Relative Importance Of Ecological Processes Research Articles

Intermediate irrigation with low fertilization promotes soil nutrient cycling and reduces CO2 and CH4 emissions via regulating fungal communities in arid agroecosystems

The field practices, including irrigation and fertilization, strongly affect greenhouse gas emissions and soil nutrient cycling from agriculture. Understanding the underlying mechanism of greenhouse gas emissions, soil nutrient cycling, and their impact factors (fungal diversity, network characteristics, soil pH, salt, and moisture) is essential for efficiently managing global greenhouse gas mitigation and agricultural production. By considering abundant and rare taxa, we determine the identities and relative importance of ecological processes that modulate the fungal communities and identify whether they are crucial contributors to soil nutrient cycling and greenhouse gas emissions. The research is based on a 4-year field fertigation experiment with low (300 kg/ha P2O5 with 150 kg/ha urea) and high (600 kg/ha P2O5 with 300 kg/ha urea) fertilization level and three irrigation levels, that is, low (200 mm), medium (300 mm), and high (400 mm). The α-diversity (richness and Shannon index) of fungal subcommunities was significantly higher under medium irrigation (300 mm) and low fertilization (300 kg/ha P2O5 with 150 kg/ha urea) than under other treatments. Intermediate irrigation with low fertilization treatment yielded the most significant higher multinutrient cycling index and the lowest CO2 and CH4 emissions. The null model indicated that abundant taxa are mainly regulated by stochastic processes (dispersal limitation), and rare taxa are mainly regulated by environmental selection, especially by soil salinity. The co-occurrence network of rare taxa explained the changes in the entire fungal network stability. The abundant taxa played vital roles in regulating soil nutrient status, owing to the stronger association between their network and multinutrient cycling index. Furthermore, we have confirmed that soil moisture and fungal network stability are crucial factors affecting greenhouse gas emissions. Together, these results provide a deep understanding of the mechanisms that reveal fungal community assembly and soil fungal-driven variations in nutrient status and network stability, link fungal network characteristics to ecosystem functions, and reveal the factors that influence greenhouse gas emissions.

Soil microbial biomass and community structure in response to agricultural use of deserts across northern China

Although desert reclamation efforts have been used for increased crop production, their impacts on the structure of soil microbial communities remain largely understudied. Here, six adjacent pairs of different native desert and newly reclaimed cropland soils across a 3300 km transect in northern China were selected to address how microbial biomass, community composition, biogeographic pattern and the relative importance of ecological processes responded to agricultural reclamation using qPCR and high-throughput amplicon sequencing of bacterial 16S rRNA and fungal ITS genes. Agricultural intensification generally increased bacterial and fungal biomasses compared to undisturbed desert soils, while most microbial α-diversities were not significantly changed across these sampling sites. The relative abundances of some dominant microbial phyla and families significantly changed in response to agricultural intensification, which was site-dependent. Bacterial and fungal communities showed similar biogeographic patterns predominantly dominated by community turnover rather than nestedness for both desert and cropland soils, while agricultural intensification made bacterial community compositions more dissimilar. Deterministic process and stochastic process dominated bacterial and fungal community assembly in both desert and cropland soils, respectively. Agricultural intensification slightly reduced the relative importance of deterministic process for bacterial community assembly, while it conversely increased the relative importance of deterministic process to fungal community assembly by shifting the contributions of different assembly components. These results suggest that short-term land-use transformation from native deserts to croplands impact desert soil microbial community structure by making bacterial community more stochastic and fungal community more deterministic.

Plant diversity on islands in the Anthropocene: Integrating the effects of the theory of island biogeography and human activities

Understanding how the complexities of biodiversity are maintained on islands has long been one of the central issues studied in conservation biology. With the global onset of anthropogenically driven biodiversity changes, the influence of anthropogenic activities challenges the applicability of the widely accepted Equilibrium Theory of Island Biogeography (ETIB). This study aimed to test how island area, isolation (MD: distance to the mainland, and ND: distance to the nearest island), and human activities (habitat heterogeneity, and proportion of road area relative to island area to refer to the human impact on island) separately and jointly affect the species diversity of vascular plants. The number of plant species with different growth forms (woody plants, herbs, and lianas) was calculated on 35 islands in Sanyang Wetland, which is a human-dominated wetland near the highly populated city of Wenzhou, China. We also evaluated the relative importance of these variables on the number of species using a random forest analysis. The number of species increased with increasing island area and habitat heterogeneity and decreased with increasing isolation for different growth forms. A significant, positive relationship was observed between the number of species and the proportion of road area for herbs, but not for woody plants and lianas. Habitat heterogeneity was the most important predictor for all plants, the proportion of road area was the most important predictor for herbs, and MD was the most important predictor for woody plants and lianas. These results indicate that ETIB remains relevant in the context of human disturbance, but the relative importance of ecological processes on species diversity differs significantly among plant growth forms. Therefore, we should consider plant functional groups when testing multifactorial effects on species diversity on human-dominated islands.

Dominant ecological processes and plant functional strategies change during the succession of a subtropical forest

Understanding community assembly process could enhance forest conservation and restoration, while which dominant ecological process drives the community assembly during forest succession is still controversial. In this study, the phylogeny-based and functional trait-based indicators were used to investigate the community assembly processes during forest succession in southern China. 30 dominant species and 33 functional trait indicators related to plant competition, reproduction, and defense strategies, 7 environmental factors related to light availability and soil nutrients, and species richness were selected to explore the dominant ecological processes during succession via Monte Carlo method, structural equation model, multiple linear regression, and one-way ANOVA analysis. Results showed that both the community phylogenetic and functional trait structures changed during succession. Phylogenetic structure clustering and functional trait clustering were evident in early succession. In middle succession, the phylogenetic structure and functional trait structure were randomly dispersed. In middle and later succession, the phylogenetic structure clustering, functional trait clustering, and functional trait evenly dispersed were found. The environmental factors, especially the soil P content, and species richness were found to have significant effects on the community assembly processes during succession. Dominant species in early succession always occupied acquisitive strategies and had high light-use ability and low investment in defense, but dominant species in later succession showed more conservative strategies and exhibited diverse defense strategy, reproductive strategy, and light and nutrient resource-use strategy, apparently in order to adapt changing and more complex environments. The results demonstrate that the relative importance of ecological processes changed during succession. Environmental filtering mainly dominated in early succession, and its strength gradually decreased as succession progressed. Both environmental filtering and competitive exclusion had important effects on community assembly in later succession. The assessment of the relative importance of ecological processes during succession could be biased if only based on one plant functional strategy.

Future climate change enhances the complexity of plastisphere microbial co-occurrence networks, but does not significantly affect the community assembly

Biobased and biodegradable plastics have been intensively used in agriculture as mulching films. They provide a distinctive habitat for soil microbes, yet much less is known about the community assembly and interactions of plastisphere microbiota in soils under future climate change. For the first time, we explored the relative importance of ecological processes and the co-occurrence networks of plastic-associated microbes under ambient and future climates. The drift primarily dominated the community assembly of bacteria and fungi after 180D and 328D incubation in both climate regimes. The neutral community model prediction indicated that the migration rate of the plastisphere community in the later decay phase was lower than that in the early decay phase, contributing to the generation of the specific niches. Furthermore, future climate promoted the complexity and modularity of plastic-associated microbial networks: more competition and cooperation were observed in bacteria (or inter-kingdom) and fungi under future climate conditions, respectively. Overall, our findings strengthened the understanding of ecological processes and interplay of plastisphere microbiota during plastic biodegradation in soils under ambient and future climate regimes.

Salinity Gradient Controls Microbial Community Structure and Assembly in Coastal Solar Salterns.

Salinity acts as a critical environmental filter on microbial communities in natural systems, negatively affecting microbial diversity. However, how salinity affects microbial community assembly remains unclear. This study used Wendeng multi-pond saltern as a model to evaluate the prokaryotic community composition and diversity and quantify the relative importance of ecological processes across salinity gradients. The results showed that low-saline salterns (45–80 g/L) exhibited higher bacterial diversity than high-saline salterns (175–265 g/L). The relative abundance of taxa assigned to Halomicrobiaceae, Rhodobacteraceae, Saprospiraceae, and Thiotrichaceae exhibited a hump-shaped dependence on increasing salinity. Salinity and pH were the primary environmental factors that directly or indirectly determined the composition and diversity of prokaryotic communities. Microbial co-occurrence network dynamics were more complex in the sediment than in the water of salterns. An infer Community Assembly Mechanisms by Phylogenetic-bin-based null model analysis (iCAMP) showed that microbial community assembly in sediment and water differed. Our findings provide more information about microbial community structure and the importance of various ecological processes in controlling microbial community diversity and succession along salinity gradients in water and sediment.

Deciphering sample size effect on microbial biogeographic patterns and community assembly processes at centimeter scale

Revealing the effects of spatial heterogeneity on microorganisms is crucial for the further understanding of microbial diversity, turnover and ecological processes. However, microbial community assembly and the factors that shape it are still unknown at a centimeter scale. To address this gap, we conducted variation partitioning and null model analyses on the microbial community composition of a soil cube, divided into up to 64 sub-cubes, to investigate microbial biogeographic patterns and microbial assembly processes of 3 cm-scale sampling schemes. The results suggested that microbial community was more dispersed and distance decay relationships were more significant in sampling schemes of smaller sample size compared with those of larger sample size. We further investigated the relative importance of ecological processes and demonstrated that bacterial community assembly processes changed from variable selection to homogenous selection as the sample size increased. The importance of spatial distance and micro-environmental variables in shaping and maintaining microbial diversity was emphasized by the dynamics of spatial heterogeneity and environmental filtering. As microorganisms are spatially distributed in soil, this sampling scale dependent diversity and assembly suggests that microbial ecology questions need to be considered in more dimensions than they usually are.

Habitat filtering drives the local distribution of congeneric species in a Brazilian white-sand flooded tropical forest.

The investigation of ecological processes that maintain species coexistence is revealing in naturally disturbed environments such as the white‐sand tropical forest, which is subject to periodic flooding that might pose strong habitat filtering to tree species. Congeneric species are a good model to investigate the relative importance of ecological processes that maintain high species diversity because they tend to exploit the same limiting resources and/or have similar tolerance limits to the same environmental conditions due to their close phylogenetic relationship. We aim to find evidence for the action and relative importance of different processes hypothesized to maintain species coexistence in a white‐sand flooded forest in Brazil, taking advantage of data on the detailed spatial structure of populations of congeneric species. Individuals of three Myrcia species were tagged, mapped, and measured for diameter at soil height in a 1‐ha plot. We also sampled seven environmental variables in the plot. We employed several spatial point process models to investigate the possible action of habitat filtering, interspecific competition, and dispersal limitation. Habitat filtering was the most important process driving the local distribution of the three Myrcia species, as they showed associations, albeit of different strength, to environmental variables related to flooding. We did not detect spatial patterns, such as spatial segregation and smaller size of nearby neighbors, that would be consistent with interspecific competition among the three congeneric species and other co‐occurring species. Even though congeners were spatially independent, they responded to differences in the environment. Last, dispersal limitation only led to spatial associations of different size classes for one of the species. Given that white‐sand flooded forests are highly threatened in Brazil, the preservation of their different habitats is of utmost importance to the maintenance of high species richness, as flooding drives the distribution of species in the community.

Homogeneous selection shapes free‐living and particle‐associated bacterial communities in subtropical coastal waters

AbstractAimIn microbial biogeography, it is crucial to link spatial patterns with underlying drivers in natural ecosystems. Bacterial communities driving key biogeochemical processes in coastal zones, which are important interfaces between terrestrial and marine ecosystems, are affected by perturbations due to both natural and anthropogenic factors. However, the assembly of bacterioplankton communities, either free‐living (FL) or particle‐associated, in coastal ecosystems is still poorly understood.LocationCoastal South China Sea influenced by the Pearl River (SCSPR).MethodsIn this study, we investigated FL, nanoparticle‐associated (NA) and microparticle‐associated (MA) bacterial communities in the SCSPR, using environmental DNA metabarcoding based on the V4 region of the 16S rRNA gene. We assessed the relative importance of ecological processes using null model analyses based on a two‐step framework.ResultsWe found that the observed amplicon sequence variants (ASVs) increased from FL, NA to MA communities, and a remarkably pervasive core set of ASVs closely belonged to potential hydrocarbonoclastic bacteria with wide habitat niche breadths. Analyses of similarity tests revealed that FL, NA and MA communities differed significantly but weakly, based on unweighted (R = 0.27, p < .001) and weighted (R = 0.18, p < .001) dissimilarities. Fundamental regulation of bacterial communities via homogeneous selection was most prominent in FL (90%), followed by NA (86.8%) and MA (73.3%), whereas the relative importance of dispersal limitation was most pronounced in MA (13.2%), followed by NA (11.7%) and FL (8.6%).Main conclusionsBacterial communities in the SCSPR can be predominantly influenced by human activities, as indicated by the core ASVs closely related to hydrocarbonoclastic bacteria. Importantly, anthropogenic influences can temporally overwhelm the large environmental heterogeneities in coastal ecosystems. This study fills knowledge gaps in bacterial community assembly, which may facilitate future studies regarding anthropogenic influences on coastal ecosystems.

Ecological drivers of tree assemblage in tropical, subtropical and subalpine forests

AbstractAimsIt is widely accepted that deterministic and neutral dispersal processes are two of the principal mechanisms driving community assembly. However, the relative importance of these ecological drivers between distinct life stages both at community and individual species levels remains poorly understood in different vegetation types. Here, we address the following questions: (a) is there a ubiquitous process shaping tree assemblage; (b) how does the relative importance of environmental and dispersal processes vary through ontogeny in different vegetation types; and (c) will the spatial patterns of trees at community and individual species levels reflect similar contribution between ecological processes?LocationYunnan province, southwest China.MethodsWe used the Homogeneous Poisson, Homogeneous Thomas, Inhomogeneous Poisson, and Inhomogeneous Thomas point process models to predict the effect of stochastic, dispersal and/or environmental processes, respectively, on the distribution of trees across ontogeny in tropical, subtropical and subalpine forests. To evaluate the relative importance of models, we compared the observed and simulated patterns of the species–area relationship and the pair correlation function g(r) at community and species level, respectively.ResultsThe Homogeneous Thomas model was the model with the lowest Akaike information criterion (AIC) scores across ontogeny and forest types at community level. At the species level, however, Homogeneous Thomas, and Inhomogeneous Thomas predicted the distribution of large and small trees, respectively, with lower AIC values in two of our three plots. In the third plot, the Homogeneous Thomas model is dominant across ontogeny at the species level.ConclusionsTree communities are assembled mainly by the dispersal process at community level. The relative importance of ecological processes for species distribution varies across life stages at the species level, suggesting that there is an ontogenetic shift of ecological processes in shaping tree distribution. Using different summary statistics at both community and species levels helps to discern the different spatial structures of species and increases our appreciation of the processes underpinning community assembly.

Uncovering the relative influences of space and environment in shaping the biogeographic patterns of mangrove mollusk diversity

AbstractDetermining the relative importance of ecological processes regulating the biogeographic patterns of marine species, especially with respect to α- and β-diversity in multi-habitat communities, is a central goal in marine ecology. We explored the relative contribution of spatial (stochastic processes) and environmental factors (deterministic processes) to the biogeographic patterns of the α- and β-diversity of mangrove mollusks. A total of 16 mangrove areas were sampled in southeast coast China from 18°N to 28°N latitude. The highest mean α-diversity was found at 20°N and that of β-diversity was at 21°N. Both spatial and environmental factors had significant effects on the α- and β-diversity patterns. The environments had greater effects than the spaces on shaping the α-diversity pattern, while the spaces were relatively more important in governing the β-diversity patterns than the environments. Our results suggest that the α-diversity pattern was mainly controlled by deterministic processes (environmental filtering), while β-diversity was primarily shaped by stochastic processes (dispersal-related), although both processes had significant impacts on α- and β-diversity patterns. Identifying the ecological variables and mechanisms that drive variations in α- and β-diversity may help guide the conservation for biodiversity in endangered mangrove ecosystems under anthropogenic and global changes.

Biogeographic patterns of abundant and rare bacterioplankton in three subtropical bays resulting from selective and neutral processes

Unraveling the relative importance of ecological processes regulating microbial community structure is a central goal in microbial ecology. Here, we used high-throughput sequencing to examine the relative contribution of selective and neutral processes in the assembly of abundant and rare subcommunities from three subtropical bays of China. We found that abundant and rare bacterial taxa were distinctly different in diversity, despite the similar biogeographic patterns and strong distance-decay relationships, but the dispersal of rare bacterial taxa was more limited than that of abundant taxa. Furthermore, the environmental (selective processes) and spatial (neutral processes) factors seemed to govern the assembly and biogeography of abundant and rare bacterial subcommunities, although both factors explained only a small fraction of variation within the rare subcommunity. More importantly, variation partitioning (based on adjusted R2 in redundancy analysis) showed that spatial factors exhibited a slightly greater influence on both abundant and rare subcommunities compared to environmental selection; however, the abundant subcommunity had a much stronger response to spatial factors (17.3% of pure variance was explained) than that shown by the rare bacteria (3.5%). These results demonstrate that environmental selection and neutral processes explained the similar biogeographic patterns of abundant and rare subcommunities, but a large proportion of unexplained variation in the rare taxa (91.1%) implies that more complex assembly mechanisms may exist to shape the rare bacterial assemblages in the three subtropical bays.

A comparative hierarchical analysis of bacterioplankton and biofilm metacommunity structure in an interconnected pond system.

It is unknown whether bacterioplankton and biofilm communities are structured by the same ecological processes, and whether they influence each other through continuous dispersal (known as mass effects). Using a hierarchical sampling approach we compared the relative importance of ecological processes structuring the dominant fraction (relative abundance ≥0.1%) of bacterioplankton and biofilm communities from three microhabitats (open water, Nuphar and Phragmites sites) at within- and among-pond scale in a set of 14 interconnected shallow ponds. Our results demonstrate that while bacterioplankton and biofilm communities are highly distinct, a similar hierarchy of ecological processes is acting on them. For both community types, most variation in community composition was determined by pond identity and environmental variables, with no effect of space. The highest β-diversity within each community type was observed among ponds, while microhabitat type (Nuphar, Phragmites, open water) significantly influenced biofilm communities but not bacterioplankton. Mass effects among bacterioplankton and biofilm communities were not detected, as suggested by the absence of within-site covariation of biofilm and bacterioplankton communities. Both biofilm and plankton communities were thus highly structured by environmental factors (i.e., species sorting), with among-lake variation being more important than within-lake variation, whereas dispersal limitation and mass effects were not observed.

The relative importance of spatial and temporal variation in predicting community structure at different scales as estimated from Markov chain models

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 583:15-34 (2017) - DOI: https://doi.org/10.3354/meps12286 The relative importance of spatial and temporal variation in predicting community structure at different scales as estimated from Markov chain models Scott L. Morello1,2,*, Ron J. Etter1 1Department of Biology, University of Massachusetts, Boston, Massachusetts 02125, USA 2The Downeast Institute, PO Box 83, Beals, Maine 04611, USA *Corresponding author: scott.morello@umb.edu ABSTRACT: Models that incorporate complex interactions are useful tools for estimating the relative importance of ecological processes in changing ecological communities. Multispecies Markov chain models (MMCMs) use transition probabilities to explore how complex interactions influence community structure. However, the accuracy of MMCMs over different spatial and temporal scales is not well known and likely influenced by the scales over which species interactions differ. Here we explore how MMCM predictions vary with scale in the Gulf of Maine intertidal by quantifying transition probabilities at increasing temporal (annual, biannual, seasonal) and spatial (local, meso-, regional) scales. Model predictions were accurate at local scales, even with data from coarse sampling frequencies (annual), suggesting short-term variations in ecological processes do not strongly affect stable-stage community composition over these time scales. Models were less accurate when incorporating spatial variation beyond local scales. Geographic differences in species persistence, mortality, and colonization probabilities reduced MMCM predictive capacity. Our work demonstrates that MMCMs can predict local community structure, even with data from coarse sampling intervals, and may also be useful for identifying regional differences in ecological processes that might be responsible for shifts in community structure. KEY WORDS: Multispecies Markov chain · Rocky intertidal · Gulf of Maine · Spatial variation · Temporal variation Full text in pdf format Supplementary material PreviousNextCite this article as: Morello SL, Etter RJ (2017) The relative importance of spatial and temporal variation in predicting community structure at different scales as estimated from Markov chain models. Mar Ecol Prog Ser 583:15-34. https://doi.org/10.3354/meps12286 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 583. Online publication date: November 16, 2017 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2017 Inter-Research.

Community assembly in harsh environments: the prevalence of ecological drift in the heath vegetation of South America

Metacommunity dynamics is marked by a gradient ranging from pure ecological determinism to pure stochasticity. This gradient encompasses compositional turnover that is governed by ecological drift, selection and dispersal. Here we estimate the influences of selection, dispersal limitation acting in concert with drift, drift acting alone and homogenizing dispersal on the structure of tropical restinga heath vegetation growing under stressful conditions in north‐eastern South America. We hypothesize that if abiotic heterogeneity is strong enough, it could select distinct sets of colonizing species from neighbor ecosystems, with stress sensitive species occupying refuges created by abiotic heterogeneity and stress tolerators dominating the more exposed areas. In this case selection would occur at both biogeographical and local scales. Under its prevalence, we expect selection to have a major signature in the woody plant community structure in a phylogenetic null model. Alternatively, if abiotic heterogeneity is not strong enough to impose significant selection, the environment would be homogeneously stressful for the majority of species, and would be dominated species selected at biogeographical scale only. Under its prevalence, we expect drift to have a major signature in the phylogenetic null model. We used an analytical framework based on phylogenetic and community structure null models to assess the relative importance of ecological processes. We also aimed to characterize the ecosystem features that impose selection and dispersal limitation. We found that 95.1% of turnover in composition is attributable to drift, 2.4% to homogenizing dispersal, 2.1% to selection, and just 0.40% to dispersal limitation, thus confirming our Neutrality hypothesis. As expected, both soil and topographic variables influenced metacommunity structure. However, contrary to our prediction, light availability and vegetation structure were also important. The predominance of coarse spatial patterns correlated to topographic and soil properties suggests that coarse differences in wind exposure and associated vegetation and soil factors represent the main selective forces acting on the studied vegetation. The dominance of drift in the assembly of restinga heath vegetation is likely to result from homogeneously stressful environmental conditions and also from the ongoing colonization process that is taking place in the restinga by immigrants from species‐rich neighboring ecosystems.

Disturbance by large herbivores alters the relative importance of the ecological processes that influence the assembly pattern in heterogeneous meta-communities.

Disturbance caused by large herbivores can affect the relative importance of ecological processes in determining community assembly and may cause a systematic loss of biodiversity across scales. To examine changes in the community assembly pattern caused by an overabundance of large herbivores in Japan, we analyzed community composition data from before and after the overabundance occurred. The community assembly pattern becomes more random after the deer overabundance. In addition, result of variation partitioning revealed decrease in importance of environmental processes and increase in importance of spatial processes. However, response of turnover rate, niche breadth, and niche overlap was heterogeneous, according to scale of each environmental gradient. Our results emphasize the importance of conserving habitat specialists that represent the local environment (habitat type and topography) at various altitudinal ranges to maintain biodiversity at regional scales under the increasing pressure of large herbivores.

Spatial variability and human disturbance of sponge assemblages associated with mangrove roots in the southern Caribbean

Assemblages growing on Caribbean red-mangrove roots are very diverse and characteristically dominated by sponges. The scales of spatial variation of this fauna in the Caribbean region have not been hierarchically quantified, although such information is necessary to understand the relative importance of ecological processes and possible responses to anthropogenic disturbances. We used a hierarchical nested design to identify patterns of spatial variability at different scales, namely among roots, sites, localities and regions within the southern Caribbean. Simultaneously, the sampling considered the relative distance from sources of human disturbance to test the null hypothesis of no difference in sponge diversity among localities as a result of anthropogenic stress. Significant spatial variability in species composition was detected at all spatial scales, especially at the among-root scale. However, there were no differences associated with distance from human disturbance. These results indicate high regional and local β diversity, and also suggest that results from small-scale experiments cannot be scaled up to the entire community. Further, spatial analysis of sponge assemblages is not enough to detect deleterious effects of human disturbances on mangrove areas.

Complex and inconsistent patterns of variation in benthos, micro-algae and sediment over multiple spatial scales

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 398:33-47 (2010) - DOI: https://doi.org/10.3354/meps08328 Complex and inconsistent patterns of variation in benthos, micro-algae and sediment over multiple spatial scales M. G. Chapman*, T. J. Tolhurst, R. J. Murphy, A. J. Underwood Centre for Research on Ecological Impacts of Coastal Cities, Marine Ecology A11, University of Sydney, New South Wales 2006, Australia *Email: gee@bio.usyd.edu.au ABSTRACT: Because of their close physical relationship, it is often assumed that there are strong functional relationships between sediments and biota. Yet, there have been few studies of the characteristics of sediments over multiple spatial scales, despite evidence that micro-algae and macro- and meiofauna vary greatly at cm to km scales. This study quantified variability in macrofauna, micro-algae, and physical and biochemical properties of sediments over scales from 50 cm to km. The benthos was most variable at small scales and, even where there were large mean differences in abundance at large scales, these were small compared to the variation from plot to plot along a shore. Only 1 of 24 analyses showed larger variation at the scale of km than that found at 50 cm. Some measures of microphytobenthos showed large variation at the scale of 100s m or more, but other measures of the same flora did not show similar patterns. Concentrations of sand were consistent at different depths and at large scales, but concentrations of mud were more variable within than among shores. Neither sand nor mud correlated significantly with most biochemical properties of sediments. For sediments, variation at the scale of km was only larger than that of 50 cm in 13 of 57 analyses. To understand the relative importance of ecological processes in determining distributions and abundances, it is important to get quantitative data on the scales at which organisms or habitats vary. These are the scales at which ecological processes are likely to have large effects because large-scale processes are unlikely to explain variation at much smaller scales. The importance of small-scale variability in sediments and the associated biota is discussed in terms of sampling protocols for understanding ecological processes, or for assessing impact or restoration. KEY WORDS: Intertidal soft sediment · Microphytobenthos · Benthic assemblage · Spatial patterns · Components of variation · Scales Full text in pdf format PreviousNextCite this article as: Chapman MG, Tolhurst TJ, Murphy RJ, Underwood AJ (2010) Complex and inconsistent patterns of variation in benthos, micro-algae and sediment over multiple spatial scales. Mar Ecol Prog Ser 398:33-47. https://doi.org/10.3354/meps08328 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 398. Online publication date: January 05, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

COMPARING CATEGORICAL AND CONTINUOUS ECOLOGICAL ANALYSES: EFFECTS OF “WAVE EXPOSURE” ON ROCKY SHORES

Development of general theories and subsequent empirical testing are fundamental ingredients in ecological science. The progress of such efforts is determined by the logical coherence among central concepts, theories, and predictions on one hand, and experimental design, statistical analyses, and interpretation of results on the other. Here, we specifically explore an example of how differences in the way ecological concepts are defined lead to differences in the formulation and statistical testing of hypotheses and ultimately to differences in conclusions about the relative importance of ecological processes. In marine intertidal habitats, the notion that wave exposure has an important structuring role is widely agreed upon. Nevertheless, generalizations about its effects and use for accurate prediction of assemblages are often limited. This may partly be explained by the frequent use of categorical rather than quantitative definitions of wave exposure. We compared the conclusions about the importance of wave exposure from (1) analyses of variance based on relative classification of wave exposure and geographic location to those of (2) regression analyses based on continuous measures from 16 locations on the Swedish west coast. Variability in richness was substantially better explained by the regression analyses, while for the cover of individual taxa there was no consistent difference between the two analytical approaches in terms of explained variability. The two approaches detected significant spatial patterns for the same taxa, but conclusions about the nature of these patterns were often divergent. Categorical analyses of relative measures of wave exposure and geographic location indicated that interactive effects and differences between geographic areas were predominant. Regression analyses of absolute, continuous measures suggested that mean significant wave height was a better predictor than geographic location and interactive terms. Thus, the choice of definition of wave exposure has important consequences for how causes of spatial patterns of intertidal assemblages are perceived. Categorical analyses appear to provide clearer indications as to which factors are important while the use of continuous predictors sometimes provides a better fit to the data. The consequences of these findings are discussed in the context of rocky shore ecology as well as in a general perspective of ecological models, hypotheses, experimentation, and analysis.

Inferring Multiple Causality: The Limitations of Path Analysis

1. Review of published ecological studies using path analysis suggests that path analysis is often misused and collinearity is a moderate to severe problem in a majority of the analyses. 2. Multiple regression is shown to be related to path analysis, and thus collinearity, which is a well-known problem in regression analysis, can also be a problem in path analysis. Collinearity occurs when independent variables are highly correlated and causes estimates of standardized partial regression coefficients and of path coefficients to be less precise, less accurate and prone to rounding error. 3. A review of 24 path analyses in 12 papers revealed incorrectly calculated path coefficients in 13 cases and problems with collinearity in 15 cases. Estimates of path coefficients are biased and lack precision if there is collinearity. 4. An additional 40 path analyses could not be evaluated because of incomplete information. Most studies lack sufficient sample size to justify the use of path analysis. Problems associated with the use of categorical variables, which were used in six cases, are unappreciated. 5. These problems suggest that path coefficients may often mislead ecologists about the relative importance of ecological processes.