Bias in the detection of negative density dependence in plant communities

Detto, Matteo; Visser, Marco D.; Wright, S. Joseph; Pacala, Stephen W.

doi:10.1111/ele.13372

Cited by 108 publications

(165 citation statements)

References 94 publications

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“…In addition, there is evidence for greater biotic interaction strength in the tropics than at higher latitudes (Roslin et al ). Observed patterns of greater impact of trees on nearby conspecifics nearer the Equator (LaManna et al , Detto et al ), suggest likely variation in effect size across latitude. Therefore, it is important to consider latitude when trying to understand geographic patterns in strength of the dilution effect.…”

Section: Introductionmentioning

confidence: 99%

Dilution effect of plant diversity on infectious diseases: latitudinal trend and biological context dependence

Liu

Chen

et al. 2020

Oikos

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Biodiversity is thought to help regulate the impacts of disease through the dilution effect, where biodiversity among potential host species helps limit the impacts of pathogens. However, our knowledge is fragmentary about the direction and magnitude of the effects of plant species richness on disease impact. Here, we gathered data from 145 comparisons presented in 21 papers to conduct a systematic meta‐analysis on the effect of plant species richness on aboveground plant disease impact. We estimated the effect size using Pearson's correlation coefficient (r) with Fisher's z‐transformation. We evaluated how the magnitude of effect size varies between systems, including ecosystem type (grassland versus forest), pathogen taxon (virus versus fungus), study design (observational versus manipulative), parasite life history (biotroph versus necrotroph) and kinds of symptoms associated with the disease. We also tested whether there was a latitudinal trend of the effect size. We found there was a significant overall dilution effect in plant communities, but the magnitude varied among systems. Studies based on manipulative experiments and those in grassland ecosystems showed a significant dilution effect, as did both viral and fungal pathogens. Furthermore, obligate biotrophic pathogens but not necrotrophs showed a significant dilution effect. Diseases with different kinds of symptom manifestation differed, but not in a consistent pattern to the life history of the pathogens. The dilution effect was notably stronger at lower latitudes in the mid‐temperate region than at higher latitudes. This latitudinal trend existed in forest ecosystems, both observational and manipulative experiments, and necrotrophs. Dilution effects occur prevalently in plant communities, although the magnitude depends on ecosystem type, pathogen life history and kinds of symptoms associated with the disease. In conclusion, this study shows the importance of preserving the biodiversity of plants for maintaining ecosystem health.

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Section: Introductionmentioning

confidence: 99%

Dilution effect of plant diversity on infectious diseases: latitudinal trend and biological context dependence

Liu

Chen

et al. 2020

Oikos

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“…Previous studies at the same site have characterized interspecific variation in seed dispersal kernels (Muller-Landau et al, 2008),found evidence for negative density dependence on seedling recruitment (Harms et al, 2000, Wright et al, 2005b, as well as distance-/ density-dependent mortality during the seedling stage (Comita et al, 2010, Murphy et al, 2017, but see Detto et al (2019) for discussion of potential biases in some of these studies. We consider seedling establishment at two stages (new recruits and seedlings 20 cm or taller) to distinguish mortality in the seed-to-seedling transition from that of the early seedling life.…”

Section: Introductionmentioning

confidence: 99%

“…We consider seedling establishment at two stages (new recruits and seedlings 20 cm or taller) to distinguish mortality in the seed-to-seedling transition from that of the early seedling life. Previous studies at the same site have characterized interspecific variation in seed dispersal kernels (Muller-Landau et al, 2008),found evidence for negative density dependence on seedling recruitment (Harms et al, 2000, Wright et al, 2005b, as well as distance-/ density-dependent mortality during the seedling stage (Comita et al, 2010, Murphy et al, 2017, but see Detto et al (2019) for discussion of potential biases in some of these studies. Drawing from the approach of Muller-Landau et al (2008), we fit hierarchical Bayesian models for each species and life stage (seed, new recruit, and 20cm seedling) to estimate the annual fecundity (total seeds or seedlings per unit of reproductive tree basal area), the seed dispersal or seedling establishment kernel, and the spatial aggregation of individuals relative to expected density simultaneously.…”

Section: Introductionmentioning

confidence: 99%

Seed‐to‐seedling transitions exhibit distance‐dependent mortality but no strong spacing effects in a Neotropical forest

Marchand

Comita

Wright

et al. 2019

Ecology

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Patterns of seed dispersal and seed mortality influence the spatial structure of plant communities and the local coexistence of competing species. Most seeds are dispersed in proximity to the parent tree, where mortality is also expected to be the highest, because of competition with siblings or the attraction of natural enemies. Whereas distance‐dependent mortality in the seed‐to‐seedling transition was often observed in tropical forests, few studies have attempted to estimate the shape of the survival‐distance curves, which determines whether the peak of seedling establishment occurs away from the parent tree (Janzen–Connell pattern) or if the peak attenuates but remains at the parent location (Hubbell pattern). In this study, we inferred the probability density of seed dispersal and two stages of seedling establishment (new recruits, and seedlings 20 cm or taller) with distance for 24 tree species present in the 50‐ha Forest Dynamics Plot of Barro Colorado Island, Panama. Using data from seed traps, seedling survey quadrats, and tree‐census records spanning the 1988–2014 period, we fit hierarchical Bayesian models including parameters for tree fecundity, the shape of the dispersal kernel, and overdispersion of seed or seedling counts. We combined predictions from multiple dispersal kernels to obtain more robust inferences. We find that Hubbell patterns are the most common and Janzen–Connell patterns are very rare among those species; that distance‐dependent mortality may be stronger in the seed stage, in the early recruit stage, or comparable in both; and that species with larger seeds experience less overall mortality and less distance‐dependent mortality. Finally, we describe how this modeling approach could be extended at a community scale to include less abundant species.

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“…S9 is the same figure taking into account only significant interactions) discrete-time Lotka-Volterra equivalent in the Supporting Information; even though there is a relationship between intra/inter ratios in both models, the relationship is not trivial when abundances vary greatly between species. Hence, to some degree, intra/inter ratios can differ between model frameworks or ways of measuring density-dependencies (e.g., a high measurement error due to using proxies of densities for plants can result in bias in interaction coefficient estimates, Detto et al, 2019). However, a ratio intra/inter at least twice larger than the ones previously found may call for other explanations.…”

Section: Strong Self-regulation and Facilitationmentioning

confidence: 89%

Strong self-regulation and widespread facilitative interactions in phytoplankton communities

Picoche

Barraquand

2019

Preprint

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AbstractThe persistence of phytoplanktonic diversity in spite of competition for basic resources has long been a source of wonder and inspiration to ecologists. To sort out, among the many coexistence mechanisms suggested by theory and experiments, which ones actually maintain diversity in natural ecosystems, long-term field studies are paramount.We analysed a large dataset of phytoplankton abundance time series using dynamic, multivariate autoregressive models. Phytoplankton was counted and identified down to the genus level, every two weeks over twenty years, at ten sites along the French coastline. Multivariate autoregressive models allowed to estimate biotic interaction networks, while also accounting for abiotic variables that may drive part of the phytoplankton fluctuations. We then analysed the ratio of intra-to inter-taxa interactions (measuring self-regulation, itself a measure of niche differentiation), the frequency of negative vs positive interactions, and how stability metrics (both at the network and genus level) relate to network complexity and genus self-regulation or abundance.We showed that a strong self-regulation, with competition strength within a taxon (genus) an order of magnitude higher than between taxa, was present in all phytoplanktonic interaction networks. This much stronger intragenus competition suggests that niche differentiation - rather than neutrality - is commonplace in phytoplankton. Furthermore, interaction networks were dominated by positive net effects between phytoplanktonic taxa (on average, more than 50% of interactions were positive). While network stability (sensu resilience) was unrelated to complexity measures, we unveiled links between self-regulation, intergenus interaction strengths and abundance. The less common taxa tend to be more strongly self-regulated and can therefore maintain in spite of competition with more abundant ones.Synthesis: We demonstrate that strong niche differentiation, widespread facilitation between phytoplanktonic taxa and stabilizing covariances between interaction strengths should be common features of coexisting phytoplankton communities in the field. These are structural properties that we can expect to emerge from plausible mechanistic models of phytoplankton communities. We discuss mechanisms, such as predation or restricted microscale movement, that are consistent with these findings, which paves the way for further research.

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Bias in the detection of negative density dependence in plant communities

Cited by 108 publications

References 94 publications

Dilution effect of plant diversity on infectious diseases: latitudinal trend and biological context dependence

Dilution effect of plant diversity on infectious diseases: latitudinal trend and biological context dependence

Seed‐to‐seedling transitions exhibit distance‐dependent mortality but no strong spacing effects in a Neotropical forest

Strong self-regulation and widespread facilitative interactions in phytoplankton communities

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