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Experimental evidence shows the importance of behavioural plasticity and body size under competition in waterfowl
Zhang, Y. ; Prins, H.H.T. ; Versluijs, Martijn ; Wessels, R. ; Cao, L. ; Boer, W.F. de - \ 2015
competition - waterbirds - behavioral - niche
The contribution of intra- and interspecific tolerance variability to biodiversity changes along chemical gradients
Laender, F. de; Melian, C. ; Bindler, R. ; Brink, P.J. van den; Daam, M. ; Roussel, H. ; Juselius, J. ; Verschuren, D.E.C.M. ; Janssen, C.R. - \ 2014
Ecology Letters 17 (2014)1. - ISSN 1461-023X - p. 72 - 81.
intraspecific variability - functional diversity - community ecology - neutral theory - central sweden - niche - model - individuals - sensitivity - ecosystems
The worldwide distribution of toxicants is an important yet understudied driver of biodiversity, and the mechanisms relating toxicity to diversity have not been adequately explored. Here, we present a community model integrating demography, dispersal and toxicant-induced effects on reproduction driven by intraspecific and interspecific variability in toxicity tolerance. We compare model predictions to 458 species abundance distributions (SADs) observed along concentration gradients of toxicants to show that the best predictions occur when intraspecific variability is five and ten times higher than interspecific variability. At high concentrations, lower settings of intraspecific variability resulted in predictions of community extinction that were not supported by the observed SADs. Subtle but significant species losses at low concentrations were predicted only when intraspecific variability dominated over interspecific variability. Our results propose intraspecific variability as a key driver for biodiversity sustenance in ecosystems challenged by environmental change.
Spatial coordination between stem cell activity and cell differentiation in the root meristem
Moubayidin, L. ; Mambro, R. Di; Sozzani, R. ; Pacifici, E. ; Salvi, E. ; Terpstra, I. ; Bao, D. ; Dijken, A. van; Dello loio, R. ; Perilli, S. ; Ljung, K. ; Benfey, P.N. ; Heidstra, R. ; Costantino, P. ; Sabatini, S. - \ 2013
Developmental cell 26 (2013)4. - ISSN 1534-5807 - p. 405 - 415.
gras gene family - arabidopsis root - auxin biosynthesis - scarecrow - expression - thaliana - transport - division - growth - niche
A critical issue in development is the coordination of the activity of stem cell niches with differentiation of their progeny to ensure coherent organ growth. In the plant root, these processes take place at opposite ends of the meristem and must be coordinated with each other at a distance. Here, we show that in Arabidopsis, the gene SCR presides over this spatial coordination. In the organizing center of the root stem cell niche, SCR directly represses the expression of the cytokinin-response transcription factor ARR1, which promotes cell differentiation, controlling auxin production via the ASB1 gene and sustaining stem cell activity. This allows SCR to regulate, via auxin, the level of ARR1 expression in the transition zone where the stem cell progeny leaves the meristem, thus controlling the rate of differentiation. In this way, SCR simultaneously controls stem cell division and differentiation, ensuring coherent root growth.
Biodiversity simultaneously enhances the production and stability of community biomass, but the effects are independent
Cardinale, B.J. ; Gross, K. ; Fritschie, K. ; Flombaum, P. ; Fox, J. ; Rixen, C. ; Ruijven, J. van; Reich, P.B. ; Scherer-Lorenzen, M. ; Wilsey, B.J. - \ 2013
Ecology 94 (2013)8. - ISSN 0012-9658 - p. 1697 - 1707.
plant diversity - ecosystem services - species-richness - statistical inevitability - grassland experiment - current knowledge - complementarity - impacts - niche - multifunctionality
Human domination of the planet is dismantling Earth's ecosystems one gene, species, and biological trait at a time. To predict the ecological consequences of biodiversity loss, researchers have spent much of the past two decades quantifying how biological variation affects the magnitude and stability of ecological processes that underlie the functioning of ecosystems. Here we add to this work by looking at how biodiversity jointly impacts two aspects of ecosystem functioning at once: (1) the production of biomass at any single point in time (biomass area-1 or volume-1), and (2) the stability of biomass production through time (the CV-1 of changes in total community biomass through time). While is often assumed that biodiversity simultaneously enhances both aspects of ecosystem functioning, the joint distribution of data describing how species richness impacts productivity and stability has yet to be quantified. Furthermore, analyses have yet to examine how diversity effects on production covary with diversity effects on stability. To overcome these two gaps, we re-analyzed 34 experiments that have manipulated the richness of terrestrial plants or aquatic algae and measured how diversity affects community biomass at multiple time points. Our re-analysis confirms that biodiversity does indeed simultaneously enhance both the production and stability of biomass, and this is broadly true for a variety of primary producers. However, the strength of diversity effects on biomass production is independent of diversity effects on temporal stability. Independence of effect sizes leads to two important conclusions. First, while it may be generally true that biodiversity enhances both productivity and stability, it is also true that the highest levels of productivity in a diverse community are not associated with the highest levels of stability. Thus, on average, diversity does not maximize the various aspects of ecosystem functioning we might wish to achieve in the conservation and management. Second, knowing how biodiversity affects productivity gives no information about how diversity affects stability (or vice versa). If we are to understand and predict the variety of ecological changes that occur in ecosystems after extinction, it is imperative that we develop separate mechanistic models for each independent aspect of ecosystem functioning.
Legume Diversity Patterns in West Central Africa
Estrella, M. de la; Mateo, M.A. ; Wieringa, J.J. ; Mackinder, B. ; Munoz, J. - \ 2012
PLoS One 7 (2012)7. - ISSN 1932-6203 - 12 p.
climate-change - sample-size - plant diversity - indicator groups - community-level - envelope models - conservation - biodiversity - performance - niche
Objectives - Species Distribution Models (SDMs) are used to produce predictions of potential Leguminosae diversity in West Central Africa. Those predictions are evaluated subsequently using expert opinion. The established methodology of combining all SDMs is refined to assess species diversity within five defined vegetation types. Potential species diversity is thus predicted for each vegetation type respectively. The primary aim of the new methodology is to define, in more detail, areas of species richness for conservation planning. Methodology - Using Maxent, SDMs based on a suite of 14 environmental predictors were generated for 185 West Central African Leguminosae species, each categorised according to one of five vegetation types: Afromontane, coastal, non-flooded forest, open formations, or riverine forest. The relative contribution of each environmental variable was compared between different vegetation types using a nonparametric Kruskal-Wallis analysis followed by a post-hoc Kruskal-Wallis Paired Comparison contrast. Legume species diversity patterns were explored initially using the typical method of stacking all SDMs. Subsequently, five different ensemble models were generated by partitioning SDMs according to vegetation category. Ecological modelers worked with legume specialists to improve data integrity and integrate expert opinion in the interpretation of individual species models and potential species richness predictions for different vegetation types. Results/Conclusions - Of the 14 environmental predictors used, five showed no difference in their relative contribution to the different vegetation models. Of the nine discriminating variables, the majority were related to temperature variation. The set of variables that played a major role in the Afromontane species diversity model differed significantly from the sets of variables of greatest relative important in other vegetation categories. The traditional approach of stacking all SDMs indicated overall centers of diversity in the region but the maps indicating potential species richness by vegetation type offered more detailed information on which conservation efforts can be focused.
Emergent neutrality leads to multimodal species abundance distributions
Vergnon, R. ; Nes, E.H. van; Scheffer, M. - \ 2012
Nature Communications 3 (2012). - ISSN 2041-1723 - 6 p.
body-size - community - biodiversity - coexistence - diversity - ecology - model - similarity - paradox - niche
Recent analyses of data sampled in communities ranging from corals and fossil brachiopods to birds and phytoplankton suggest that their species abundance distributions have multiple modes, a pattern predicted by none of the existing theories. Here we show that the multimodal pattern is consistent with predictions from the theory of emergent neutrality. This adds to the observations, suggesting that natural communities may be shaped by the evolutionary emergence of groups of similar species that coexist in niches. Such self-organized similarity unifies niche and neutral theories of biodiversity.
Trait assembly of woody plants in communities across sub-alpine gradients: Identifying the role of limiting similarity
Yan, B. ; Zhang, J. ; Liu, Y. ; Li, Z. ; Huang, X. ; Yang, W. ; Prinzing, A. - \ 2012
Journal of Vegetation Science 23 (2012)4. - ISSN 1100-9233 - p. 698 - 708.
functional traits - amazonian forest - neutral theory - niche - coexistence - height - growth - consequences - convergence - equivalence
Questions - Plant species can be assembled into communities through habitat filtering or species competition, but their relative roles are still debated. We do not know whether there is limited similarity between co-existing species when accounting for the parallel effect of abiotic habitat filtering and biotic competition. By accounting for such effects, we test the predictions of three theories (classic niche theory, the Hubbell neutrality theory and the Scheffer and van Nes theory) of community assembly. Location - Two vegetation transitions (a grazing gradient and a timber line ecotone) in a sub-alpine area of western Sichuan Province, China (31° 51'N, 102° 41'E). Methods - We used a null model to investigate the above plant community assembly theories on two sub-alpine gradients of woody vegetation. In the null model, species traits were constrained between the maximum and minimum trait values of observed communities to test the principle of limiting similarity between co-existing species by testing for even spacing of traits. We analysed traits characterizing growth strategies of stems, leaves and twigs, measured at the level of individuals in situ. Results - After accounting for variations in trait range, it became evident that six out of eight traits showed significantly uneven spacing within some plots, notably towards the forest end of the gradient, i.e. under increased competition pressure among woody plants. The Wilcoxon rank test showed that seven out of eight traits were significantly unevenly spaced within plots. The two transitions studied showed surprisingly similar patterns, despite their dissimilar precise drivers.
Invasion success depends on invader body size in a size-structured mixed predation-competition community
Schroder, A. ; Nilsson, K.A. ; Persson, L. ; Kooten, T. van; Reichstein, B. - \ 2009
Journal of Animal Ecology 78 (2009)6. - ISSN 0021-8790 - p. 1152 - 1162.
whole-lake experiments - intraguild predation - heterandria-formosa - food webs - interspecific interactions - age structure - prey - populations - dynamics - niche
P>1. The size of an individual is an important determinant of its trophic position and the type of interactions it engages in with other heterospecific and conspecific individuals. Consequently an individual's ecological role in a community changes with its body size over ontogeny, leading to that trophic interactions between individuals are a size-dependent and ontogenetically variable mixture of competition and predation. 2. Because differently sized individuals thus experience different biotic environments, invasion success may be determined by the body size of the invaders. Invasion outcome may also depend on the productivity of the system as productivity influences the biotic environment. 3. In a laboratory experiment with two poeciliid fishes the body size of the invading individuals and the daily amount of food supplied were manipulated. 4. Large invaders established persistent populations and drove the resident population to extinction in 10 out of 12 cases, while small invaders failed in 10 out of 12 trials. Stable coexistence was virtually absent. Invasion outcome was independent of productivity. 5. Further analyses suggest that small invaders experienced a competitive recruitment bottleneck imposed on them by the resident population. In contrast, large invaders preyed on the juveniles of the resident population. This predation allowed the large invaders to establish successfully by decreasing the resident population densities and thus breaking the bottleneck. 6. The results strongly suggest that the size distribution of invaders affects their ability to invade, an implication so far neglected in life-history omnivory systems. The findings are further in agreement with predictions of life-history omnivory theory, that size-structured interactions demote coexistence along a productivity gradient.
Oak seedling survival and growth along resource gradients in Mediterranean forests: implications for regeneration in current and future environmental scenarios
Gómez-Aparicio, L. ; Pérez-Ramos, I.M. ; Mendoza, L. ; Matías, L. ; Quero, J.L. ; Castro, J. ; Zamora, R. ; Marañón, T. - \ 2008
Oikos 117 (2008)11. - ISSN 0030-1299 - p. 1683 - 1699.
water-use efficiency - pinus-halepensis - southern spain - global change - tree - establishment - niche - heterogeneity - drought - recruitment
Understanding seedling performance across resource gradients is crucial for defining the regeneration niche of plant species under current environmental conditions and for predicting potential changes under a global change scenario. A 2-year field experiment was conducted to determine how seedling survival and growth of two evergreen and two deciduous Quercus species vary along gradients of light and soil properties in two Mediterranean forests with contrasting soils and climatic conditions. Half the seedlings were subjected to an irrigation treatment during the first year to quantify the effects on performance of an alteration in the summer drought intensity. Linear and non-linear models were parameterized and compared to identify major resources controlling seedling performance. We found both site-specific and general patterns of regeneration. Strong site-specificity was found in the identity of the best predictors of seedling survival: survival decreased linearly with increasing light (i.e. increasing desiccation risk) in the drier site, whereas it decreased logistically with increasing spring soil water content (i.e. increasing waterlogging risk) in the wetter site. We found strong empirical support for multiple resource limitation at the drier site, the response to light being modulated by the availability of soil resources (water and P). Evidence for regeneration niche partitioning among Quercus species was only found at the wetter site. However, at both sites Quercus species shared the same response to summer drought alleviation through water addition: increased first-year survival but not final survival (i.e. after two years). This suggests that extremely dry summers (i.e. the second summer in the experiment) can cancel out the positive effects of previous wetter summers. Therefore, an increase in the intensity and frequency of summer drought with climate change might cause a double negative impact on Quercus regeneration, due to a general reduction in survival probability and the annulment of the positive effects of (infrequent) 'wet' years. Overall, results presented in this study are a major step towards the development of a mechanistic model of Mediterranean forest dynamics that incorporates the idiosyncrasies and generalities of tree regeneration in these systems, and that allow simulation and prediction of the ecological consequences of resource level alterations due to global change.
Less lineages - more trait variation: phylogenetically clustered plant communities are functionally more diverse
Prinzing, A. ; Reiffers, R.C. ; Braakhekke, W.G. ; Hennekens, S.M. ; Tackenberg, O. ; Ozinga, W.A. ; Schaminée, J.H.J. ; Groenendael, J.M. van - \ 2008
Ecology Letters 11 (2008)8. - ISSN 1461-023X - p. 809 - 819.
environmental-conditions - niche - evolution - similarity - phylogeny - grassland - depends - signal - scale
Functional diversity within communities may influence ecosystem functioning, but which factors drive functional diversity? We hypothesize that communities assembled from many phylogenetic lineages show large functional diversity if assembly is random, but low functional diversity if assembly is controlled by interactions between species within lineages. We combined > 9000 descriptions of Dutch plant communities, a species-level phylogeny, and information on 16 functional traits (including eight dispersal traits). We found that all traits were conserved within lineages, but nevertheless communities assembled from many lineages showed a smaller variation in trait-states of most traits (including dispersal traits) than communities assembled from few lineages. Hence, within lineages, species are not randomly assembled into communities, contradicting Neutral Theory. In fact, we find evidence for evolutionary divergence in trait-states as well as present-day mutual exclusion among related, similar species, suggesting that functional diversity of communities increased due to past and present interactions between species within lineages.
Habitat-mediated cannibalism and microhabitat restriction in the stream invertebrate Gammarus pulex
McGrath, K.E. ; Peeters, E.T.H.M. ; Beijer, J.A.J. ; Scheffer, M. - \ 2007
Hydrobiologia 589 (2007)1. - ISSN 0018-8158 - p. 155 - 164.
size-structured populations - threespine stickleback - amphipoda - predation - niche - dynamics - drift
In cannibalistic species, small individuals often shift habitats to minimize risk of predation by larger conspecifics. The availability of diverse size-structured habitats may mediate the incidence of cannibalism by larger individuals on smaller individuals and increase fitness of smaller individuals. We tested these hypotheses in a series of laboratory studies with Gammarus pulex, a freshwater amphipod inhabiting substrates with varying interstitial pore space sizes. In the absence of larger, potentially cannibalistic individuals, small Gammarus actively used all pore space sizes offered. They used only substrates containing food and preferred food items that provided cover to food items that did not. In the presence of larger G. pulex, small individuals almost exclusively used smaller pore spaces from which larger individuals were excluded. Small individual survival was significantly lower in the presence of larger Gammarus than in controls without larger individuals regardless of substrate size, but availability of mixed pore sizes significantly increased survival. Food consumption and growth per individual were not affected by the presence of larger individuals or substrate composition. Our results suggest that the distribution and availability of complex and high-quality habitats may affect the occurrence and significance of cannibalism in size-structured populations.
Conflicts between traditional pastoralism and conservation of Himalayan ibex (Capra sibirica) in the Trans-Himalayan mountains
Bagchi, S. ; Mishra, C. ; Bhatnagar, Y.V. - \ 2004
Animal Conservation 7 (2004). - ISSN 1367-9430 - p. 121 - 128.
interspecific competition - biodiversity conservation - patterns - degradation - communities - serengeti - exclusion - behavior - overlap - niche
There is recent evidence to suggest that domestic livestock deplete the density and diversity of wild herbivores in the cold deserts of the Trans-Himalaya by imposing resource limitations. To ascertain the degree and nature of threats faced by Himalayan ibex (Capra sibirica) from seven livestock species, we studied their resource use patterns over space, habitat and food dimensions in the pastures of Pin Valley National Park in the Spiti region of the Indian Himalaya. Species diet profiles were obtained by direct observations. We assessed the similarity in habitat use and diets of ibex and livestock using Non-Metric Multidimensional Scaling. We estimated the influence of the spatial distribution of livestock on habitat and diet choice of ibex by examining their co-occurrence patterns in cells overlaid on the pastures. The observed co-occurrence of ibex and livestock in cells was compared with null-models generated through Monte Carlo simulations. The results suggest that goats and sheep impose resource limitations on ibex and exclude them from certain pastures. In the remaining suitable habitat, ibex share forage with horses. Ibex remained relatively unaffected by other livestock such as yaks, donkeys and cattle. However, most livestock removed large amounts of forage from the pastures (nearly 250 kg of dry matter/day by certain species), thereby reducing forage availability for ibex. Pertinent conservation issues are discussed in the light of multiple-use of parks and current socio-economic transitions in the region, which call for integrating social and ecological feedback into management planning.