Dung‐associated arthropods influence foraging ecology and habitat selection in Black‐necked Cranes (Grus nigricollis) on the Qinghai–Tibet Plateau

Variation in grassland vegetation structure influences the habitat selection of insectivorous birds. This variation presents a trade‐off for insectivorous predators: Arthropod abundance increases with vegetation height and heterogeneity, but access to arthropod prey items decreases. In contrast, grazing by large herbivores reduces and homogenizes vegetation, decreasing total arthropod abundance and diversity. However, the presence of livestock dung may help counteract the overall reduction in invertebrates by increasing arthropods associated with dung. It is unclear, however, how the presence of arthropod prey in dung contributes to overall habitat selection for insectivorous birds or how dung‐associated arthropods affect trade‐offs between vegetation structure, arthropod abundance, and access to prey. To explore these relationships, we studied habitat selection of the Black‐necked Crane (Grus nigricollis), a large omnivorous bird that breeds on the Qinghai–Tibet Plateau. We assessed the relationships between habitat selection of cranes and vegetation structure, arthropod abundance, and the presence of yak dung. We found that Black‐necked Cranes disproportionately foraged in grassland patches with short sward height, low sward height heterogeneity, and high numbers of dry yak dung, despite these habitats having lower total arthropod abundance. Although total arthropod abundance is lower, these habitats are supplemented with dry yak dung, which are associated with coleopteran larvae, making dung pats an indicator of food resources for breeding Black‐necked Cranes. Coleopteran adults and larvae in yak dung appear to be an important factor influencing the habitat selection of Black‐necked Cranes and should be considered when assessing grassland foraging trade‐offs of insectivorous birds. This research provides new insights into the role of livestock dung in defining foraging habitats and resources for insectivorous predators.     

Non-lethal effects of predation in birds

Predators can affect individual fitness and population and community processes through lethal effects (direct consumption or ‘density’ effects), where prey is consumed, or through non‐lethal effects (trait‐mediated effects or interactions), where behavioural compensation to predation risk occurs, such as animals avoiding areas of high predation risk. Studies of invertebrates, fish and amphibians have shown that non‐lethal effects may be larger than lethal effects in determining the behaviour, condition, density and distribution of animals over a range of trophic levels. Although non‐lethal effects have been well described in the behavioural ecology of birds (and also mammals) within the context of anti‐predation behaviour, their role relative to lethal effects is probably underestimated. Birds show many behavioural and physiological changes to reduce direct mortality from predation and these are likely to have negative effects on other aspects of their fitness and population dynamics, as well as affecting the ecology of their own prey and their predators. As a consequence, the effects of predation in birds are best measured by trade‐offs between maximizing instantaneous survival in the presence of predators and acquiring or maintaining resources for long‐term survival or reproduction. Because avoiding predation imposes foraging costs, and foraging behaviour is relatively easy to measure in birds, the foraging–predation risk trade‐off is probably an effective framework for understanding the importance of non‐lethal effects, and so the population and community effects of predation risk in birds and other animals. Using a trade‐off approach allows us to predict better how changes in predator density will impact on population and community dynamics, and how animals perceive and respond to predation risk, when non‐lethal effects decouple the relationship between predator density and direct mortality rate. The trade‐off approach also allows us to identify where predation risk is structuring communities because of avoidance of predators, even when this results in no observable direct mortality rate.     

Do predators influence the behaviour of bats?

Many aspects of animal behaviour are affected by real‐time changes in the risk of predation. This conclusion holds for virtually all taxa and ecological systems studied, but does it hold for bats? Bats are poorly represented in the literature on anti‐predator behaviour, which may reflect a lack of nocturnal predators specialized on bats. If bats actually experience a world with minimal anti‐predator concerns, then they will provide a unique contrast within the realm of vertebrate ecology. Alternatively, such predator‐driven behaviour in bats may not yet be fully understood, given the difficulties in working with these highly mobile and nocturnal animals. We provide a wide‐ranging exploration of these issues in bat behaviour. We first cover the basic predator‐prey information available on bats, both on potential predators and the ways in which bats might perceive predators and respond to attacks. We then cover work relevant to key aspects of bat behaviour, such as choice of daytime roosts, the nature of sleep and torpor, evening roost departures, moonlight avoidance, landscape‐related movement patterns, and habitat selection. Overall, the evidence in favour of a strong influence of predators on bat behaviour is equivocal, with the picture clouded by contradictory results and a lack of information on potential predators and the perception of risk by bats. It seems clear that day‐active bats run a considerable risk of being killed by diurnal raptors, which are able to capture bats with relative ease. Thus, bats taking advantage of a pulse of insects just prior to sunset are likely taking risks to gain much‐needed energy. Further, the choice of daytime roosts by bats is probably strongly influenced by roost safety. Few studies, however, have directly addressed either of these topics. As a group, insectivorous temperate‐zone bats show no clear tendency to avoid apparently risky situations, such as activity on moonlit nights. However, some observations are consistent with the idea that predation risk affects choice of movement paths and feeding areas by temperate‐zone bats, as well as the timing of roost departures. The behaviour of tropical bats, on the other hand, seems more generally influenced by predators; this is especially true for tropical nectarivores and frugivores, but also for insectivorous bats. Presumably there are more serious predators on bats in the tropics (e.g. specialized raptors or carnivorous bats), but the identity of these predators is unclear. More information is needed to assess fully the influence of predators on bat behaviour. There is much need for work on the ways in which bats perceive predators via auditory, visual, and olfactory cues, and whether bats have some knowledge of the risks posed by different predators. Also needed is information on how predators attack bats and how bats react to attacking predators. Difficult to obtain, but of critical value, will be information on the nature of the predation risk experienced by bats while away from roosts and during the full darkness of night.     

Within‐season increase in parental investment in a long‐lived bird species: investment shifts to maximize successful reproduction?

In nest‐building species predation of nest contents is a main cause of reproductive failure and parents have to trade off reproductive investment against antipredatory behaviours. While this trade‐off is modified by lifespan (short‐lived species prioritize current reproduction; long‐lived species prioritize future reproduction), it may vary within a breeding season, but this idea has only been tested in short‐lived species. Yet, life history theory does not make any prediction how long‐lived species should trade off current against future reproductive investment within a season. Here, we investigated this trade‐off through predator‐exposure experiments in a long‐lived bird species, the brown thornbill. We exposed breeding pairs that had no prior within‐season reproductive success to the models of a nest predator and a predator of adults during their first or second breeding attempt. Overall, parents reduced their feeding rate in the presence of a predator, but parents feeding second broods were more risk sensitive and almost ceased feeding when exposed to both types of predators. However, during second breeding attempts, parents had larger clutches and a higher feeding rate in the absence of predators than during first breeding attempts and approached both types of predators closer when mobbing. Our results suggest that the trade‐off between reproductive investment and risk‐taking can change in a long‐lived species within a breeding season depending on both prior nest predation and renesting opportunities. These patterns correspond to those in short‐lived species, raising the question of whether a within‐season shift in reproductive investment trade‐offs is independent of lifespan.     

Nectar-feeding bird and bat niches in two worlds: pantropical comparisons of vertebrate pollination systems

Aim We review several aspects of the structure of regional and local assemblages of nectar‐feeding birds and bats and their relationships with food plants to determine the extent to which evolutionary convergence has or has not occurred in the New and Old World tropics. Location Our review is pantropical in extent and also includes the subtropics of South Africa and eastern Australia. Within the tropics, it deals mostly with lowland forest habitats. Methods An extensive literature review was conducted to compile data bases on the regional and local species richness of nectar‐feeding birds and bats, pollinator sizes, morphology, and diets. Coefficients of variation (CVs) were used to quantify the morphospace occupied by the various families of pollinators. The extent to which plants have become evolutionarily specialized for vertebrate pollination was explored using several criteria: number and diversity of growth forms of plant families providing food for all the considered pollinator families; the most common flower morphologies visited by all the considered pollinator families; and the number of plant families that contain genera with both bird‐ and bat‐specialized species. Results Vertebrate pollinator assemblages in the New World tropics differ from those in the Old World in terms of their greater species richness, the greater morphological diversity of their most specialized taxa, and the greater degree of taxonomic and ecological diversity and morphological specialization of their food plants. Within the Old World tropics, Africa contains more specialized nectar‐feeding birds than Asia and Australasia; Old World nectar‐feeding bats are everywhere less specialized than their New World counterparts. Main conclusions We propose that two factors – phylogenetic history and spatio‐temporal predictability (STP) of flower resources – largely account for hemispheric and regional differences in the structure of vertebrate pollinator assemblages. Greater resource diversity and resource STP in the New World have favoured the radiation of small, hovering nectar‐feeding birds and bats into a variety of relatively specialized feeding niches. In contrast, reduced resource diversity and STP in aseasonal parts of Asia as well as in Australasia have favoured the evolution of larger, non‐hovering birds and bats with relatively generalized feeding niches. Tropical Africa more closely resembles the Neotropics than Southeast Asia and Australasia in terms of resource STP and in the niche structure of its nectar‐feeding birds but not its flower‐visiting bats.     

Exploitation of distant Antarctic waters and close neritic waters by short‐tailed shearwaters breeding in South Australia

Identifying the primary foraging grounds of abundant top predators is of importance in marine management to identify areas of high biological significance, and to assess the extent of competition with fisheries. We studied the search effort and habitat selection of the highly abundant short‐tailed shearwater Puffinus tenuirostris to assess the search strategies employed by this wide‐ranging seabird. During the chick‐rearing period 52 individuals were tracked performing 39 short foraging trips (1–2 days), and 13 long trips (11–32 days). First‐passage time analysis revealed that 46% of birds performing short trips employed area‐restricted searches, concentrating search effort at an average scale of 14 ± 5 km. Foraging searches were more continuous for the other 54%, who travelled faster to cover greater distances, with little evidence of area‐restricted searches. The prey returned indicated that continuous searchers consumed similar prey mass, but greater prey diversity than area‐restricted search birds. On long trips 23% of birds travelled 500–1000 km to neritic (continental shelf) habitats, showing weak evidence of preference for areas of higher chlorophyll a concentration, and foraged at a similar spatial scale to short trips. The other 76% performed rapid outbound flights of 1000–3600 km across oceanic habitats commuting to regions with higher chlorophyll a. The spatial scale of search effort in oceanic habitat varied widely with some performing broad‐scale searches (260–560 km) followed by finer‐scale nested searches (16–170 km). This study demonstrates that a range of search strategies are employed when exploiting prey across ocean basins. The trade‐offs between different search strategies are discussed to identify the value of these contrasting behaviours to wide‐ranging seabirds.     

Dietary specialization is conditionally associated with increased ant predation risk in a temperate forest caterpillar community

The enemy‐free space hypothesis (EFSH) contends that generalist predators select for dietary specialization in insect herbivores. At a community level, the EFSH predicts that dietary specialization reduces predation risk, and this pattern has been found in several studies addressing the impact of individual predator taxa or guilds. However, predation at a community level is also subject to combinatorial effects of multiple‐predator types, raising the question of how so‐called multiple‐predator effects relate to dietary specialization in insect herbivores. Here, we test the EFSH with a field experiment quantifying ant predation risk to insect herbivores (caterpillars) with and without the combined predation effects of birds. Assessing a community of 20 caterpillar species, we use model selection in a phylogenetic comparative framework to identify the caterpillar traits that best predict the risk of ant predation. A caterpillar species' abundance, dietary specialization, and behavioral defenses were important predictors of its ant predation risk. Abundant caterpillar species had increased risk of ant predation irrespective of bird predation. Caterpillar species with broad diet breadth and behavioral responsiveness to attack had reduced ant predation risk, but these ant effects only occurred when birds also had access to the caterpillar community. These findings suggest that ant predation of caterpillar species is density‐ or frequency‐dependent, that ants and birds may impose countervailing selection on dietary specialization within the same herbivore community, and that contingent effects of multiple predators may generate behaviorally mediated life‐history trade‐offs associated with herbivore diet breadth.     

A distance–performance trade‐off in the phenotypic basis of dispersal

Across taxa, individuals vary in how far they disperse, with most individuals staying close to their origin and fewer dispersing long distances. Costs associated with dispersal (e.g., energy, risk) are widely believed to trade off with benefits (e.g., reduced competition, increased reproductive success) to influence dispersal propensity. However, this framework has not been applied to understand variation in dispersal distance, which is instead generally attributed to extrinsic environmental factors. We alternatively hypothesized that variation in dispersal distances results from trade‐offs associated with other aspects of locomotor performance. We tested this hypothesis in the stream salamander Gyrinophilus porphyriticus and found that salamanders that dispersed farther in the field had longer forelimbs but swam at slower velocities under experimental conditions. The reduced swimming performance of long‐distance dispersers likely results from drag imposed by longer forelimbs. Longer forelimbs may facilitate moving longer distances, but the proximate costs associated with reduced swimming performance may help to explain the rarity of long‐distance dispersal. The historical focus on environmental drivers of dispersal distances misses the importance of individual traits and associated trade‐offs among traits affecting locomotion.     

Greenhead ants Rhytidoponera metallica make trade‐offs between food temperature and food concentration

1. Foraging animals are often faced with foods that vary in several important attributes, some of which may be in conflict with one another. For ectothermic animals, food temperature can be an important characteristic, as the consumption of cold foods is metabolically costly. 2. Here, the effect of food temperature on food preferences in the green‐headed ant Rhytidoponera metallica (Smith, 1858) was investigated. The first aim of the study was to determine how food concentration (caloric value) and relative food temperature influenced colony‐level preferences. We found that, all else being equal, green‐headed ant colonies preferred warmer food solutions over colder solutions, and more concentrated food solutions over less concentrated ones. 3. Next, the question of whether green‐head ant colonies could make trade‐offs between temperature and food concentration was tested. It was found that ant colonies switched their preferences in favour of a colder food solution when the colder food solution was 10 times more concentrated than the warmer food solution. 4. These experiments show that temperature is an important characteristic shaping food preferences in ants. Moreover, we show that colonies can make trade‐offs between food concentration and food temperature.     

Short‐ and long‐term consequences of early developmental conditions: a case study on wild and domesticated zebra finches

Divergent selection pressures among populations can result not only in significant differentiation in morphology, physiology and behaviour, but also in how these traits are related to each other, thereby driving the processes of local adaptation and speciation. In the Australian zebra finch, we investigated whether domesticated stock, bred in captivity over tens of generations, differ in their response to a life‐history manipulation, compared to birds taken directly from the wild. In a ‘common aviary’ experiment, we thereto experimentally manipulated the environmental conditions experienced by nestlings early in life by means of a brood size manipulation, and subsequently assessed its short‐ and long‐term consequences on growth, ornamentation, immune function and reproduction. As expected, we found that early environmental conditions had a marked effect on both short‐ and long‐term morphological and life‐history traits in all birds. However, although there were pronounced differences between wild and domesticated birds with respect to the absolute expression of many of these traits, which are indicative of the different selection pressures wild and domesticated birds were exposed to in the recent past, manipulated rearing conditions affected morphology and ornamentation of wild and domesticated finches in a very similar way. This suggests that despite significant differentiation between wild and domesticated birds, selection has not altered the relationships among traits. Thus, life‐history strategies and investment trade‐offs may be relatively stable and not easily altered by selection. This is a reassuring finding in the light of the widespread use of domesticated birds in studies of life‐history evolution and sexual selection, and suggests that adaptive explanations may be legitimate when referring to captive bird studies.     

Relationships among oxidative status,breeding conditions and life‐history traits in free‐living Great Tits Parus major and Common Starlings Sturnus vulgaris

The interest shown by ecologists in antioxidants and oxidative stress as potential modulators of life‐history trade‐offs has expanded greatly in recent years. However, we still know very little about natural variation in oxidative damage and antioxidant capacity in free‐living animals. In this study, we describe the natural variation in three components of oxidative balance in nestlings and breeding females in free‐living Great Tits Parus major and Common Starlings Sturnus vulgaris in central Italy, and relate these to breeding conditions and life‐history traits. Our results suggest that there are associations among oxidative physiology, reproductive activity, growth pattern and season in wild birds, but that the nature of these associations might be species‐specific rather than general across species.     

Having the guts to compete: how intestinal plasticity explains costs of inducible defences

Predators commonly induce phenotypic changes that make prey better at surviving predation at the cost of reduced growth. While we have a good understanding of how trait changes affect predation risk, we lack a mechanistic understanding of why predator‐induced phenotypes differ in growth. Using two mesocosm experiments, we combined phenotypic plasticity theory with predictions from optimal digestion theory to demonstrate that intra‐ and interspecific competition induced relatively long guts while predators induced relatively short guts. The longer guts induced by competition appear to be an adaptive response that allows more efficient digestion and more rapid growth whereas the shorter guts induced by predators appear to result from a tradeoff of building larger tails in predator environments at the cost of smaller bodies. By combining these two bodies of theory, we now have a much better understanding of the mechanisms that cause the phenotypic trade‐offs that select for inducible defences.     

Elevational trends in life histories: revising the pace‐of‐life framework

Life‐history traits in birds, such as lifespan, age at maturity, and rate of reproduction, vary across environments and in combinations imposed by trade‐offs and limitations of physiological mechanisms. A plethora of studies have described the diversity of traits and hypothesized selection pressures shaping components of the survival–reproduction trade‐off. Life‐history variation appears to fall along a slow–fast continuum, with slow pace characterized by higher investment in survival over reproduction and fast pace characterized by higher investment in reproduction over survival. The Pace‐of‐Life Syndrome (POLS) is a framework to describe the slow–fast axis of variation in life‐history traits and physiological traits. The POLS corresponds to latitudinal gradients, with tropical birds exhibiting a slow pace of life. We examined four possible ways that the traits of high‐elevation birds might correspond to the POLS continuum: (i) rapid pace, (ii) tropical slow pace, (iii) novel elevational pace, or (iv) constrained pace. Recent studies reveal that birds breeding at high elevations in temperate zones exhibit a combination of traits creating a unique elevational pace of life with a central trade‐off similar to a slow pace but physiological trade‐offs more similar to a fast pace. A paucity of studies prevents consideration of the possibility of a constrained pace of life. We propose extending the POLS framework to include trait variation of elevational clines to help to investigate complexity in global geographic patterns.     

The evolution of growth trajectories: what limits growth rate?

According to life‐history theory, growth rates are subject to strong directional selection due to reproductive and survival advantages associated with large adult body size. Yet, growth is commonly observed to occur at rates lower than the maximum that is physiologically possible and intrinsic growth rates often vary among populations. This implies that slower growth is favoured under certain conditions. Realized growth rate is thus the result of a compromise between the costs and advantages of growing rapidly, and the optimal rate of growth is not equivalent to the fundamental maximum rate. The ecological and evolutionary factors influencing growth rate are reviewed, with particular emphasis on how growth might be constrained by direct fitness costs. Costs of accelerating growth might contribute to the variance in fitness that is not attributable to age or size at maturity, as well as to the variation in life‐history strategies observed within and among species. Two main approaches have been taken to study the fitness trade‐offs relating to growth rate. First, environmental manipulations can be used to produce treatment groups with different rates of growth. Second, common garden experiments can be used to compare fitness correlates among populations with different intrinsic growth rates. Data from these studies reveal a number of potential costs for growth over both the short and long term. In order to acquire the energy needed for faster growth, animals must increase food intake. Accordingly, in many taxa, the major constraint on growth rate appears to arise from the trade‐off between predation risk and foraging effort. However, growth rates are also frequently observed to be submaximal in the absence of predation, suggesting that growth trajectories also impact fitness via other channels, such as the reallocation of finite resources between growth and other traits and functions. Despite the prevalence of submaximal growth, even when predators are absent, there is surprisingly little evidence to date demonstrating predator‐independent costs of growth acceleration. Evidence that does exist indicates that such costs may be most apparent under stressful conditions. Future studies should examine more closely the link between patterns of resource allocation to traits in the adult organism and lifetime fitness. Changes in body composition at maturation, for example, may determine the outcome of trade‐offs between reproduction and survival or between early and late reproduction. A number of design issues for studies investigating costs of growth that are imposed over the long term are discussed, along with suggestions for alternative approaches. Despite these issues, identifying costs of growth acceleration may fill a gap in our understanding of life‐history evolution: the relationships between growth rate, the environment, and fitness may contribute substantially to the diversification of life histories in nature.     

The control of risk hypothesis: reactive vs. proactive antipredator responses and stress‐mediated vs. food‐mediated costs of response

Inducible defences against predators evolve because they reduce the rate of direct predation, but this benefit is offset by the cost (if any) of defence. If antipredator responses carry costs, the effect of predators on their prey is partitioned into two components, direct killing and risk effects. There is considerable uncertainty about the strength of risk effects, the factors that affect their strength, and the mechanisms that underlie them. In some cases, antipredator responses are associated with a glucocorticoid stress response, and in other cases they are associated with trade‐offs between food and safety, but there is no general theory to explain this variation. Here, I develop the control of risk (COR) hypothesis, predicting that proactive responses to predictable and controllable aspects of risk will generally have food‐mediated costs, while reactive responses to unpredictable or uncontrollable aspects of predation risk will generally have stress‐mediated costs. The hypothesis is grounded in laboratory studies of neuroendocrine stressors and field studies of food‐safety trade‐offs. Strong tests of the COR hypothesis will require more studies of responses to natural variation in predation risk and the physiological consequences of these responses, but its explanatory power can be illustrated with existing case studies.     

Differences in boldness are repeatable and heritable in a long‐lived marine predator

Animal personalities, composed of axes of consistent individual behaviors, are widely reported and can have important fitness consequences. However, despite theoretical predictions that life‐history trade‐offs may cause and maintain personality differences, our understanding of the evolutionary ecology of personality remains poor, especially in long‐lived species where trade‐offs and senescence have been shown to be stronger. Furthermore, although much theoretical and empirical work assumes selection shapes variation in personalities, studies exploring the genetic underpinnings of personality traits are rare. Here we study one standard axis of personality, the shy–bold continuum, in a long‐lived marine species, the wandering albatross from Possession Island, Crozet, by measuring the behavioral response to a human approach. Using generalized linear mixed models in a Bayesian framework, we show that boldness is highly repeatable and heritable. We also find strong differences in boldness between breeding colonies, which vary in size and density, suggesting birds are shyer in more dense colonies. These results demonstrate that in this seabird population, boldness is both heritable and repeatable and highlights the potential for ecological and evolutionary processes to shape personality traits in species with varying life‐history strategies.     

Seasonal occurrence and local movements of the grey-headed (brown-necked) parrot Poicephalus fuscicollis suahelicus in southern Africa

Seasonal movements of grey‐headed (brown‐necked) parrots were recorded in parts of its range and are likely a response to breeding and availability of specific food sources. Breeding occurred in the northern Kruger National Park and lowveld near the Mutale–Luvhuvhu river confluence from April to August. Aggregations and movements of birds occurred during the post‐breeding season (August–December) in response to seasonally abundant food sources. In north‐eastern South Africa, grey‐headed parrots occurred at Levubu, following the breeding season and their arrival in the area was correlated with the availability of unripe Mabola Plum, Parinari curatellifolia fruit. Similar regional movements occurred in Zimbabwe, the Caprivi of northern Namibia and Zambia. During these movements, flocks of up to 50 individuals were observed, whilst during breeding months singletons and pairs were more frequently seen. This increased abundance in time and space suggests that seasonal migratory movements occur.     

Impact of external odor on self‐grooming of lesser flat‐headed bats,Tylonycteris pachypus

Grooming is a common behavior of some mammals. Previous studies have shown that grooming is a means by which animals clean themselves, remove ectoparasites, and lower their body temperature. It is also involved in olfactory communication. Bats belong to the order Chiroptera and, like most mammals, are the natural host of many ectoparasites. Bat grooming, including licking and scratching, is one of the ways to reduce the adverse effects caused by ectoparasites. Bat grooming may also be induced by exogenous odor. In this study, we used lesser flat‐headed bats (Tylonycteris pachypus) to test the hypothesis that exogenous odor affects the self‐grooming behavior of bats. Results showed that external odor from distantly related species caused lesser flat‐headed bats to spend more time in self‐grooming. Lesser flat‐headed bats that received odor from humans spent the longest time in self‐grooming, followed by those that received odor from a different species of bats (T. robustula). Lesser flat‐headed bats that received odor form the same species of bats, either from the same or a different colony, spent the least amount of time in self‐grooming. These results suggest that bats can recognize conspecific and heterospecific through body scent.     

Genetic variation in herbivore resistance and tolerance: the role of plant life‐history stage and type of damage

Information of the patterns of genetic variation in plant resistance and tolerance against herbivores and genetic trade‐offs between these two defence strategies is central for our understanding of the evolution of plant defence. We found genetic variation in resistance to two specialist herbivores and in tolerance to artificial damage but not to a specialist leaf herbivore in a long‐lived perennial herb. Seedlings tended to have genetic variation in tolerance to artificial damage. Genetic variation in tolerance of adult plants to artificial damage was not consistent in time. Our results suggest that the level of genetic variation in tolerance and resistance depends on plant life‐history stage, type of damage and timing of estimating the tolerance relative to the occurrence of the damage, which might reflect the pattern of selection imposed by herbivory. Furthermore, we found no trade‐offs between resistance and tolerance, which suggests that the two defence strategies can evolve independently.     

What shall I do now? State-dependent variations of life-history traits with aging in Wandering Albatrosses

Allocation decisions depend on an organism's condition which can change with age. Two opposite changes in life‐history traits are predicted in the presence of senescence: either an increase in breeding performance in late age associated with terminal investment or a decrease due to either life‐history trade‐offs between current breeding and future survival or decreased efficiency at old age. Age variation in several life‐history traits has been detected in a number of species, and demographic performances of individuals in a given year are influenced by their reproductive state the previous year. Few studies have, however, examined state‐dependent variation in life‐history traits with aging, and they focused mainly on a dichotomy of successful versus failed breeding and non‐breeding birds. Using a 50‐year dataset on the long‐lived quasi‐biennial breeding wandering albatross, we investigated variations in life‐history traits with aging according to a gradient of states corresponding to potential costs of reproduction the previous year (in ascending order): non‐breeding birds staying at sea or present at breeding grounds, breeding birds that failed early, late or were successful. We used multistate models to study survival and decompose reproduction into four components (probabilities of return, breeding, hatching, and fledging), while accounting for imperfect detection. Our results suggest the possible existence of two strategies in the population: strict biennial breeders that exhibited almost no reproductive senescence and quasi‐biennial breeders that showed an increased breeding frequency with a strong and moderate senescence on hatching and fledging probabilities, respectively. The patterns observed on survival were contrary to our predictions, suggesting an influence of individual quality rather than trade‐offs between reproduction and survival at late ages. This work represents a step further into understanding the evolutionary ecology of senescence and its relationship with costs of reproduction at the population level. It paves the way for individual‐based studies that could show the importance of intra‐population heterogeneity in those processes.