundance distribution pattern in a community to reveal the mechanism of community assembly. Six abundance models (log-normal distribution model, Zipf model, Zipf–Mandelbrot model, broken stick model, niche preemption model, and Volkov model) were used to fit the species-abundance distribution pattern of six scales (10 m × 10 m, 20 m × 20 m, 40 m ×40 m, 60 m × 60 m, 80 m × 80 m, 100 m × 100 m) in fixed, semifixed, and mobile sand dunes in the Gurbantünggüt Desert, respectively. The best-fitting model was determined using the K-S test, the Chi-square test, and the Akaike information criterion. The results showed that the values of soil salinity, nutrients, water content, Shannon–Wiener diversity index (H′), Pielou evenness index (E), and Simpson index (D) were ranked in all three habitats as fixed dunes > semifixed dunes > mobile dunes. The rank curves span a narrow range on the horizontal axis at scales of 10 m × 10 m and 20 m × 20 m, and species richness is minimal. As the scale increases, the span range of the curve gradually increases, and species richness becomes higher at scales of 40 m × 40 m, 60 m × 60 m, 80 m × 80 m, and 100 m × 100 m. At the 10 m × 10 m and 20 m × 20 m scales, the broken stick model fits best in the three dune habitats. At the 40 m × 40 m and 60 m × 60 m scales, the niche preemption model fits best in the three dune habitats. At the 80 m × 80 m and 100 m × 100 m scales, the Volkov neutral model fits best in the fixed and semifixed dune habitats, and the niche preemption model fits best in the mobile dune habitats. In fixed, semifixed, and mobile dunes, both niche and neutral processes played important roles in community construction, reflecting the manifestation of the community niche-neutral continuum.

Maximum‐likelihood estimation of the geometric niche preemption model

AbstractThe geometric series or niche preemption model is an elementary ecological model in biodiversity studies. The preemption parameter of this model is usually estimated by regression or iteratively by using May's equation. This article proposes a maximum‐likelihood estimator for the niche preemption model, assuming a known number of species and multinomial sampling. A simulation study shows that the maximum‐likelihood estimator outperforms the classical estimators in this context in terms of bias and precision. We obtain the distribution of the maximum‐likelihood estimator and use it to obtain confidence intervals for the preemption parameter and to develop a preemption t test that can address the hypothesis of equal geometric decay in two samples. We illustrate the use of the new estimator with some empirical data sets taken from the literature and provide software for its use.

Species-abundance distribution patterns of Quercus aliena var. acutiserrata forest in Taibai Mountain, China.

The statistical model (log-normal model), niche models (Zipf model, broken stick mo-del, niche preemption model), and neutral model were used to fit the species-abundance distribution patterns based on the measurements of environmental factors and inventory data of trees with DBH≥1 cm in a 1.5 hm2 plot in the primary forest (PF) and a 1.5 hm2 plot in the secondary forest (SF). The results showed that species-abundance distribution was affected by habitat heterogeneity in Q. aliena var. acutiserrata forest. Topography had a predominant impact on the species-abundance distribution in PF. Species distribution was affected by both neutral and niche processes, with neutral process having a less prominent effect in large convexity habitats. While the neutral model was rejected by the K-S and Chi-square test in low convexity habitats, the species-abundance distribution satisfied the assumption of niche theory. Niche process and neutral process were equally important in the community in areas with steep slopes, while niche differentiation was the dominant in flat areas. In SF, the main factors affecting species distribution were soil nutrients. The niche process was the mainly ecological process affected species-abundance distribution in habitats with high soil available phosphorus, while the niche and neutral processes existed simultaneously in habitats with low soil phosphorus availability. There was a significant scale effect on the species-abundance distribution pattern of Q. aliena var. acutiserrata forests in Taibai Mountain. The niche and neutral processes could protect the species-abundance distribution at the 20 m×20 m scale in PF, while the niche process could explain the species-abundance distribution at the 40 m×40 m and 70 m×70 m scales. The niche and neutral processes combined acted on the species abundance distribution at the 20 m×20 m, 40 m×40 m and 70 m×70 m scales in SF, with niche process being more important than neutral process. Moreover, besides the scale and habitat heterogeneity, the species-abundance distribution patterns of Q. aliena var. acutiserrata forests differed significantly between primary forest and secondary forest under anthropogenic disturbance.

Species abundance distribution models of Toona ciliata communities in Hubei Province, China

The study of plant species abundance distribution (SAD) in natural communities is of considerable importance to understand the processes and ecological rules of community assembly. With the distribution of tree, shrub and herb layers of eight natural communities of Toona ciliata as research targets, three different ecological niche models were used: broken stick model, overlapping niche model and niche preemption model, as well as three statistical models: log-series distribution model, log-normal distribution model and Weibull distribution model, to fit SAD of the different vegetation layers based on data collected. Goodness-of-fit was compared with Chi square test, Kolmogorov–Smirnov (K–S) test and Akaike Information Criterion (AIC). The results show: (1) based on the criteria of the lowest AIC value, Chi square value and K–S value with no significant difference (p > 0.05) between theoretic and observed SADs. The suitability and goodness-of-fit of the broken stick model was the best of three ecological niche models. The log-series distribution model did not accept the fitted results of most vegetation layers and had the lowest goodness-of-fit. The Weibull distribution model had the best goodness-of-fit for SADs. Overall, the statistical SADs performed better than the ecological ones. (2) T. ciliata was the dominant species in all the communities; species richness and diversity of herbs were the highest of the vegetation layers, while the diversities of the tree layers were slightly higher than the shrub layers; there were fewer common species and more rare species in the eight communities. The herb layers had the highest community evenness, followed by the shrub and the tree layers. Due to the complexity and habitat diversity of the different T. ciliata communities, comprehensive analyses of a variety of SADs and tests for optimal models together with management, are practical steps to enhance understanding of ecological processes and mechanisms of T. ciliata communities, to detect disturbances, and to facilitate biodiversity and species conservation.

Species Abundance Distribution Patterns of a Toona ciliata Community in Xingdoushan Nature Reserve

With the goal of model fitting species abundance distribution patterns of the tree, shrub and herb layers of the natural Toona ciliata community in Xingdoushan Nature Reserve, Enshi Autonomous Prefecture, Hubei Province, we used the data collected from the field survey and employed different ecological niche models. The models tested were the broken stick model (BSM), the overlapping niche model (ONM) and the niche preemption model (NPM), as well as three statistic models, the log-series distribution model (LSD), the log-normal distribution model (LND) and the Weibull distribution model (WDM). To determine the fitted model most suitable to each layer, the fitting effects were judged by criteria of the lowest value of Akaike Information Criterion (AIC), Chi-square and the K-S values with no significant difference (P>0.05) between the theoretical predictions and observed species abundance distribution values. The result showed: (1) The fitting suitability and goodness of fit of the tree, shrub and herb layers by using the three ecological niche models were ranked as: NPM>BSM>ONM. Of the three statistical models, by accepting the fitting results of the three layers, WDM was the best fitting model, followed by LND. By rejecting the fitting tests of the herb layer, LSD had the worst fitting effect. The goodness of the statistical models was ranked as: WDM>LND>LSD. In general, the statistical models had better fitting results than the ecological models. (2) T. ciliata was the dominant species of the tree layer. The species richness and diversity of the herb layer were much higher than those of either the tree layer or the shrub layer. The species richness and diversity of the shrub layer were slightly higher than those of the tree layer. The community evenness accorded to the following order: herb>shrub>tree. Considering the fitting results of the different layers, different ecological niche models or statistical models with optimal goodness of fit and ecological significance can be given priority to in studying the species abundance distribution patterns of T. ciliata communities.

Fitting competing models and evaluation of model parameters of the abundance distribution of the land snail Vallonia pulchella (Pulmonata, Valloniidae)

This paper summarizes the mechanisms behind the patterning of the intra-population abundance distribution of the land snail Vallonia pulchella (Müller, 1774). The molluscs were collected in recultivated soil formed on red-brown clays (Pokrov, Ukraine). Data obtained in this study reveal that V. pulchella population abundance ranges from 1 to 13 individuals per 100 g of soil sample. To obtain estimates of the mean, three models were used: the model of the arithmetic mean, the Poisson model and a log-normal model. The arithmetic mean of the occurrence of this species during the study period was 1.84 individuals/sample. Estimation of the average number of molluscs in one sample calculated using the Poisson model is lower and equals 1.40 individuals/sample. The distribution of the number of individuals in a population was described by the graphics "rank – abundance". The individual sample plot sites with molluscs may be regarded as equivalents of individual species in the community. For the analysis, the following models were used: broken sticks model, niche preemption model, log-normal model, Zipf model, and Zipf-Mandelbrot model. Applying the log-normal distribution gives a lower estimate of the mean density at 1.28 individuals/sample. Median value and mode is estimated at 1.00 individuals/sample. The Zipf-Mandelbrot model was shown as the most adequate to describe distribution of the V. pulchella population within the study area. The Zipf-Mandelbrot model belongs to the family of so-called non-Gaussian distributions. This means that the sample statistics do not possess asymptotic properties and by increasing the sample size, they tend to infinity, and are not close to the values of the general population. Therefore, the average value of the random variable that describes the non-Gaussian distribution has no statistical meaning. From an environmental point of view, this means that within the study area the capacity of the habitat is large, and for some combination of environmental conditions the rapid growth of the abundance of a given species is possible.

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 Log-Normal 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.

Diversity maintenance mechanism changes with vegetation type and the community size in a tropical nature reserve

AbstractSpecies‐abundance distribution (SAD) is an essential tool to explain the mechanism of diversity maintenance in ecological communities. Most of the studies on diversity maintenance in a specific forest dynamics plot just consider stems with a certain minimum size class to include into the tree community to be examined. However, the species in the juvenile stage are easily disturbed by a variety of factors; here, we define the minimum stem size to tag trees in a community as the community size (DBHmintag), which implies that the communities with different minimum diameter at breast height (DBH) sizes to tag trees are tree assemblages containing tree populations of different minimum DBH. We used data from 17 1‐ha forest dynamics plots across six old‐growth forest types in a tropical nature reserve to explore diversity maintenance mechanism by SAD curves (at three levels of DBHmintag) fitting to neutral model and niche preemption model. We found that the SADs of the two zonal vegetation types (tropical montane rain forest and tropical lowland rain forest) were best fitted by neutral model at each level of DBHmintag; meanwhile, the best fitted models for the four azonal vegetation types (tropical coniferous forest, tropical deciduous monsoon rain forest, tropical montane evergreen forest, and tropical montane dwarf forest) varied with DBHmintag levels, for communities with DBHmintag ≥ 1 cm and DBHmintag ≥ 5 cm, the fitting effect of neutral model was better than niche preemption model's for the forest dynamics plots in the four azonal vegetation types, and for communities with DBHmintag ≥ 10 cm, the four azonal vegetation types were all best fitted by the niche model. Our results suggest that species diversity maintenance mechanisms of the two zonal vegetation types derived from the neutral model increased the predictive accuracy at each level of DBHmintag, and meanwhile, the four azonal vegetation types derived from the neutral model increased the predictive accuracy at smaller community size; however, with the increase in DBHmintag, these communities derived from the niche theory model increased the predictive accuracy. Habitat heterogeneity might be the major constraints in determining the neutral or niche process for diversity maintenance of a specific forest community.

Distribution of species abundance of evergreen and deciduous woody plants in the evergreen broad-leaved forests at Tiantong, Zhejiang

Species abundance distribution (SAD) delineates abundance of all species sampled within a community. As one major stepping stone in understanding the community, the generation mechanisms of SAD have attracted much attention. Evergreen and deciduous plants are two types of species with distinct phenological traits and growth strategies. They widely coexist in evergreen broad-leaved forests (EBLFs). Compared to deciduous plants, evergreen species have slightly lower species richness but substantially higher abundance and basal area in the 20 ha EBLF plot at Tiantong. This study independently analyzing their SAD characteristics provided a new perspective on the understanding of species diversity maintenance in EBLFs. Therefore, in order to compare SADs and determine reasons for differences, an empirical cumulative distri·研究报告· 630 生 物 多 样 性 Biodiversity Science 第 24 卷 bution function (ECDF) was utilized to describe the SADs of evergreen and deciduous trees in Tiantong plot. A Kolmogorov-Smirnov test (K-S test) was employed to detect the significance of these differences. Additionally, three types of models, including statistic model (log-normal model and log-series model), niche model (broken-stick model and niche preemption model) and neutral theory model (metacommunity zero-sum multinomial distribution model and Volkov model), were used to fit the SAD of each lifeform. The K-S test and AIC values were applied to test the goodness of fit for each model. We found that the differences in SAD between the two life forms were not significant based on the results of the K-S test. Among the three types of models, the neutral theory model was the best fitting model, and the niche model was the poorest fit. Thus we conclude that evergreen and deciduous trees had similar SAD patterns, although they differed in species richness and abundance. However, the model fitting results were found to be a necessary but insufficient condition in understanding the maintenance mechanism of biodiversity. Hence we may only preliminarily conclude that neutral processes had a major effect on the generation of biodiversity patterns of both evergreen and deciduous trees, whereas the possible contributions made by other processes, such as niche differentiations, could not be excluded and measured by this method.

Community structure during a 27-year study of the macroinvertebrate fauna of a chemically unstable lake

Data are given on summer temperatures, conductivity, vegetation cover and the quantitative species composition of macroinvertebrates in each of the years 1968–1994. It is demonstrated that species composition, species richness and numbers of individuals varied from year to year. Community structure is expressed by species richness, species diversity, equitability and rank-abundance graphs. Species richness showed a highly significant negative correlation with conductivity and a highly significant positive correlation with vegetation cover. However, the highest significance found was with the sum of vegetation cover and the reciprocal of conductivity. Species diversity and equitability showed patterns of minima coinciding with summer temperature maxima. Rank-abundance graphs remained relatively constant throughout the study period and were used to demonstrate that a niche pre-emption model, with modification to accomodate a power graph, provided an adequate model for all years. This model suggests a deterministic explanation, but with fluctuations dependent upon random or cyclical environmental factors.

Population dynamics and community structure of fish in the mangroves of Pagbilao, Philippines

128 fish species were recorded for the mangroves of Pagbilao. Aspects of the population dynamics of the common species, Ambassis kopsi, Secutor ruconius. Leiognathus brevirostris and Prosopodasys gogorzae were investigated. Growth coefficients varied from 0.41 to 1.2. Mortality in the mangroves was high, and most species there breed once per year.Species diversity (H') of the community ranged from 1.05 to 2.9. It was influenced by evenness rather than by species richness. Species abundance gave a log normal distribution, except during the typhoon, when it fitted the niche preemption model.

Pinus banksiana forests of the Fort Vermilion area, northern Alberta

Thirteen undisturbed Pinus banksiana Lamb. forests on Eutric Brunisols, derived from dune sands in the lower Peace River Valley, were analyzed quantitatively. Fort Vermilion has a dry, continental, subarctic macroclimate. Stands varied in age from 15 to 97 years, with tree volume increasing from 19 in younger to 193 m3 ha−1 in older stands. Cover of trees averaged 49%, shrubs 7%, dwarf shrubs 27%, forbs 6%, graminoids 1%, feather mosses 4%, caribou lichens 2%. Based on recurrently dominant species of well-developed vascular strata and growth-form guilds, a PINUS BANKSIANA/ROSA ACICULARIS/ARCTOSTAPHYLOS UVA-URSI – LATHYRUS OCHROLEUCUS community type is postulated for xeric sandhill habitats. This type is probably seral to a Picea glauca (Moench) Voss climax, but frequent fires prevent this. Plant succession during the sampled 80-year age interval is characterized by (i) increasing dwarf shrub, forb, and graminoid cover, (ii) stabilization of vascular species richness at ca. 35 species per stand, (iii) decline and stabilization of Simpson's dominance index, (iv) increasing Shannon–Weaver diversity, and (v) progressively gentler dominance–diversity slope angles. The niche preemption model (geometric series) of species structure fits younger and older better than middle-aged stands, based on goodness of fit of regression lines (r2) to dominance–diversity curves.