Catalogue Search | MBRL
Are you sure you want to remove the book from the shelf?
{{itemTitle}}
13,565
result(s) for
"Smith, Matthew"
Sort by:
The Effect of Intra- and Interspecific Competition on Coexistence in Multispecies Communities
For two competing species, intraspecific competition must exceed interspecific competition for coexistence. To generalize this well-known criterion to multiple competing species, one must take into account both the distribution of interaction strengths and community structure. Here we derive a multispecies generalization of the two-species rule in the context of symmetric Lotka-Volterra competition and obtain explicit stability conditions for random competitive communities. We then explore the influence of community structure on coexistence. Results show that both the most and least stabilized cases have striking global structures, with a nested pattern emerging in both cases. The distribution of intraspecific coefficients leading to the most and least stabilized communities also follows a predictable pattern that can be justified analytically. In addition, we show that the size of the parameter space allowing for feasible communities always increases with the strength of intraspecific effects in a characteristic way that is independent of the interspecific interaction structure. We conclude by discussing possible extensions of our results to nonsymmetric competition.
Journal Article
Impact of anthropogenic CO2 emissions on global human nutrition
Atmospheric CO2 is on pace to surpass 550 ppm in the next 30–80 years. Many food crops grown under 550 ppm have protein, iron and zinc contents that are reduced by 3–17% compared with current conditions. We analysed the impact of elevated CO2 concentrations on the sufficiency of dietary intake of iron, zinc and protein for the populations of 151 countries using a model of per-capita food availability stratified by age and sex, assuming constant diets and excluding other climate impacts on food production. We estimate that elevated CO2 could cause an additional 175 million people to be zinc deficient and an additional 122 million people to be protein deficient (assuming 2050 population and CO2 projections). For iron, 1.4 billion women of childbearing age and children under 5 are in countries with greater than 20% anaemia prevalence and would lose >4% of dietary iron. Regions at highest risk—South and Southeast Asia, Africa, and the Middle East—require extra precautions to sustain an already tenuous advance towards improved public health.
Journal Article
Hyperactive : the controversial history of ADHD
Attention deficit hyperactivity disorder, or ADHD, is one of the most common developmental disorders, with an average of 9 per cent of U.S. children between the ages of five and seventeen diagnosed each year. It is also one of the most controversial. Since the 1950s, when hyperactivity in children was first diagnosed, psychiatrists, educators, parents and politicians have debated the causes, treatment and implications of the disorder.
Book
The Effects of Sampling Bias and Model Complexity on the Predictive Performance of MaxEnt Species Distribution Models
Species distribution models (SDMs) trained on presence-only data are frequently used in ecological research and conservation planning. However, users of SDM software are faced with a variety of options, and it is not always obvious how selecting one option over another will affect model performance. Working with MaxEnt software and with tree fern presence data from New Zealand, we assessed whether (a) choosing to correct for geographical sampling bias and (b) using complex environmental response curves have strong effects on goodness of fit. SDMs were trained on tree fern data, obtained from an online biodiversity data portal, with two sources that differed in size and geographical sampling bias: a small, widely-distributed set of herbarium specimens and a large, spatially clustered set of ecological survey records. We attempted to correct for geographical sampling bias by incorporating sampling bias grids in the SDMs, created from all georeferenced vascular plants in the datasets, and explored model complexity issues by fitting a wide variety of environmental response curves (known as \"feature types\" in MaxEnt). In each case, goodness of fit was assessed by comparing predicted range maps with tree fern presences and absences using an independent national dataset to validate the SDMs. We found that correcting for geographical sampling bias led to major improvements in goodness of fit, but did not entirely resolve the problem: predictions made with clustered ecological data were inferior to those made with the herbarium dataset, even after sampling bias correction. We also found that the choice of feature type had negligible effects on predictive performance, indicating that simple feature types may be sufficient once sampling bias is accounted for. Our study emphasizes the importance of reducing geographical sampling bias, where possible, in datasets used to train SDMs, and the effectiveness and essentialness of sampling bias correction within MaxEnt.
Journal Article
The first resort : the history of social psychiatry in the United States
\"Social psychiatry was a mid-twentieth-century approach to mental health that stressed the prevention of mental illness rather than its treatment. Its proponents developed environmental explanations of mental health, arguing that socioeconomic problems such as poverty, inequality, and social isolation were the underlying causes of mental illness. The influence of social psychiatry contributed to the closure of psychiatric hospitals and the emergence of community mental health care during the 1960s. By the 1980s, however, social psychiatry was in decline, having lost ground to biological psychiatry and its emphasis on genetics, neurology, and psychopharmacology. The First Resort is a history of the rise and fall of social psychiatry that also explores the lessons this largely forgotten movement has to offer today. Matthew Smith examines four ambitious projects that investigated the relationship between socioeconomic factors and mental illness in Chicago, New Haven, New York City, and Nova Scotia. He contends that social psychiatry waned not because of flaws in its preventive approach to mental health but rather because the economic and political crises of the 1970s and the shift to the right during the 1980s foreclosed the social changes required to create a more mentally healthy society. Smith also argues that social psychiatry provides timely insights about how progressive social policies, such as a universal basic income, can help stem rising rates of mental illness in the present day\"-- Provided by publisher.
BOOK
The Empirical Implications of the Interest-Rate Lower Bound
Using Bayesian methods, we estimate a nonlinear DSGE model in which the interest-rate lower bound is occasionally binding. We quantify the size and nature of disturbances that pushed the US economy to the lower bound in late 2008 as well as the contribution of the lower bound constraint to the resulting economic slump. We find that the interest-rate lower bound was a significant constraint on monetary policy that exacerbated the recession and inhibited the recovery, as our mean estimates imply that the zero lower bound (ZLB) accounted for about 30 percent of the sharp contraction in US GDP that occurred in 2009 and an even larger fraction of the slow recovery that followed.
Journal Article
Higher-order interactions stabilize dynamics in competitive network models
Communities that are very rich in species could persist thanks to the stabilizing role of higher-order interactions, in which the presence of a species influences the interaction between other species.
High order interactions maintain species diversity
How the tremendous biodiversity observed in nature is maintained is a central question in ecology. Simple models of interacting competitors fail to reproduce the stable persistence of very large ecological communities, while neutral models in which species do not interact and diversity is maintained by immigration and speciation yield unrealistically small fluctuations in population abundance. Using competitive network models, Stefano Allesina and colleagues show that higher order interactions, whereby the presence of one species influences the interaction between other species, allow highly diverse communities to persist in closed systems with a fixed number and identity of species and in more realistic open systems, which gain new species through immigration and speciation.
Ecologists have long sought a way to explain how the remarkable biodiversity observed in nature is maintained. On the one hand, simple models of interacting competitors cannot produce the stable persistence of very large ecological communities
1
,
2
,
3
,
4
,
5
. On the other hand, neutral models
6
,
7
,
8
,
9
, in which species do not interact and diversity is maintained by immigration and speciation, yield unrealistically small fluctuations in population abundance
10
, and a strong positive correlation between a species’ abundance and its age
11
, contrary to empirical evidence. Models allowing for the robust persistence of large communities of interacting competitors are lacking. Here we show that very diverse communities could persist thanks to the stabilizing role of higher-order interactions
12
,
13
, in which the presence of a species influences the interaction between other species. Although higher-order interactions have been studied for decades
14
,
15
,
16
, their role in shaping ecological communities is still unclear
5
. The inclusion of higher-order interactions in competitive network models stabilizes dynamics, making species coexistence robust to the perturbation of both population abundance and parameter values. We show that higher-order interactions have strong effects in models of closed ecological communities, as well as of open communities in which new species are constantly introduced. In our framework, higher-order interactions are completely defined by pairwise interactions, facilitating empirical parameterization and validation of our models.
Journal Article