Auditory physiology: cortical assistance for the auditory signals-to-symbols transformation

How the temporal information that is crucial for understanding speech and music is processed in the brain is poorly understood, but a new study shows how the auditory cortex is tuned to the spectro-temporal acoustic features characteristic of natural biological sounds.     

Designing convergent cellular automata

Cellular automata (CA) have been used by biologists to study dynamic non-linear systems where the interaction between cell behaviour and end-pattern is investigated. It is difficult to achieve convergence of a CA towards a specific static pattern and a common solution is to use genetic algorithms and evolve a ruleset that describes cell behaviour. This paper presents an alternative means of designing CA to converge to specific static patterns. A matrix model is introduced and analysed then a design algorithm is demonstrated. The algorithm is significantly less computationally intensive than equivalent evolutionary algorithms, and not limited in scale, complexity or number of dimensions.     

Where do species' geographic ranges stop and why? Landscape impermeability and the Afrotropical avifauna

Although understanding large-scale spatial variation in species'' distributions is a major goal in macroecology, relatively little attention has been paid to the factors limiting species'' ranges. An understanding of these factors may improve predictions of species'' movements in response to global change. We present a measure of landscape impermeability, defined as the proportion of resident species whose ranges end in an area. We quantify and map impermeability for Afrotropical birds and use multi-model inference to assess support for a wide suite of hypotheses about its potential environmental correlates. Non-spatial analyses emphasize the importance of broad-scale environmental patterns of energy availability and habitat heterogeneity in limiting species'' distributions. Conversely, spatial analyses focus attention on small-scale factors of habitat and topographic complexity. These results hold even when only species from the top quartile of range sizes are assessed. All our analyses highlight that range edges are concentrated in heterogeneous habitats. Global change is expected to alter the nature and distribution of such habitats, necessitating range movement by many resident species. Therefore, impermeability provides a simple measure for identifying regions, where continuing global change and human encroachment are likely to cause profound changes in regional diversity patterns.     

Geographical variation in predictors of mammalian extinction risk: big is bad, but only in the tropics

Whereas previous studies have investigated correlates of extinction risk either at global or regional scales, our study explicitly models regional effects of anthropogenic threats and biological traits across the globe. Using phylogenetic comparative methods with a newly-updated supertree of 5020 extant mammals, we investigate the impact of species traits on extinction risk within each WWF ecoregion. Our analyses reveal strong geographical variation in the influence of traits on risk: notably, larger species are at higher risk only in tropical regions. We then relate these patterns to current and recent-historical human impacts across ecoregions using spatial modelling. The body–mass results apparently reflect historical declines of large species outside the tropics due to large-scale land conversion. Narrow-ranged and rare species tend to be at high risk in areas of high current human impacts. The interactions we describe between biological traits and anthropogenic threats increase understanding of the processes determining extinction risk.     

The life history legacy of evolutionary body size change in carnivores

We estimate the body sizes of direct ancestors of extant carnivores, and examine selected aspects of life history as a function not only of species' current size, but also of recent changes in size. Carnivore species that have undergone marked recent evolutionary size change show life history characteristics typically associated with species closer to the ancestral body size. Thus, phyletic giants tend to mature earlier and have larger litters of smaller offspring at shorter intervals than do species of the same body size that are not phyletic giants. Phyletic dwarfs, by contrast, have slower life histories than nondwarf species of the same body size. We discuss two possible mechanisms for the legacy of recent size change: lag (in which life history variables cannot evolve as quickly as body size, leading to species having the 'wrong' life history for their body size) and body size optimization (in which life history and hence body size evolve in response to changes in energy availability); at present, we cannot distinguish between these alternatives. Our finding that recent body size changes help explain residual variation around life history allometries shows that a more dynamic view of character change enables comparative studies to make more precise predictions about species traits in the context of their evolutionary background.     

Phylogenetic diversity does not capture body size variation at risk in the world's mammals

Mammals contribute to important ecosystem processes and services, but many mammalian species are threatened with extinction. We compare how global patterns in three measures of mammalian diversity—species richness, phylogenetic diversity (PD) and body mass variance (BMV)—would change if all currently threatened species were lost. Given that many facets of species'' ecology and life history scale predictably with body mass, the BMV in a region roughly reflects the diversity of species'' roles within ecosystems and so is a simple proxy for functional diversity (FD). PD is also often considered to be a proxy for FD, but our results suggest that BMV losses within ecoregions would be much more severe than losses of PD or species richness, and that its congruence with the latter two measures is low. Because of the disproportionate loss of large mammals, 65 per cent of ecoregions would lose significantly more BMV than under random extinction, while only 11 per cent would lose significantly more PD. Ecosystem consequences of these selective losses may be profound, especially throughout the tropics, but are not captured by PD. This low surrogacy stresses a need for conservation prioritization based on threatened trait diversity, and for conservation efforts to take an ecosystem perspective.     

Detecting shifts in diversity limits from molecular phylogenies: what can we know?

Large complete species-level molecular phylogenies can provide the most direct information about the macroevolutionary history of clades having poor fossil records. However, extinction will ultimately erode evidence of pulses of rapid speciation in the deep past. Assessment of how well, and for how long, phylogenies retain the signature of such pulses has hitherto been based on a--probably untenable--model of ongoing diversity-independent diversification. Here, we develop two new tests for changes in diversification 'rules' and evaluate their power to detect sudden increases in equilibrium diversity in clades simulated with diversity-dependent speciation and extinction rates. Pulses of diversification are only detected easily if they occurred recently and if the rate of species turnover at equilibrium is low; rates reported for fossil mammals suggest that the power to detect a doubling of species diversity falls to 50 per cent after less than 50 Myr even with a perfect phylogeny of extant species. Extinction does eventually draw a veil over past dynamics, suggesting that some questions are beyond the limits of inference, but sudden clade-wide pulses of speciation can be detected after many millions of years, even when overall diversity is constrained. Applying our methods to existing phylogenies of mammals and angiosperms identifies intervals of elevated diversification in each.