Niches versus neutrality: uncovering the drivers of diversity in a species-rich community.
TL;DR: This work provides the first empirical evidence that a niche-neutral model can explain niche space occupancy pattern in a natural species-rich community and suggests this class of model may be a useful hypothesis for the generation and maintenance of species diversity in other size-structured communities.
Abstract: Ecological models suggest that high diversity can be generated by purely niche-based, purely neutral or by a mixture of niche-based and neutral ecological processes. Here, we compare the degree to which four contrasting hypotheses for coexistence, ranging from niche-based to neutral, explain species richness along a body mass niche axis. We derive predictions from these hypotheses and confront them with species body-mass patterns in a highly sampled marine phytoplankton community. We find that these patterns are consistent only with a mechanism that combines niche and neutral processes, such as the emergent neutrality mechanism. In this work, we provide the first empirical evidence that a niche-neutral model can explain niche space occupancy pattern in a natural species-rich community. We suggest this class of model may be a useful hypothesis for the generation and maintenance of species diversity in other size-structured communities.
Citations
More filters
TL;DR: Volume, mucilage, flagella and siliceous exoskeleton are found to be the most important traits to explain the niche centres in phytoplankton communities, and the trait-modulated Gaussian logistic model is proposed in which the niche parameters are made linearly dependent on species traits.
Abstract: In this paper we attempt to explain observed niche differences among species (i.e. differences in their distribution along environmental gradients) by differences in trait values (e.g. volume) in phytoplankton communities. For this, we propose the trait-modulated Gaussian logistic model in which the niche parameters (optimum, tolerance and maximum) are made linearly dependent on species traits. The model is fitted to data in the Bayesian framework using OpenBUGS (Bayesian inference Using Gibbs Sampling) to identify according to which environmental variables there is niche differentiation among species and traits. We illustrate the method with phytoplankton community data of 203 lakes located within four climate zones and associated measurements on 11 environmental variables and six morphological species traits of 60 species. Temperature and chlorophyll-a (with opposite signs) described well the niche structure of all species. Results showed that about 25% of the variance in the niche centres with respect to chlorophyll-a were accounted for by traits, whereas niche width and maximum could not be predicted by traits. Volume, mucilage, flagella and siliceous exoskeleton are found to be the most important traits to explain the niche centres. Species were clustered in two groups with different niches structures, group 1 high temperature-low chlorophyll-a species and group 2 low temperature-high chlorophyll-a species. Compared to group 2, species in group 1 had larger volume but lower surface area, had more often flagella but neither mucilage nor siliceous exoskeleton. These results might help in understanding the effect of environmental changes on phytoplankton community. The proposed method, therefore, can also apply to other aquatic or terrestrial communities for which individual traits and environmental conditioning factors are available.
28 citations
Cites background from "Niches versus neutrality: uncoverin..."
...Now-a-days new studies are recognizing this theory as potential explanation [93,94] but still more research is needed....
[...]
TL;DR: The results support the hypothesis of higher functional redundancy in warmer areas and the relevance of increasing herbivory in colder regions as a main driving process of latitudinal patterns.
Abstract: It has been suggested that the overwhelming number of species in tropical ecosystems consist largely of "neutral" and functionally equivalent species. In phytoplankton, differences in functionality have been shown to be clearly distinguishable from morphological traits. Here we examine whether the increase in species towards the tropics goes together with an increase in functional richness or not. We analyse the latitudinal distribution of phytoplankton morphology-based functional groups (MBFG), the within-group richness and community morphological traits in 83 shallow lakes across South America (5-55°S). We further looked into explaining environmental variables. Despite the increment in species richness towards the (sub)tropics, the average number of MBFG remained constant. Furthermore, size average and variance decreased towards warmer regions. In warm lakes, phytoplankton communities were species rich but redundant in terms of belonging to a MBFG. Increasing species richness only translated into increasing number of rare species in some of the MBFG. In contrast, cold lakes were species poor but less redundant (i.e. essential to maintain the number of MBFG) and had a higher morphological variability. Our results support the hypothesis of higher functional redundancy in warmer areas and the relevance of increasing herbivory in colder regions as a main driving process of latitudinal patterns.
27 citations
Cites background from "Niches versus neutrality: uncoverin..."
...A composite of niche-based and neutral ecological processes (Scheffer and van Nes, 2006; Vergnon et al., 2009; Segura et al., 2013) might be structuring phytoplankton communities along the latitudinal gradient and promoting species co-occurrence or avoidance....
[...]
TL;DR: It is concluded that stochastic and deterministic processes formed ends of a continuum from grazing to fertilization when grazers were excluded in an alpine meadow plant community, and the importance of niche differences between species in structuring grassland communities increased with increasing fertilization and decreased with grazing.
Abstract: To predict the consequences of environmental change on the structure and composition of communities, it is necessary to also understand the regional drivers underlying the structuring of these communities. Here, we have taken a hypothesis-based approach to test the relative importance of niche versus neutral processes using niche overlap, species traits and population asynchrony in two crossed treatments of fertilization and grazing in an alpine meadow community. Our results suggested that the observed species biomass overlap was not significantly different between treatments of grazing, grazing × fertilization and grazer exclusion. In contrast, the species biomass overlap was higher than expected in fertilization treatments when grazers were excluded. On the one hand, we found no relationship between species traits and relative abundance in grazing, grazing × fertilization and grazer-exclusion treatments; on the other hand, mechanistic trait-based theory could be used to predict species relative abundance patterns in fertilization treatments when grazers were excluded. From grazing to fertilization, when grazers were excluded, there was a slight increase in species synchrony, which indicated that the complementary dynamic of species gradually changed from complete independence into synchronously fluctuating with increasing fertilization. Based on the above results, we concluded that stochastic and deterministic processes formed ends of a continuum from grazing to fertilization when grazers were excluded in an alpine meadow plant community, and the importance of niche differences between species in structuring grassland communities increased with increasing fertilization and decreased with grazing.
27 citations
Cites background from "Niches versus neutrality: uncoverin..."
...where IObs is observed species biomass overlap, S is species richness in the community, Iij is the distance between the positions of species i and j on the species biomass axis and Pi and Pj represent the biomass of species i and j, respectively (Vergnon et al. 2009)....
[...]
...…¼ XS 1 i¼1 X j¼iþ1 IijPiPj ð1Þ where IObs is observed species biomass overlap, S is species richness in the community, Iij is the distance between the positions of species i and j on the species biomass axis and Pi and Pj represent the biomass of species i and j, respectively (Vergnon et al. 2009)....
[...]
...After half a century of research, it is still not understood how species richness in communities is maintained (Vergnon et al. 2009)....
[...]
TL;DR: In exploring the occurrence of 59 taxa within the dipteran family Chironomidae in relation to key-environmental variables in alpine and sub-alpine streams, it was showed that sediment load, water temperature, periphyton density, and fine particulate organic matter mostly explain assemblage structures.
Abstract: Macroinvertebrates are widely used as indicators to detect and assess anthropogenic impacts on freshwater ecosystems. However, despite being considered useful in indicating effects of environmental change in alpine catchments, little is known about species preferences for local conditions in such environments. In exploring the occurrence of 59 taxa within the dipteran family Chironomidae in relation to key-environmental variables in alpine and sub-alpine streams, we showed that sediment load, water temperature, periphyton density, and fine particulate organic matter mostly explain assemblage structures. Two-way-cluster analyses identified stream-type specific assemblages, indicator value analysis defined indicator species for glacial and non-glacial streams, and weighted averaging regression models confined preferences for local environmental conditions by summing their optima and tolerance widths regarding environmental key factors. The definition of habitat requirements identified stenoecious taxa with preferences for high and low values of respective variables thus identified most suitable indicators for future studies. Our work reveals manifold preferences within the dominant benthic invertebrate family, underlines their enormous potential for monitoring purposes, and is a step forward in better understanding ecosystem properties and biodiversity. Fundamental requirements for these kinds of indicative traits, essential to understand cause–effect relationships in environmental change issues, are a robust taxonomy and a comprehensive set of physical and chemical data.
27 citations
TL;DR: Re reef fish community reassembly after a catastrophic coral mortality in a relatively unfished archipelago is tracked, and the stochastic model underlying MacArthur and Wilson's Island Biogeography Theory is revisited, with a simple extension to account for trophic identity.
Abstract: Since Gleason and Clements, our understanding of community dynamics has been influenced by theories emphasising either dispersal or niche assembly as central to community structuring. Determining the relative importance of these processes in structuring real-world communities remains a challenge. We tracked reef fish community reassembly after a catastrophic coral mortality in a relatively unfished archipelago. We revisited the stochastic model underlying MacArthur and Wilson's Island Biogeography Theory, with a simple extension to account for trophic identity. Colonisation and extinction rates calculated from decadal presence-absence data based on (1) species neutrality, (2) trophic identity and (3) site-specificity were used to model post-disturbance reassembly, and compared with empirical observations. Results indicate that species neutrality holds within trophic guilds, and trophic identity significantly increases overall model performance. Strikingly, extinction rates increased clearly with trophic position, indicating that fish communities may be inherently susceptible to trophic downgrading even without targeted fishing of top predators.
26 citations
References
More filters
Book•
30 May 2017
TL;DR: In this article, a simple linear model is proposed to describe the geometry of linear models, and a general linear model specification in R is presented. But the theory of linear model theory is not discussed.
Abstract: LINEAR MODELS A simple linear model Linear models in general The theory of linear models The geometry of linear modelling Practical linear models Practical modelling with factors General linear model specification in R Further linear modelling theory Exercises GENERALIZED LINEAR MODELS The theory of GLMs Geometry of GLMs GLMs with R Likelihood Exercises INTRODUCING GAMS Introduction Univariate smooth functions Additive models Generalized additive models Summary Exercises SOME GAM THEORY Smoothing bases Setting up GAMs as penalized GLMs Justifying P-IRLS Degrees of freedom and residual variance estimation Smoothing Parameter Estimation Criteria Numerical GCV/UBRE: performance iteration Numerical GCV/UBRE optimization by outer iteration Distributional results Confidence interval performance Further GAM theory Other approaches to GAMs Exercises GAMs IN PRACTICE: mgcv Cherry trees again Brain imaging example Air pollution in Chicago example Mackerel egg survey example Portuguese larks example Other packages Exercises MIXED MODELS and GAMMs Mixed models for balanced data Linear mixed models in general Linear mixed models in R Generalized linear mixed models GLMMs with R Generalized additive mixed models GAMMs with R Exercises APPENDICES A Some matrix algebra B Solutions to exercises Bibliography Index
8,393 citations
"Niches versus neutrality: uncoverin..." refers methods in this paper
...All GAM fitting was performed using the R mgcv package (Wood 2006)....
[...]
Book•
01 Jan 2001TL;DR: A study of the issue indicates that it is not a serious problem for neutral theory, and there is sometimes a difference between some of the simulation-based results of Hubbell and the analytical results of Volkov et al. (2003).
Abstract: study of the issue indicates that it is not a serious problem for neutral theory, for reasons we discuss below. First, a bit of background. Hubbell (2001) derived the analytical expression for the stochastic mean and variance of the abundance of a single arbitrary species in a neutral community undergoing immigration from a metacommunity source area. However, his approach did not lend itself to an analytical solution for the distribution of relative species abundance (RSA) in a multispecies community for community sizes larger than a handful of individuals. As a result, all of Hubbell's RSA distributions for local communities were based on simulations. This problem was solved by Volkov et al. (2003), who derived an analytical expression for the RSA distribution in local communities of arbitrary size. However, as Chisholm and Burgman noted, there is sometimes a difference between some of the simulation-based results of Hubbell and the analytical results of Volkov et al. (2003). Chisholm and Burgman computed Volkov's equation and resimulated Hubbell's results for the four cases
5,317 citations
TL;DR: Stabilizing mechanisms are essential for species coexistence and include traditional mechanisms such as resource partitioning and frequency-dependent predation, as well as mechanisms that depend on fluctuations in population densities and environmental factors in space and time.
Abstract: ▪ Abstract The focus of most ideas on diversity maintenance is species coexistence, which may be stable or unstable. Stable coexistence can be quantified by the long-term rates at which community members recover from low density. Quantification shows that coexistence mechanisms function in two major ways: They may be (a) equalizing because they tend to minimize average fitness differences between species, or (b) stabilizing because they tend to increase negative intraspecific interactions relative to negative interspecific interactions. Stabilizing mechanisms are essential for species coexistence and include traditional mechanisms such as resource partitioning and frequency-dependent predation, as well as mechanisms that depend on fluctuations in population densities and environmental factors in space and time. Equalizing mechanisms contribute to stable coexistence because they reduce large average fitness inequalities which might negate the effects of stabilizing mechanisms. Models of unstable coexitence...
5,240 citations
"Niches versus neutrality: uncoverin..." refers background in this paper
...Niche-based models assume differences in resource use between species; species thereby avoid competition and are able to coexist (Gause 1934; Hardin 1960; Chesson 2000)....
[...]
TL;DR: By emphasizing the very aspects that might result in their denial of them were they less plain the authors can keep the principle explicitly present in their minds untit they see if its implications are, or are noty as unpleasant as their subconscious might suppose.
Abstract: because of a belief that it is best to use that wording which is least likely to hide the fact that we still do not comprehend the exact limits of the principle. For the present, I think the 6'threat of clarity\" (3) is a serious one that is best miniInized by using a formulation that is admittedly unclear; thus can we keep in the forefront of our minds the unfinished work before us. The wording given has, I think, another point of superiority in that it seems brutal and dogmatic. By emphasizing the very aspects that might result in our denial of them were they less plain we can keep the principle explicitly present in our minds untit we see if its implications are, or are noty as unpleasant as our subconscious might suppose. The meaning of these somewhat cryptic remarks should be come clear further on iIl the discussion. What does the exclusion principle mean? Itoughly this: that (i) if two noninterbreeding populations \"do the same thing\"-that is, occupy precisely the same ecological niche in Elton's sense (4)-and (ii) if they are \"sympatric\"that is, if they occupy the same geographic territory-and (iii) if population A multiplies even the least bit faster than population B, then ultimately A will completely displace B, which will become extinct. This is the 44weak form' of the principle. A1ways in practice a stronger form is used, based on the removal of the hypothetical character of condition (iii). We do this because we adhere to what may be caIled the axiom of inequality, which states that no two things or processes
3,062 citations
"Niches versus neutrality: uncoverin..." refers background in this paper
...Niche-based models assume differences in resource use between species; species thereby avoid competition and are able to coexist (Gause 1934; Hardin 1960; Chesson 2000)....
[...]
TL;DR: The problem that is presented by the phytoplankton is essentially how it is possible for a number of species to coexist in a relatively isotropic or unstructured environment all competing for the same sorts of materials.
Abstract: The problem that I wish to discuss in the present contribution is raised by the very paradoxical situation of the plankton, particularly the phytoplankton, of relatively large bodies of water. We know from laboratory experiments conducted by many workers over a long period of time (summary in Provasoli and Pintner, 1960) that most members of the phytoplankton are phototrophs, able to reproduce and build up populations in inorganic media containing a source of CO2, inorganic nitrogen, sulphur, and phosphorus compounds and a considerable number of other elements (Na, K, Mg, Ca, Si, Fe, Mn, B, C1, Cu, Zn, Mo, Co and V) most of which are required in small concentrations and not all of which are known to be required by all groups. In addition, a number of species are known which require one or more vitamins, namely thiamin, the cobalamines (B or related compounds), or biotin. The problem that is presented by the phytoplankton is essentially how it is possible for a number of species to coexist in a relatively isotropic or unstructured environment all competing for the same sorts of materials. The problem is particularly acute because there is adequate evidence from enrichment experiments that natural waters, at least in the summer, present an environment of striking nutrient deficiency, so that competition is likely to be extremely severe. According to the principle of competitive exclusion (Hardin, 1960) known by many names and developed over a long period of time by many investigators (see Rand, 1952; Udvardy, 1959; and Hardin, 1960, for historic reviews), we should expect that one species alone would outcompete all the others so that in a final equilibrium situation the assemblage would reduce to a population of a single species. The principle of competitive exclusion has recently been under attack from a number of quarters. Since the principle can be deduced mathematically from a relatively simple series of postulates, which with the ordinary postulates of mathematics can be regarded as forming an axiom system, it follows that if the objections to the principle in any cases are valid, some or all the biological axioms introduced are in these cases incorrect. Most objections to the principle appear to imply the belief that equilibrium under a given set of environmental conditions is never in practice obtained. Since the deduction of the principle implies an equilibrium system, if such sys-
2,898 citations
"Niches versus neutrality: uncoverin..." refers background in this paper
...…a century of research, it is still not understood how species-rich communities are maintained in the face of the theoretical prediction that single-species dominance is more likely than the stable coexistence of numerous species competing for small numbers of common resources (Hutchinson 1961)....
[...]