scholarly journals An experimental manipulation of species’ phenologies overturns competitive hierarchies

2019 ◽  
Author(s):  
Christopher Blackford ◽  
Rachel M. Germain ◽  
Benjamin Gilbert
Keyword(s):  
Head Start ◽  
Species Coexistence ◽  
Experimental Manipulation ◽  
Grass Species ◽  
Relative Timing ◽  
Niche Differences ◽  
Competitive Hierarchies ◽  
Germination Timing ◽  
Phenological Event

AbstractEcological theory produces opposing predictions about whether differences in the timing of life history transitions, or ‘phenology’, promote or limit coexistence. Phenological separation is predicted to create temporal niche differences, increasing coexistence, yet phenological separation may competitively favour one species, increasing fitness differences and hindering coexistence. We experimentally manipulated relative germination timing, a critical phenological event, of two annual grass species,Vulpia microstachysandV. octoflora, to test these contrasting predictions. We parameterized a competition model to estimate within-season niche differences, fitness differences, and coexistence, and to estimate coexistence when among-year fluctuations of germination timing occur. Increasing germination separation caused parallel changes in niche and fitness differences, with the net effect of weakening within-year coexistence. Both species experienced a competitive advantage by germinating earlier, strongly enough to allow the generally inferior competitor to exclude the other with at least a four day head start. The overall consequence of germination separation was to limit coexistence within a given year, although among-year variation in relative timing of germination was sufficient to support long-term coexistence. Our results clarify how phenological differences structure competitive interactions, and highlight the need to quantify among-year variation in these differences to better understand species coexistence.

scholarly journals An Empiricist’s Guide to Modern Coexistence Theory for Competitive Communities

2019 ◽  
Author(s):  
Casey M. Godwin ◽  
Feng-Hsun Chang ◽  
Bradley Cardinale
Keyword(s):  
Species Coexistence ◽  
Empirical Studies ◽  
Empirical Work ◽  
Relative Fitness ◽  
Empirical Methods ◽  
Coexistence Theory ◽  
Niche Differences ◽  
Rate Versus ◽  
Resource Requirements ◽  
Competitive Hierarchies

AbstractWhile most ecological theories have historically invoked niche differences as the primary mechanism allowing species coexistence, we now know that species coexistence in competitive communities actually depends on the balance of two opposing forces: niche differences (ND) that determine how species limit their own growth rate versus that of their competitor, and relative fitness differences (RFD) that establish competitive hierarchies among species. Several different empirical methods have been proposed for measuring ND and RFD in order to make predictions about coexistence of species, yet it remains unclear which method(s) are appropriate for a given empirical study and whether or not those methods actually yield the same information. Here we summarize and compare five different empirical methods, with the aim of providing a practical guide for empiricists who want to predict coexistence among species. These include two phenomenological methods that estimate ND and RFD based on observing competitive interactions among species; two mechanistic methods that estimate ND and RFD based solely on information about species’ resource requirements; and a fifth method that does not yield ND and RFD but describes the impacts of those forces within communities. Based on the specific requirements, limitations, and assumptions of each approach, we offer a series of decision steps that can be used to determine which method(s) are best for a given study system. In particular, we show there are important tradeoffs between mechanistic methods, which require detailed understanding of species niches and physiology but are more tractable experimentally, and phenomenological methods which do not require this detailed information but can be impractical for some study designs. Importantly, we show that although each method can be used to estimate ND and RFD, the methods do not always yield the same values. Therefore we caution against future syntheses that compile these estimates from different empirical studies. Finally, we highlight several areas where modern coexistence theory could benefit from additional empirical work.

Implications of Long-Term Studies of Three Model Preschool Programs for Head Start

2008 ◽  
Author(s):  
Lawrence J. Schweinhart ◽  
Elena V. Malofeeva ◽  
Lawrence J. Schweinhart ◽  
Michelle M. Englund ◽  
Arthur J. Reynolds ◽  
...  
Keyword(s):  
Head Start ◽  
Preschool Programs ◽  
Long Term Studies

scholarly journals Table Talk: development of an observational tool to assess verbal feeding communications in early care and education settings

2017 ◽  
Vol 20 (16) ◽  
pp. 2869-2877 ◽  
Author(s):  
Taren Swindle ◽  
Julie M Rutledge ◽  
Belynda Dix ◽  
Leanne Whiteside-Mansell
Keyword(s):  
Head Start ◽  
Weight Status ◽  
Early Care And Education ◽  
Early Care ◽  
Observational Tool ◽  
Potential Applications ◽  
Table Talk ◽  
Short And Long Term ◽  
Trained Observers

AbstractObjectiveChildren’s dietary intake impacts weight status and a range of short- and long-term health outcomes. Accurate measurement of factors that influence children’s diet is critical to the development and evaluation of interventions designed to improve children’s diets. The purpose of the current paper is to present the development of the Table Talk observational tool to measure early care and education teachers’ (ECET) verbal feeding communications.DesignAn observational tool to assess ECET verbal communication at mealtimes was deigned based on the extant literature. Trained observers conducted observations using the tool during lunch for both lead and assistant ECET. Descriptive statistics, test–retest for a subgroup, interclass correlations for each item, and comparisons between leads and assistants were conducted.SettingHead Start centres, Southern USA.SubjectsSeventy-five Head Start educators.ResultsOn average, 17·2 total verbal feeding communications (sd8·9) were observed per ECET. For lead ECET, the most prevalent Supportive Comment was Exploring Foods whereas for assistants Making Positive Comments was the most prevalent. Overall, lead ECET enacted more Supportive Comments than assistant ECET (F(2,72)=4·8,P=0·03). The most common Unsupportive Comment was Pressuring to Eat, with a mean of 3·8 (sd4·3) and a maximum of 25. There was no difference in Unsupportive Comments between lead and assistant ECET.ConclusionsTable Talk may be a useful tool to assess verbal feeding communications of ECET, with potential applications such as informing ECET training and assessing intervention efforts.

Grazing intensity rather than host plant’s palatability shape the community of arbuscular mycorrhizal fungi in a steppe grassland

2021 ◽  
Author(s):  
Maede Faghihinia ◽  
Yi Zou ◽  
Yongfei Bai ◽  
Martin Dudáš ◽  
Rob Marrs ◽  
...  
Keyword(s):  
Arbuscular Mycorrhizal Fungi ◽  
Community Composition ◽  
Mycorrhizal Fungi ◽  
Rhizosphere Soil ◽  
Grazing Intensity ◽  
Arbuscular Mycorrhizal ◽  
Grass Species ◽  
Α Diversity ◽  
Steppe Grassland

Abstract Arbuscular mycorrhizal fungi (AMF) are the predominant type of mycorrhizal fungi in roots and rhizosphere soil of grass species worldwide. Grasslands are currently experiencing increasing grazing pressure, but it is not yet clear how grazing intensity and host plant grazing preference by large herbivores interact with soil- and root-associated AMF communities. Here, we tested whether the diversity and community composition of AMF in the roots and rhizosphere soil of two dominant perennial grasses grazed differently by livestock change in response to grazing intensity. We conducted a study in a long-term field experiment in which seven levels of field-manipulated grazing intensities were maintained for 13 years in a typical steppe grassland in northern China. We extracted DNA from the roots and rhizosphere soil of two dominant grasses, Leymus chinense (Trin.) Tzvel. and Stipa grandis P. Smirn, with contrasting grazing preference by sheep. AMF DNA from root and soil samples were then subjected to molecular analysis. Our results showed that AMF α-diversity (richness) at the virtual taxa (VT) level varied as a function of grazing intensity. Different VTs showed completely different responses along the gradient, one increasing, one decreasing and others showing no response. Glomeraceae was the most abundant AMF family along the grazing gradient, which fits well with the theory of disturbance tolerance of this group. In addition, sheep grazing preference for host plants did not explain a considerable variation in AMF α-diversity. However, the two grass species exhibited different community composition in their roots and rhizosphere soils. Roots exhibited a lower α-diversity and higher β-diversity within the AMF community than soils. Overall, our results suggest that long-term grazing intensity might have changed the abundance of functionally-diverse AMF taxa in favor of those with disturbance-tolerant traits. We suggest our results would be useful in informing the choice of mycorrhizal fungi indicator variables when assessing the impacts of grassland management choices on grassland ecosystem functioning.

scholarly journals Stratigraphy of the Anthropocene

2011 ◽  
Vol 369 (1938) ◽  
pp. 1036-1055 ◽  
Author(s):  
Jan Zalasiewicz ◽  
Mark Williams ◽  
Richard Fortey ◽  
Alan Smith ◽  
Tiffany L. Barry ◽  
...  
Keyword(s):  
Sediment Flux ◽  
Relative Timing ◽  
Sequence Stratigraphic ◽  
The Earth ◽  
Time Space ◽  
Marine Realm ◽  
Physical And Chemical ◽  
The Impact ◽  
Long Term Preservation

The Anthropocene, an informal term used to signal the impact of collective human activity on biological, physical and chemical processes on the Earth system, is assessed using stratigraphic criteria. It is complex in time, space and process, and may be considered in terms of the scale, relative timing, duration and novelty of its various phenomena. The lithostratigraphic signal includes both direct components, such as urban constructions and man-made deposits, and indirect ones, such as sediment flux changes. Already widespread, these are producing a significant ‘event layer’, locally with considerable long-term preservation potential. Chemostratigraphic signals include new organic compounds, but are likely to be dominated by the effects of CO 2 release, particularly via acidification in the marine realm, and man-made radionuclides. The sequence stratigraphic signal is negligible to date, but may become geologically significant over centennial/millennial time scales. The rapidly growing biostratigraphic signal includes geologically novel aspects (the scale of globally transferred species) and geologically will have permanent effects.

scholarly journals Pulling on multiple threads of evidence to reveal tree species coexistence

2021 ◽  
Author(s):  
Gordon G McNickle ◽  
Morgan V Ritzi ◽  
Kliffi M.S. Blackstone ◽  
John J Couture ◽  
Taylor Nelson ◽  
...  
Keyword(s):  
Tree Species ◽  
Species Coexistence ◽  
Analysis Data ◽  
The United States ◽  
United States Department ◽  
Hardwood Species ◽  
Niche Differences ◽  
The Usa ◽  
Multiple Threads ◽  
Occurrence Patterns

Understanding drivers of species coexistence is a central challenge in ecology. Coexistence cannot be observed directly, and while species co-occurrence in time and space is necessary for coexistence, it is not sufficient to prove coexistence. Species exclusion from a region is potentially observable, but can take decades to occur, and still might occur stochastically. Thus, ecologists generally use theory to identify indirect observations that are indicative of mechanisms driving coexistence or exclusion. Various methods have been developed to indirectly infer coexistence, each of which requires different data, and none of which are usually conclusive on their own. Here, we demonstrate agreement using three different approaches examining coexistence of multiple hardwood species. First, in an experimental planting of three mature tree species we found no relationship between productivity and species diversity, which could be due to a lack of niche differences among species. Second, we used modern coexistence theory to calculate niche and fitness differences for each pair of species, which confirmed the lack of niche differences among species, and showed high fitness differences that could create a neutral distribution of species in nature. Third, we used the United States Department of Agriculture Forest Inventory and Analysis data to examine co-occurrence patterns of our species across thousands of natural forest stands and found that indeed, these three species were distributed randomly throughout the USA. Given that these independent methods agree, we take this as strong evidence about a lack of coexistence.

scholarly journals Species coexistence and overlapping distributions in a metacommunity are compatible with niche differences and competition at a local scale

2020 ◽  
Author(s):  
Maxime Dubart ◽  
Patrice David ◽  
Frida Ben-Ami ◽  
Christoph R. Haag ◽  
V. Ilmari Pajunen ◽  
...  
Keyword(s):  
Species Coexistence ◽  
Scale Up ◽  
Niche Partitioning ◽  
Niche Differentiation ◽  
Apparent Paradox ◽  
Extinction Rates ◽  
Interspecific Differences ◽  
Baltic Coast ◽  
Species Specific

AbstractNiche partitioning is the most studied factor structuring communities of competing species. In fragmented landscapes, however, a paradox can exist: different taxa may competitively dominate different types of habitat patches, resulting in a form of spatial niche partitioning, yet differences in long-term distributions among species can appear surprisingly small. This paradox is illustrated by an emblematic metacommunity - that of Daphnia spp. in rockpools on the Finnish Baltic coast, where three species compete with each other, have distinct ecological preferences, yet largely overlap in long-term distributions. Here we examine how metacommunity models that explicitly estimate species-specific demographic parameters can solve the apparent paradox. Our research confirms previous studies that local extinction rates are influenced by environmental variables in a strong and species-specific way and are considerably increased by interspecific competition. Yet, our simulations show that this situation exists alongside interspecific differences in realized niches that are, overall, small, and identified three main explanations for this compatibility. Our results illustrate how state-space modelling can clarify complex metacommunity dynamics and explain why local competition and niche differentiation do not always scale up to the landscape level.

scholarly journals The impact of drought stress on the yields and food value of selected forage grasses

2016 ◽  
Vol 69 (2) ◽  
Author(s):  
Mariola Staniak
Keyword(s):  
Soil Moisture ◽  
Water Stress ◽  
Drought Stress ◽  
Dry Matter ◽  
Nutritional Value ◽  
Lolium Multiflorum ◽  
Grass Species ◽  
Forage Grasses ◽  
The Impact

<p>The aim of the study was to compare yields and nutritional value of selected species and cultivars of forage grasses under the optimal moisture conditions and long-term drought stress. The regenerative capacity of plants after dehydration was also assessed. The pot experiment was conducted in years 2009–2010 in IUNG-PIB’s greenhouse in Puławy, Poland. Nine cultivars of four species: <em>Dactylis glomerata</em> (‘Amera’, ‘Minora’), <em>Festuca pratensis</em> (‘Skra’, ‘Fantazja’), <em>Festulolium braunii</em> (‘Felopa’, ‘Agula’, ‘Sulino’), and <em>Lolium multiflorum</em> (‘Gisel’, ‘Lotos’) were investigated in well-watered conditions (70% field water capacity – FWC) and under a long-term drought stress (40% FWC).</p><p>The study showed that stress caused by soil moisture deficiency significantly reduced yields of <em>D. glomerata</em>, <em>F. pratensis</em>, <em>F. braunii</em>, and <em>L. multiflorum</em>. The total yield of dry matter under stress conditions was about 31% lower, compared to the performance achieved on the optimally moisturized treatment. The smallest reduction in dry matter yield under the conditions of water deficit was recorded for <em>D. glomerata</em>, which makes it the most resistant to stress, followed by <em>F. pratensis</em>. The resistance of <em>F. braunii</em> and <em>L. multiflorum</em> to stress was similar and significantly lower. There was a various response of different grasses to the water stress. On the basis of the value of the DSI (drought susceptibility index), the tested cultivars were ranked depending on the sensitivity to drought, starting with the most resistant cultivar: ‘Minora’, ‘Skra’, ‘Fantazja’, ‘Amera’, ‘Sulino’, ‘Agula’, ‘Gisel’, ‘Lotos’, and ‘Felopa’. The digestibility of dry matter and nutrient value of the grasses depended on both the level of soil moisture and grass species. Under the water stress, the digestibility and protein value increased compared to the control objects. <em>Lolium multiflorum</em> and <em>F. braunii</em> had the best nutritional value, while <em>D. glomerata</em> – the weakest.</p>

scholarly journals Order of arrival promotes coexistence via spatial niche preemption by the weak competitor

2021 ◽  
Author(s):  
Inês Fragata ◽  
Raul Costa-Pereira ◽  
Agnieszka Majer (Kiedrowicz) ◽  
Oscar Godoy ◽  
Sara Magalhães
Keyword(s):  
Competitive Ability ◽  
Species Coexistence ◽  
Mite Species ◽  
Priority Effects ◽  
Historical Contingency ◽  
Niche Differences ◽  
Competitive Outcomes ◽  
Two Generations ◽  
Weak Competitor ◽  
Spatial Niche

Historical contingency, such as the order of species arrival, can modify competitive outcomes via niche modification or preemption. However how these mechanisms ultimately modify stabilising niche and average fitness differences remains largely unknown. By experimentally assembling two congeneric spider mite species feeding on tomato plants during two generations, we show that order of arrival interacts with species’ competitive ability to determine competitive outcomes. Contrary to expectations, we did not observe that order of arrival cause priority effects. In fact, coexistence was predicted when the inferior competitor (Tetranychus urticae) arrived first. In that case, T. urticae colonized the preferred feeding stratum (leaves) of T. evansi leading to spatial niche preemption, which equalized fitness but also increased niche differences, driving community assembly to a close-to-neutrality scenario. Our study demonstrates how the spatial context of competitive interactions interact with species competitive ability to influence the effect of order of arrival on species coexistence.

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