Charlie W. Rayner

Artificial light at night (ALAN), from streetlights and other sources, is ubiquitous across modern towns and cities and has wide-ranging impacts upon the natural environment. The extent, spectra and timing of light influence the physiology, behaviour and fitness of individuals of many species, shape the structure of ecological communities and the functioning of ecosystems. To date, however, it has been challenging to characterize this lighting at sufficiently fine spatial resolutions across city-wide extents. Here, we apply a Monte Carlo radiative transfer model to simulate in three dimensions the light environment resulting from emission from streetlights using the city of Exeter, UK, as an exemplar. We show that this technique can model the evolving lighting landscape of modern cities at scales, and through observables, suitable for both ecological studies and lighting professionals. We estimate measures of melatonin suppression, induced photosynthesis and phytochrome photostationary state from our models, probing how the transition towards light-emitting diode street lighting impacts physiological processes in plants and animals throughout the city. Our simulations illustrate that although the area lit by ALAN is decreasing overall at metre scales, which is lit is becoming more hostile towards many organisms.

Contests over resources are widespread in nature. To optimize outcomes, animals assess fighting abilities, deciding to escalate conflicts based on their own strength (self-assessment) or comparing their own strength with that of their rival (mutual assessment). While most research focuses on one-on-one (dyadic) contests, the assessment strategies employed by groups remain poorly understood, even though animal groups from ants to humans engage in intergroup conflict. Mutual assessment is frequently assumed, as more information is thought to improve decision-making; however, this assumption has rarely been tested. Here we used a dataset spanning 21 years and 633 intergroup contests in a banded mongoose (Mungos mungo) population in Queen Elizabeth National Park, Uganda. Our results support a model of self-assessment: groups with many males tend to escalate conflicts regardless of the rival group's strength, thus contrasting the commonly held assumption that decisions during intergroup contests are made by mutual assessment. We suggest that assessing rival group strength during conflict could be disproportionately costly, compared with assessing own group strength, which can be done over longer time periods and is easier to obtain. Greater understanding of these dynamics can shed light on the drivers and escalation patterns of intergroup conflict across social species, including humans.