417 research outputs found
The shape of ecological networks
We study the statistics of ecosystems with a variable number of co-evolving
species. The species interact in two ways: by prey-predator relationships and
by direct competition with similar kinds. The interaction coefficients change
slowly through successful adaptations and speciations. We treat them as
quenched random variables. These interactions determine long-term topological
features of the species network, which are found to agree with those of
biological systems.Comment: 4 pages, 2 figure
Cannibalism as a life boat mechanism
Under certain conditions a cannibalistic population can survive when food for the adults is too scarce to support a non-cannibalistic population. Cannibalism can have this lifeboat effect if (i) the juveniles feed on a resource inaccessible to the adults; and (ii) the adults are cannibalistic and thus incorporate indirectly the inaccessible resource. Using a simple model we conclude that the mechanism works when, at low population densities, the average yield, in terms of new offspring, due to the energy provided by one cannibalized juvenile is larger than one
Transition probabilities for general birth-death processes with applications in ecology, genetics, and evolution
A birth-death process is a continuous-time Markov chain that counts the
number of particles in a system over time. In the general process with
current particles, a new particle is born with instantaneous rate
and a particle dies with instantaneous rate . Currently no robust and
efficient method exists to evaluate the finite-time transition probabilities in
a general birth-death process with arbitrary birth and death rates. In this
paper, we first revisit the theory of continued fractions to obtain expressions
for the Laplace transforms of these transition probabilities and make explicit
an important derivation connecting transition probabilities and continued
fractions. We then develop an efficient algorithm for computing these
probabilities that analyzes the error associated with approximations in the
method. We demonstrate that this error-controlled method agrees with known
solutions and outperforms previous approaches to computing these probabilities.
Finally, we apply our novel method to several important problems in ecology,
evolution, and genetics
The Influence of Chronotype and Grit on Lifestyle and Physical Activity
Background:  The chronotype of a person refers to an individual's natural sleep-wake cycle and whether that individual prefers morning or evening activities, and grit is an individual's perseverance and passion for long-term goals.Aim: The purpose of this study was to investigate the relationship between grit, chronotype, physical activity, and leading a healthy lifestyle in college-age students.Methods: Health and fitness data (i.e., chronotype, grit, lifestyle assessment score, and daily steps) from 431 first-semester university students at a private college were collected and analyzed. Results: This study found that grit and chronotype both have significant correlations with living a healthy lifestyle and with physical activity. Grit more accurately predicts a person's lifestyle (β = -13.712, r = 0.39, p < 0.0001) while chronotype more accurately predicts the physical activity, or steps, of a person (β = 66.48, r = .19, p = .0001). Chronotype can also accurately predict the grit of a person (r = .25, p < .0001), and it was found that morning people tend to have more grit.Conclusions: This study concluded that grit, chronotype, steps, and a healthy lifestyle are all significantly correlated with each other. Knowing the relationship between endogenous chronotype, grit, and living a physically active and healthy lifestyle can help inform policy decisions related to the goal of strengthening an institution's inclusive and healthy academic community
European packaging industry foresight study—identifying global drivers and driven packaging industry implications of the global megatrends
Individual Preferences and Social Interactions Determine the Aggregation of Woodlice
n°e17389.info:eu-repo/semantics/publishe
Self-Assemblage and Quorum in the Earthworm Eisenia fetida (Oligochaete, Lumbricidae)
Despite their ubiquity and ecological significance in temperate ecosystems, the behavioural ecology of earthworms is not well described. This study examines the mechanisms that govern aggregation behaviour specially the tendency of individuals to leave or join groups in the compost earthworm Eisenia fetida, a species with considerable economic importance, especially in waste management applications. Through behavioural assays combined with mathematical modelling, we provide the first evidence of self-assembled social structures in earthworms and describe key mechanisms involved in cluster formation. We found that the probability of an individual joining a group increased with group size, while the probability of leaving decreased. Moreover, attraction to groups located at a distance was observed, suggesting a role for volatile cues in cluster formation. The size of earthworm clusters appears to be a key factor determining the stability of the group. These findings enhance our understanding of intra-specific interactions in earthworms and have potential implications for extraction and collection of earthworms in vermicomposting processes
Reduction and Return of Infectious Trachoma in Severely Affected Communities in Ethiopia
Trachoma is one of the leading causes of blindness in the developing world. The World Health Organization has a multi-pronged approach to controlling the ocular chlamydial infection that causes the disease, including distributing antibiotics to entire communities. Even a single community treatment dramatically reduces the prevalence of the infection. Unfortunately, infection returns back into communities after treatment, at least in severely affected areas such as rural Ethiopia. Here, we assess whether additional scheduled treatments in 16 communities in the Gurage area of Ethiopia further reduce infection, and whether the disease returns after distributions are stopped. In communities with the highest levels of trachoma ever studied, we find that repeated mass oral azithromycin distributions gradually reduce the prevalence of trachoma infection in a community, as long as these treatments are given frequently enough and to enough people in the community. Unfortunately, infection returns into the communities after the last treatment. Sustainable changes or complete local elimination of infection will be necessary to stop the return of ocular chlamydial in communities with very high prevalence of the disease
The rate of beneficial mutations surfing on the wave of a range expansion
Many theoretical and experimental studies suggest that range expansions can
have severe consequences for the gene pool of the expanding population. Due to
strongly enhanced genetic drift at the advancing frontier, neutral and weakly
deleterious mutations can reach large frequencies in the newly colonized
regions, as if they were surfing the front of the range expansion. These
findings raise the question of how frequently beneficial mutations successfully
surf at shifting range margins, thereby promoting adaptation towards a
range-expansion phenotype. Here, we use individual-based simulations to study
the surfing statistics of recurrent beneficial mutations on wave-like range
expansions in linear habitats. We show that the rate of surfing depends on two
strongly antagonistic factors, the probability of surfing given the spatial
location of a novel mutation and the rate of occurrence of mutations at that
location. The surfing probability strongly increases towards the tip of the
wave. Novel mutations are unlikely to surf unless they enjoy a spatial head
start compared to the bulk of the population. The needed head start is shown to
be proportional to the inverse fitness of the mutant type, and only weakly
dependent on the carrying capacity. The second factor is the mutation
occurrence which strongly decreases towards the tip of the wave. Thus, most
successful mutations arise at an intermediate position in the front of the
wave. We present an analytic theory for the tradeoff between these factors that
allows to predict how frequently substitutions by beneficial mutations occur at
invasion fronts. We find that small amounts of genetic drift increase the
fixation rate of beneficial mutations at the advancing front, and thus could be
important for adaptation during species invasions.Comment: 21 pages, 7 figures; to appear in PLoS Computational Biolog
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