Community Completeness: Linking Local and Dark Diversity within the Species Pool Concept

Pärtel, Meelis; Szava‐Kovats, Robert; Zobel, Martin

doi:10.1007/s12224-013-9169-x

Cited by 74 publications

(114 citation statements)

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“…While relative richness has the advantage of being simple and intuitive, recent studies have advocated the use of an alternative measure based on the log‐ratio of observed/“dark” diversity. This measure (termed “completeness,” Partel, Szava‐Kovats, & Zobel, ) can be quantified for any pair of nested spatial scales (habitats within a region, plots within a habitat, etc. ), and indicates the (log) ratio between the number of species observed at the smaller scale and those that are absent from the smaller scale, but do occur at the larger scale (referred to as “dark” diversity, Partel, Szava‐Kovats, & Zobel, ).…”

Section: Methodsmentioning

confidence: 99%

The role of species pools in determining species diversity in spatially heterogeneous communities

2017

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The “habitat‐specific species pool hypothesis” proposes that differences between habitats in the sizes of their species pools are the main drivers of diversity responses to habitat heterogeneity. Empirical tests of this hypothesis are not trivial as species might be missing from ecologically suitable habitats due to limited dispersal, while others may occur in unsuitable habitats by means of source–sink dynamics and mass effect. We tested the habitat‐specific species pool hypothesis in a local, environmentally heterogeneous community of annual plants using a novel “ecological selection” experiment. Mixtures of seeds representing the whole community were sown in each habitat, and the emerging species were exposed to six generations of selection by environmental filtering and competition while being blocked from dispersal. A comparison of the total number of species that were able to survive in each habitat (i.e. to pass the selection test) with data on species richness in the natural community allowed us to test the degree to which observed differences in species richness between habitats could be explained by differences in the sizes of the respective species pools. Results supported the species pool hypothesis, showing that differences in the sizes of the habitat‐specific species pools were important in determining diversity responses to habitat heterogeneity. Moreover, species richness showed a unimodal response to local‐scale gradients in habitat productivity, and this response could be attributed to underlying differences in species pool sizes. Both results were robust to properties of the data and the method of analysis. Synthesis. Our results provide a strong experimental evidence that differences in the sizes of habitat‐specific species pools might be important in shaping the diversity of local communities. Future theoretical and empirical studies in community ecology should explore the potential sources and implications of such differences.

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Section: Methodsmentioning

confidence: 99%

The role of species pools in determining species diversity in spatially heterogeneous communities

2017

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“…When plotting richness against species pool, there is an upper limit where we do not have on May 11, 2018 http://science.sciencemag.org/ data points because richness cannot be larger than the pool. We can, however, apply a recently developed technique to model the overall trend between pool and richness using a log-ratio method of community completeness: log(local richness/ dark diversity), dark diversity includes species that belong to the species pool but are currently not present locally (10,12,13). We cannot calculate completeness for sites where there is no dark diversity-i.e., two monoculture sites were excluded, but these two points were outliers in any event.…”

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confidence: 99%

Response to Comment on “Worldwide evidence of a unimodal relationship between productivity and plant species richness”

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et al. 2015

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Laanisto and Hutchings claim that the local species pool is a more important predictor of local plant species richness than biomass and that when the species pool is considered, there is no hump-backed relationship between biomass and richness. However, we show that by calculating a more appropriate measure of species pool, community completeness, both regional and local processes shape local richness. Species diversity varies from habitat to habitat. Because species diversity has been related to ecological processes and ecosystem functions, it is important to predict whether species diversity may be high or low in any given environment (1). Our recent Report (2) provides evidence from data collected from grasslands in 19 countries and six continents of a unimodal relationship between herbaceous species richness and aboveground plant biomass plus plant litter, such that the maximum potential species richness occurs at intermediate levels of biomass production. We tackled the question of the diversity-productivity relationship because of its foundational role in ecological research and its controversial history (2-7). The data were collected at the 1-m 2 scale, within 8-m-by-8-m grids, so that we could test linear and quadratic regressions at 1, 2, 4, 9, 16, 25, and 64 m 2 scales. At each scale, the best descriptor of the relationship was a concave quadratic regression, but explanatory power diminished with increasing scale (2).We point to the relevance of our findings and the scaling approach in our analysis because it provides a comparative to Laanisto and Hutchings (8). Through a reanalysis of our data, Laanisto and Hutchings (8) argue that the local species pool has a stronger effect on species richness than primary productivity. We are in agreement that large-scale processes play a role in governing local-scale diversity, but it is challenging to account for large-scale processes in an empirical study such as ours. Thus, instead of addressing whether it is more reasonable to seek for a relationship between species richness and primary productivity, or local species pool, we would rather ask what the relative role of local and regional factors is in shaping the empirically observed relationship between diversity and productivity.Laanisto and Hutchings emphasize geographic variation in the shape of the response curve ("While the HBM [hump-backed model] certainly applies in some regions and habitats, such as high-latitude grasslands … richness-productivity relationships tend to be positive in tropical areas"). In fact, there are two confounding aspects in this statement: geographical region (with different biogeographic history) and ecosystem type (grassland versus forest). Positive relationships come predominantly from forests (9). We chose to avoid mixing different ecosystems because of the different processes that may be acting.In their figure 1, Laanisto and Hutchings's regression of local richness versus species pool is problematic because these two variables are inherently related, not independent, and ...

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“…Semi‐natural temperate grasslands are considered to be the most species‐rich communities in the world at small spatial scales (Wilson et al ), making them valuable for nature conservation and an important study system for exploring biodiversity patterns and processes (Kull and Zobel , van der Maarel and Sykes , Eriksson and Jakobsson , Pärtel and Zobel , Reitalu et al ). Although raw species richness values or diversity indices have been widely used in ecology, small‐scale diversity patterns may be better understood if species richness is described in relation to the dark diversity – the set of species that are absent from the community at any particular time, despite the fact that they are present within the surrounding region and adapted to the prevailing habitat conditions (Pärtel et al , ). Dark diversity therefore represents the absent portion of the habitat‐specific species pool, and may be expected to vary between different grassland sites (Huston , Pärtel et al ).…”

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Dark diversity in dry calcareous grasslands is determined by dispersal ability and stress‐tolerance

et al. 2014

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Temperate calcareous grasslands are characterized by high levels of species richness at small spatial scales. Nevertheless, many species from a habitat‐specific regional species pool may be absent from local communities and represent the ‘dark diversity’ of these sites. Here we investigate dry calcareous grasslands in northern Europe to determine what proportion of the habitat‐specific species pool is realized at small scales (i.e. how the community completeness varies) and which mechanisms may be contributing to the relative sizes of the observed and dark diversity. We test whether the absence of particular species in potentially suitable grassland sites is a consequence of dispersal limitation and/or a low ability to tolerate stress (e.g. drought and grazing). We analysed a total of 1223 vegetation plots (1 × 1 m) from dry calcareous grasslands in Sweden, Estonia and western Russia. The species co‐occurrence approach was used to estimate the dark diversity for each plot. We calculated the maximum dispersal distance for each of the 291 species in our dataset by using simple plant traits (dispersal syndrome, growth form and seed characteristics). Large seed size was used as proxy for small seed number; tall plant height and low S‐strategy type scores were used to characterise low stress‐tolerance. Levels of small‐scale community completeness were relatively low (more species were absent than present) and varied between the grasslands in different geographic areas. Species in the dark diversity were generally characterized by shorter dispersal distances and greater seed weight (fewer seeds) than species in the observed diversity. Species within the dark diversity were generally taller and had a lower tolerance of stressful conditions. We conclude that, even if temperate grasslands have high levels of small‐scale plant diversity, the majority of potentially suitable species in the regional species pool may be absent as a result of dispersal limitation and low stress‐tolerance.

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Community Completeness: Linking Local and Dark Diversity within the Species Pool Concept

Cited by 74 publications

References 56 publications

The role of species pools in determining species diversity in spatially heterogeneous communities

The role of species pools in determining species diversity in spatially heterogeneous communities

Response to Comment on “Worldwide evidence of a unimodal relationship between productivity and plant species richness”

Dark diversity in dry calcareous grasslands is determined by dispersal ability and stress‐tolerance

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