A consistent occupancy-climate relationship across birds and mammals of the Americas

Global erosion of terrestrial environmental space by artificial light at night

Artificial light at night (ALAN) disrupts natural light cycles, with biological impacts that span from behaviour of individual organisms to ecosystem functions, and across bacteria, fungi, plants and animals. Global consequences have almost invariably been inferred from the geographic distribution of ALAN. How ALAN is distributed in environmental space, and the extent to which combinations of environmental conditions with natural light cycles have been lost, is also key. Globally (between 60°N and 56°S), we ordinated four bioclimatic variables at 1.61 * 1.21 km resolution to map the position and density of terrestrial pixels within nighttime environmental space. We then used the Black Marble Nighttime Lights product to determine where direct ALAN emissions were present in environmental space in 2012 and how these had expanded in environmental space by 2022. Finally, we used the World Atlas of Artificial Sky Brightness to determine the proportion of environmental space that is unaffected by ALAN across its spatial distribution. We found that by 2012 direct ALAN emissions occurred across 71.9 % of possible nighttime terrestrial environmental conditions, with temperate nighttime environments and highly modified habitats disproportionately impacted. From 2012 to 2022 direct ALAN emissions primarily grew within 34.4 % of environmental space where it was already present, with this growth concentrated in tropical environments. Additionally considering skyglow, just 13.2 % of environmental space now only experiences natural light cycles throughout its distribution. With opportunities to maintain much of environmental space under such cycles fast disappearing, the removal, reduction and amelioration of ALAN from areas of environmental space in which it is already widespread is critical.

How Dispersal Evolution and Local Adaptation Affect the Range Dynamics of Species Lagging Behind Climate Change

AbstractAs climate changes, species' ability to spatially track suitable climate depends on their spread velocity, a function of their population growth and dispersal capacity. When climate changes faster than species can spread, the climate experienced at species' expanding range edges may ameliorate as conditions become increasingly similar to those of the range core. When this boosts species' growth rates, their spread accelerates. Here, we use simulations of a spreading population with an annual life history to explore how climatic amelioration interacts with dispersal evolution and local adaptation to determine the dynamics of spread. We found that depending on the timing of dispersal evolution, spread velocity can show contrasting trajectories, sometimes transiently exceeding the climate velocity before decelerating. Climatic amelioration can also accelerate the spread of populations composed of genotypes best adapted to local climatic conditions, but the exact dynamics depends on the pattern of climatic adaptation. We conclude that failing to account for demographic variation across climatic gradients can lead to erroneous conclusions about species' capacity to spatially track suitable climate.

The shape of abundance distributions across temperature gradients in reef fishes

Improving predictions of ecological responses to climate change requires understanding how local abundance relates to temperature gradients, yet many factors influence local abundance in wild populations. We evaluated the shape of thermal‐abundance distributions using 98 422 abundance estimates of 702 reef fish species worldwide. We found that curved ceilings in local abundance related to sea temperatures for most species, where local abundance declined from realised thermal ‘optima’ towards warmer and cooler environments. Although generally supporting the abundant‐centre hypothesis, many species also displayed asymmetrical thermal‐abundance distributions. For many tropical species, abundances did not decline at warm distribution edges due to an unavailability of warmer environments at the equator. Habitat transitions from coral to macroalgal dominance in subtropical zones also influenced abundance distribution shapes. By quantifying the factors constraining species’ abundance, we provide an important empirical basis for improving predictions of community re‐structuring in a warmer world.

Environmental suitability models predict population density, performance and body condition for microendemic salamanders

Species can show strong variation of local abundance across their ranges. Recent analyses suggested that variation in abundance can be related to environmental suitability, as the highest abundances are often observed in populations living in the most suitable areas. However, there is limited information on the mechanisms through which variation in environmental suitability determines abundance. We analysed populations of the microendemic salamander Hydromantes flavus, and tested several hypotheses on potential relationships linking environmental suitability to population parameters. For multiple populations across the whole species range, we assessed suitability using species distribution models, and measured density, activity level, food intake and body condition index. In high-suitability sites, the density of salamanders was up to 30-times higher than in the least suitable ones. Variation in activity levels and population performance can explain such variation of abundance. In high-suitability sites, salamanders were active close to the surface, and showed a low frequency of empty stomachs. Furthermore, when taking into account seasonal variation, body condition was better in the most suitable sites. Our results show that the strong relationship between environmental suitability and population abundance can be mediated by the variation of parameters strongly linked to individual performance and fitness.

Spatial Autocorrelation Can Generate Stronger Correlations between Range Size and Climatic Niches Than the Biological Signal - A Demonstration Using Bird and Mammal Range Maps

Species’ geographic ranges could primarily be physiological tolerances drawn in space. Alternatively, geographic ranges could be only broadly constrained by physiological climatic tolerances: there could generally be much more proximate constraints on species’ ranges (dispersal limitation, biotic interactions, etc.) such that species often occupy a small and unpredictable subset of tolerable climates. In the literature, species’ climatic tolerances are typically estimated from the set of conditions observed within their geographic range. Using this method, studies have concluded that broader climatic niches permit larger ranges. Similarly, other studies have investigated the biological causes of incomplete range filling. But, when climatic constraints are measured directly from species’ ranges, are correlations between species’ range size and climate necessarily consistent with a causal link? We evaluated the extent to which variation in range size among 3277 bird and 1659 mammal species occurring in the Americas is statistically related to characteristics of species’ realized climatic niches. We then compared how these relationships differed from the ones expected in the absence of a causal link. We used a null model that randomizes the predictor variables (climate), while retaining their broad spatial autocorrelation structure, thereby removing any causal relationship between range size and climate. We found that, although range size is strongly positively related to climatic niche breadth, range filling and, to a lesser extent, niche position in nature, the observed relationships are not always stronger than expected from spatial autocorrelation alone. Thus, we conclude that equally strong relationships between range size and climate would result from any processes causing ranges to be highly spatially autocorrelated.