The Evolution of Bias - Generalized

Fry (1996) showed that galaxy bias has the tendency to evolve towards unity, i.e. in the long run, the galaxy distribution tends to trace that of matter. Generalizing slightly Fry's reasoning, we show that his conclusion remains valid in theories of modified gravity (or equivalently, complex clustered dark energy). This is not surprising: as long as both galaxies and matter are subject to the same force, dynamics would drive them towards tracing each other. This holds, for instance, in theories where both galaxies and matter move on geodesics. This relaxation of bias towards unity is tempered by cosmic acceleration, however: the bias tends towards unity but does not quite make it, unless the formation bias were close to unity. Our argument is extended in a straightforward manner to the case of a stochastic or nonlinear bias. An important corollary is that dynamical evolution could imprint a scale dependence on the large scale galaxy bias. This is especially pronounced if non-standard gravity introduces new scales to the problem: the bias at different scales relaxes at different rates, the larger scales generally more slowly and retaining a longer memory of the initial bias. A consistency test of the current (general relativity + uniform dark energy) paradigm is therefore to look for departure from a scale independent bias on large scales. A simple way is to measure the relative bias of different populations of galaxies which are at different stages of bias relaxation. Lastly, we comment on the possibility of directly testing the Poisson equation on cosmological scales, as opposed to indirectly through the growth factor.Comment: 8 pages, 2 figures. References added. Accepted for publication in Physical Review

Ecological boundaries and constraints on viable eco-evolutionary pathways

Evolutionary dynamics are subject to constraints ranging from limitations on what is physically possible to limitations on the pathways that evolution can take. One set of evolutionary constraints, known as ‘demographic constraints’, constrain what can occur evolutionarily due to the demographic or dynamical consequences of evolution leading to conditions that make populations susceptible to extinction. These demographic constraints can limit the strength of selection or the rates of environmental change populations can experience while remaining extant and the trait values a population can express. Here we further hypothesize that the population demographic and dynamic consequences of evolution also can constrain the eco-evolutionary pathways that populations can traverse by defining ecological boundaries represented by areas of likely extinction. We illustrate this process using a model of predator evolution. Our results show that the populations that persist over time tend to be those whose eco-evolutionary dynamics have avoided ecological boundaries representing areas of likely extinction due to stochastic deviations from a deterministic eco-evolutionary expectation. We term this subset of persisting pathways viable eco-evolutionary pathways. The potential existence of ecological boundaries constraining evolutionary pathways has important implications for predicting evolutionary dynamics, interpreting past evolution, and understanding the role of stochasticity and ecological constraints on eco-evolutionary dynamics

Ecological boundaries and constraints on viable eco-evolutionary pathways

Evolutionary dynamics are subject to constraints ranging from limitations on what is physically possible to limitations on the pathways that evolution can take. One set of evolutionary constraints, known as ‘demographic constraints’, constrain what can occur evolutionarily due to the demographic or dynamical consequences of evolution leading to conditions that make populations susceptible to extinction. These demographic constraints can limit the strength of selection or the rates of environmental change populations can experience while remaining extant and the trait values a population can express. Here we further hypothesize that the population demographic and dynamic consequences of evolution also can constrain the eco-evolutionary pathways that populations can traverse by defining ecological boundaries represented by areas of likely extinction. We illustrate this process using a model of predator evolution. Our results show that the populations that persist over time tend to be those whose eco-evolutionary dynamics have avoided ecological boundaries representing areas of likely extinction due to stochastic deviations from a deterministic eco-evolutionary expectation. We term this subset of persisting pathways viable eco-evolutionary pathways. The potential existence of ecological boundaries constraining evolutionary pathways has important implications for predicting evolutionary dynamics, interpreting past evolution, and understanding the role of stochasticity and ecological constraints on eco-evolutionary dynamics

Predator-Dependent Functional Responses Alter the Coexistence and Indirect Effects among Prey that Share a Predator

Predator functional responses describe predator feeding rates as a function of prey abundance and are central to pred-ator–prey theory. Despite ample evidence that functional responses also depend on predator abundance, theory incor-porating predator-dependent functional responses has focused almost exclusively on specialist predator–prey pairs or linear food chains. This leaves a large gap in our knowledge as many predators feed on multiple prey, and in so doing, generate indirect effects among prey that can alter their coexistence. Here we investigate how predator-dependent functional responses in a one predator–two prey model alter the coexistence among prey and their net effects on one another. We use two different functional response forms (the Beddington–DeAngelis and Crowley–Martin functional responses) and consider situations in which the prey do not directly interact and in which they directly compete with one another. We find that predator dependence can facilitate, hinder, or have no effect on prey coexistence depending on whether prey compete directly and the role of predation in mediating coexistence among the prey in the absence of predator dependence. We also show that the negative net effects of prey on one another are generally weakened by predator dependence and can become positive under the Crowley–Martin functional response. Together, these results suggest that predator dependence may have widespread effects on ecological communities by altering the coexistence among prey species and the strength and signs of the interactions among them

Coloration in the polymorphic frog Oophaga pumilio associates with level of aggressiveness in intraspecific and interspecific behavioral interactions

© 2015, Springer-Verlag Berlin Heidelberg. Intraspecific morphological variation may correspond to behavioral variation that helps determine the nature of species interactions. Color variation among populations of variably toxic organisms has been shown to associate with alternative anti-predator behaviors. However, the effects of these alternative behavioral tendencies on the outcomes of interspecific interactions other than predator–prey remain largely unexplored. We investigated how coloration and body size variation in Oophaga pumilio, one of the most phenotypically diverse amphibians known, associated with territorial aggressiveness and how this association influenced the outcome of agonistic male–male interactions with conspecifics and heterospecifics of two sympatric species (Andinobates claudiae and Phyllobates lugubris). Irrespective of body size, resident frogs from more conspicuous, red-colored O. pumilio populations responded to same-morph conspecifics and P. lugubris more quickly and exhibited more aggressive behaviors and more energetically expensive behaviors than resident frogs from green populations under these same treatments. Furthermore, red-colored resident frogs dominated most of the interactions in which they were involved, whereas green residents dominated only a few of the interactions, despite their status as residents. Because conspecific and heterospecific intruders did not behave more aggressively toward red resident frogs, aggressiveness of red residents does not appear to be a response to higher aggression being directed toward them. These results suggest that coloration in O. pumilio is a good indicator of aggressiveness that associates with the outcome of intraspecific and some interspecific behavioral male–male interactions, providing support for a positive association among anti-predator traits, agonistic behavior, and dominance in both intraspecific and interspecific, intraguild interactions

Literacy and phonological skills in oral deaf children and hearing children with a history of dyslexia

Oral deaf children and hearing children with dyslexia both experience literacy challenges, although their reasons differ. This paper explores the problems underlying poor literacy in each group and draws implications for reading interventions. Data were collected using standardised literacy and phonological measures from 69 severe-profoundly prelingually-deaf children aged 10-11 years, all communicating with spoken language, and compared with equivalent data from 20 hearing children with a history of dyslexia matched on reading ability. Children were given a large battery of tasks assessing word and nonword reading, spelling, vocabulary and reading-related skills including lettersound knowledge, phonological awareness, rapid automated naming and verbal short-term memory. Striking similarities were observed for word reading, nonword reading and spelling across groups, and associations between the measures and reading-related skills were similar. However, differences between the two groups emerged in the strength of association between literacy and vocabulary. Regression analyses confirmed vocabulary as a key predictor of literacy in the oral deaf group. These results suggest that not only children with a history of dyslexia but also oral deaf children who struggle with reading should receive specialist literacy support. Reading interventions for oral deaf children should target phonological and language skills within a fully integrated approach

Reading and Dyslexia in Deaf Children

Literacy difficulties are more widespread among deaf children than hearing children but reasons for their problems differ. Hearing children are likely to be described as dyslexic and once diagnosed, may benefit from specialist support. However, for deaf children, their hearing difficulties are seen as primary. In this Briefing Paper, we report findings from a two-phase research study on deaf children’s reading, funded by the Nuffield Foundation. Phase 1 focused on a large sample of 82 same-age deaf children aged 10-11 years who communicated using spoken language (oral deaf children) and Phase 2, on a sample of 59 same-age deaf children who used sign language to communicate (signing deaf children). Our analysis identified that literacy scores in both deaf groups were lower than expected for their age, and lower in the signing group compared to the oral group. An exception was the small group of signing children with two deaf parents, who achieved reading levels comparable to oral deaf children. Overall, 48% of the oral group and 82% of the signing children were reading below age level. Scores for spelling were better than reading but in both groups, many children had below average scores. In both groups, literacy outcomes were associated with phonological skills and language. Profiles of poor readers in each group were similar, and displayed low scores on English expressive vocabulary and phonological measures. Using our hearing dyslexic participants as a reference group, we were able to identify dyslexia-sensitive measures that were effective in differentiating poor readers in the oral deaf sample since children in the oral deaf group were able to access the full range of measures developed for hearing children. Identification of a dyslexic profile among the signing participants was more complex as different phonological measures were used that did not rely on speech perception or production, and also because of their very low scores on many of the measures: the percentage of poor readers with scores falling below -2 SDs was nearly four times higher in the signing group compared with the oral deaf group, accounting for nearly a quarter of the signing sample. Our findings highlight the scale of reading difficulties in deaf children. Regardless of communication approach, all deaf poor readers are in urgent need of specialist intervention to address the deficits underlying poor literacy. Interventions known to be effective with hearing children with reading difficulties should also be used with deaf poor readers. In addition, deaf children require support to develop their language skills. Our findings also suggest that spelling, a relative strength in deaf children, may offer a useful route to improving literacy in this group