scholarly journals Multispecies coexistence of trees in tropical forests: spatial signals of topographic niche differentiation increase with environmental heterogeneity

2013 ◽  
Vol 280 (1764) ◽  
pp. 20130502 ◽  
Author(s):  
C. Brown ◽  
D. F. R. P. Burslem ◽  
J. B. Illian ◽  
L. Bao ◽  
W. Brockelman ◽  
...  
Keyword(s):  
Spatial Structure ◽  
Environmental Heterogeneity ◽  
Neutral Theory ◽  
Strong Support ◽  
Empirical Support ◽  
Niche Differentiation ◽  
Heterogeneous Environments ◽  
Strong Positive Relationship ◽  
Species Pairs ◽  
Topographic Heterogeneity

Neutral and niche theories give contrasting explanations for the maintenance of tropical tree species diversity. Both have some empirical support, but methods to disentangle their effects have not yet been developed. We applied a statistical measure of spatial structure to data from 14 large tropical forest plots to test a prediction of niche theory that is incompatible with neutral theory: that species in heterogeneous environments should separate out in space according to their niche preferences. We chose plots across a range of topographic heterogeneity, and tested whether pairwise spatial associations among species were more variable in more heterogeneous sites. We found strong support for this prediction, based on a strong positive relationship between variance in the spatial structure of species pairs and topographic heterogeneity across sites. We interpret this pattern as evidence of pervasive niche differentiation, which increases in importance with increasing environmental heterogeneity.

scholarly journals Region-specific elevations of glutamate + glutamine correlate with the sensory symptoms of autism spectrum disorders

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jason L. He ◽  
Georg Oeltzschner ◽  
Mark Mikkelsen ◽  
Alyssa Deronda ◽  
Ashley D. Harris ◽  
...  
Keyword(s):  
Autism Spectrum Disorders ◽  
Strong Support ◽  
Empirical Support ◽  
Brain Regions ◽  
Autism Spectrum ◽  
Resonance Spectroscopy ◽  
Primary Sensorimotor Cortex ◽  
Spectrum Disorders ◽  
Inhibitory Signaling

AbstractIndividuals on the autism spectrum are often reported as being hyper- and/or hyporeactive to sensory input. These sensory symptoms were one of the key observations that led to the development of the altered excitation-inhibition (E-I) model of autism, which posits that an increase ratio of excitatory to inhibitory signaling may explain certain phenotypical expressions of autism spectrum disorders (ASD). While there has been strong support for the altered E-I model of autism, much of the evidence has come from animal models. With regard to in-vivo human studies, evidence for altered E-I balance in ASD come from studies adopting magnetic resonance spectroscopy (MRS). Spectral-edited MRS can be used to provide measures of the levels of GABA + (GABA + macromolecules) and Glx (glutamate + glutamine) in specific brain regions as proxy markers of inhibition and excitation respectively. In the current study, we found region-specific elevations of Glx in the primary sensorimotor cortex (SM1) in ASD. There were no group differences of GABA+ in either the SM1 or thalamus. Higher levels of Glx were associated with more parent reported difficulties of sensory hyper- and hyporeactivity, as well as reduced feed-forward inhibition during tactile perception in children with ASD. Critically, the finding of elevated Glx provides strong empirical support for increased excitation in ASD. Our results also provide a clear link between Glx and the sensory symptoms of ASD at both behavioral and perceptual levels.

scholarly journals Environmental heterogeneity decreases reproductive success via effects on foraging behaviour

2019 ◽  
Vol 286 (1904) ◽  
pp. 20190795 ◽  
Author(s):  
Alice M. Trevail ◽  
Jonathan A. Green ◽  
Jonathan Sharples ◽  
Jeff A. Polton ◽  
Peter I. Miller ◽  
...  
Keyword(s):  
Reproductive Success ◽  
Environmental Heterogeneity ◽  
Optimal Foraging Theory ◽  
Gps Tracking ◽  
Heterogeneous Environments ◽  
Rissa Tridactyla ◽  
Distribution Of Resources ◽  
Resource Patches ◽  
Patch Density ◽  
The Cost

Environmental heterogeneity shapes the uneven distribution of resources available to foragers, and is ubiquitous in nature. Optimal foraging theory predicts that an animal's ability to exploit resource patches is key to foraging success. However, the potential fitness costs and benefits of foraging in a heterogeneous environment are difficult to measure empirically. Heterogeneity may provide higher-quality foraging opportunities, or alternatively could increase the cost of resource acquisition because of reduced patch density or increased competition. Here, we study the influence of physical environmental heterogeneity on behaviour and reproductive success of black-legged kittiwakes, Rissa tridactyla . From GPS tracking data at 15 colonies throughout their British and Irish range, we found that environments that were physically more heterogeneous were associated with longer trip duration, more time spent foraging while away from the colony, increased overlap of foraging areas between individuals and lower breeding success. These results suggest that there is greater competition between individuals for finite resources in more heterogeneous environments, which comes at a cost to reproduction. Resource hotspots are often considered beneficial, as individuals can learn to exploit them if sufficiently predictable. However, we demonstrate here that such fitness gains can be countered by greater competition in more heterogeneous environments.

scholarly journals Casting Ballots When Knowing Results

2021 ◽  
pp. 1-19
Author(s):  
Victor Araújo ◽  
Malu A.C. Gatto
Keyword(s):  
Presidential Elections ◽  
Strong Support ◽  
Empirical Support ◽  
Access To Information ◽  
Bandwagon Effect ◽  
It Impacts ◽  
Run Off ◽  
Information Exposure ◽  
Key Factor ◽  
The Impact

Abstract Access to information about candidates' performance has long stood as a key factor shaping voter behaviour, but establishing how it impacts behaviour in real-world settings has remained challenging. In the 2018 Brazilian presidential elections, unpredictable technical glitches caused by the implementation of biometrics as a form of identification led some voters to cast ballots after official tallies started being announced. In addition to providing a source of exogenous variation of information exposure, run-off elections also enable us to distinguish between different mechanisms underlying the impact of information exposure. We find strong support for a vote-switching bandwagon effect: information exposure motivates voters to abandon losing candidates and switch support for the frontrunner – a finding that stands in the second round, when only two candidates compete against each other. These findings provide theoretical nuance and stronger empirical support for the mechanisms underpinning the impact of information exposure on voter behaviour.

Niche differentiation of tallgrass prairie plants species along soil hydrological gradients

Botany ◽  
2019 ◽  
Vol 97 (9) ◽  
pp. 487-494
Author(s):  
John Markham
Keyword(s):  
Tallgrass Prairie ◽  
Niche Overlap ◽  
Niche Differentiation ◽  
Vegetation Survey ◽  
Soil Hydrology ◽  
Hydrological Conditions ◽  
Species Analysis ◽  
Species Pairs ◽  
Tallgrass Prairies ◽  
Study Sites

This study addressed whether the distribution of species in frequently burned lowland tallgrass prairies is driven by gradients in soil hydrology. On three study sites, the hydrological conditions in 1 m2 vegetation survey plots where quantified as the number of days the soil was anaerobic less than 15 cm below the surface, and the surface of the soil was drier than 0.4 m3·m−3. On each site, the centroid of each species hydrological niche was defined as the hydrological conditions in plots where it occurred, weighted by its abundance. Species found on all sites maintained a consistent ranking between sites along the soil drying gradient, but not the anaerobic gradient. The levels of niche overlap between species pairs along both hydrological gradients were significantly less than the overlap from randomly assigning species to the hydrological gradients. Indicator species analysis suggested that on each site the communities were best described as consisting of two subgroups. The hydrological niches of the species in these subgroups were significantly different from one another, suggesting that these subgroups are associated with wet or dry habitats. Overall, these analyses suggest that hydrology plays a major role in determining the structure of these frequently disturbed communities.

The ecology of plants: from seed to seed

2019 ◽  
pp. 88-132
Author(s):  
Richard T. Corlett
Keyword(s):  
Tropical Forests ◽  
Community Assembly ◽  
Forest Succession ◽  
Neutral Theory ◽  
Niche Differentiation ◽  
Life Forms ◽  
Reproductive Phenology ◽  
Plant Community Ecology ◽  
Trade Offs ◽  
Ground Herbs

This chapter deals with the ecology of Tropical East Asia from a plant perspective. The life cycle of forest trees is covered in detail, including their vegetative and reproductive phenology, pollination, seed dispersal, seed predation, and the seedling, sapling, and adult stages. Other life forms, including lianas, ground herbs, epiphytes, hemi-epiphytes, and parasites are considered in less detail. Recent advances in plant community ecology are discussed, including the mechanisms responsible for the maintenance of species diversity in tropical forests (niche differentiation, growth–survival trade-offs, conspecific negative density-dependent mortality, neutral theory), and the influence of functional traits and phylogeny on community assembly. Forest succession is discussed in a regional context.

Biconditional Rule-Difficulty

1974 ◽  
Vol 35 (2) ◽  
pp. 955-962
Author(s):  
Tom Ciborowski
Keyword(s):  
Present Experiment ◽  
Strong Support ◽  
Empirical Support ◽  
Rule Learning ◽  
Learning Problems ◽  
Direct Test ◽  
College Age ◽  
Arbitrary Assumption

Three different groups of college age Ss received biconditional rule-learning problems that were altered in such a way as to permit a direct test of an unpublished model of Ss' behavior proposed by C. K. Sawyer and P. Johnson and substantially extended by Salatas and Bourne (1972). The present experiment obtained strong support for the model and evidence to support the widely reported suggestion that the principal difficulty with a biconditional rule is that S must learn to classify together two groups of elements that share no elements in common. The major outcome of the experiment was that strong empirical support was obtained for a useful but arbitrary assumption by Salatas and Bourne concerning a metric for evaluating biconditional rule-difficulty.

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