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Mammals that possess elaborate antipredator defences such as body armour, spines and quills are usually well protected, intermediate in size, primarily insectivorous and live in simple open environments. The benefits of such defences seem clear and may relax selection on maintaining cognitive abilities that aid in vigilance and predator recognition, and their bearers may accrue extensive production and maintenance costs. Here, in this comparative phylogenetic analysis of measurements of encephalization quotient and morphological defence scores of 647 mammal species representing nearly every order, we found that as lineages evolve stronger defences, they suffer a correlated reduction in encephalization. The only exceptions were those that live in trees—a complex three-dimensional world probably requiring greater cognitive abilities. At the proximate level, because brain tissue is extremely energetically expensive to build, mammals may be trading off spending more on elaborate defences and saving by building less powerful brains. At the ultimate level, having greater defences may also reduce the need for advanced cognitive abilities for constant assessment of environmental predation risk, especially in simple open environments.

Combat weaponry, including elaborate horns and antlers and complex dentition, evolved independently several times among mammals. While it is evident that tusk and tusk-like dentition have emerged primarily among males for intrasexual combat, it is unclear what ecological factors favor the retention or re-evolution of tusks. We investigated patterns of tusk evolution in artiodactyls while exploring specific ecological factors that might favor their use over other cranial weapons (e.g., antlers, horns). We show that among males, small (<15 kg), solitary species tend to retain well-developed canines, and more solitary species live in more closed habitats. These results suggest that tusks are a better weapon option for smaller, slinking artiodactyls in forested environments with low visibility, whereas larger taxa living in more open environment can bear the cost of elaborate headgear and are better served by communicating across distances an honest signal of fighting ability. Small species in dense habitats may also be more likely to be ambushed by predators and have a need to defend themselves; small, slicing daggers may be a better defensive weapon and allow more maneuverability and faster escape than cumbersome headgear in densely vegetated habitats.

The amount of risk animals perceive in a given circumstance (i.e. their degree of 'fear') is a difficult motivational state to study. While many studies have used flight initiation distance as a proxy for fearfulness and examined the factors influencing the decision to flee, there is no general understanding of the relative importance of these factors. By identifying factors with large effect sizes, we can determine whether anti-predator strategies reduce fear, and we gain a unique perspective on the coevolution of predator and anti-predator behaviour. Based on an extensive review and formal meta-analysis, we found that predator traits that were associated with greater risk (speed, size, directness of approach), increased prey distance to refuge and experience with predators consistently amplified the perception of risk (in terms of flight initiation distance). While fish tolerated closer approach when in larger schools, other taxa had greater flight initiation distances when in larger groups. The presence of armoured and cryptic morphologies decreased perception of risk, but body temperature in lizards had no robust effect on flight initiation distance. We find that selection generally acts on prey to be sensitive to predator behaviour, as well as on prey to modify their behaviour and morphology.

Mammals have independently evolved a wide variety of morphological adaptations for use in avoiding death by predation, including spines, quills, dermal plates, and noxious sprays. Although these traits appear to protect their bearer from predatory attack, it is less obvious why some species evolved them and others have not. We investigated the ecological correlates favoring the evolution of specialized defenses in mammals, focusing on conspicuousness to predators due to body size and openness of habitat. We scored species for the degree to which they are protected by spines, quills, dermal plating, and sprays and used phylogenetic comparative analyses to study the morphological and ecological factors that may favor their evolution. We show that medium-sized insectivorous mammals (~800 g to 9 kg) that live in open habitats are more likely to possess one of these defensive traits to reduce predation. Smaller species (<200 g) and those in closed habitats can typically rely on crypsis to avoid predators, and larger species (>10 kg) are less susceptible to predation by most small- to medium-sized predators. We discuss how diet, metabolic rate, and defensive strategy evolve in concert to allow species to exploit this ecomorphological \"danger zone\" niche.

Weaponry is ubiquitous in male ungulates and is driven by intrasexual selection, but the mystery surrounding its sporadic presence in females remains unsolved. Female horns are often smaller and shaped differently to male horns, suggesting a different function; indeed, hypotheses explaining the presence of female horns include competition for food, male mollification and defence against predators. Here we use comparative phylogenetic analyses to show that females are significantly more likely to bear horns in bovids that are conspicuous due to large body size and living in open habitats than inconspicuous species living in closed habitats or that are small. An inability to rely on crypsis or take refuge in deep vegetation has apparently driven the evolution of horns for defence against predators in female bovids, a finding supported by many field observations. Typically, exceptions are small species where females are territorial (e.g. duikers) and use horns in intrasexual contests. Furthermore, we suggest that conspicuousness and territoriality hypotheses may explain other instances of female cranial weaponry (i.e. antlers and ossicones) in other horned ruminants. Our phylogenetic reconstruction indicates that the primary function of horns in females is linked to antipredator defence in most clades, but occasionally to intrasexual competition in others.

Conspicuous coloration in animals has many possible functions including signaling to conspecifics, or predator deterrence through confusion, intimidation, and duping; the last includes flash behavior where predators are deceived into looking for conspicuous cues exhibited in flight but that are hidden when the animal comes to rest. In an effort to see if flash behavior occurs in mammals, we made predictions about situations where conspicuous coloration (as based on human assessment) might occur in artiodactyls and lagomorphs, and other predictions as to where such coloration might be found under an intraspecific signaling hypothesis. Using phylogenetically controlled analyses, we found that across species of artiodactyls, conspicuous rumps are more likely to have evolved in larger-sized group-living species supporting an intraspecific signaling function; this was not replicated in lagomorphs. Examining those artiodactyls that can facultatively expose color patches (putative flash behavior), we discovered that this trait occurred in artiodactyls that are solitary or living in very small groups irrespective of their body size. It is therefore possible that species such as white- and black-tailed deer, which display white rumps and tails during pursuit but hide them when stationary, are using flash behavior to confuse the predator into looking for the wrong object and thereby avoid detection and suggests that this form of antipredator defense in mammals needs greater attention. We found no effects of group size or body mass on conspicuous tail or ear markings in these taxa.

Animal body armour is often considered an adaptation that protects prey against predatory attacks, yet comparative studies that link the diversification of these allegedly protective coverings to differential predation risk or pressure are scarce. Here, we examine the evolution of body armour, including spines and osteoderms, in Cordylinae, a radiation of southern African lizards. Using phylogenetic comparative methods, we attempt to identify the ecological and environmental correlates of body armour that may hint at the selective pressures responsible for defensive trait diversification. Our results show that species inhabiting arid environments are more likely to possess elaborated body armour, specifically osteoderms. We did not find any effect of estimated predation pressure or risk on the degree of body armour. These findings suggest that body armour might not necessarily evolve in response to direct interactions with predators, but rather as a result of increased habitat-mediated predation risk. Furthermore, we discuss the possibility that osteoderms might have been shaped by factors unrelated to predation.

Several species of terrestrial carnivores (Mammalia: Carnivora) have bold contrasting color patterns that in some species, apparently signal possession of noxious anal gland secretions, or even physical strength and great ferocity; yet the evolutionary drivers of both placement and patterning of these contrasting pelage colors on the body, and the ecological selection pressures underlying them, have yet to be systematically examined. Here we explore these issues and find not only that both boldly colored and dichromatic species do indeed often use anal gland secretions for defense, but also that such species are stockier, and live in more exposed habitats where other forms of antipredator defense are limited. We also show that white dorsa are found in sprayers that are primarily nocturnal; that horizontal stripes are found in species that have an ability to spray anal secretions accurately; and that facial stripes are found in burrowing species that typically leave only their heads exposed to attack. Our phylogenetic reconstructions suggest that aposematic coloration has evolved more than once in terrestrial carnivores. We finish by outlining five evolutionary routes for patterns of pelage coloration in this taxon.

Time is a fundamental component of ecological processes. How animal behavior changes over time has been explored through well-known ecological theories like niche partitioning and predator–prey dynamics. Yet, changes in animal behavior within the shorter 24-hr light–dark cycle have largely gone unstudied. Understanding if an animal can adjust their temporal activity to mitigate or adapt to environmental change has become a recent topic of discussion and is important for effective wildlife management and conservation. While spatial habitat is a fundamental consideration in wildlife management and conservation, temporal habitat is often ignored. We formulated a temporal resource selection model to quantify the diel behavior of 8 mammal species across 10 US cities. We found high variability in diel activity patterns within and among species and species-specific correlations between diel activity and human population density, impervious land cover, available greenspace, vegetation cover, and mean daily temperature. We also found that some species may modulate temporal behaviors to manage both natural and anthropogenic risks. Our results highlight the complexity with which temporal activity patterns interact with local environmental characteristics, and suggest that urban mammals may use time along the 24-hr cycle to reduce risk, adapt, and therefore persist, and in some cases thrive, in human-dominated ecosystems.

Cities are seen as quintessentially human; however, because they can offer viable habitat to many plants, animals and other forms of life, cities are also dynamic ecosystems. As urban areas expand to house more of the global human population and reduce natural habitat for wildlife, the need for wildlife‐inclusive urban planning and design becomes increasingly pressing. The 2019 Urban Wildlife Information Network Summit responded to this need by connecting a group of 80 scientists, urban planners and designers to examine the role of cities in combating the global biodiversity crisis. The Summit focused on identifying and addressing barriers to transdisciplinary work between these communities, such as disciplinary silos, varying incentive structures, funding, differences in spatio‐temporal scale, existing infrastructure and values and bias. We explore the challenges to network building for wildlife‐inclusive design and planning revealed by the Summit and offer potential solutions for overcoming these obstacles for more effective collaboration around wildlife‐inclusive cities. A free Plain Language Summary can be found within the Supporting Information of this article. A free Plain Language Summary can be found within the Supporting Information of this article.