No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Environmental Uncertainty and the Global Biogeography of Cooperative Breeding in Birds
Abstract
Understanding why organisms as different as amoebas, ants, and birds cooperate remains an important question in evolutionary biology. Although ecology can influence cooperation and conflict within animal societies and has been implicated in species differences in sociality, the environmental predictors of sociality across broad geographic and taxonomic scales remain poorly understood. In particular, the importance of temporal variation in selection pressure has been underestimated in most evolutionary studies. Environmental uncertainty resulting from climatic variation is likely to be an important driver of temporal variation in selection pressure and therefore is expected to impact the evolution of behavioral, morphological, and physiological traits, including cooperation. Using a data set of over 95% of the world's birds, we examine the global geography and environmental, biotic, and historical biogeographic predictors of avian social behavior. We find dramatic spatial variation in social behavior for which environmental and biotic factors--namely, among-year environmental variability in precipitation--are important predictors. Although the clear global biogeographic structure in avian social behavior carries a strong signal of evolutionary history, environmental uncertainty plays an additional key role in explaining the incidence and distribution of avian cooperative breeding behavior.
... Social living can give rise to emergent strategies for coping with climatic stressors (Arnold, 1988;Fahrenholz et al., 1989;Klok and Chown, 1999). Observed patterns in global biogeography support hypotheses linking climate to social evolution, with distributions of social organisms falling along gradients of temperature, precipitation, and climatic stochasticity (Jetz and Rubenstein, 2011;Lukas and Clutton-Brock, 2017;Purcell, 2011). These interactions between climate and sociality raise important questions about the fate of social organisms and social phenotypes under changing climate. ...
... These traits can broadly influence how bees respond to climatic variables, and therefore their vulnerability to environmental change ( Figure 1). Group living has been proposed to provide buffering effects against environmental variability (Kennedy et al., 2018;Komdeur and Ma, 2021), which may explain why cooperatively breeding animals to thrive in regions characterized by strong climatic variability (Jetz and Rubenstein, 2011;Lukas and Clutton-Brock, 2017;Sheehan et al., 2015). While a considerable body of literature explores effects of climate change on bees that are social, many fewer investigate social effects at the species level, i.e., by assessing social behavior as a predictor variable across bee species. ...
... Climatic selective pressures have been implicated in social evolutionary transitions across animal taxa (Guevara and Avilés, 2015; Jetz and Rubenstein, 2011;Liu et al., 2020;Lukas and Clutton-Brock, 2017). These patterns support the hypothesis that sociality can facilitate the colonization of unpredictable environments, or can expand species' ranges (Brooks et al., 2017;Cornwallis et al., 2017). ...
... Foremost, comparative studies often classify species in a binary manner as cooperative or noncooperative breeders according to a specific definition, and use this list of classified species as a predictor or response variable in their analyses (e.g. Jetz & Rubenstein, 2011;Leighton, 2017). Hence, if comparative studies use different operational definitions, the same group of species will be classified differently and the results of these studies will not be comparable. ...
... Nevertheless, communal breeding species are considered cooperative breeders in some analyses [often in ornithology (e.g. Jetz & Rubenstein, 2011;Leighton, 2017)], but as non-cooperative breeders in others [often in mammalogy (e.g. Lukas & Clutton-Brock, 2012a;Federico et al., 2020)]. ...
... Inconsistency in applying inclusive or restrictive definitions of cooperative breeding hampers comparison across studies and taxonomic groups as demonstrated in the following example. Lukas & Clutton-Brock (2017) and Jetz & Rubenstein (2011) investigated the relationships between the same climatic factors and the distribution of cooperative breeding in mammals and birds, respectively. In mammals, only mean annual rainfall was found to affect the distribution of cooperative breeding, while in birds, additional climatic factors were found to have explanatory power (e.g. ...
Cooperative breeding (i.e. when alloparents care for the offspring of other group members) has been studied for nearly a century. Yet, inconsistent definitions of this breeding system still hamper comparative research. Here, we identify two major inconsistencies, discuss their consequences and propose a way forward. First, some researchers restrict the term 'cooperative breeding' to species with non-breeding alloparents. We show that such restrictive definitions lack distinct quantitative criteria to define non-breeding alloparents. This ambiguity, we argue, reflects the reproductive-sharing continuum among cooperatively breeding species. We therefore suggest that cooperative breeding should not be restricted to the few species with extreme reproductive skew and should be defined independent of the reproductive status of alloparents. Second, definitions rarely specify the type, extent and prevalence of alloparental care required to classify species as cooperative breeders. We thus analysed published data to propose qualitative and quantitative criteria for alloparental care. We conclude by proposing the following operational definition: cooperative breeding is a reproductive system where >5% of broods/litters in at least one population receive species-typical parental care and conspecifics provide proactive alloparental care that fulfils >5% of at least one type of the offspring's needs. This operational definition is designed to increase comparability across species and disciplines while allowing to study the intriguing phenomenon of cooperative breeding as a behaviour with multiple dimensions.
... Several comparative studies in a variety of taxa suggest that both the mean and variation in climatic conditions have shaped the evolution of animal societies (Fisher et al., 2021). For example, harsh mean environmental conditions and/or fluctuating environments have favoured the evolution of cooperative breeding behaviour in ants (La Richelière et al., 2022), wasps (Sheehan et al., 2015), bees (Kocher et al., 2014), birds (Jetz & Rubenstein, 2011;Rubenstein & Lovette, 2007), and mammals (Firman et al., 2020;Lukas & Clutton-Brock, 2017), including humans (Martin et al., 2020). Yet, high population density and habitat saturation, both characteristics of species living in benign and/or stable environments, have also been suggested to favour the evolution of cooperative breeding behaviour in insects (Choe & Crespi, 1997;Costa, 2006), arachnids (Choe & Crespi, 1997), birds , and mammals (Solomon & French, 1997). ...
... The avian species used in this study came from published data (Jetz & Rubenstein, 2011). Because we were interested in how climatic factors influence the evolution of cooperatively breeding behaviour, we excluded clades containing 100% non-cooperatively breeding species (2409 species belonging to 52 clades) and 100% cooperatively breeding species (58 species belonging to 5 clades). ...
... We also compared the species list with the most recent Handbook of the Birds of the World and BirdLife Taxonomic Checklist v5 (BirdLife International, 2020) to exclude subspecies from our analysis (N = 290 species). The social system of each species was classified as "cooperative" or "non-cooperative" and was determined through published accounts (Cockburn, 2006;Jetz & Rubenstein, 2011). Following Griesser and Suzuki (2016), we also reran our comparative analyses excluding 152 species that only occasionally breed cooperatively, finding nearly identical results (see Tables S1-S3). ...
Although social species as diverse as humans and ants are among the most abundant organisms on Earth, animals cooperate and form groups for many reasons. How these different reasons for grouping affect a species' ecological dominance remains unknown. Here we use a theoretical model to demonstrate that the different fitness benefits that animals receive by forming groups depend on the quality of their environment, which in turn impacts their ecological dominance and resilience to global change. We then test the model's key predictions using phylogenetic comparative analysis of >6500 bird species. As predicted, we find that cooperative breeders occurring in harsh and fluctuating environments have larger ranges and greater abundances than non‐cooperative breeders, but cooperative breeders occurring in benign and stable environments do not. Using our model, we further show that social species living in harsh and fluctuating environments will be less vulnerable to climate change than non‐social species.
... Accumulating evidence suggests that the interplay between environmental variation and contributions of helpers to breeding output has in fact shaped the evolution and occurrence of cooperative breeding species. For example, species in which helpers provide alloparental care (care directed towards non-descendant young) are more prevalent in habitats with high environmental variability, whereas species without alloparental care are more prevalent in less variable environments [11,17,18]. Further, clade-specific analyses within birds reveal that the relationships between environmental conditions and the distribution of cooperative breeding species differ between clades with different types of within-group dynamics. ...
... These scales represent two ways climate may impact social group size. If social group size is shaped by environmental effects on social evolution, then variation across populations should relate to a metric which encompasses variation in climate over a long timescale [17]. However, social group size may also be the product of year-to-year variation in reproductive success, thus the climate in the year preceding the observation may have a strong effect on group size. ...
... Within this time window, a single year's annual data was considered to span March-February, such that each year begins in the austral fall and ends with the austral summer. For each checklist location, we generated one average annual value and two measures of variation in both rainfall and temperature from the long-term climate grids (sensu Jetz & Rubenstein [17]). Average annual rainfall was calculated by summing rainfall totals for each month in a year, then averaging rainfall across years and log transforming the result. ...
Cooperatively breeding species exhibit a range of social behaviours associated with different costs and benefits to group living, often in association with different environmental conditions. For example, recent phylogenetic studies have collectively shown that the evolution and distribution of cooperative breeding behaviour is related to the environment. However, little is known about how environmental variation may drive differences in social systems across populations within species, and how the relationship between environmental conditions and sociality may differ across species. Here, we examine variation in social group size along a steep environmental gradient for two congeneric cooperatively breeding species of fairywrens (Maluridae) and show that they exhibit opposing ecogeographic patterns. Purple-backed fairywrens, a species in which helpers increase group productivity, have larger groups in hot, dry environments and smaller groups in cool, wet environments. By contrast, superb fairywrens, a species with helpers that do not increase group productivity despite the presence of alloparental care, exhibit the opposite trend. We suggest differences in the costs and benefits of sociality contribute to these opposing ecogeographical patterns and demonstrate that comparisons of intraspecific patterns of social variation across species can provide insight into how ecology shapes social systems.
... One hypothesised way through which organisms may buffer the negative effects induced by environmental change is by forming groups, becoming social, and cooperatively breeding (Rubenstein and Lovette 2007;Cockburn and Russell 2011;Jetz and Rubenstein 2011;Rubenstein 2011;Griesser et al. 2017;Komdeur and Ma 2021). Most cooperative breeding species live in unpredictable and variable environments (Jetz and Rubenstein 2011;Komdeur and Ma 2021), or in harsh environments (Lukas and Clutton-Brock 2017). ...
... One hypothesised way through which organisms may buffer the negative effects induced by environmental change is by forming groups, becoming social, and cooperatively breeding (Rubenstein and Lovette 2007;Cockburn and Russell 2011;Jetz and Rubenstein 2011;Rubenstein 2011;Griesser et al. 2017;Komdeur and Ma 2021). Most cooperative breeding species live in unpredictable and variable environments (Jetz and Rubenstein 2011;Komdeur and Ma 2021), or in harsh environments (Lukas and Clutton-Brock 2017). Becoming social can decrease predation risk (e.g. ...
... In comparative studies, Rubenstein and Lovette (2007), Jetz andRubenstein (2011), Sheehan et al. (2015), and Cornwallis et al. (2017) all showed that cooperative breeding mainly occurs in unpredictable environments. Consequently, it was hypothesised Fig. 3 a Association between offspring sex (1 = son, 0 = daughter) and rainfall (n = 959 offspring, from 1995 to 2015). ...
Species are facing environmental challenges caused by rapidly changing environments. Globally, extreme weather events, like droughts or extreme rainfall, are increasing in frequency. Natural selection usually acts slowly, while adaptations through phenotypic plasticity are limited. Therefore, organisms may utilise other mechanisms to cope with such rapid change. Cooperative breeding is hypothesised to be one such mechanism, as helpers could increase survival probabilities of offspring, especially in harsh years. Rainfall is a cue for onset of breeding in many tropical species, to ensure young are born when food abundance is highest. Using 21 years of data, we investigate the effect of rainfall on social behaviour and life history in the insectivorous Seychelles warbler ( Acrocephalus sechellensis ), a facultative cooperative breeder. We found that low rainfall is associated with reduced reproductive output and possibly with decreased survival. However, there were no statistical differences in response between groups with helpers, groups with only non-helping subordinates, and breeding pairs without subordinates. With low rainfall, more sons (the sex less likely to help) were produced, and those subordinate males already present were less likely to help. Thus, in contrast to expectations, cooperative breeding does not seem to buffer against harsh environments in Seychelles warblers, indicating that group living may be costly and thus not a mechanism for coping with changing environments. Our study showed that the interaction between the environment and life histories, including social behaviour, is complex, but that this interaction is important to consider when studying the impact of changing environments on species survival.
... Climate has been repeatedly implicated as a causal factor mediating the 411 evolution of vertebrate social behaviour (Jetz & Rubenstein 2011;Lukas & Clutton-412 Brock 2017;Firman et al. 2020). We show that social grouping in lizards also exhibits a 413 strong climatic signature, typically occurring in species that occupy cool, dry climates. ...
... First, associations between climate and complex social behaviour in birds and 431 mammals are largely related to offspring provisioning (Qi et al. 2023;Cornwallis et al. 432 2017;Jetz & Rubenstein 2011). In this context, climate influences resource availability 433 and thus the costs and benefits of prolonged investment in parental and alloparental 434 care (Hatchwell 2009;Hatchwell & Komdeur 2000). ...
Identifying the environmental factors associated with group living is important for understanding how social systems originate, persist and diversify. In endothermic birds and mammals, living in social groups is associated with habitat constraints and harsh climatic conditions. We use phylogenetic comparative analyses to test whether climate and habitat have played similar roles in the evolution of social grouping in a globally distributed clade of ectothermic vertebrates, lizards (Nspecies = 1696). Social grouping was strongly associated with cool, dry climates across the lizard phylogeny. However, this climatic signature arose indirectly, by association with live birth (common in cool climates) and a reliance on rock crevices (common in dry climates), traits which increase parent-offspring associations and reduce offspring dispersal. In contrast, direct effects of cool temperature on the evolution of social grouping were marginal and restricted to live bearing species. Our results demonstrate that relationships between climate and sociality may result from climatic adaptations that go on to promote the emergence of grouping behaviour.
... Mathematical models simulating human social structure and life history suggest that harsh and unpredictable conditions favour the emergence of cooperative behaviour [11] and that only cooperatively foraging phenotypes are likely to survive the harshest environmental conditions [12]. Recent evidence supports this hypothesis, showing that cooperation is often linked to environmental adversity in humans, primates and birds [13][14][15][16]. For example, in Diana monkeys between-group tolerance increases when conditions are physiologically stressful (i.e. ...
... low resources and high predation risk [15]), and increased predation risk enhances cooperation among breeding pied flycatchers Ficedula hypoleuca [16]. Furthermore, alloparental care in birds, humans and other mammals is associated with unproductive and unpredictable environments with low rainfall [13,14,17,18]. The benefits linked to cooperation under harsh conditions could then promote structured associations among individuals as they increase mutual tolerance and develop social bonds to gain benefits from reciprocal cooperative behaviours [2]. ...
Cooperation may emerge from intrinsic factors such as social structure and extrinsic factors such as environmental conditions. Although these factors might reinforce or counteract each other, their interaction remains unexplored in animal populations. Studies on multilevel societies suggest a link between social structure, environmental conditions and individual investment in cooperative behaviours. These societies exhibit flexible social configurations, with stable groups that overlap and associate hierarchically. Structure can be seasonal, with upper-level units appearing only during specific seasons, and lower-level units persisting year-round. This offers an opportunity to investigate how cooperation relates to social structure and environmental conditions. Here, we study the seasonal multilevel society of superb fairy-wrens (Malurus cyaneus), observing individual responses to experimental playback of conspecific distress calls. Individuals engaged more in helping behaviour and less in aggressive/territorial song during the harsher non-breeding season compared to the breeding season. The increase in cooperation was greater for breeding group members than for members of the same community, the upper social unit, comprised of distinct breeding groups in association. Results suggest that the interaction between social structure and environmental conditions drives the seasonal switch in cooperation, supporting the hypothesis that multilevel societies can emerge to increase cooperation during harsh environmental conditions.
... Birds generally prefer food items that they can process quickly. In other words, birds are more concerned with how quickly they can digest and absorb food than with the nutritional value of the food [39]. This is because birds need to eat frequently in order to maintain their energy levels. ...
... The starches in seeds are a good source of energy for birds, and granivorous birds have adapted to efficiently digest and absorb these starches, and there are over 1,000 different species of birds that are primarily granivores, and they can be found all over the world [18]. The way that birds choose food suggests that the evolution of bird granivory has focused on developing physical adaptations for mechanically digesting seeds, while chemical adaptations for digesting seeds have been less important [39]. ...
Birds are essential bio-or eco-engineers that play a vital role in regulating nature, and their interactions with other environmental aspects can be complex and varied. Forests and birds are intricately intertwined. Through their mutual interaction, they create a harmonious living system that supports both parties. Forest birds play a crucial role in maintaining the balance of nature by dispersing seeds, pollinating flowers, and controlling insect populations. In addition to housing and food, forests offer bird's places to nest, wintering grounds, and thermal refuges. The diversity and distribution of forest birds are critical indicators of forest health and ecosystem function. However, factors such as climate change, habitat loss and fragmentation, and human activities profoundly impact the distribution and abundance of forest birds. Addressing these issues and taking action to mitigate their effects is essential. The forest ecosystem and its avian inhabitants can be protected by restoring degraded habitats, putting conservation practices into place, and promoting sustainable forestry practices.
... However, it is often the case that a 37 clear distinction between these categories and scales is not made (Dornhaus et al. 2011;Jetz & Rubenstein 38 2011). For example, a meta-analysis identified that birds in general will live in groups where rainfall patterns are 39 fluctuating at large geographic scales (Jetz & Rubenstein 2011), yet local environmental conditions and smaller 40 taxonomic scales have yielded alternative results (Gonzalez et al. 2013). Group size also tends to be the primary 41 measure of sociality in several studies, and yet several species exhibit strong reproductive skew that requires 42 more detailed assessment of the number of breeders and nonbreeders in a group ( Here, we introduce a multi-level sociality framework that identifies four categories of social variation (from 47 large to fine-scale variation) that highlights the extent of sociality amongst a variety of social species. ...
... high disturbances). In comparison, 601In comparison, based on global study, many birds evolved social living as a strategy to ensure survival in 602 environments that are constantly fluctuating and challenging(Jetz & Rubenstein 2011). Similarly, naked mole-603 rats have some of the highest degrees of sociality and are strictly eusocial, like Heterocephalus glaber (0.95) 604and Fukomys damarensis (0.80-91) (Avilés & Harwood 2012), and they live socially due to challenging 605 environments that fluctuate substantially in rainfall(Faulkes et al. 1997). ...
Understanding variation in social organization that does not have a strong phylogenetic signal represents a key focus of research in behavioural and evolutionary ecology. In light of this, we established a sociality framework that identifies four categories of variation in social organisation that range from large-scale to fine-scale and can each be related to various ecological factors: (1) forms of sociality, (2) degree of sociality, (3) social plasticity, and (4) within-group plasticity. We modelled this framework by quantifying the four categories of variation over time, space and disturbance regime using multiple species of coral-dwelling gobies from the genus Gobiodon. Gobies are a particularly interesting model system as they vary in social structure, have within-group cooperation and form mutualistic relationships with their coral hosts which are vulnerable to climatic disturbances. We found that gobies varied in forms of sociality -- from being solitary, to paired or group-living depending on location and disturbance regime. Only low or moderate degrees of sociality were observed in gobies, and this was influenced by location or disturbance regime depending on species. Gobies were more often solitary or pair-forming than group-forming (which became extremely rare) in a high disturbance regime whereas they were more often found in groups in a moderate disturbance regime. The size of coral hosts affected the social plasticity of gobies, and corals were smaller due to climatic disturbances. Gobies did not exhibit within-group social plasticity, as there were no changes to the structure of size-based hierarchies or sex allocation patterns with location or disturbance regime. Lastly, by combining the four categories of variation, we find that there is a high loss of sociality in coral-dwelling gobies due environmental disturbances, which likely affects overall goby survival as living in groups can improve survival and fitness. By using our structured framework, we identified which categories of social variation were influenced by ecological factors like location and disturbance. This framework therefore provides an excellent tool for predicting future responses of animal societies to environmental stressors.
... Many authors highlight the distinctiveness of Australia's hard-leaved (sclerophyllous), fire-adapted plants (Beadle, 1966;Braithwaite, 1990;Orians and Milewski, 2007;Bradstock et al., 2012). Reduced and lesspredictable resource availability is also considered to have exerted selective pressure on characteristics of Australian fauna such as body size, growth and metabolic rates, sociality and reproductive output, and may contribute to Australia's absence of large carnivorous mammals and food chains with relatively few apex predators compared to other continents (Orians and Milewski, 2007 and references therein;Lee and Cockburn, 1985;Braithwaite, 1990;Milewski and Diamond, 2000;Burness et al., 2001;Ritchie and Johnson, 2009;Jetz and Rubenstein, 2011). Low nutrient concentrations and unique oceanographic patterns underpin globally low annual yields in Australian marine wild fisheries (Savage, 2015;FAO, 2016). ...
... Life history strategies of Australian animals were also expected to indicate resource-conservative ecological strategies (Braithwaite, 1990;Jetz and Rubenstein, 2011). Australian birds live for an average of ~21 years, which is significantly longer than birds from other continents, which live, on average, for ~16 years (p = 0.023; Figure 2E). ...
Australia’s distinctive biogeography means that it is sometimes considered an ecologically unique continent with biological and abiotic features that are not comparable to those observed in the rest of the world. This leaves some researchers unclear as to whether findings from Australia apply to systems elsewhere (or vice-versa), which has consequences for the development of ecological theory and the application of ecological management principles. We analyzed 594,612 observations spanning 85 variables describing global climate, soil, geochemistry, plants, animals, and ecosystem function to test if Australia is broadly different to the other continents and compare how different each continent is from the global mean. We found significant differences between Australian and global means for none of 15 climate variables, only seven of 25 geochemistry variables, three of 16 soil variables, five of 12 plant trait variables, four of 11 animal variables, and one of five ecosystem function variables. Seven of these differences remained significant when we adjusted for multiple hypothesis testing: high soil pH, high soil concentrations of sodium and strontium, a high proportion of nitrogen-fixing plants, low plant leaf nitrogen concentration, low annual production rate to birth in mammals, and low marine productivity. Our analyses reveal numerous similarities between Australia and Africa and highlight dissimilarities between continents in the northern vs. southern hemispheres. Australia ranked the most distinctive continent for 26 variables, more often than Europe (15 variables), Africa (13 variables), Asia (12 variables each), South America (11 variables) or North America (8 variables). Australia was distinctive in a range of soil conditions and plant traits, and a few bird and mammal traits, tending to sit at a more extreme end of variation for some variables related to resource availability. However, combined analyses revealed that, overall, Australia is not significantly more different to the global mean than Africa, South America, or Europe. In conclusion, while Australia does have some unique and distinctive features, this is also true for each of the other continents, and the data do not support the idea that Australia is an overall outlier in its biotic or abiotic characteristics.
... The investment that helpers make in young may be additive to that of parents, increasing the overall amount of care provided to young (Canestrari, Chiarati, et al. 2008;Pike et al. 2019), or compensatory, enabling parents to reduce their investment while young still receive a similar amount of care overall (Hatchwell 1999;Savage et al. 2015;van Boheemen et al. 2019), a phenomenon known as "load-lightening" (Crick 1992;Meade et al. 2010;Mumme et al. 2015;Langmore et al. 2016). Global comparative studies have shown that the distribution of cooperatively breeding (Rubenstein and Lovette 2007;Jetz and Rubenstein 2011;Lukas and Clutton-Brock 2017;Shen et al. 2017) and group-living (Griesser et al. 2017;Firman et al. 2020) species is associated with harsh environments characterized by high spatial and temporal variability in rainfall, such as arid and semi-arid systems (although see Gonzalez et al. 2013;Lin et al. 2019). This association suggests that the contribution made by additional group members may buffer against environmental uncertainty (Rubenstein and Lovette 2007;Jetz and Rubenstein 2011;Russell 2016;Cornwallis et al. 2017;Lukas and Clutton-Brock 2017;Shen et al. 2017), at least up to an optimal group size (Markham et al. 2015;Ridley 2016). ...
... Global comparative studies have shown that the distribution of cooperatively breeding (Rubenstein and Lovette 2007;Jetz and Rubenstein 2011;Lukas and Clutton-Brock 2017;Shen et al. 2017) and group-living (Griesser et al. 2017;Firman et al. 2020) species is associated with harsh environments characterized by high spatial and temporal variability in rainfall, such as arid and semi-arid systems (although see Gonzalez et al. 2013;Lin et al. 2019). This association suggests that the contribution made by additional group members may buffer against environmental uncertainty (Rubenstein and Lovette 2007;Jetz and Rubenstein 2011;Russell 2016;Cornwallis et al. 2017;Lukas and Clutton-Brock 2017;Shen et al. 2017), at least up to an optimal group size (Markham et al. 2015;Ridley 2016). The buffering effect of cooperation under conditions of environmental uncertainty assumes that the influence of helpers on reproductive success varies with environmental conditions and becomes more important as conditions worsen (Hatchwell 1999;Langmore et al. 2016). ...
Cooperative breeding, where more than two individuals invest in rearing a single brood, occurs in many bird species globally and often contributes to improved breeding outcomes. However, high temperatures are associated with poor breeding outcomes in many species, including cooperative species. We used data collected over three austral summer breeding seasons to investigate the contribution that helpers make to daytime incubation in a cooperatively breeding species, the Southern Pied Babbler Turdoides bicolor, and the ways in which their contribution is influenced by temperature. Helpers spent a significantly higher percentage of their time foraging (41.8 ± 13.7%) and a significantly lower percentage of their time incubating (18.5 ± 18.8%) than members of the breeding pair (31.3 ± 11% foraging and 37.4 ± 15.7% incubating). In groups with only one helper, the helper’s contribution to incubation was similar to that of breeders. However, helpers in larger groups contributed less to incubation, individually, with some individuals investing no time in incubation on a given observation day. Helpers significantly decrease their investment in incubation on hot days (>35.5°C), while breeders tend to maintain incubation effort as temperatures increase. Our results demonstrate that pied babblers share the workload of incubation unequally between breeders and helpers, and this inequity is more pronounced during hot weather. These results may help to explain why recent studies have found that larger group size does not buffer against the impacts of high temperatures in this and other cooperatively breeding species.
... Moreover, the improvement in female survival may balance population sex ratios (Bright Ross et al., 2020). In addition to broadening the knowledge of sociality-senescence link, the current exploration gives insight into the evolution of avian cooperative breeding, which is associated with harsh environments (Cornwallis et al., 2017;Jetz & Rubenstein, 2011). The strategy that cooperative breeding prioritizes improving survival over reproduction of females over males could be the mechanism underlying the evolutionary success of the social systems in challenging environments. ...
... Nevertheless, we notice that the helper effect differs among bird species, being stronger on either reproduction or survival of mothers or fathers (Downing et al., 2020(Downing et al., , 2021Li et al., 2015). The variability may be attributed to divergence in life-history strategy among species, which are distributed across a gradient of climate stability, including tropical, subtropical, and temperate zones and savannas (Cornwallis et al., 2017;Jetz & Rubenstein, 2011). The current research thus offers a framework to investigate the evolution of cooperative breeding systems in different environments. ...
Sociality is known to be capable of slowing individual senescence, but it is unclear whether the effect differs for reproduction versus survival in a sex‐specific manner. Here we predict that social benefits are directed toward (1) somatic maintenance in harsh environments where high survival prospects of adults over young intensify the trade‐off between current and future reproduction, and (2) females that invest more in reproduction and have a greater marginal effect if their survival is improved by reducing the cost of reproduction. These two predictions are tested with cooperatively breeding Tibetan ground tits (Pseudopodoces humilis). Across the lifetime, both mothers and fathers with helpers did not differ in brood size at fledging from their counterparts without helpers. The presence of helpers reduced survival senescence of both parents, but mothers benefited more than fathers from receiving help. Consequently, the inherent sex difference in life span and along with lifetime reproductive success, as expressed in breeders of never‐receiving help, became no longer obvious. The model of social modulation for senescence should facilitate the persistence of cooperative breeding in challenging environments.
... log BF = 17.75, which is greater than 10], indicating that cold conditions may have selected for increased group size in both clades of Asian colobines (SM section 4.3.2). This pattern of enhanced sociality in cold and dry environments has also been reported in Australian rodents (33) and cooperative breeding birds (34). In the case of Asian colobines, transitions from one social system to another appear to have occurred at ancient evolutionary nodes and have been retained over long periods of time. ...
... log BF = 17.75, which is greater than 10], indicating that cold conditions may have selected for increased group size in both clades of Asian colobines (SM section 4.3.2). This pattern of enhanced sociality in cold and dry environments has also been reported in Australian rodents (33) and cooperative breeding birds (34). In the case of Asian colobines, transitions from one social system to another appear to have occurred at ancient evolutionary nodes and have been retained over long periods of time. ...
... log BF = 17.75, which is greater than 10], indicating that cold conditions may have selected for increased group size in both clades of Asian colobines (SM section 4.3.2). This pattern of enhanced sociality in cold and dry environments has also been reported in Australian rodents (33) and cooperative breeding birds (34). In the case of Asian colobines, transitions from one social system to another appear to have occurred at ancient evolutionary nodes and have been retained over long periods of time. ...
... Positive interdependence also exists where individuals derive benefits from assorting with others. For example, group members can become interdependent because increased group size reduces predation risk (favouring cooperative investments to increase the size of one's social group, [58]) or because life in groups can buffer against the environmental extremes individuals might otherwise experience [59][60][61]. In some cases, this buffering is achieved via food sharing (e.g. ...
Interdependence occurs when individuals have a stake in the success or failure of others, such that the outcomes experienced by one individual also generate costs or benefits for others. Discussion on this topic has typically focused on positive interdependence (where gains for one individual result in gains for another) and on the consequences for cooperation. However, interdependence can also be negative (where gains for one individual result in losses for another), which can spark conflict. In this article, we explain when negative interdependence is likely to arise and, crucially, the role played by (mis)perception in shaping an individual's understanding of their interdependent relationships. We argue that, owing to the difficulty in accurately perceiving interdependence with others, individuals might often be mistaken about the stake they hold in each other's outcomes, which can spark needless, resolvable forms of conflict. We then discuss when and how reducing misperceptions can help to resolve such conflicts. We argue that a key mechanism for resolving interdependent conflict, along with better sources of exogenous information, is to reduce reliance on heuristics such as stereotypes when assessing the nature of our interdependent relationships.
... Group living has been linked to adverse environmental conditions in many different types of animals see. 3 For example, cooperatively breeding birds are more prevalent in regions that experience harsh, unpredictable environments. 1,2,4 Results from this study indicate that similar relationships may also occur in plants. ...
Harsh, unpredictable environments are known to favor cooperative groups in animals. Whether plants exhibit similar relationships is unknown. Staghorn ferns (Platycerium bifurcatum, Polypodiaceae) are epiphytes that form cooperative groups which build communal water and nutrient ‘nests’ at the tops of trees, a habitat characterized by water and nutrient stress. We conducted field observations to test whether staghorn ferns continue to live in large, reproductively active groups after they become dislodged from the canopy and fall to the forest floor, where they are less limited by water and nutrient deprivation. To rule out the potentially confounding effects of light limitation on the forest floor, we also conducted a multi-year glasshouse experiment where we transplanted individual plants into soil and onto vertically oriented boards under standardized light conditions. Results from field observations showed that dislodged colonies formed smaller groups that reproduced less than epiphytic colonies. Results from the glasshouse experiment showed that even when growing in full sun, terrestrial individuals tended to remain solitary, while epiphytic individuals tended to recruit new individuals into colonies. Results also showed that plants growing in potting soil and exposed to full sunlight sporulated more heavily than plants growing epiphytically. However, localities that are characterized by both elevated soil and light resources are generally not available to staghorn ferns in the wild, perhaps with the exception of large, epiphytic colonies with well-developed nests at the top of tree canopies. Overall results indicate that the harsh environmental conditions at the tops of trees trigger the formation of colonies in staghorn ferns, similarly to group living animals.
... Although the relationship between the model and field observations is rather loose, it is interesting to note that cooperative breeding in birds is more common in more rugged (Cornwallis et al., 2017) and more uncertain habitats (Jetz & Rubenstein, 2011;Rubenstein & Lovette, 2007), which is entirely consistent with what we have seen in the model. ...
The threshold public goods game is one of the best-known models of nonlinear public goods dilemmas. Cooperators and defectors typically coexist in this game when the population is assumed to follow the so-called structured deme model. In this paper we develop a dynamical model of a general N-player game in which there is no deme structure: individuals interact with randomly chosen neighbours and selection occurs between randomly chosen pairs of indi- viduals. We show that in the deterministic limit the dynamics in this model leads to the same replicator dynamics as in the structured deme model, i.e. coexistence of cooperators and defectors is typical in threshold public goods game even when the population is completely well-mixed. We extend the model to study the effect of density dependence and density fluctuation on the dynamics. We show analytically and numerically that decreasing population density increases the equilibrium frequency of cooperators till the fixation of this strategy, but below a critical density coop- erators abruptly disappear from the population. Our numerical investigations show that weak density fluctuations enhance cooperation, while strong fluctuations suppress it.
... In addition, because the helper performs the same behaviors as the parents (e.g., feeding the nestlings), this strategy may also increase the nestling's growth rate and/or reduce the time spent in the nest, thereby avoiding the risk of starvation (Emlen & Wrege 1991, Skutch 1999. Because wetlands of Rio Grande do Sul are historically degraded habitats (Burguer 2000), the presence of helpers may suggest a strategy to maximize fitness under poor conditions (Jetz & Rubenstein 2011). ...
The Streamer-tailed Tyrant (Gubernetes yetapa) is an exclusively neotropical bird, associated with wetlands and widely distributed in Brazil. This study aimed to fill gaps in knowledge about this species, especially regarding its reproductive biology. We monitor a population of G. yetapa with the aim of describing its reproductive behavior, nest characteristics, and territory use in a wetland in the state of Rio Grande do Sul. Our findings revealed that this wetland serves as an important breeding site, where the total home range of the species was 28.2 ha, significantly reduced to 3.37 ha during the breeding season. The nest described here contained three eggs, two of which hatched successfully. After leaving the nest, the young birds foraged independently before joining mixed flocks with other species of birds. This study sheds light on the breeding ecology of the species and highlights the importance of wetlands for its conservation.
... Water availability shapes the distributions of social strategies by shaping the costs and benefits of grouping in a given environmental context (Purcell and Avilés 2008, Jetz and Rubenstein 2011, Lukas and Clutton-Brock 2017, La Richelière et al. 2022. Grouping can promote individual water conservation by generating a more favorable microclimate (Klok and Chown 1999, Danks 2002, Derhé et al. 2010, perhaps in part by increasing local humidity. ...
Climatic stressors are important drivers in the evolution of social behavior. Social animals tend to thrive in harsh and unpredictable environments, yet the precise benefits driving these patterns are often unclear. Here, we explore water conservation in forced associations of a solitary bee (Melissodes tepidus timberlakei Cockerell, 1926) to test the hypothesis that grouping can generate synergistic physiological benefits in an incipient social context. Paired bees displayed mutual tolerance and experienced reduced water loss relative to singleton bees when exposed to acute low-humidity stress, with no change in activity levels. While the mechanism underlying these benefits remains unknown, social advantages like these can facilitate the evolution of cooperation among nonrelatives and offer important insights into the social consequences of climate change.
... Loadlightening allows breeders to decrease investment in the current brood in favor of their future survival and reproduction (Hatchwell 1999, Cockburn et al. 2008, Russell et al. 2008. Understanding all the ways helpers may benefit a breeding pair can be difficult, and in many cases, helper benefits may be concealed or difficult to isolate because of confounding factors such as territory quality and breeder experience (Mumme 1992, Mumme et al. 2015, Downing et al. 2020, stage in the nesting cycle (Rensel et al. 2010), or annual and spatial variability in ecological conditions (Jetz andRubenstein 2011, Koenig et al. 2011). ...
... Birds currently offer the best available system for a global synthesis of sexual selection because we know more about their breeding behaviour than any other major taxonomic group (Jetz & Rubenstein 2011;Valcu et al. 2021;Gonzalez-Voyer et al. 2022). In particular, a growing number of studies report information on relatively cryptic forms of sexual selection, including molecular analyses of parentage revealing the degree of EPP (Brouwer & Gri th 2019;Valcu et al. 2021). ...
Sexual selection, one of the central pillars of evolutionary theory, has powerful effects on organismal morphology, behaviour and population dynamics. However, current knowledge about geographical variation in this evolutionary mechanism and its underlying drivers remains highly incomplete, in part because standardized data on the strength of sexual selection is sparse even for well-studied organisms. Here we use information on mating systems – including the incidence of polygamy and extra-pair paternity – to quantify the intensity of sexual selection in 10671 (> 99.9%) bird species distributed worldwide. We show that avian sexual selection varies latitudinally, peaking at higher latitudes, although the gradient is reversed in the world’s most sexually selected birds – specialist frugivores – which are strongly associated with tropical forests. Phylogenetic models further reveal that the strength of sexual selection is explained by temperature seasonality coupled with a suite of climate-associated factors, including migration, diet, and territoriality. Overall, these analyses suggest that climatic conditions leading to short, intense breeding seasons, or highly abundant and patchy food resources, increase the potential for polygamy in birds, driving latitudinal gradients in sexual selection. Our findings help to resolve longstanding debates about spatial variation in evolutionary mechanisms linked to reproductive biology, and provide a comprehensive species-level dataset for further studies of selection and phenotypic evolution in the context of global climatic change.
... We therefore join many other behavioural ecologists [35,[62][63][64][65][66][67][68] and evolutionary anthropologists [69,70] in defining cooperative breeding as the provision of systematic alloparental care regardless of the reproductive status of alloparents. The extent of within-group reproductive sharing can then be examined as one of the continuous characteristics of cooperative breeding species [12,34,38]. ...
Extreme reproductive skew occurs when a dominant female/male almost monopolizes reproduction within a group of multiple sexually mature females/males, respectively. It is sometimes considered an additional, restrictive criterion to define cooperative breeding. However, datasets that use this restrictive definition to classify species as cooperative breeders systematically overestimate reproductive skew by including groups in which reproduction cannot be shared by definition (e.g. groups with a single female/male). Here, we review the extent of reproductive sharing in 41 mammal and 37 bird species previously classified as exhibiting alloparental care and extreme reproductive skew, while only considering multi-female or multi-male groups. We demonstrate that in groups where unequal reproduction sharing is possible, extreme reproductive skew occurs in a few species only (11/41 mammal species and 12/37 bird species). These results call for significant changes in datasets that classify species' caring and mating system. To facilitate these changes, we provide an updated dataset on reproductive sharing in 63 cooperatively breeding species. At the conceptual level, our findings suggest that reproductive skew should not be a defining criterion of cooperative breeding and support the definition of cooperative breeding as a care system in which alloparents provide systematic care to other group members' offspring.
... Water availability shapes the distributions of social organisms by shaping the costs and benefits of grouping in a given environmental context [7][8][9][10][11]. Complex social organization can generate novel strategies for regulating nest humidity and collective water balance, particularly among the eusocial insects [12][13][14][15]. ...
... log BF = 17.75, which is greater than 10], indicating that cold conditions may have selected for increased group size in both clades of Asian colobines (SM section 4.3.2). This pattern of enhanced sociality in cold and dry environments has also been reported in Australian rodents (33) and cooperative breeding birds (34). In the case of Asian colobines, transitions from one social system to another appear to have occurred at ancient evolutionary nodes and have been retained over long periods of time. ...
The biological mechanisms that underpin primate social evolution remain poorly understood. Asian colobines display a range of social organizations, which makes them good models for investigating social evolution. By integrating ecological, geological, fossil, behavioral, and genomic analyses, we found that colobine primates that inhabit colder environments tend to live in larger, more complex groups. Specifically, glacial periods during the past 6 million years promoted the selection of genes involved in cold-related energy metabolism and neurohormonal regulation. More-efficient dopamine and oxytocin pathways developed in odd-nosed monkeys, which may have favored the prolongation of maternal care and lactation, increasing infant survival in cold environments. These adaptive changes appear to have strengthened interindividual affiliation, increased male-male tolerance, and facilitated the stepwise aggregation from independent one-male groups to large multilevel societies.
... Complex group structure may arise as a by-product of demographic processes that influence the long-term persistence of animal societies, particularly in the face of environmental challenges (25)(26)(27). Obligate cooperative breeders, for example, commonly exhibit high rates of group extinction due to inverse density dependence (i.e., Allee effect) at small group sizes (28). Below a threshold group size, there are too few individuals within a social group to successfully recruit offspring, and those group members are also less likely to survive (29,30), resulting in the group spiraling toward extinction (31)(32)(33). ...
Although kin selection is assumed to underlie the evolution of sociality, many vertebrates-including nearly half of all cooperatively breeding birds-form groups that also include unrelated individuals. Theory predicts that despite reducing kin structure, immigration of unrelated individuals into groups can provide direct, group augmentation benefits, particularly when offspring recruitment is insufficient for group persistence. Using population dynamic modeling and analysis of long-term data, we provide clear empirical evidence of group augmentation benefits favoring the evolution and maintenance of complex societies with low kin structure and multiple reproductives. We show that in the superb starling (Lamprotornis superbus)-a plural cooperative breeder that forms large groups with multiple breeding pairs, and related and unrelated nonbreeders of both sexes-offspring recruitment alone cannot prevent group extinction, especially in smaller groups. Further, smaller groups, which stand to benefit more from immigration, exhibit lower reproductive skew for immigrants, suggesting that reproductive opportunities as joining incentives lead to plural breeding. Yet, despite a greater likelihood of becoming a breeder in smaller groups, immigrants are more likely to join larger groups where they experience increased survivorship and greater reproductive success as breeders. Moreover, immigrants form additional breeding pairs, increasing future offspring recruitment into the group and guarding against complete reproductive failure in the face of environmental instability and high nest predation. Thus, plural breeding likely evolves because the benefits of group augmentation by immigrants generate a positive feedback loop that maintains societies with low and mixed kinship, large group sizes, and multiple reproductives.
... Short-term unpredictable weather conditions and scarce resources characterise desert environments (Morton et al. 2011;Botai et al. 2018) and desert species are adapted to survive their environment (Tieleman et al. 2003;Williams and Tieleman 2005;McKechnie et al. 2012;Wu et al. 2014;Cunningham et al. 2015). Desert birds show dramatic variations in annual reproductive output (Yosef and Zduniak 2008, Mares et al. 2017, Bourne et al. 2020, van de Ven et al. 2020, and some avian traits and mating systems are thought to be selected by these arid environments (du Plessis et al. 1995, Ward et al. 2002, Cockburn 2006, Rubenstein and Lovette 2007, Hatchwell 2009, Cockburn and Russell 2011, Jetz and Rubenstein 2011, van de Ven et al. 2016. High unpredictability and variation emphasise the need for long-term studies of these demographic and life history traits to get a holistic understanding of the variation that occurs between different years and seasons (Hughes et al. 2017). ...
Birds of prey are apex predators and understanding their life history can serve as a valuable baseline for investigating their ecological role. Pygmy Falcons ( Polihierax semitorquatus ), Africa’s smallest diurnal raptor, have evolved to be obligate associates of Sociable Weaver ( Philetairus socius ) colonies throughout their southern African range. As a predator, Pygmy Falcons likely impact prey communities in this system including their host and other colony associates. However, no study has explored their breeding biology in detail using long-term data. We provide results from 10 years of data collected between 2011 and 2020. We followed 66 unique Pygmy Falcon territories and 323 breeding attempts in the Kalahari, South Africa. We explored annual variation in the population density of Pygmy Falcons and investigated between- and within-season variation in reproductive investment and output. The highest average density was recorded in 2015 and the lowest in 2019 and 2020. Our results show that the breeding occurs between early austral spring (August) and late summer (February), with a peak from September to December. The maximum and most frequent clutch size was three eggs and falcons usually initiated only one breeding attempt (but up to three) in a season. The incubation and nestling periods lasted on average 33 (±SD 4) and 37 (± 5) days, respectively. A three-egg clutch size and number of fledglings produced varied between seasons, and breeding success showed a seasonal decline across the breeding season. Falcons were 7 times less likely to lay a 3-egg clutch in 2019 than in 2011 and 2012, and breeding attempts initiated in September were 3.4 times more likely to be successful than those initiated in November. Predation accounted for 49.5% of breeding failures. Our results show significant variation in the breeding parameters of these falcons, but further studies are needed to understand what drives these variations.
... Cooperative behaviour evolved and developed during the Pliocene and Pleistocene eras (approximately 5-10 million years ago) in specimens that branched from a common ancestor with chimpanzees (Meindl et al., 2018). These individuals experienced severe environmental selection pressure in an arid, unstable ecosystem, which contributed to the development and selection of cooperative traits for survival (Jetz and Rubenstein, 2011). Individuals with these abilities were selected via the evolutionary process. ...
Since the time of Darwin, theories have been proposed on the origin and functions of music; however, the subject remains enigmatic. The literature shows that music is closely related to important human behaviours and abilities, namely, cognition, emotion, reward and sociality (co-operation, entrainment, empathy and altruism). Notably, studies have deduced that these behaviours are closely related to testosterone (T) and oxytocin (OXT). The association of music with important human behaviours and neurochemicals is closely related to the understanding of reproductive and social behaviours being unclear. In this paper, we describe the endocrinological functions of human social and musical behaviour and demonstrate its relationship to T and OXT. We then hypothesised that the emergence of music is associated with behavioural adaptations and emerged as humans socialised to ensure survival. Moreover, the proximal factor in the emergence of music is behavioural control (social tolerance) through the regulation of T and OXT, and the ultimate factor is group survival through co-operation. The “survival value” of music has rarely been approached from the perspective of musical behavioural endocrinology. This paper provides a new perspective on the origin and functions of music.
... The question of why individuals live in groups and cooperate is central to all of biology, as it pertains to the origin of not only social groups but also multicellular organisms (Wilson 1975;Maynard Smith and Szathmáry 1995;Krause and Ruxton 2002;Rubenstein and Abbot 2017). A variety of abiotic and biotic factors have been postulated to favor group living, such as strong predator pressure (Hamilton 1971;Foster and Treherne 1981;Ioannou et al. 2011), unpredictable resources (Jetz and Rubenstein 2011), or prey too large or too difficult for single individuals to capture (Beauchamp 2013). Often, however, it is not a single factor but a combination of factors that favor group living in particular systems. ...
The emergence of animal societies offers unsolved problems for both evolutionary and ecological studies. Social spiders are especially well suited to address this problem given their multiple independent origins and distinct geographic distribution. On the basis of long-term research on the spider genus Anelosimus, we developed a spatial model that re-creates observed macroecological patterns in the distribution of social and subsocial spiders. We show that parallel gradients of increasing insect size and disturbance (rain, predation) with proximity to the lowland tropical rain forest would explain why social species are concentrated in the lowland wet tropics but absent from higher elevations and latitudes. The model further shows that disturbance, which disproportionately affects small colonies, not only creates conditions that require group living but also tempers the dynamics of large social groups. Similarly simple underlying processes, albeit with different players on a somewhat different stage, may explain the diversity of other social systems.
... Recent comparative studies by Jetz and Rubenstein (2011), and Rubenstein and Lovette(2007) argue that environmental uncertainty in climate is a powerful selective force on behavior as well as on physiology and morphology. First using starlings in Africa and then a collection of over 95% of the world's birds, they show that cooperative breeding tends to occur in habitats where climate is highly unpredictable even after accounting for phylogenies and common ancestry. ...
Conservation behavior assists the investigation of species endangerment associated with managing animals impacted by anthropogenic activities. It employs a theoretical framework that examines the mechanisms, development, function, and phylogeny of behavior variation in order to develop practical tools for preventing biodiversity loss and extinction. Developed from a symposium held at the International Congress on Conservation Biology in 2011, this is the first book to offer an in-depth, logical framework that identifies three vital areas for understanding conservation behavior: anthropogenic threats to wildlife, conservation and management protocols, and indicators of anthropogenic threats. Bridging the gap between behavioral ecology and conservation biology, this volume ascertains key links between the fields, explores the theoretical foundations of these linkages, and connects them to practical wildlife management tools and concise applicable advice. Adopting a clear and structured approach throughout, this book is a vital resource for graduate students, academic researchers, and wildlife managers.
... Territoriality and cooperative breeding data were from Tobias and Pigot (2019). Species were classified as either 'cooperative' or 'non-cooperative' according to the breeding systems described by Jetz and Rubenstein (2011). Territoriality was scored as either 'none' (never territorial or at most defending very small areas around nest sites), 'weak' (weak or seasonal territoriality, including species with broadly overlapping home ranges or habitually joining mixed species flocks), or 'strong' (territories maintained throughout year). ...
Conflicting theories have been proposed to explain variation in relative brain size across the animal kingdom. Ecological theories argue that the cognitive demands of seasonal or unpredictable environments have selected for increases in relative brain size, whereas the ‘social brain hypothesis’ argues that social complexity is the primary driver of brain size evolution. Here, we use a comparative approach to test the relative importance of ecology (diet, foraging niche and migration), sociality (social bond, cooperative breeding and territoriality) and developmental mode in shaping brain size across 1886 bird species. Across all birds, we find a highly significant effect of developmental mode and foraging niche on brain size, suggesting that developmental constraints and selection for complex motor skills whilst foraging generally imposes important selection on brain size in birds. We also find effects of social bonding and territoriality on brain size, but the direction of these effects do not support the social brain hypothesis. At the same time, we find extensive heterogeneity among major avian clades in the relative importance of different variables, implying that the significance of particular ecological and social factors for driving brain size evolution is often clade- and context-specific. Overall, our results reveal the important and complex ways in which ecological and social selection pressures and developmental constraints shape brain size evolution across birds.
The occurrence of interspecific feeding events, involving non‐obligate nest parasite species, is rare but has been documented in numerous avian species worldwide, particularly in Europe and North America. Our report presents an observation from southwest China, where we observed a Greater Necklaced Laughingthrush (Pterorhinus pectoralis) nest containing three laughingthrush nestlings and two nestlings of Chestnut‐winged Cuckoos (Clamator coromandus). They were being fed by the adult laughingthrush and a male White‐browed Shrike‐Babbler (Pteruthius aeralatus). However, after the cuckoo nestling fledged, we did not observe the Shrike‐Babbler feeding the laughingthrush nestlings remaining in the nest. Through a systematic examination of potential driving factors, we infer that the begging calls of the cuckoo nestlings likely played a crucial role in the misfeeding events observed in our study. However, it is essential to consider the potential influence of the male shrike‐babbler's status, including mateless, brood loss or female incubation. We highlight the further observations using digital recordings (for both images and sounds) to document detailed information on interspecific feeding events.
Understanding variation in social organization that lacks a strong phylogenetic signal represents a key focus of research in behavioural ecology. Accordingly, we established a framework that identifies whether a range of ecological and social factors are affecting the social maintenance of taxa across multiple categories of social variation (ranging from large to fine‐scale): 1) forms of sociality, 2) degree of sociality, 3) social plasticity and 4) hierarchy maintenance. Each category of variation can then be assessed in combination to provide an outlook for social maintenance in light of predictor factors. We modelled this framework by quantifying each category over time, space and disturbance regime using multiple species of coral‐dwelling gobies, genus Gobiodon . Gobies are an interesting model system as they vary in social structure, have within‐group cooperation, and form mutualisms with coral hosts, which are vulnerable to climatic disturbances. We found that gobies varied in forms of sociality – from being more solitary or pair‐forming in high disturbance regimes, versus group‐forming in moderate disturbance regimes at some locations. Only low or moderate degrees of sociality were observed in gobies, with location or disturbance regime affecting some species. The size of coral hosts influenced the social plasticity of gobies, which was affected by climatic disturbances. Gobies did not exhibit direct changes to hierarchy maintenance, as location and disturbance regime did not affect their size‐based hierarchies. Lastly, by combining the four categories of variation, we found a high loss of sociality in coral‐dwelling gobies due to environmental disturbances, which likely affects overall goby survival as group‐forming can improve survival and fitness. By using our structured framework, we identified which categories of social variation were influenced by ecological factors like location and disturbance. This framework therefore provides an excellent tool for predicting future responses of animal societies to environmental stressors.
The evolution of symbiotic interactions may be affected by unpredictable conditions. However, a link between prevalence of these conditions and symbiosis has not been widely demonstrated. We test for these associations using Dictyostelium discoideum social amoebae and their bacterial endosymbionts. D. discoideum commonly hosts endosymbiotic bacteria from three taxa: Paraburkholderia, Amoebophilus and Chlamydiae. Three species of facultative Paraburkholderia endosymbionts are the best studied and give hosts the ability to carry prey bacteria through the dispersal stage to new environments. Amoebophilus and Chlamydiae are obligate endosymbiont lineages with no measurable impact on host fitness. We tested whether the frequency of both single infections and coinfections of these symbionts were associated with the unpredictability of their soil environments by using symbiont presence-absence data from D. discoideum isolates from 21 locations across the eastern United States. We found that symbiosis across all infection types, symbiosis with Amoebophilus and Chlamydiae obligate endosymbionts, and symbiosis involving coinfections were not associated with any of our measures. However, unpredictable precipitation was associated with symbiosis in two species of Paraburkholderia , suggesting a link between unpredictable conditions and symbiosis.
Research on cooperative breeding (a system with the core characteristic of individuals providing care for the offspring of others) is important for understanding sociality and cooperation. However, large-scale comparative analyses on the drivers and consequences of cooperation frequently use considerably inaccurate datasets (e.g. due to inconsistent definitions and outdated information). To advance comparative research on cooperative breeding, we introduce the Cooperative-Breeding Database (Co-BreeD), a growing database of key socio-biological parameters of birds and mammals. First, we describe Co-BreeD's structure as a (i) sample-based (i.e. multiple samples per species linked to an exact sampling location and period), (ii) peer-reviewed and (iii) updatable resource. Respectively, these curating principles allow for (i) investigating intra- and inter-species variation and linking between fine-scale social and environmental parameters, (ii) accuracy and (iii) continuous correction and expansion with the publication of new data. Second, we present the first Co-BreeD dataset, which estimates the prevalence of breeding events with potential alloparents in 265 samples from 233 populations of 150 species, including 2 human societies (N = 26,366 breeding events). We conclude by demonstrating (i) how Co-BreeD facilitates more accurate comparative research (e.g. increased explanatory power by enabling the study of cooperative breeding as a continuous trait, and statistically accounting for the sampling error probabilities), and (ii) that cooperative breeding in birds and mammals is more prevalent than currently estimated.
Cooperative breeding occurs when individuals contribute parental care to offspring that are not their own. Numerous intra- and inter-specific studies have aimed to explain the evolution of this behaviour. Recent comparative work suggests that family living (i.e., when offspring remain with their parents beyond independence) is a critical steppingstone in the evolution of cooperative breeding. Thus, it is key to understand the factors that facilitate the evolution of family living. Within-species studies suggest that protection from predators is a critical function of group living, through both passive benefits such as dilution effects, and active benefits such as prosocial antipredator behaviours in family groups. However, the association between predation risk and the formation and prevalence of family groups and cooperative breeding remains untested globally. Here we use phylogenetic comparative analyses including 2984 bird species to show that family living and cooperative breeding are associated with increased occurrence of avian predators. These cross-species findings lend support to previous suggestions based on intraspecific studies that social benefits of family living, such as protection against predation, could favour the evolution of delayed dispersal and cooperative breeding.
The cooperative breeding system of birds is an ideal model for studying and exploring social evolution in animals. However, a basic question, i.e., how many cooperative-breeding bird species exist in the world, remains controversial due to the lack of accumulated knowledge of the natural history of many birds, which prevents a generalized understanding of the evolution of cooperative breeding in birds and challenges the accuracy of results in many comparative studies. In this paper, we provide the first evidence of cooperative breeding in red-billed blue magpies ( Urocissa erythrorhyncha ). Moreover, we document and discuss potential relationships between cooperative breeding and nest predation, brood parasitism and breeding performance in U. erythrorhyncha . These findings about cooperative breeding in red-billed blue magpie will lay a foundation for further research on this species’ sociality and provide useful insights into the evolution of cooperative breeding and other social systems in birds.
This review examines the impact of global warming in different Drosophilid species and other ectotherms. Global warming has been a hot topic since the rapid rise in average surface temperature of the earth over the last 3-4 decades. This rise in temperature/global warming is likely to have a major impact on all organisms living in earth's surface area. Ecothermic organisms like Drosophilids are likely to get more affect by this phenomenon. The effect of temperature on Drosophilids will be both genotypic and phenotypic. Phenotypic effects of temperature will lead to changes like melanisation pattern, shift in boundaries of species and change in phenology. Genotypic effects of temperature are also reported in recent studies which lead to chromosomal inversion polymorphisms in Drosophilids. Hence, many species which responds to change in temperature can be used as a good indicator to understand the impact of global warming and its effect on ectotherms surviving in various anthropogenic stressful environmental conditions. Such studies will also help us to establish better ecosystem conservation policies and might also change our research priorities in future.
In cooperative breeding systems, inclusive fitness theory predicts that nonbreeding helpers more closely related to the breeders should be more willing to provide costly alloparental care and thus have more impact on breeder fitness. In the red-cockaded woodpecker (Dryobates borealis), most helpers are the breeders' earlier offspring, but helpers do vary within groups in both relatedness to the breeders (some even being unrelated) and sex, and it can be difficult to parse their separate impacts on breeder fitness. Moreover, most support for inclusive fitness theory has been positive associations between relatedness and behavior rather than actual fitness consequences. We used functional linear models to evaluate the per capita effects of helpers of different relatedness on eight breeder fitness components measured for up to 41 years at three sites. In support of inclusive fitness theory, helpers more related to the breeding pair made greater contributions to six fitness components. However, male helpers made equal contributions to increasing prefledging survival regardless of relatedness. These findings suggest that both inclusive fitness benefits and other direct benefits may underlie helping behaviors in the red-cockaded woodpecker. Our results also demonstrate the application of an underused statistical approach to disentangle a complex ecological phenomenon.
After eggs hatch, the extent to which adult birds care for young exhibits considerable variation, ranging from no care to extensive care lasting weeks or even months. Factors contributing to this variation are discussed in this chapter. For species where young are fed by adults, the begging behavior of young and responses to that begging by adults is explained. Factors that influence the extent to which adults defend nests and young from potential predators are also discussed. For species where young are cared for in nests, departure from those nests by young birds is a critical step in their development. How nestling age and condition and adult behavior can influence nest departure, or fledging, is discussed. Most young disperse from their natal territories and I also explain the factors that influence the timing of that decision and how far fledglings disperse. Examples of the importance of learning by young birds are provided and, finally, this chapter closes with an extensive discussion of avian brood parasitism, including facultative versus obligatory brood parasitism and, for obligatory brood parasitism, the pre- and post-laying adaptions and post-hatching adaptions of both hosts and brood parasites.
The ways by which male and female birds locate and choose each other for mating, the number of mates during a breeding season and during a bird’s life, the duration of interactions between males and females, and the respective roles of males and females in providing care (or not) for eggs and young after fertilization vary among species and, to a lesser extent, within species. The different ways that birds of different species interact to produce young are referred to as mating systems. In this chapter, I discuss the various mating systems of birds, including monogamy, polygyny, polyandry, polygynandry, and promiscuity, and explain the factors that have likely contributed to their evolution. Also in this chapter is a discussion of sexual conflict and cooperation, and factors that contribute to variation among and within species in extra-pair mating. Some species of birds breed cooperatively and the social and environmental variables that contribute to such behavior are discussed. The choice of a mate is critical for birds attempting to maximize their reproductive fitness, and both female and male mate choice and the role of sexual selection in mate choice are discussed in detail.
Sexual selection, one of the central pillars of evolutionary theory, has powerful effects on organismal morphology, behaviour and population dynamics. However, current knowledge about geographical variation in this evolutionary mechanism and its underlying drivers remains highly incomplete, in part because standardized data on the strength of sexual selection is sparse even for well-studied organisms. Here we use information on mating systems - including the incidence of polygamy and extra-pair paternity - to quantify the intensity of sexual selection in 10671 (>99.9%) bird species distributed worldwide. We show that avian sexual selection varies latitudinally, peaking at higher latitudes, although the gradient is reversed in the world's most sexually selected birds - specialist frugivores - which are strongly associated with tropical forests. Phylogenetic models further reveal that the strength of sexual selection is explained by temperature seasonality coupled with a suite of climate-associated factors, including migration, diet, and territoriality. Overall, these analyses suggest that climatic conditions leading to short, intense breeding seasons, or highly abundant and patchy food resources, increase the potential for polygamy in birds, driving latitudinal gradients in sexual selection. Our findings help to resolve longstanding debates about spatial variation in evolutionary mechanisms linked to reproductive biology, and provide a comprehensive species-level dataset for further studies of selection and phenotypic evolution in the context of global climatic change.
Animal societies are rife with conflict over resources and reproduction, raising the question of how such societies nonetheless persist. A long-term study on birds shows that larger groups are less likely to go extinct, making individuals offer reproductive concessions to unrelated competitors joining the group.
Despite the prominence of kin selection as a framework for understanding the evolution of sociality, many animal groups are comprised of unrelated individuals. These non-kin systems provide valuable models that can illuminate drivers of social evolution beyond indirect fitness benefits. Within the Hymenoptera, whose highly related eusocial groups have long been cornerstones of kin selection theory, groups may form even when indirect fitness benefits for helpers are low or absent. These non-kin groups are widespread and abundant, yet have received relatively little attention. We review the diversity and organization of non-kin sociality across the Hymenoptera, particularly among the communal bees and polygynous ants and wasps. Further, we discuss common drivers of sociality across these groups, with a particular focus on ecological factors. Ecological contexts that favor non-kin sociality include those dominated by resource scarcity or competition, climatic stressors, predation and parasitism, and/or physiological constraints associated with reproduction and resource exploitation. Finally, we situate Hymenopteran non-kin sociality within a broader biological context by extending insights from these systems across diverse taxa, especially the social vertebrates. Non-kin social groups thus provide unique demonstrations of the importance of ecological factors in mediating the evolutionary transition from solitary to group living.
The evolutionary repercussions of parental effects are often discussed as static effects that can have negative influences on offspring fitness that may even persist across generations. However, individuals are not passive recipients and may mitigate the persistence of parental effects through their behaviour. Here, we tested how the burying beetle Nicrophorus orbicollis , a species with complex parental care, responded to poor parenting. We manipulated the duration of parental care received and measured the impact on traits of both F1 and F2 offspring. As expected, reducing parental care negatively affected traits that are ecologically important for burying beetles, including F1 offspring development time and body size. However, F1 parents that received reduced care as larvae spent more time feeding F2 offspring than parents that received full care as larvae. As a result, both the number and mass of F2 offspring were unaffected by the developmental experience of their parents. Our results show that flexible parental care may be able to overcome poor developmental environments and limit negative parental effects to a single generation.
While direct influences of the environment on population growth and resilience are well studied, indirect routes linking environmental changes to population consequences are less explored. We suggest that social behavior is key for understanding how anthropogenic environmental changes affect the resilience of animal populations. Social structures of animal groups are evolved and emergent phenotypes that often have demographic consequences for group members. Importantly, environmental drivers may directly influence the consequences of social structure or indirectly influence them through modifications to social interactions, group composition, or group size. We have developed a framework to study these demographic consequences. Estimating the strength of direct and indirect pathways will give us tools to understand, and potentially manage, the effect of human-induced rapid environmental changes.
Cooperative breeders are species in which individuals beyond a pair assist in the production of young in a single brood or litter. Although relatively rare, cooperative breeding is widespread taxonomically and continues to pose challenges to our understanding of the evolution of cooperation and altruistic behavior. Bringing together long-term studies of cooperatively breeding birds, mammals, and fishes, this volume provides a synthesis of current studies in the field. The chapters are organised by individual studies of particular species or (in the case of mole-rats) two closely related cooperatively breeding species. Each focuses not only on describing behavior and ecology but also on testing evolutionary hypotheses for the form and function of the diverse and extraordinary cooperative breeding lifestyles that have been discovered. This unique and comprehensive text will be of interest to graduate students and researchers of behavioral ecology and the evolution of cooperation.
In approximately 3.2% of bird species individuals regularly forgo the opportunity to breed independently and instead bree cooperatively with other conspecifics, either as non–reproductive ‘helpers’ or as co–breeders. The traditional explanatio for cooperative breeding is that the opportunities for breeding independently are limited owing to peculiar features of th specie's breeding ecology. However, it has proved remarkably difficult to find any common ecological correlates of cooperativ breeding in birds. This difficulty has led to the ‘life history hypothesis’, which suggests that the common feature of cooperativel breeding birds is their great longevity, rather than any particular feature of their breeding ecology. Here, we use a comparativ method to test the life history hypothesis by looking for correlations between life history variation and variation in th frequency of cooperative breeding. First, we find that cooperative breeding in birds is not randomly distributed, but concentrate in certain families, thus supporting the idea that there may be a common basis to cooperative breeding in birds. Second, increase in the level of cooperative breeding are strongly associated with decreases in annual adult mortality and modal clutch size.
Third, the proportion of cooperatively breeding species per family is correlated with a low family–typical value of annua mortality, suggesting that low mortality predisposes cooperative breeding rather than vice versa. Finally, the low rate o mortality typically found in cooperatively breeding species is associated with increasing sedentariness, lower latitudes and decreased environmental fluctuation. We suggest that low annual mortality is the key factor that predisposes avian lineage to cooperative breeding, then ecological changes, such as becoming sedentary, further slow population turnover and reduc opportunities for independent breeding. As the traditional explanation suggests, the breeding habitat of cooperatively breedin species is saturated, but this saturation is not owing to any peculiar feature of the breeding ecology of cooperative breeders.
Rather, the saturation arises because the local population turnover in these species is unusually slow, as predicted by th life history hypothesis.
Cooperative breeding is an unusual kind of social behaviour, found in a few hundred species worldwide, in which individuals other than the parents help raise young. Understanding the apparently altruistic behaviour of helpers has provided numerous challenges to evolutionary biologists. This book includes detailed first-hand summaries of many of the major empirical studies of cooperatively breeding birds. It provides comparative information on the demography, social behaviour and behavioural ecology of these unusual species and explores the diversity of ideas and the controversies which have developed in this field. The studies are all long-term and consequently the book summarises some of the most extensive studies of the behaviour of marked individuals ever undertaken. Graduate students and research workers in ornithology, sociobiology, behavioural ecology and evolutionary biology will find much of value in this book.
Selection is a central process in nature. Although our understanding of the strength and form of selection has increased, a general understanding of the temporal dynamics of selection in nature is lacking. Here, we assembled a database of temporal replicates of selection from studies of wild populations to synthesize what we do (and do not) know about the temporal dynamics of selection. Our database contains 5519 estimates of selection from 89 studies, including estimates of both direct and indirect selection as well as linear and nonlinear selection. Morphological traits and studies focused on vertebrates were well-represented, with other traits and taxonomic groups less well-represented. Overall, three major features characterize the temporal dynamics of selection. First, the strength of selection often varies considerably from year to year, although random sampling error of selection coefficients may impose bias in estimates of the magnitude of such variation. Second, changes in the direction of selection are frequent. Third, changes in the form of selection are likely common, but harder to quantify. Although few studies have identified causal mechanisms underlying temporal variation in the strength, direction and form of selection, variation in environmental conditions driven by climatic fluctuations appear to be common and important.
Australia has many cooperatively breeding species of birds. These tend to occur in eucalypt and semi-arid woodlands rather than in rainforests or deserts. They tend to be insectivores that pursue rather than sit and wait for their prey, and tend to forage on the ground rather than above it. We propose that environments where resources do not show marked seasonal fluctuations are those in which cooperative breeding is most likely to evolve. Under these conditions birds might experience difficulty acquiring the extra food necessary to breed, especially if inexperienced. When adult survival was high, young and inexperienced birds could delay breeding. Unpredictable environments may also favor cooperative breeding, but our data do not strongly support this. Groupliving would be favored further if young birds are particularly vulnerable to predators when alone. They should therefore remain in the family group and delay their dispersal unitl a suitable breeding vacancy becomes available. These hypotheses are not mutually exclusive, but are complementary. Both may be required to ensure that at least some year-old birds do not breed and also do not disperse. We believe that they give rise to predictions, which can be tested in future field studies.
Some studies on the effects of helpers in cooperatively breeding vertebrates show a positive effect of helper presence on
reproductive output whereas others find no effect. One possibility for this discrepancy is that helpers may have a positive
effect when breeding conditions are adverse, while their effect might go unnoticed under good conditions. We investigate this
hypothesis on sociable weavers Philetairus socius, a colonial cooperatively breeding passerine that inhabits a semi-arid region where breeding conditions vary markedly. We
used multivariate mixed models to analyse the effect of helpers on reproduction under contrasting environmental and social
conditions while controlling for parental and colony identity. We found that reproductive success in sociable weavers was
primarily influenced by nest predation and rainfall. In addition, colony size was negatively associated with hatching and
fledging success and number of young fledged per season. Helpers had a less prominent but significant influence on feeding
rates and reproductive outcome. In agreement with expectations, the presence of helpers counteracted some of the negative
effects of breeding in periods of low rainfall or in large colonies and was also associated with an increased number of young
fledged per season. Our results illustrate that the effect of helpers might be detectable mostly under unfavourable conditions,
but can contribute to improve reproductive performance in those situations.
Comparative analyses were carried out for some life-history traits of cooperatively and non-cooperatively breeding Australian Corvida (i.e. old-endemic passerines). Multivariate statistical analyses at the family and genus levels revealed no significant differences between cooperative and non-cooperative breeders. A matched-pairs analysis between congeneric species showed that cooperatively breeding species lay smaller clutches than non-cooperatively breeding congenerics. Preliminary results also suggest that cooperative breeders have higher probabilities of rearing a second brood in the season and lower probabilities of survival than do non-cooperative breeders. However, the result for survival was significant in only one out of three tests. We conclude that cooperatively and non-cooperatively breeding Australian Corvida cannot be separated into distinct groups showingK- andr-selected life-history traits, respectively. Some life-history traits follow the prediction of ther-K selection model, others show evidence of co-adaptation instead, whereas still others show evidence of trade-offs.
Theory predicts that cooperative breeding should only occur in species in which certain individuals are constrained from breeding independently by some peculiarity of the species' ecology. Here, we use comparative methods to examine the role of variation in ecology in explaining differences between taxa in the frequency of cooperative breeding. We address three questions. First, does the frequency of cooperative breeding vary at just one phylogenetic level, or across several levels? Second, are differences in the frequency of cooperative breeding among closely-related species correlated with ecology! Last, are ecological differences between ancient lineages important in predisposing certain lineages to cooperative breeding? We find that variation in the frequency of cooperative breeding occurs across all phylogenetic levels, with 40% among families and 60% within families. Also, variation in the frequency of cooperative breeding between closely related species is associated with ecological differences. However, differences in the frequency of cooperative breeding among more ancient lineages are not correlated with differences in ecology. Together, our results suggest that cooperative breeding is not due to any single factor, but is a two step-process: life-history predisposition and ecological facilitation. Low annual mortality predisposes certain lineages to cooperative breeding. Subsequently, changes in ecology facilitate the evolution of cooperative breeding within these predisposed lineages. The key ecological changes appear to be sedentariness and living in a relatively invariable and warm climate. Thus, although ecological variation is not the most important factor in predisposing lineages to cooperative breeding, it is important in determining exactly which species or populations in a predisposed lineage will adopt cooperative breeding. Key words: birds, comparative methods, cooperative breeding, ecological constraints, mating system.
Darwin insisted that evolutionary change occurs very slowly over long periods of time, and this gradualist view was accepted by his supporters and incorporated into the infinitesimal model of quantitative genetics developed by R. A. Fisher and others. It dominated the first century of evolutionary biology, but has been challenged in more recent years both by field surveys demonstrating strong selection in natural populations and by quantitative trait loci and genomic studies, indicating that adaptation is often attributable to mutations in a few genes. The prevalence of strong selection seems inconsistent, however, with the high heritability often observed in natural populations, and with the claim that the amount of morphological change in contemporary and fossil lineages is independent of elapsed time. I argue that these discrepancies are resolved by realistic accounts of environmental and evolutionary changes. First, the physical and biotic environment varies on all time-scales, leading to an indefinite increase in environmental variance over time. Secondly, the intensity and direction of natural selection are also likely to fluctuate over time, leading to an indefinite increase in phenotypic variance in any given evolving lineage. Finally, detailed long-term studies of selection in natural populations demonstrate that selection often changes in direction. I conclude that the traditional gradualist scheme of weak selection acting on polygenic variation should be supplemented by the view that adaptation is often based on oligogenic variation exposed to commonplace, strong, fluctuating natural selection.
The evolution of cooperation among animals has posed a major problem for evolutionary biologists, and despite decades of research into avian cooperative breeding systems, many questions about the evolution of their societies remain unresolved. A review of the kin structure of avian societies shows that a large majority live in kin-based groups. This is consistent with the proposed evolutionary routes to cooperative breeding via delayed dispersal leading to family formation, or limited dispersal leading to kin neighbourhoods. Hypotheses proposed to explain the evolution of cooperative breeding systems have focused on the role of population viscosity, induced by ecological/demographic constraints or benefits of philopatry, in generating this kin structure. However, comparative analyses have failed to generate robust predictions about the nature of those constraints, nor differentiated between the viscosity of social and non-social populations, except at a coarse level. I consider deficiencies in our understanding of how avian dispersal strategies differ between social and non-social species, and suggest that research has focused too narrowly on population viscosity and that a broader perspective that encompasses life history and demographic processes may provide fresh insights into the evolution of avian societies.
Climatic variability and unpredictability affect the distribution and abundance of resources and the timing and duration of breeding opportunities. In vertebrates, climatic variability selects for enhanced cognition when organisms compensate for environmental changes through learning and innovation. This hypothesis is supported by larger brain sizes, higher foraging innovation rates, higher reproductive flexibility, and higher sociality in species living in more variable climates. Male songbirds sing to attract females and repel rivals. Given the reliance of these displays on learning and innovation, we hypothesized that they could also be affected by climatic patterns. Here we show that in the mockingbird family (Aves: Mimidae), species subject to more variable and unpredictable climates have more elaborate song displays. We discuss two potential mechanisms for this result, both of which acknowledge that the complexity of song displays is largely driven by sexual selection. First, stronger selection in more variable and unpredictable climates could lead to the elaboration of signals of quality. Alternatively, selection for enhanced learning and innovation in more variable and unpredictable climates might lead to the evolution of signals of intelligence in the context of mate attraction.
Author Summary
Why do some bird species lay only one egg in their nest, and others ten? The clutch size of birds is one of the best-studied life-history traits of animals. Nevertheless, research has so far focused either on a comparative approach, relating clutch size to other biological traits of the species, such as body weight; or on a macroecological approach, testing how environmental factors, such as seasonality, influence clutch size. We used the most comprehensive dataset on clutch size ever compiled, including 5,290 species, and combined it with data on the biology and the environment of these species. This approach enabled us to merge comparative and macroecological methods and to test biological and environmental factors together in one analysis. With this approach, we are able to explain a major proportion of the global variation in clutch size and also to predict with high confidence the average clutch size of a bird assemblage on earth. For example, cavity nesters, such as woodpeckers, have larger clutches than open-nesting species; and species in seasonal environments, especially at northern latitudes, have larger clutches than tropical birds. The findings offer a bridge between macroecology and comparative biology, and provide a global and integrative understanding of a core life-history trait.
The question is often raised whether it is statistically necessary to control for phylogenetic associations in comparative studies. To investigate this question, we explore the use of a measure of phylogenetic correlation, lambda, introduced by Pagel (1999), that normally varies between 0 (phylogenetic independence) and 1 (species' traits covary in direct proportion to their shared evolutionary history). Simulations show lambda to be a statistically powerful index for measuring whether data exhibit phylogenetic dependence or not and whether it has low rates of Type I error. Moreover, lambda is robust to incomplete phylogenetic information, which demonstrates that even partial information on phylogeny will improve the accuracy of phylogenetic analyses. To assess whether traits generally show phylogenetic associations, we present a quantitative review of 26 published phylogenetic comparative data sets. The data sets include 103 traits and were chosen from the ecological literature in which debate about the need for phylogenetic correction has been most acute. Eighty-eight percent of data sets contained at least one character that displayed significant phylogenetic dependence, and 60% of characters overall (pooled across studies) showed significant evidence of phylogenetic association. In 16% of tests, phylogenetic correlation could be neither supported nor rejected. However, most of these equivocal results were found in small phylogenies and probably reflect a lack of power. We suggest that the parameter lambda be routinely estimated when analyzing comparative data, since it can also be used simultaneously to adjust the phylogenetic correction in a manner that is optimal for the data set, and we present an example of how this may be done.
Open Access provided by the University of Chicago Press.
Cooperative breeding in birds is much more prevalent than has been previously realized, occurring in 18.5% of oscine passerines known to have biparental care, and is the predominant social system of some ancient oscine clades. Cooperation is distributed unevenly in clades that contain both cooperative and pair breeders, and is usually confined to a few related genera in which it can be ubiquitous. Cooperative clades are species poor compared with pair-breeding clades, because pair breeders evolve migratory habits, speciate on oceanic islands and are more likely to have distributions spread across more than one biogeographic region. These differences reflect the increased capacity for colonization by pair breeders because their young disperse. Thus cooperative breeding has macroevolutionary consequences by restricting rates of speciation and macroecological implications by influencing the assembly of island and migrant faunas.
The order Passeriformes ("perching birds") comprises extant species diversity comparable to that of living mammals. For over a decade, a single phylogenetic hypothesis based on DNA-DNA hybridization has provided the primary framework for numerous comparative analyses of passerine ecological and behavioral evolution and for tests of the causal factors accounting for rapid radiations within the group. We report here a strongly supported phylogenetic tree based on two single-copy nuclear gene sequences for the most complete sampling of passerine families to date. This tree is incongruent with that derived from DNA-DNA hybridization, with half of the nodes from the latter in conflict and over a third of the conflicts significant as assessed under maximum likelihood. Our historical framework suggests multiple waves of passerine dispersal from Australasia into Eurasia, Africa, and the New World, commencing as early as the Eocene, essentially reversing the classical scenario of oscine biogeography. The revised history implied by these data will require reassessment of comparative analyses of passerine diversification and adaptation.
Cooperative breeding is comparatively rare among birds in the mainly temperate and boreal Northern Hemisphere. Here we test if the distribution of breeding systems reflects a response to latitude by means of a phylogenetic analysis using correlates with geographical range among the corvids (crows, jays, magpies and allied groups). The corvids trace their ancestry to the predominantly cooperative 'Corvida' branch of oscine passerines from the Australo-Papuan region on the ancient Gondwanaland supercontinent, but we could not confirm the ancestral state of the breeding system within the family, while family cohesion may be ancestral. Initial diversification among pair-breeding taxa that are basal in the corvid phylogeny, represented by genera such as Pyrrhocorax and Dendrocitta, indicates that the corvid family in its current form could have evolved from pair-breeding ancestors only after they had escaped the Australo-Papuan shield. Within the family, cooperative breeding (alloparental care/family cohesion) is strongly correlated to latitude and its predominance in species maintaining a southerly distribution indicates a secondary evolution of cooperative breeding in the lineage leading away from the basal corvids. Multiple transitions show plasticity in the breeding system, indicating a response to latitude rather than evolutionary inertia. The evolutionary background to the loss of cooperative breeding among species with a northerly distribution is complex and differs between species, indicating a response to a variety of selection forces. Family cohesion where the offspring provide alloparental care is a main route to cooperatively breeding groups among corvids. Some corvid species lost only alloparental care, while maintaining coherent family groups. Other species lost family cohesion and, as a corollary, they also lost the behaviour where retained offspring provide alloparental care.
Estimates of the incidence of major classes of parental care by birds are drawn from classical studies that preceded both the publication of a massive secondary literature and the revolution driven by molecular approaches to avian phylogeny. Here, I review this literature in the light of new phylogenetic hypotheses and estimate the prevalence of six distinct modes of care: use of geothermal heat to incubate eggs, brood parasitism, male only care, female only care, biparental care and cooperative breeding. Female only care and cooperative breeding are more common than has previously been recognized, occurring in 8 and 9% of species, respectively. Biparental care by a pair-bonded male and female is the most common pattern of care but at 81% of species, the pattern is less common than once believed. I identify several problems with existing hypotheses for the evolution of parental care and highlight a number of poorly understood contrasts which, once resolved, should help elucidate avian social evolution.
In cooperatively breeding species, reproductive decisions and breeding roles may be influenced by environmental (food resources) or social factors (reproductive suppression of subordinates by dominants). Studies of glucocorticoid stress hormones in cooperatively breeding species suggest that breeding roles and hormone levels are related to the relative costs of dominance and subordination, which are driven primarily by social interactions. Few studies, however, have considered how environmental factors affect glucocorticoid levels and breeding roles in cooperative breeders, even though environmental stressors modulate seasonal glucocorticoid release and often influence breeding roles. I examined baseline and stress-induced levels of the glucocorticoid corticosterone (CORT) across 4 years in the plural breeding superb starling, Lamprotornis superbus, to determine whether (i) environmental factors (namely rainfall) directly influence breeding roles or (ii) environmental factors influence social interactions, which in turn drive breeding roles. Chronic baseline and maximal stress-induced CORT changed significantly across years as a function of pre-breeding rainfall, but dominant and subordinate individuals responded differently. Pre-breeding rainfall was also correlated directly with breeding roles. The results are most consistent with the hypothesis that environmental conditions influenced the relative costs of dominance and subordination, which in turn affected the degree and intensity of social interactions and ultimately reproductive decisions and breeding roles.
The reason why some bird species live in family groups is an important question of evolutionary biology that remains unanswered. Families arise when young delay the onset of independent reproduction and remain with their parents beyond independence. Explanations for why individuals forgo independent reproduction have hitherto focused on dispersal constraints, such as the absence of high-quality breeding openings. However, while constraints successfully explain within-population dispersal decisions, they fail as an ultimate explanation for variation in family formation across species. Most family-living species are long-lived and recent life-history studies demonstrated that a delayed onset of reproduction can be adaptive in long-lived species. Hence, delayed dispersal and reproduction might be an adaptive life-history decision rather than 'the best of a bad job'. Here, we attempt to provide a predictive framework for the evolution of families by integrating life-history theory into family formation theory. We suggest that longevity favours a delayed onset of reproduction and gives parents the opportunity of a prolonged investment in offspring, an option which is not available for short-lived species. Yet, parents should only prolong their investment in offspring if this increases offspring survival and outweighs the fitness cost that parents incur, which is only possible under ecological conditions, such as a predictable access to resources. We therefore propose that both life-history and ecological factors play a role in determining the evolution of family living across species, yet we suggest different mechanisms than those proposed by previous models.
Cooperative breeding is an unusual kind of social behaviour, found in a few hundred species worldwide, in which individuals other than the parents help raise young. Understanding the apparently altruistic behaviour of helpers has provided numerous challenges to evolutionary biologists. This book includes detailed first-hand summaries of many of the major empirical studies of cooperatively breeding birds. It provides comparative information on the demography, social behaviour and behavioural ecology of these unusual species and explores the diversity of ideas and the controversies which have developed in this field. The studies are all long-term and consequently the book summarises some of the most extensive studies of the behaviour of marked individuals ever undertaken. Graduate students and research workers in ornithology, sociobiology, behavioural ecology and evolutionary biology will find much of value in this book.
A terminology is introduced that can be used for describing as well as theorizing and is thus useful for hierarchically classifying observations. All known communally breeding species in Australia are tabulated: sixty-five in twenty families. Evidence is presented for species being described as communal breeders for the first time and for species in which additional data have become available since the last major review (Rowley 1976). Published maps of the ranges of thirty-ope species were coded digitally by degree-block for analysis by computer as were maps of vegetation, faunal zones and eleven environmental variables. The distribution of these species is tabulated by the vegetational and faunal zones that they occupy and a detailed statistical tabulation is included of all the environmental variables for each species separately. A composite map shows the density of species throughout Australia. The greatest number (24) of communally breeding species was found in northern New South Wales. The pattern of distribution did not merely reflect that of land birds in general and numbers of species were not strongly associated with particular faunal zones or vegetational types. A regression model was constructed that accounted for seventy-eight per cent of the variation in numbers of species by simple geographical variables, longitude being the most important. Two analytical strategies were used. The first suggested that the most important environmental variables were moisture in the driest sixteen-week period, temperature in the coldest week, and moisture in winter; the second, plant growth in summer, temperature in the coldest week, variation in rainfall and seasonal variation in plant growth. The possible relations between these variables and communally breeding species are discussed and it is concluded that the enviromental data neither strongly favour nor exclude three hypotheses regarding the origin or adaptive maintenance of communal breeding generally. The analysis does not support the view that because taxonomic diversity of communally breeding species is high, there must be common factors in their ecology. Species are considered to be opportunistic communal breeders or obligate communal breeders and a simple model incorporating physiological condition, social attraction and group facilitation illustrates the concept of 'levels' of communal breeding that have been observed in nature. The distinction between opportunistic and obligate species is considered important because these may represent different evolutionary strategies for behaviour hitherto lumped as communal breeding.
The ecological factors underlying the evolution of helping behavior in birds and mammals are examined. I argue that a necessary first step for the evolution of cooperative breeding is a substructuring of the population into small, stable, social units; in most known cases these are extended-family units. The ecological conditions leading to the development of such units are explored, and a general model is presented that emphasizes ecological constraints that limit the possibility of personal, independent breeding. When severe constraints occur, selection will favor delayed dispersal and continued retention of grown offspring within their natal units. Differing proximate factors can be responsible for limiting the option of personal reproduction. In stable, predictable environments where marginal habitat is scarce, high population density and resulting habitat saturation can lead to a severe shortage of territory openings (Brown 1974; Koenig and Pitelka 1981). This decreases the chance for independent est...
An overview of the extensive and frequently controversial literature on communally breeding birds developed since the early 1960s, when students of evolution began to examine sociality as a product of natural selection. Jerram Brown provides original data from his own theoretical and empirical studies and summarizes the wide array of results and interpretations made by others.Originally published in 1987.The Princeton Legacy Library uses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These paperback editions preserve the original texts of these important books while presenting them in durable paperback editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.
Grimes, L. G. 1976. The occurrence of cooperative breeding behaviour in African birds. Osrich 47: 1–15The paper summarises present knowledge of the occurrence of cooperative breeding behaviour in African birds (52 species representing 30 families or subfamilies), and lists the species in which it may also occur. An analysis of the ecology of these species suggests that the behaviour occurs more frequently in those inhabiting dry and moist woodlands. However, the data is weighted in favour of non-fcrest birds and the socio-ecology of the behaviour is, therefore, not clear.
COOPERATIVE breeding, which often involves young remaining on their natal territory and helping their parents to raise subsequent broods1–3 is mostly explained by habitat saturation: young are constrained from becoming independent breeders by a shortage of breeding territories2,4. Here I present two lines of evidence against this hypothesis for the cooperatively breeding Seychelles warbler Acrocephalus sechellensis. first, territory quality has a significant effect on dispersal: vacancies arising on territories are mostly filled by prebreeding birds from territories of the same or lower quality. Second, individuals that delay reproduction in high-quality territories, but which eventually breed there, have greater lifetime fitness than those that disperse at one year of age and breed immediately in lower-quality territories. These results support the 'benefits of philopatry,5,6 hypothesis, which emphasizes the lifetime inclusive fitness benefits from staying at home. The transfers of warblers to unoccupied islands was the strictest experimental test of this hypothesis. At first there was no cooperative breeding, but as all high-quality areas became occupied, young birds born on high-quality territories began to stay as helpers, rather than occupying breeding vacancies on low-quality territories. Therefore habitat saturation and territory quality are both involved in the evolution of cooperative breeding.
Our analyses of the incidence of cooperative breeding among South African birds differ from previous studies performed elsewhere in two respects. First, we distinguish between obligate (i.e. regular) and facultative (i.e. opportunistic) cooperative breeding species (OCS and FCS). Second, we have restricted our analyses to 217 South African bird species considered to be sufficiently well-studied in terms of their basic biology and life-history characteristics. This was done in order to control for the well-known bias against the often poorly-studied avifaunas of extreme environments such as rainforests and deserts. The results of our analysis do not accord fully with those of Australian birds by Ford et al. (1988). Cooperative breeding in South Africa is associated with seasonal environments, whereas in Australia the opposite is the case. Analyses of ecological factors that promote cooperative breeding among South African birds suggest that the evolutionary pathway to obligate and facultative breeding may be fundamentally different. First, OCS live mainly in savanna habitats that have predictable seasonal peaks in food availability, yet where the baseline level of food availability during the nonbreeding season is sufficient to support permanent residence by groups. Small to medium-sized birds of the African savannas are particularly vulnerable to avian predators, and foraging and roosting in permanent groups may enhance their survival. We propose that the benefits of obligate cooperative breeding are derived chiefly from survival of individuals away from the nest (i.e. during the nonbreeding season). Secondly, FCS live largely in unpredictable, seasonal steppe habitats. Under these conditions it may be impossible for birds to maintain permanent group territories, and variation in the tendency to breed cooperatively may depend largely on the opportunistic assessment of environmental conditions. We therefore suggest that birds (i.e. FCS) will opt to breed cooperatively only when conditions are unfavourable for independent breeding, and that the benefits thus accrued are chiefly related to reproduction.
The appreciation by earlier workers of the importance of studying avian cooperative breeding (CB) in an explicitly phylogenetic context has waned in most recent studies of the subject. Newer statistical and conceptual methods correct for correlations among species inherent in their phylogenetic relationships and are used to study the evolution and adaptive status of CB in the context of phylogenetic trees. Statistical, simulation, and phylogenetic analyses of the taxonomic distribution of CB among passerine genera confirm the suspicion that CB is nonrandomly distributed among genera and extend the conclusion of E. Russell that CB may be ancient in some lineages, many of which include well-studied species. Phylogenetic reconstruction of ancestral states of ecological factors hypothesized to have promoted CB revealed a variety of temporal relationships between the inferred invasion of selective environments and the origin of CB that were not immediately apparent from nonphylogenetic analyses and that clarified the mechanistic relationship between these events. In some lineages the persistence of CB after substantial change in the selective environments presumed responsible for its origin suggests that "phylogenetic inertia" may partly explain the observed taxonomic distribution of CB. Phylogenetic effects cannot explain the observed plasticity and context-specific variation in many aspects of CB and helping; the joint effects of phylogeny and ecology for explaining such variation are illustrated. The data suggest that many lineages experience evolutionary forces promoting long-term stasis in life histories conducive to CB in addition to the better-characterized environmental responses modifying its short-term expression.
The ecological constraints hypothesis is widely accepted as an explanation for the evolution of delayed dispersal in cooperatively breeding birds. Intraspecific studies offer the strongest support. Observational studies have demonstrated a positive association between the severity of ecological constraints and the prevalence of cooperation, and experimental studies in which constraints on independent breeding were relaxed resulted in helpers moving to adopt the vacant breeding opportunities. However, this hypothesis has proved less successful in explaining why cooperative breeding has evolved in some species or lineages but not in others. Comparative studies have failed to identify ecological factors that differ consistently between cooperative and noncooperative species. The life history hypothesis, which emphasizes the role of life history traits in the evolution of cooperative breeding, offers a solution to this difficulty. A recent analysis showed that low adult mortality and low dispersal predisposed certain lineages to show cooperative behaviour, given the right ecological conditions. This represents an important advance, not least by offering an explanation for the patchy phylogenetic distribution of cooperative breeding. We discuss the complementary nature of these two hypotheses and suggest that rather than regarding life history traits as predisposing and ecological factors as facilitating cooperation, they are more likely to act in concert. While acknowledging that different cooperative systems may be a consequence of different selective pressures, we suggest that to identify the key differences between cooperative and noncooperative species, a broad constraints hypothesis that incorporates ecological and life history traits in a single measure of 'turnover of breeding opportunities' may provide the most promising avenue for future comparative studies. Copyright 2000 The Association for the Study of Animal Behaviour.
Many vertebrates breed in cooperative groups in which more than two members provide care for young. Studies of cooperative breeding behavior within species have long highlighted the importance of environmental factors in mediating the paradox of why some such individuals delay independent breeding to help raise the offspring of others. In contrast, studies involving comparisons among species have not shown a similarly clear evolutionary-scale relationship between the interspecific incidence of cooperative breeding and any environmental factors. Here, we use a phylogenetically controlled comparative analysis of a complete, socially diverse group of birds-45 species of African starlings-to show that cooperative breeding is positively associated with living in semiarid savanna habitats and with temporal variability in rainfall. Savanna habitats are not only highly seasonal, but also temporally variable and unpredictable, and this temporal variability directly influences individual reproductive decisions in starlings and helps explain interspecific patterns of sociality. Cooperative breeding is likely to be adaptive in temporally variable environments because it allows for both reproduction in harsh years and sustained breeding during benign years. This "temporal variability" hypothesis might help explain the phylogenetic and geographic concentrations of cooperatively breeding vertebrates in savanna-like habitats and other temporally variable environments worldwide.
Why do so many Australian birds cooperate? Social evolution in the Corvida
- Cockburn
Why do so many Australian birds cooperate? Social evolution in the Corvida In Frontiers in Population Ecology
- A Cockburn
Cockburn, A. (1996). Why do so many Australian birds cooperate? Social evolution in the Corvida. In Frontiers in Population Ecology, R.B. Floyd, A.W. Sheppard, and P.J. De Barro, eds. (Melbourne, Australia: CSIRO Publishing), pp. 451–472.