Jiang L, Patel SN.. Community assembly in the presence of disturbance: A microcosm experiment. Ecology 89: 1931-1940
School of Biology, Georgia Institute of Technology, 310 Ferst Drive, Atlanta, Georgia 30332, USA.Ecology (Impact Factor: 4.66). 08/2008; 89(7):1931-40. DOI: 10.1890/07-1263.1
Ecologists know relatively little about the manner in which disturbance affects the likelihood of alternative community stable states and how the history of community assembly affects the relationship between disturbance and species diversity. Using microbial communities comprising bacterivorous ciliated protists assembled in laboratory microcosms, we experimentally investigated these questions by independently manipulating the intensity of disturbance (in the form of density-independent mortality) and community assembly history (including a control treatment with simultaneous species introduction and five sequential assembly treatments). Species diversity patterns consistent with the intermediate disturbance hypothesis emerged in the controls, as several species showed responses indicative of a tradeoff between competitive ability and ability to recover from disturbance. Species diversity in communities with sequential assembly, however, generally declined with disturbance, owing to the increased extinction risk of later colonizers at the intermediate level of disturbance. Similarities among communities subjected to different assembly histories increased with disturbance, a result due possibly to increasing disturbance reducing the importance of competition and hence priority effects. This finding is most consistent with the idea that increasing disturbance tends to reduce the likelihood of alternative stable states. Collectively, these results indicate the strong interactive effects of disturbance and assembly history on the structure of ecological communities.
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- "We observed an increase in alpha diversity in the reassembled rhizobacterial community after heat disturbance which is consistent with the 'intermediate disturbance hypothesis' that predicts a maximum level of diversity at intermediate disturbance levels and assumes that species exhibit a trade-off between their ability to cope with disturbance and their competitive ability (Connell 1978; Jiang & Patel 2008). It is important toFigure 1 Cluster analysis using Bray–Curtis similarity of the bacterial communities assembled in the rhizosphere of sugar beet seedlings grown in the suppressive soil (S, control), suppressive soil heat treated for 1 h at 50 °C (S50) or at 80 °C (S80). "
ABSTRACT: The rhizosphere microbiome offers a range of ecosystem services to the plant, including nutrient acquisition and tolerance to (a)biotic stress. Here, analysing the data by Mendes et al. (2011), we show that short heat disturbances (50 or 80 °C, 1 h) of a soil suppressive to the root pathogenic fungus Rhizoctonia solani caused significant increase in alpha diversity of the rhizobacterial community and led to partial or complete loss of disease protection. A reassembly model is proposed where bacterial families that are heat tolerant and have high growth rates significantly increase in relative abundance after heat disturbance, while temperature-sensitive and slow-growing bacteria have a disadvantage. The results also pointed to a potential role of slow-growing, heat-tolerant bacterial families from Actinobacteria and Acidobacteria phyla in plant disease protection. In conclusion, short heat disturbance of soil results in rearrangement of rhizobacterial communities and this is correlated with changes in the ecosystem service disease suppression.
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- "Although there is general consensus that both concepts play a role in natural community assemblages (Gravel et al. 2006; Adler, HilleRislambers & Levine 2007; Myers & Harms 2009; G€ otzenberger et al. 2012), the assessment of their relative importance across time, space or ecosystem types remains challenging (Chase & Myers 2011; Shipley, Paine & Baraloto 2012). Recent studies suggest that environment-driven community assembly may become more important under stressful environmental conditions (Chase 2007; Jiang & Patel 2008; Lepori & Malmqvist 2009), whereas dispersal filtering may become more prevalent under benign conditions (Myers & Harms 2009; Germain et al. 2013). In existing communities, species interactions may enforce both types of filtering by competitive displacement of subordinates towards peripheral ends of environmental gradients (Wisheu & Keddy 1992), narrowing species' realized niche ranges (Hutchinson 1957; Pickett & Bazzaz 1978; Silvertown et al. 1999), or by preventing establishment of later arriving species ('priority effects'), especially in more productive environments (Kardol, Souza & Classen 2013; Chase 2010). "
ABSTRACT: 1. Both environmental filtering and dispersal filtering are known to influence plant species distribution patterns and biodiversity. Particularly in dynamic habitats, however, it remains unclear whether environmental filtering (stimulated by stressful conditions) or dispersal filtering (during recolonization events) dominates in community assembly, or how they interact. Such a fundamental understanding of community assembly is critical to the design of biodiversity conservation and restoration strategies. 2. Stream riparian zones are species-rich dynamic habitats. They are characterized by steep hydrological gradients likely to promote environmental filtering, and by spatiotemporal variation in the arrival of propagules likely to promote dispersal filtering. We quantified the contributions of both filters by monitoring natural seed arrival (dispersal filter) and experimentally assessing germination, seedling survival and growth of 17 riparian plant species (environmental filter) along riparian gradients of three lowland streams that were excavated to bare sub-strate for restoration. Subsequently, we related spatial patterns in each process to species distribution and diversity patterns after 1 and 2 years of succession. 3. Patterns in initial seed arrival were very clearly reflected in species distribution patterns in the developing vegetation and were more significant than environmental filtering. However, environmental filtering intensified towards the wet end of the riparian gradient, particularly through effects of flooding on survival and growth, which strongly affected community diversity and generated a gradient in the vegetation. Strikingly, patterns in seed arrival foreshadowed the gradient that developed in the vegetation; seeds of species with adult optima at wetter conditions dominated seed arrival at low elevations along the riparian gradient, while seeds of species with drier optima arrived higher up. Despite previous assertions suggesting a dominance of environmental filtering , our results demonstrate that non-random dispersal may be an important driver of early successional riparian vegetation zonation and biodiversity patterns as well. 4. Synthesis. Our results demonstrate (and quantify) the strong roles of both environmental and dispersal filtering in determining plant community assemblies in early successional dynamic habitats. Furthermore, we demonstrate that dispersal filtering can already initiate vegetation gradients, a mechanism that may have been overlooked along many environmental gradients where interspecific interactions are (temporarily) reduced.
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- "A commonly applied disturbance in microcosm experiments is density-independent mortality, where either a part of the community is replaced by autoclaved medium (e.g. Warren 1996; Haddad et al. 2008; Altermatt et al. 2011a), or where a part of the community is killed (by heating or sonication), but the medium retained in the culture, such that chemical and nutritional conditions remain as constant as possible (e.g. Jiang & Patel 2008; Violle, Pu & Jiang 2010; M€ achler & Altermatt 2012). This type of pulsed disturbance is easy to apply but does not allow species-specific resistance to disturbance, but rather reflects different recoveries from disturbances, strongly determined by a species' growth rate. "
ABSTRACT: 1.Laboratory microcosm experiments using protists as model organisms have a long tradition and are widely used to investigate general concepts in population biology, community ecology and evolutionary biology. Many variables of interest are measured in order to study processes and patterns at different spatiotemporal scales and across all levels of biological organization. This includes measurements of body size, mobility, or abundance, in order to understand population dynamics, dispersal behaviour, and ecosystem processes. Also, a variety of manipulations are employed, such as temperature changes or varying connectivity in spatial microcosm networks. 2.Past studies, however, have used varying methods for maintenance, measurement, and manipulation, which hinders across-study comparisons and meta-analyses, and the added value they bring. Furthermore, application of techniques such as flow-cytometry, image and video analyses, and in-situ environmental probes provide novel and improved opportunities to quantify variables of interest at unprecedented precision and temporal resolution. 3.Here, we take the first step towards a standardization of well-established and novel methods and techniques within the field of protist microcosm experiments. We provide a comprehensive overview of maintenance, measurement, and manipulation methods. An extensive supplement contains detailed protocols of all methods, and these protocols also exist in a community updateable online repository. 4.We envision that such a synthesis and standardization of methods will overcome shortcomings and challenges faced by past studies, and also promote activities such as meta-analyses and distributed experiments conducted simultaneously across many different laboratories at a global scale.