Invariant properties in coevolutionary networks of plant–animal interactions

Plant–animal mutualistic networks are interaction webs consisting of two sets of entities, plant and animal species, whose evolutionary dynamics are deeply influenced by the outcomes of the interactions, yielding a diverse array of coevolutionary processes. These networks are two‐mode networks sharing many common properties with others such as food webs, social, and abiotic networks. Here we describe generalized patterns in the topology of 29 plant–pollinator and 24 plant–frugivore networks in natural communities. Scale‐free properties have been described for a number of biological, social, and abiotic networks; in contrast, most of the plant–animal mutualistic networks (65.6%) show species connectivity distributions (number of links per species) with a power‐law regime but decaying as a marked cut‐off, i.e. truncated power‐law or broad‐scale networks and few (22.2%) show scale‐invariance. We hypothesize that plant–animal mutualistic networks follow a build‐up process similar to complex abiotic nets, based on the preferential attachment of species. However, constraints in the addition of links such as morphological mismatching or phenological uncoupling between mutualistic partners, restrict the number of interactions established, causing deviations from scale‐invariance. This reveals generalized topological patterns characteristic of self‐organized complex systems. Relative to scale‐invariant networks, such constraints may confer higher robustness to the loss of keystone species that are the backbone of these webs.     

Natural cooperators: Food sharing in humans and other primates

The study of cooperation is rich with theoretical models and laboratory experiments that have greatly advanced our knowledge of human uniqueness, but have sometimes lacked ecological validity. We therefore emphasize the need to tie discussions of human cooperation to the natural history of our species and its closest relatives, focusing on behavioral contexts best suited to reveal underlying selection pressures and evolved decision rules. 1 - 3 Food sharing is a fundamental form of cooperation that is well‐studied across primates and is particularly noteworthy because of its central role in shaping evolved human life history, social organization, and cooperative psychology. 1 - 16 Here we synthesize available evidence on food sharing in humans and other primates, tracing the origins of offspring provisioning, mutualism, trade, and reciprocity throughout the primate order. While primates may gain some benefits from sharing, humans, faced with more collective action problems in a risky foraging niche, expanded on primate patterns to buffer risk and recruit mates and allies through reciprocity and signaling, and established co‐evolving social norms of production and sharing. Differences in the necessity for sharing are reflected in differences in sharing psychology across species, thus helping to explain unique aspects of our evolved cooperative psychology.     

The costs and benefits of resource sharing: reciprocity requires resource heterogeneity

The evolution of resource sharing requires that the fitness benefits to the recipients be much higher than the costs to the giver, which requires heterogeneity among individuals in the fitness value of acquiring additional resources. We develop four models of the evolution of resource sharing by either direct or indirect reciprocity, with equal or unequal partners. Evolution of resource sharing by reciprocity requires differences between interacting individuals in the fitness value of the resource, and these differences must reverse although previous acts of giving are remembered and both participants survive. Moreover, inequality in the expected reproductive value of the interacting individuals makes reciprocity more difficult to evolve, but may still allow evolution of sharing by kin selection. These constraints suggest that resource sharing should evolve much more frequently by kin selection than by reciprocity, a prediction that is well supported by observations in the natural world.     

BaYaka forager food sharing networks in the Congo Basin: The roles of gender homophily and kin sharing

Objectives

Food sharing is a costly form of cooperation that was likely critical to human evolutionary success, including the emergence of human's life history strategy. Food sharing in human communities may be maintained through a number of pathways, including direct dyadic reciprocity, reputation-based processes, and kin-biased exchange. Differences in reproductive demands, labor, and cultural norms may also result in gendered differences in cooperative networks. Here, we examine cooperative networks in egalitarian BaYaka foragers from the Congo Basin.

Materials and Methods

We collected social network data from 112 adults in 41 households in this subsistence community. We implement a Bayesian latent network model to assess individual-, dyadic-, and block-level predictors of food sharing partners.

Results

Conditioning on covariates, we found limited evidence for direct dyadic reciprocity in food sharing. Despite local norms regarding prestige avoidance, we found status-based homophily. High-status individuals—council members and local healers—were more likely to share with one another. Importantly, our results highlight gender differences in patterns of food sharing, interacting with genetic relatedness. Women were more likely to share with one another, especially with kin as genetic relatedness increased.

Discussion

Our results align with evolutionary framing emphasizing kin selection in costly cooperation. The results showing that women cooperate with other women, particularly kin, also complement sex-based patterns in some other mammalian species, potentially reflecting the social support necessary to manage reproductive costs and childcare. BaYaka women's subsistence productivity and local cultural dynamics for autonomy and egalitarianism may likewise help facilitate women's preferential cooperation with one another.

     

Food-Sharing Networks in Lamalera,Indonesia

Exponential random graph modeling (ERGM) is used here to test hypotheses derived from human behavioral ecology about the adaptive nature of human food sharing. Respondents in all (n = 317) households in the fishing and sea-hunting village of Lamalera, Indonesia, were asked to name those households to whom they had more frequently given (and from whom they had more frequently received) food during the preceding sea-hunting season. The responses were used to construct a social network of between-household food-sharing relationships in the village. The results show that kinship, proximity, and reciprocal sharing all strongly increase the probability of giving food to a household. The effects of kinship and distance are relatively independent of each other, although reciprocity is more common among residentially and genealogically close households. The results show support for reciprocal altruism as a motivation for food sharing, while kinship and distance appear to be important partner-choice criteria.     

Saint cults and political alignments in Southern Italy

Conclusion People are seldom able to account for the meanings implied in the particulars of the rituals, but the most important element in the interaction with the saint seems to be of a reciprocal character-exchange of gifts for miracles or protection. The saint cult can be seen as part of a total social phenomenon which articulates the symmetrical reciprocity in the interpersonal relationships in the social structure and asymmetrical relationships in the clientela system. The feasts amount to a popular gathering with multiple functions where all the activities that are being performed renew and confirm networks that constitute village solidarity. The saint cult also joins all these functions and meanings in a complex cultural-personal metaphor that relates expressions of reciprocity as instances of the underlying forms of the society.The saint cult does not merely express a metaphor.A metaphor uses imagery from one domain or level of experience to illuminate relationships, objects and processes in a different domain or at a different level. It follows from this that the domain of thought or experience which is being explicated by metaphor is that which metaphor is used to illuminate, not that from which the idioms of metaphor is fetched .There is also a formal similarity between the gift-giving to a patron saint and to a profane patron. But the rituals in the saint cults do not account for a divine justification of the order in the substantial world. On the contrary, the rituals of the saint cults use a known and common language of reciprocity to get hold of a difficult and inexplicable world. I thus argue that the rituals of the saint cults use idioms similar to the profane political and social relations to express the quality of the relationship between saint and devotee, but this in no way implies that the two domains are substantively confounded. The forms are part of the same world view that emphasizes reciprocity as the basis for social solidarity; receiving evokes obligations for return giving, a favor for a gift. Ritual is not a substitute for the world or displacement of action in it; it is part of, an expression of, a world articulated by those values/views of reciprocity. Consequently, the saint cults which have been analyzed here do not represent an alternative to political or other activities, but a continuation and a completion of that activity into the total means by which one seeks goals in a world so conceived.Mia Di Tota is associated with the Ethnographic Museum at the University of Oslo.

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灵长类动物的食物分享行为

食物分享是灵长类动物的一种重要社会交往行为,主要发生在成体-幼体间和成体-成体之间。本文从这两个方面对灵长类动物食物分享的行为表现、特点以及功能进行总结,着重比较了无亲缘关系的成年个体间食物分享的互惠解释和骚扰解释。通过对以上内容的综合分析,进一步提出了食物分享行为的未来研究方向以及对人类合作行为演化的启示。     

Spatial relationships in a dendritic network: the herpetofaunal metacommunity of the Mattole River catchment of northwest California

We investigated the aquatic and riparian herpetofauna in a 789 km² river catchment in northwest California to examine competing theories of biotic community structuring in catchment stream networks. Research in fluvial geomorphology has resulted in multi‐scale models of dynamic processes that cyclically create, maintain, and destroy environments in stream networks of mountain catchments. These models have been applied to understanding distributions of invertebrates, algae, fishes and their habitats across entire basin networks, but similar approaches with herpetofauna are rare. We examined multi‐scale spatial patterns of multiple species as they related to variation in channel types, channel settings, and within‐channel attributes that result from these processes. From 83 reaches distributed randomly throughout the watershed, we distinguished four channel types: 1) high gradient with cascade structure; 2) 2–4% gradient with step‐pool structure controlled by moderately steep valleys; 3) slightly entrenched, lower gradient, plane‐bed structure; and 4) low gradient, shallow, unconfined, multiple or migrating pool/riffle channels in broad alluvial valleys. The composition of herpetofauna differed in five of six pair‐wise comparisons among these channel types, indicating a minimum of three distinct mesoscale assemblages. We used non‐parametric multiple regression (NPMR) to examine relationships at multiple spatial scales. NPMR revealed species‐specific associations with channel settings and within‐channel environments among species sharing the same sets of channel types. Morphological adaptations, biophysical limits and natural histories of each species best explained their associations with distinct sets of attributes surrounding and within channel types. While each set of species has similarly adapted to fluvial and geomorphic disturbance processes structuring channels at the mesoscale, species within each set have adapted to a unique set of attributes that are best discerned when their spatial relationships are examined across multiple spatial scales. We evaluated the various spatial patterns against hypotheses of stream community organization and metacommunity perspectives.     

Food sharing and affiliation: An experimental and longitudinal study in cockatiels (Nymphicus hollandicus)

Food sharing has attracted much attention because of its apparently altruistic nature and its link to prosociality. However, food sharing has been mostly studied in a reproductive context, during courtship and parental care, where the fitness benefits are obvious. We still lack a clear understanding of the functions of food sharing outside any reproductive context and within social groups of same‐aged peers. Previous studies suggest that cofeeding, the action to let another animal feed from the same monopolizable food source, may be used to build and strengthen bonds between individuals. This may be particularly crucial in social birds forming long‐term associations between mates or siblings such as psittacids and corvids. Here, we investigated food sharing and affiliative behaviors such as allopreening in a psittacine species, namely in a group of captive juvenile cockatiels (Nymphicus hollandicus) consisting of five siblings and five unrelated birds. Our main objective was to study the developmental pattern of food sharing over time and its implication in social bonding depending on kinship, affiliation, and sex. Studying cockatiels in this context is providing many new information since most of the studies on food sharing in birds focused on corvids. We found that, contrary to jackdaws, cockatiels continued to share food with multiple individuals, although the frequency of cofeeding as well as the number of cofeeding partners decreased over time. Cockatiels shared more food with their siblings than with other conspecifics but they were not more likely to do cofeeding with birds of the opposite sex. We also found evidence that young cockatiels exchanged more food with those from whom they received food (reciprocity) and, to a lesser extent, allopreening (interchange), than from other cockatiels. Our findings suggest that in cockatiels, food sharing within social groups serves the formation (and maintenance) of affiliative bonds, especially between siblings, rather than pair bonds, but might additionally be explained by reciprocity, interchange, and harassment avoidance.     

A proximate perspective on reciprocal altruism

The study of reciprocal altruism, or the exchange of goods and services between individuals, requires attention to both evolutionary explanations and proximate mechanisms. Evolutionary explanations have been debated at length, but far less is known about the proximate mechanisms of reciprocity. Our own research has focused on the immediate causes and contingencies underlying services such as food sharing, grooming, and cooperation in brown capuchin monkeys and chimpanzees. Employing both observational and experimental techniques, we have come to distinguish three types of reciprocity. Symmetry-based reciprocity is cognitively the least complex form, based on symmetries inherent in dyadic relationships (e.g., mutual association, kinship). Attitudinal reciprocity, which is more cognitively complex, is based on the mirroring of social attitudes between partners and is exhibited by both capuchin monkeys and chimpanzees. Finally, calculated reciprocity, the most cognitively advanced form, is based on mental scorekeeping and is found only in humans and possibly chimpanzees. Sarah F. Brosnan is a graduate student in the Population Biology, Ecology, and Evolution Program at Emory University. Her interests include proximate mechanisms of cooperation and reciprocity in primates, and social learning in primates and other species. Frans B. M. de Waal is the C. H. Candler Professor of Psychology and the director of the Living Links Center at Emory University. His interests include social behavior and cognition of monkeys and apes, and their relevance for questions on the evolution of human politics, economy, morality, and culture.     

Why hunt? Why gather? Why share? Hadza assessments of foraging and food-sharing motive

Over the last half century, anthropologists have vigorously debated the adaptive motivations underlying food acquisition choices and food-sharing among hunter-gatherer groups. Numerous explanations have been proposed to account for high-levels of generosity in food-sharing, including self- and family-provisioning, reciprocity, tolerated theft and pro-social- or skill-signaling. However, few studies have asked foragers directly and systematically about the motivations underlying their foraging and sharing decisions. We recruited 110 Hadza participants and employed a combination of free-response, yes/no, ranking and forced-choice questions to do just this. In free-response answers, respondents typically gave outcome-oriented accounts of foraging motive (e.g., to get food) and moralistic accounts of sharing motive (e.g., I have a good heart). In ranking tasks, participants gave precedence to reciprocity as a motive for sharing food beyond the household. We found small but clear gender differences in foraging motive, in line with previous predictions: women were more likely than men to rank family-provisioning highly whereas men were more likely than women to rank skill-signaling highly. However, despite these gender differences, the relative importance of different motivations was similar across genders and skill-signaling, sharing and family-provisioning were the most important motivators of foraging activity for both men and women. Contrary to the expectations of tolerated theft, peer complaints and requests for food ranked very low. There are several compelling reasons that evolutionary thinkers, typically interested in ultimate-level adaptive processes, have traditionally eschewed direct and explicit investigations of motive. However, these data may yet provide important insights.     

Tolerant food sharing and reciprocity is precluded by despotism among bonobos but not chimpanzees

Tolerant food sharing among human foragers can largely be explained by reciprocity. In contrast, food sharing among chimpanzees and bonobos may not always reflect reciprocity, which could be explained by different dominance styles: in egalitarian societies reciprocity is expressed freely, while in more despotic groups dominants may hinder reciprocity. We tested the degree of reciprocity and the influence of dominance on food sharing among chimpanzees and bonobos in two captive groups. First, we found that chimpanzees shared more frequently, more tolerantly, and more actively than bonobos. Second, among chimpanzees, food received was the best predictor of food shared, indicating reciprocal exchange, whereas among bonobos transfers were mostly unidirectional. Third, chimpanzees had a shallower and less linear dominance hierarchy, indicating that they were less despotic than bonobos. This suggests that the tolerant and reciprocal sharing found in chimpanzees, but not bonobos, was made possible by the absence of despotism. To investigate this further, we tested the relationship between despotism and reciprocity in grooming using data from an additional five groups and five different study periods on the main groups. The results showed that i) all chimpanzee groups were less despotic and groomed more reciprocally than bonobo groups, and ii) there was a general negative correlation between despotism and grooming reciprocity across species. This indicates that an egalitarian hierarchy may be more common in chimpanzees, at least in captivity, thus fostering reciprocal exchange. We conclude that a shallow dominance hierarchy was a necessary precondition for the evolution of human‐like reciprocal food sharing. Am J Phys Anthropol 143:41–51, 2010. © 2010 Wiley‐Liss, Inc.     

Effects of trophic similarity on community composition

Understanding how ecological processes determine patterns among species coexisting within ecosystems is central to ecology. Here, we explore relationships between species’ local coexistence and their trophic niches in terms of their feeding relationships both as consumers and as resources. We build on recent concepts and methods from community phylogenetics to develop a framework for analysing mechanisms responsible for community composition using trophic similarity among species and null models of community assembly. We apply this framework to 50 food webs found in 50 Adirondack lakes and find that species composition in these communities appears to be driven by both bottom‐up effects by which the presence of prey species selects for predators of those prey, and top‐down effects by which prey more tolerant of predation out‐compete less tolerant prey of the same predators. This approach to community food webs is broadly applicable and shows how species interaction networks can inform an increasingly large array of theory central to community ecology.     

Respiratory health and air pollution: additive mixed model analyses

We conduct a reanalysis of data from the Utah Valley respiratory health/air pollution study of Pope and co-workers (Pope et al., 1991) using additive mixed models. A relatively recent statistical development (e.g. Wang, 1998; Verbyla et al., 1999; Lin and Zhang, 1999), the methods allow for smooth functional relationships, subject-specific effects and time series error structure. All three of these are apparent in the Utah Valley data.     

Upstream reciprocity in heterogeneous networks

Many mechanisms for the emergence and maintenance of altruistic behavior in social dilemma situations have been proposed. Indirect reciprocity is one such mechanism, where other-regarding actions of a player are eventually rewarded by other players with whom the original player has not interacted. The upstream reciprocity (also called generalized indirect reciprocity) is a type of indirect reciprocity and represents the concept that those helped by somebody will help other unspecified players. In spite of the evidence for the enhancement of helping behavior by upstream reciprocity in rats and humans, theoretical support for this mechanism is not strong. In the present study, we numerically investigate upstream reciprocity in heterogeneous contact networks, in which the players generally have different number of neighbors. We show that heterogeneous networks considerably enhance cooperation in a game of upstream reciprocity. In heterogeneous networks, the most generous strategy, by which a player helps a neighbor on being helped and in addition initiates helping behavior, first occupies hubs in a network and then disseminates to other players. The scenario to achieve enhanced altruism resembles that seen in the case of the Prisoner's Dilemma game in heterogeneous networks.     

Do Food Web Models Reproduce the Structure of Mutualistic Networks?

Background

Simple models inspired by processes shaping consumer-resource interactions have helped to establish the primary processes underlying the organization of food webs, networks of trophic interactions among species. Because other ecological interactions such as mutualisms between plants and their pollinators and seed dispersers are inherently based in consumer-resource relationships we hypothesize that processes shaping food webs should organize mutualistic relationships as well.

Methodology/Principal Findings

We used a likelihood-based model selection approach to compare the performance of food web models and that of a model designed for mutualisms, in reproducing the structure of networks depicting mutualistic relationships. Our results show that these food web models are able to reproduce the structure of most of the mutualistic networks and even the simplest among the food web models, the cascade model, often reproduce overall structural properties of real mutualistic networks.

Conclusions/Significance

Based on our results we hypothesize that processes leading to feeding hierarchy, which is a characteristic shared by all food web models, might be a fundamental aspect in the assembly of mutualisms. These findings suggest that similar underlying ecological processes might be important in organizing different types of interactions.     

Interspecific social networks promote information transmission in wild songbirds

Understanding the functional links between social structure and population processes is a central aim of evolutionary ecology. Multiple types of interactions can be represented by networks drawn for the same population, such as kinship, dominance or affiliative networks, but the relative importance of alternative networks in modulating population processes may not be clear. We illustrate this problem, and a solution, by developing a framework for testing the importance of different types of association in facilitating the transmission of information. We apply this framework to experimental data from wild songbirds that form mixed-species flocks, recording the arrival (patch discovery) of individuals to novel foraging sites. We tested whether intraspecific and interspecific social networks predicted the spread of information about novel food sites, and found that both contributed to transmission. The likelihood of acquiring information per unit of connection to knowledgeable individuals increased 22-fold for conspecifics, and 12-fold for heterospecifics. We also found that species varied in how much information they produced, suggesting that some species play a keystone role in winter foraging flocks. More generally, these analyses demonstrate that this method provides a powerful approach, using social networks to quantify the relative transmission rates across different social relationships.     

Comparative analysis of protein interaction networks

Recent advances in proteomics and computational biology have lead to a flood of protein interaction data and resulting interaction networks (e.g. (Gavin et al., 2002)). Here I first analyse the status and quality of parts lists (genes and proteins), then comparatively assess large-scale protein interaction data (von Mering et al., 2002) and finally try to identify biological meaningful units (e.g. pathways, cellular processes) within interaction networks that are derived from the conservation of gene neighborhood (Snel et al., 2002). Possible extensions of gene neighborhood analysis to eukaryotes (von Mering and Bork, 2002) will be discussed.     

Neighbor-net: an agglomerative method for the construction of phylogenetic networks

We present Neighbor-Net, a distance based method for constructing phylogenetic networks that is based on the Neighbor-Joining (NJ) algorithm of Saitou and Nei. Neighbor-Net provides a snapshot of the data that can guide more detailed analysis. Unlike split decomposition, Neighbor-Net scales well and can quickly produce detailed and informative networks for several hundred taxa. We illustrate the method by reanalyzing three published data sets: a collection of 110 highly recombinant Salmonella multi-locus sequence typing sequences, the 135 "African Eve" human mitochondrial sequences published by Vigilant et al., and a collection of 12 Archeal chaperonin sequences demonstrating strong evidence for gene conversion. Neighbor-Net is available as part of the SplitsTree4 software package.     

Parsimony Score of Phylogenetic Networks: Hardness Results and a Linear-Time Heuristic

Phylogenies—the evolutionary histories of groups of organisms—play a major role in representing the interrelationships among biological entities. Many methods for reconstructing and studying such phylogenies have been proposed, almost all of which assume that the underlying history of a given set of species can be represented by a binary tree. Although many biological processes can be effectively modeled and summarized in this fashion, others cannot: recombination, hybrid speciation, and horizontal gene transfer result in networks of relationships rather than trees of relationships. In previous works, we formulated a maximum parsimony (MP) criterion for reconstructing and evaluating phylogenetic networks, and demonstrated its quality on biological as well as synthetic data sets. In this paper, we provide further theoretical results as well as a very fast heuristic algorithm for the MP criterion of phylogenetic networks. In particular, we provide a novel combinatorial definition of phylogenetic networks in terms of “forbidden cycles,” and provide detailed hardness and hardness of approximation proofs for the "small” MP problem. We demonstrate the performance of our heuristic in terms of time and accuracy on both biological and synthetic data sets. Finally, we explain the difference between our model and a similar one formulated by Nguyen et al., and describe the implications of this difference on the hardness and approximation results.