Situational Specificity in Alpine-marmot Alarm Communication

We studied the degree to which alpine marmot (Marmota marmota L.) alarm calls function as communication about specific external stimuli. Alpine marmots emit variable alarm calls when they encounter humans, dogs, and several species of aerial predators. The first part of the study involved observations and manipulations designed to document contextual variation in alarm calls. Alarm calls varied along several acoustic parameters, but only along one that we examined, the number of notes per call, was significantly correlated with the type of external stimulus. Marmots were more likely to emit single-note alarm calls as their first or only call in response to an aerial stimulus, and multiple-note alarm calls when first calling to a terrestrial stimulus. This relationship was not without exceptions; there was considerable variation in the number of notes they emitted to both aerial and terrestrial stimuli, and a single stimulus type — humans — elicited a wide range of acoustic responses. The second part of the study involved playing back three types of alarm calls to marmots and observing their responses. Marmots did not have overtly different responses to the three types of played-back alarm calls. Our results are consistent with the hypotheses that: 1. Alarm calls do not refer to specific external stimuli; 2. Alarm calls function to communicate the degree of risk a caller experiences; and 3. Alarm calls require additional contextual cues to be properly interpreted by conspecifics.     

Golden-marmot Alarm Calls. II. Asymmetrical Production and Perception of Situationally Specific Vocalizations?

Many species produce alarm calls that vary according to situation. An implicit assumption for these species is that production and perception of situationally specific alarm calls is symmetrical: perceivers respond to variation produced by signalers. The companion paper to this one (Blumstein 1995) showed that golden marmots (Marmota caudata aurea) produce variable alarm calls that vary in proportion to the degree of risk the caller perceives. Calls produced in higher-risk situations have fewer notes than calls produced in lower-risk situations. In this study, to determine the salience of the number of notes per call in eliciting different responses in conspecific perceivers, I played back three-note alarm calls, eight-note alarm calls, and the non-alarm vocalization of a local bird to adult golden marmots. Although marmots responded differently to bird calls and alarm calls, vigilance responses to the different alarm calls were similar. Several explanations may account for the apparent insensitivity to alarm-call variation: golden marmots may require additional contextual cues to properly interpret alarm calls, perceptual abilities do not parallel production abilities, or calls may serve a generalized alerting function.     

Persistence of antipredator behavior in an island population of California quail

Island populations may provide unique insights into the evolution and persistence of antipredator behavior. If antipredator behavior is costly and islands have reduced predation risk, then we expect the reduction or loss of antipredator behavior on islands. However, if even a single predator remains, the multipredator hypothesis predicts that antipredator behaviors will be conserved. We compared the flight initiation distances (FID) of California quail (Callipepla californica) on Santa Catalina Island (a location with reduced predation pressure) with quail on the mainland. We found no differences in FID between mainland and island quail. However, despite employing consistent testing methods, the starting distance from which quail were approached was significantly reduced for quail studied on the island when compared with quail studied on the mainland. Our results are consistent with the multipredator hypothesis because, while the island population had substantially fewer predators, some predators remained and some antipredator behavior persisted.     

The benefits of being dominant: health correlates of male social rank and age in a marmot

The benefits of dominance may not come without costs, particularly for males. For example, the “immunocompetence handicap hypothesis” states that males with enhanced mating success allocate resources to enhance reproductive output at a cost to their current health, whereas the “resource quality hypothesis” predicts that high-ranking males may benefit from increased reproduction and good health. Whereas the predictions from each have been well tested in captive animals and in a variety of highly social primates, fewer studies have been carried out in free-living, facultatively social animals. Using adult male yellow-bellied marmots (Marmota flaviventer), we evaluated predictions of these hypotheses by examining the relationship between social rank and 2 health indicators—fecal glucocorticoid metabolite (FCM) levels, and neutrophil/lymphocyte (N/L) ratios—after accounting for variation explained by age, body mass, and seasonality. We found that higher-ranking males tended to have a lower N/L ratio (reflecting good health) than lower-ranking individuals, whereas FCM levels were not significantly related to rank. In addition, heavier male marmots had lower N/L ratios, whereas body mass was not associated with FCM levels. We also found that older adult males had lower FCM levels (reflecting less physiological stress) but higher N/L ratios than younger adults. Finally, we found that FCM levels decreased as the active season progressed and FCM levels were associated with the time of the day. Overall, our results suggest that socially-dominant male marmots enjoyed better, not worse health in terms of lower N/L ratios.     

Feeling Vulnerable? Indirect Risk Cues Differently Influence How Two Marsupials Respond to Novel Dingo Urine

In Tasmania, introduced predators are becoming more common. How Tasmanian prey respond to novel predator cues is of particular interest for their survival and management. Prey response to predator scents may depend on whether predator and prey share an evolutionary history and may be influenced by indirect risk cues such as perceived shelter or safety in the environment. To simultaneously explore the effects of indirect and direct risk cues (predator scent) on free‐living Tasmanian pademelons (Thylogale billardierii) and brush tail possums (Trichosurus vulpecula), we placed dingo (Canis lupus dingo) urine scents inside and outside a 25 ‐m² selective feeding enclosure to mimic a heterogeneous risk landscape. Despite the lack of a historical relationship between dingoes and Tasmanian fauna, pademelons and possums demonstrated flight and vigilance when confronted with the novel scent outside the enclosure. According to our index of deterrence, number of successful entries/approaches, both species were deterred. However, responses inside the safe enclosure differed according to species. For instance, pademelons made more approaches/entries into the enclosure and fled more following approaches to scent marks both inside and outside the enclosure. In comparison, possums only exhibited similar responses outside the enclosure, and there was no effect of stimulus inside the safe compound. Our findings suggest that small animals may be pre‐adapted to avoid some predators they have not previously been in contact with, and that brush tail possums are more likely to respond to predation cues when exposed and vulnerable. Ultimately, the cumulative effects of direct and indirect risk cues may either increase or reduce a repellent response.     

Understanding predator densities for successful co‐existence of alien predators and threatened prey

The high failure rate of threatened species translocations has prompted many managers to fence areas to protect wildlife from introduced predators. However, conservation fencing is expensive, restrictive and exacerbates prey naïveté reducing the chance of future co‐existence between native prey and introduced predators. Here, we ask whether two globally threatened mammal species protected in fenced reserves, with a history of predation‐driven decline and reintroduction failure, could co‐exist with introduced predators. We defined co‐existence as population persistence for at least 3 years and successful recruitment. We manipulated the density of feral cats within a large fenced paddock and measured the impact on abundance and reproduction of 353 reintroduced burrowing bettongs and 47 greater bilbies over 3 years. We increased cat densities from 0.038 to 0.46 per square km and both threatened species survived, reproduced and increased their population size. However, a previous reintroduction trial of 66 bettongs into the same paddock found one red fox (Vulpes vulpes), at a density of 0.027 per square km, drove the bettong population extinct within 12 months. Our results show that different predator species vary in their impact and that despite a history of reintroduction failure, threatened mammal species can co‐exist with low densities of feral cats. There may be a threshold density below which it is possible to maintain unfenced populations of reintroduced marsupials. Understanding the numerical relationships between population densities of introduced predators and threatened species is urgently needed if these species are to be re‐established at landscape scales. Such knowledge will enable a priori assessment of the risk of reintroduction failure thereby increasing the likelihood of reintroduction success and reducing the financial and ethical cost of failed translocations.     

Isolation from mammalian predators differentially affects two congeners

Evolutionary isolation from predators can profoundly influencethe morphology, physiology, and behavior of prey, but littleis known about how species respond to the loss of only someof their predators. We studied antipredator behavior of tammarwallabies (Macropus eugenii) and western gray kangaroos (Macropusfuliginosus) on Kangaroo Island (KI), South Australia, andat Tutanning Nature Reserve on the mainland of western Australia.Both species on KI have been isolated from native mammalian predators for several thousand years. On KI, wallabies (becauseof their size) are vulnerable to diurnal aerial predators.In contrast, on the mainland both species have been exposedcontinuously to native and introduced mammalian and avian predators.At both locations, wallabies modified the amount of time they allocated to vigilance and foraging in response to group size,whereas kangaroos did so only at the higher risk Tutanningsite. Both species modified overall time budgets (they werewarier at the higher risk site), and both species modifiedspace-use patterns as a function of risk. At the higher risk site, tammars were closer to cover, whereas kangaroos were,on average, farther from cover. We hypothesize that the presenceof a single predator, even if it is active at a different timeof day, may profoundly affect the way a species responds tothe loss of other predators by maintaining certain antipredatorbehaviors. Such an effect of ancestral predators may be expected as long as species encounter some predators.     

Social trajectories and the evolution of social behavior

Current research on the evolution of sociality seeks to integrate a wealth of species-specific studies to draw more generalized conclusions. Developing a unified theory of social evolution has been a challenging process, hampered by the inherent complexity of social systems. By viewing a species' social structure as the result of a series, or "trajectory", of decisions individuals make about whether or not to disperse from their natal territory, whether to co-breed or refrain from breeding, and whether or not to provide alloparental care, we can more easily evaluate whether selective factors influencing each social decision are similar across taxa. At the same time, the social trajectory framework highlights the interrelationships among different social decisions, both throughout the life of an individual and over evolutionary time. There are likely to be multiple unifying themes within sociality research; we hope that the simple framework outlined here will promote exchange between researchers across taxonomic disciplines to begin to identify common principles.     

Global variation in nonstructural carbohydrate stores in response to climate

Woody plant species store nonstructural carbohydrates (NSCs) for many functions. While known to buffer against fluctuations in photosynthetic supply, such as at night, NSC stores are also thought to buffer against environmental extremes, such as drought or freezing temperatures by serving as either back-up energy reserves or osmolytes. However, a clear picture of how NSCs are shaped by climate is still lacking. Here, we update and leverage a unique global database of seasonal NSC storage measurements to examine whether maximum total NSC stores and the amount of soluble sugars are associated with clinal patterns in low temperatures or aridity, indicating they may confer a benefit under freezing or drought conditions. We examine patterns using the average climate at each study site and the unique climatic conditions at the time and place in which the sample was taken. Altogether, our results support the idea that NSC stores act as critical osmolytes. Soluble Sugars increase with both colder and drier conditions in aboveground tissues, indicating they can plastically increase a plants' tolerance of cold or arid conditions. However, maximum total NSCs increased, rather than decreased, with average site temperature and had no relationship to average site aridity. This result suggests that the total amount of NSC a plant stores may be more strongly determined by its capacity to assimilate carbon than by environmental stress. Thus, NSCs are unlikely to serve as reservoir of energy. This study is the most comprehensive synthesis to date of global NSC variation in relation to climate and supports the idea that NSC stores likely serve as buffers against environmental stress. By clarifying their role in cold and drought tolerance, we improve our ability to predict plant response to environment.