Tim Caro

Flagship species on covers of US conservation and nature magazines

Some conservation organizations publish magazines that showcase current conservation and research projects, attract new subscribers and maintain membership, often using flagship species to promote these objectives. This study investigates the nature of flagship species featured on the covers of ten representative US conservation and nature magazines, Defenders, National Wildlife, Wildlife Conservation, Zoonooz, Nature Conservancy, Outdoor America, Sierra, Audubon, California Wild and Natural History. Operationally defining flagship species by diet, taxonomic order, body size and IUCN status, we found that magazines tend to use mammal and bird species rather than invertebrate, fish, amphibian, reptile or plant taxa on their covers. Featured birds were mostly omnivorous or piscivorous, large-bodied and of little conservation concern; featured mammals were mainly carnivorous or herbivorous, large-bodied and of considerable conservation concern. These analyses confirm, for the first time, anecdotal observations about conservation organizations focusing their publicity and programmes on large, charismatic species to raise awareness and funds and raise the spectre that the public may be exposed to only a selected sample of conservation problems.

Contrasting coloration in terrestrial mammals

Here I survey, collate and synthesize contrasting coloration in 5000 species of terrestrial mammals focusing on black and white pelage. After briefly reviewing alternative functional hypotheses for coloration in mammals, I examine nine colour patterns and combinations on different areas of the body and for each mammalian taxon to try to identify the most likely evolutionary drivers of contrasting coloration. Aposematism and perhaps conspecific signalling are the most consistent explanations for black and white pelage in mammals; background matching may explain white pelage. Evidence for contrasting coloration is being involved in crypsis through pattern blending, disruptive coloration or serving other functions, such as signalling dominance, lures, reducing eye glare or in temperature regulation has barely moved beyond anecdotal stages of investigation. Sexual dichromatism is limited in this taxon and its basis is unclear. Astonishingly, the functional significance of pelage coloration in most large charismatic black and white mammals that were new to science 150 years ago still remains a mystery.

Evolution of weaponry in female bovids

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.

The functional significance of colouration in cetaceans

Cetaceans show many of the classic mammalian colouration patterns, such as uniform colouration, countershading, and prominent patches of colour, all within one relatively small taxon. We collated all the functional hypotheses for cetacean colouration that have been put forward in the literature and systematically tested them using comparative phylogenetic analyses. We found that countershading is a mechanism by which smaller cetacean species may avoid being seen by their prey. We discovered that prominent markings are associated with group living, fast swimming, and ostentatious behaviour at the surface, suggesting that they function in intraspecific communication. White markings on several parts of the body seem to be involved in the capture of fish, squid, and krill. Therefore, several different selection pressures have shaped the great diversity of skin colouration seen in extant cetaceans, although background matching, disruptive colouration and interspecific communication do not appear to be involved.

The ecology of multiple colour defences

Individuals of many species are considered to rely on a single type of external appearance to escape predation but there are many notable exceptions. To develop an ecological framework to explain why some individuals employ different colour patterns as part of their defensive repertoire, we collate examples of colour change that are associated with living in different environments and microhabitats, examples of age-related colour change, colour defences tailored to different predators, and startle displays, where hidden conspicuous colour patterns are suddenly revealed. The over-arching commonality to all these examples is that the use of more than one defense-related external appearance is associated with a spatial or temporal change in predation risk. For example, coarse scale temporal changes in an animal’s background frequently select for gradual colour changes, while fine-scale spatial heterogeneity selects for more rapid colour changes and we provide a graphical framework for this. Irrespective of the mechanisms underlying colour change, using more than one colour defence appears driven by variation in predation risk rather than by idiosyncratic abilities to alter external appearances as is commonly believed, although physiological and energetic factors will play some role.

Animal coloration research: why it matters

While basic research on animal coloration is the theme of this special edition, here we highlight its applied significance for industry, innovation and society. Both the nanophotonic structures producing stunning optical effects and the colour perception mechanisms in animals are extremely diverse, having been honed over millions of years of evolution for many different purposes. Consequently, there is a wealth of opportunity for biomimetic and bioinspired applications of animal coloration research, spanning colour production, perception and function. Fundamental research on the production and perception of animal coloration is contributing to breakthroughs in the design of new materials (cosmetics, textiles, paints, optical coatings, security labels) and new technologies (cameras, sensors, optical devices, robots, biomedical implants). In addition, discoveries about the function of animal colour are influencing sport, fashion, the military and conservation. Understanding and applying knowledge of animal coloration is now a multidisciplinary exercise. Our goal here is to provide a catalyst for new ideas and collaborations between biologists studying animal coloration and researchers in other disciplines. This article is part of the themed issue ‘Animal coloration: production, perception, function and application’.

Interspecific visual signalling in animals and plants: a functional classification

Organisms frequently gain advantages when they engage in signalling with individuals of other species. Here, we provide a functionally structured framework of the great variety of interspecific visual signals seen in nature, and then describe the different signalling mechanisms that have evolved in response to each of these functional requirements. We propose that interspecific visual signalling can be divided into six major functional categories: anti-predator, food acquisition, anti-parasite, host acquisition, reproductive and agonistic signalling, with each function enabled by several distinct mechanisms. We support our classification by reviewing the ecological and behavioural drivers of interspecific signalling in animals and plants, principally focusing on comparative studies that address large-scale patterns of diversity. Collating diverse examples of interspecific signalling into an organized set of functional and mechanistic categories places anachronistic behavioural and morphological labels in fresh context, clarifies terminology and redirects research effort towards understanding environmental influences driving interspecific signalling in nature. This article is part of the themed issue ‘Animal coloration: production, perception, function and application’.

Animal coloration: production, perception, function and application

Research on animal coloration is a vibrant area of biology currently involving evolutionary biologists, behavioural ecologists, psychologists, optical physicists, visual ecologists, geneticists and anthropologists. The proliferation of recent work requires that we take stock of the field, aiming to identify major themes, questions and future directions. This was the goal of the year-long Wissenschaftskolleg zu Berlin ‘focus group’ (2015–2016), in which many of the authors in this issue participated either as fellows or visitors. The result is this 19-chapter theme issue, in which we pinpoint the breakthroughs and challenges in animal coloration research, focusing on production, perception, function and evolution. We also explore animal coloration research as it applies to humans. This theme issue is by no means exhaustive but our goal has been to summarize …

The evolution of anterior coloration in carnivorans

Some carnivorans have striking patches of fur on their faces (spots, bands, eye masks) and blazes on their chests that are primarily visible from a frontal view. We tested five hypotheses to explain the evolution of the complexity and contrast of these color patches. These were: signals of species identity to avoid hybridization, communication between conspecifics, signals used to warn of defensive anal secretions, signals of belligerence or pugnacity, and camouflage-related coloration used to break up the outline and facial features of the predator when approaching prey. Using phylogenetically controlled multifactorial analyses in six different families of carnivorans, examined separately, our analyses uncovered significant positive associations between measures of color pattern complexity and sociality across herpestid faces and canid chests, suggesting use in social communication. Mustelid facial color complexity was associated with ability to direct anal secretions accurately at predators, and facial markings were significantly or marginally associated with pugnacity in mustelids, viverrids, and herpestids. Facial complexity of viverrid and herpestid species was significantly or marginally related to a mammal-based diet. In ursids, facial contrast appeared less variable in species living in greater sympatry with other bears. Facial and chest coloration in Carnivora appears to have evolved under different selection pressures in different families.Significance statementThe reasons that many carnivorans have colorful and memorable faces and chests are not yet understood. Here, we pit five different hypotheses against each other: species recognition, advertising either toxic anal defenses or pugnacity, recognizing group members, and trying to remain concealed when approaching mammalian prey. We find that measures of facial and chest complexity and contrast have evolved for different reasons depending on the carnivoran family. Anterior coloration appears to be involved with social communication in herpestids and canids; facial coloration is associated noxious secretions in mustelids, with pugnacity in mustelids, viverrids and herpestids; with reliance on a mammal-based diet in viverrids and herpestids; and with avoiding hybridization in bear species. There is no overriding evolutionary explanation for varied facial and chest pelage coloration across carnivorans.

Concordance on zebra stripes: a comment on Larison et al. (2015)

The functional significance of the extraordinary black and white stripes of zebras is still mysterious but now an active field of research. Four major hypotheses have been put forward: stripes are an antipredator defence operating through crypsis [1] or confusion of predators [2], are a means of reinforcing social bonds [3], are defence against ectoparasites [4] or are a means of cooling zebras [5]. Now, in the second multifactorial analysis of striping in zebras to date, Larison et al. [6] investigated the environmental factors that explain geographical variation in striping within a single species, the plains zebra ( Equus quagga or Equus burchellii ). They matched variation in striping patterns at 16 sites across its geographical range to a suite of environmental variables as well as tsetse fly (glossinid) distribution and lion ( Panthera leo ) presence. They found that greater intensities of intraspecific striping were associated with warmer temperatures and high precipitation. Last year we published a similar but phylogenetically controlled analysis using all seven species of equids, namely the three striped zebra species, the African wild ass ( Equus africanus ) which has leg stripes but no body stripes, and the unstriped species of equids ( E. hemionus, E. kiang, E. ferus przewalski ), and 20 of their subspecies, and compared several aspects of the four hypotheses [7]. These were camouflage in woodlands, antipredator defence against both lions and spotted hyaenas ( Crocuta crocuta ), social interactions, tsetse fly distribution, tabanid distribution using both temperature and humidity ranges as a proxy for abundance, and temperature isoclines to assess the cooling hypothesis. First we ran univariate tests on individual factors to identify the hypotheses with the strongest predictive ability, then subsequently used AICc model selection procedures to pit the most promising predictors against each other—a …