Transaction costs of community-based forest management: empirical evidence from Tanzania

Levels of transaction costs in community‐based forest management (CBFM) in four communities adjacent to the Ambangulu mountain forests of the north‐east of Tanzania were assessed through questionnaire responses from 120 households. Costs and benefits of CBFM to the rich, medium and poor groups of forest users were estimated. Costs of CBFM were participation in forest monitoring and time spent in meetings. Benefits included forest products consumed at household level. Transaction costs relative to benefits for CBFM were found to be higher for poorer households compared with medium income and richer households. Higher income groups obtained the most net benefits followed by medium and poorer households. Community involvement in forest management may lower the transaction costs incurred by government, but a large proportion of these costs are borne by poorer members of the community. Transaction costs are critical factors in the success or failure of CBFM and need to be incorporated into policies and legislation related to community‐based natural resource management.     

A simple rule reduces costs of extragroup parasitism in a communally breeding bird

How do cooperatively breeding groups resist invasion by parasitic "cheaters," which dump their eggs in the communal nest but provide no parental care [1,2]? Here I show that Greater Anis (Crotophaga major), Neotropical cuckoos that?nest in social groups containing several breeding females [3], use a simple rule based on the timing of laying to recognize and reject eggs laid by extragroup parasites. I experimentally confirmed that Greater Anis cannot recognize parasitic eggs based on the appearance of host egg phenotypes or on the number of eggs in the clutch. However, they can discriminate between freshly laid eggs and those that have already been incubated, and they accordingly eject asynchronous eggs. This mechanism is reliable in naturally parasitized nests, because group members typically lay their?eggs in tight synchrony, whereas the majority of parasitic eggs are laid several days later. Rejection of asynchronous eggs therefore provides a rare empirical example of a complex, group-level behavior that arises through relatively simple "rules of thumb" without requiring advanced cognitive mechanisms such as learning, counting, or individual recognition.     

Quinean social skills: empirical evidence from eye-gaze against information encapsulation

Since social skills are highly significant to the evolutionary success of humans, we should expect these skills to be efficient and reliable. For many Evolutionary Psychologists efficiency entails encapsulation: the only way to get an efficient system is via information encapsulation. But encapsulation reduces reliability in opaque epistemic domains. And the social domain is darkly opaque: people lie and cheat, and deliberately hide their intentions and deceptions. Modest modularity [Currie and Sterelny (2000) Philos Q 50:145–160] attempts to combine efficiency and reliability. Reliability is obtained by placing social skills in un-encapsulated central cognition; efficiency by having the social system sensitive to encapsulated socially tagged cues. In this paper, I argue that this approach fails. I focus on eye-gaze as a plausible example of a socially significant encapsulated cue. I demonstrate contra modest modularity that eye-gaze is subject to influence from central cognition.

Games fish play: Making decisions as a social forager

Suppose a customer wishes to buy a bag of fruit in a market hall during his lunch break and has the choice between two crowded fruiterers' shops. The complexity of problems inherent in such a situation has been increasingly appreciated by behavioural ecologists interested in social foraging of animals. The recognition of consistent individual differences in competitive ability and their incorporation into classical game theoretical models has recently facilitated a step forward in our understanding of social foraging. Here I review theoretical developments in connection with experiments on resource sharing in foraging fish.     

Processing power limits social group size: computational evidence for the cognitive costs of sociality

Sociality is primarily a coordination problem. However, the social (or communication) complexity hypothesis suggests that the kinds of information that can be acquired and processed may limit the size and/or complexity of social groups that a species can maintain. We use an agent-based model to test the hypothesis that the complexity of information processed influences the computational demands involved. We show that successive increases in the kinds of information processed allow organisms to break through the glass ceilings that otherwise limit the size of social groups: larger groups can only be achieved at the cost of more sophisticated kinds of information processing that are disadvantageous when optimal group size is small. These results simultaneously support both the social brain and the social complexity hypotheses.     

Hubbell's local abundance distribution: insights from a simple colonization rule

A simple colonization rule yields Hubbell's local abundance distribution with less math, more intuition, and weaker assumptions.     

A simple rule of thumb for elegant prehension

Reaching out to grasp an object (prehension) is a deceptively elegant and skilled behavior. The movement prior to object contact can be described as having two components, the movement of the hand to an appropriate location for gripping the object, the "transport" component, and the opening and closing of the aperture between the fingers as they prepare to grip the target, the "grasp" component. The grasp component is sensitive to the size of the object, so that a larger grasp aperture is formed for wider objects; the maximum grasp aperture (MGA) is a little wider than the width of the target object and occurs later in the movement for larger objects. We present a simple model that can account for the temporal relationship between the transport and grasp components. We report the results of an experiment providing empirical support for our "rule of thumb." The model provides a simple, but plausible, account of a neural control strategy that has been the center of debate over the last two decades.     

Thermal ecology and behaviour of the nomadic social forager Malacosoma disstria

The present study examines whether the nomadic social caterpillar Malacosoma disstria Hübner (Lepidoptera: Lasiocampidae) can thermoregulate despite the lack of a tent, and evaluates the role of thermoregulation in directing the colony's behaviour. The presence of a radiant heat and light source (i.e. a lamp in the laboratory experiments and the sun in the field observations) enables caterpillar colonies to increase body temperature by basking (remaining still under a heat source) and this is only effective when caterpillars cluster in groups. Body temperatures achieved when basking in a group coincide with the temperatures at which the development rate is maximal for this species. Indeed, in the laboratory experiments, the presence of a lamp results in higher growth rates, confirming that thermoregulation is an advantage to group living. When a radiant heat/light source is provided at a distance from the food in the laboratory, caterpillars behave to maximize thermal gains: colonies move away from the food to bivouac (i.e. group together and remain still on a silk mat) under the lamp, spend more time on the bivouac and cluster in a more cohesive group. Thermal needs thus influence habitat selection and colony aggregation. Malacosoma disstria relies on developing rapidly, despite low seasonal temperatures, aiming to benefit from springtime high food quality and low predation rates; however, unlike others in its genus, it does not build a tent but instead exhibits collective nomadic foraging (i.e. the whole colony moves together between temporary resting and feeding sites). In this species, collective thermoregulatory behaviour is not only possible and advantageous, but also drives much of the colony's behaviour, in large part dictating the temporal and spatial patterns of movement. These findings suggest that thermoregulation may be an important selection pressure keeping colonies together.     

Testing a simple rule for dominance in resource competition

Competition for limiting resources long has been considered an important factor generating community structure. A minimal model of resource competition predicts that the species that reduces the limiting resource R to the lowest level ([Formula: see text]) will exclude its competitors. Whether this "[Formula: see text] rule" is robust to violations of model assumptions remains largely unknown. I conducted a competition experiment with four species of bacterivorous protists in laboratory microcosms and predicted the outcome from each species' [Formula: see text] value. I also examined how the outcome of competition, species abundances, and the effect of protists on bacterial density varied with productivity. Microcosms were unstirred batch cultures containing a variety of bacteria, challenging the robustness of the simplest competition models. Protists with low [Formula: see text] values were less affected by competition, although competing protists often coexisted. The values of [Formula: see text] can predict competitive dominance, even in the absence of competitive exclusion. Other model predictions were less robust. Contrary to expectation, densities of grazed bacteria increased with productivity, and the effect of some protists on bacterial density did not vary with productivity. Bacterial heterogeneity may account for deviations from model predictions. Further experiments should examine the conditions under which simple rules can be expected to identify dominant species.     

Net costs of group living in a solitary forager, the Eurasian badger (Meles meles)

Group living is expected to evolve under two extreme conditions:when there are net benefits to the individual of living in agroup and when there are net costs to living in a group togetherwith strong ecological constraints on dispersal and independentbreeding. A third condition may facilitate group formation:when the territorial defense of resources that are dispersedwidely or renewed at high rates allows groups to form at nocost to group members. Eurasian badgers are solitary over alarge part of their geographic distribution and forage aloneeven where diey live in territorial groups. To determine whichof the three conditions best explains group living in badgers,we analyzed dispersal and breeding patterns. Using these datawe describe the mechanism of group formation and the net costsor benefits of group living in 16 badger groups in one population.Groups form primarily by the retention of young on their natalterritory. Typically, groups contain one or more sexually maturebut nonbreeding females in addition to one or more breedingfemales. Females do not benefit from group living as indicatedby the lack of relationships, or perhaps negative relationships,between the proportion of adult females that bred in a groupand mean reproductive success, on the one hand, and group sizeand components of group size, on the other. A high reproductivefailure rate among females in this and other populations ofsocial badgers, as compared with a population of solitary badgers,suggests that there is a cost of group living to females. Wepropose that if badgers defend resources whose spatial distributionor high renewal rates allow groups to form on a territory atlitde or no cost to group members, weak ecological constraintson dispersal and independent breeding are sufficient to explainthe formation of groups. Badgers appear to have not evolvedcooperative breeding in response to these ecological conditions,perhaps because badger groups represent an early stage in theevolution of carnivore sociality.     

A simple rule for the evolution of contingent cooperation in large groups

Humans cooperate in large groups of unrelated individuals, and many authors have argued that such cooperation is sustained by contingent reward and punishment. However, such sanctioning systems can also stabilize a wide range of behaviours, including mutually deleterious behaviours. Moreover, it is very likely that large-scale cooperation is derived in the human lineage. Thus, understanding the evolution of mutually beneficial cooperative behaviour requires knowledge of when strategies that support such behaviour can increase when rare. Here, we derive a simple formula that gives the relatedness necessary for contingent cooperation in n-person iterated games to increase when rare. This rule applies to a wide range of pay-off functions and assumes that the strategies supporting cooperation are based on the presence of a threshold fraction of cooperators. This rule suggests that modest levels of relatedness are sufficient for invasion by strategies that make cooperation contingent on previous cooperation by a small fraction of group members. In contrast, only high levels of relatedness allow the invasion by strategies that require near universal cooperation. In order to derive this formula, we introduce a novel methodology for studying evolution in group structured populations including local and global group-size regulation and fluctuations in group size.     

Exploring the costs and benefits of social information use: an appraisal of current experimental evidence

Research on social learning has focused traditionally on whether animals possess the cognitive ability to learn novel motor patterns from tutors. More recently, social learning has included the use of others as sources of inadvertent social information. This type of social learning seems more taxonomically widespread and its use can more readily be approached as an economic decision. Social sampling information, however, can be tricky to use and calls for a more lucid appraisal of its costs. In this four-part review, we address these costs. Firstly, we address the possibility that only a fraction of group members are actually providing social information at any one time. Secondly, we review experimental research which shows that animals are circumspect about social information use. Thirdly, we consider the cases where social information can lead to incorrect decisions and finally, we review studies investigating the effect of social information quality. We address the possibility that using social information or not is not a binary decision and present results of a study showing that nutmeg mannikins combine both sources of information, a condition that can lead to the establishment of informational cascades. We discuss the importance of empirically investigating the economics of social information use.     

A simple mechanism for complex social behavior

The evolution of cooperation is a paradox because natural selection should favor exploitative individuals that avoid paying their fair share of any costs. Such conflict between the self-interests of cooperating individuals often results in the evolution of complex, opponent-specific, social strategies and counterstrategies. However, the genetic and biological mechanisms underlying complex social strategies, and therefore the evolution of cooperative behavior, are largely unknown. To address this dearth of empirical data, we combine mathematical modeling, molecular genetic, and developmental approaches to test whether variation in the production of and response to social signals is sufficient to generate the complex partner-specific social success seen in the social amoeba Dictyostelium discoideum. Firstly, we find that the simple model of production of and response to social signals can generate the sort of apparent complex changes in social behavior seen in this system, without the need for partner recognition. Secondly, measurements of signal production and response in a mutant with a change in a single gene that leads to a shift in social behavior provide support for this model. Finally, these simple measurements of social signaling can also explain complex patterns of variation in social behavior generated by the natural genetic diversity found in isolates collected from the wild. Our studies therefore demonstrate a novel and elegantly simple underlying mechanistic basis for natural variation in complex social strategies in D. discoideum. More generally, they suggest that simple rules governing interactions between individuals can be sufficient to generate a diverse array of outcomes that appear complex and unpredictable when those rules are unknown.     

Choice and context: testing a simple short-term choice rule

Psychological studies of animal choice show that the immediate consequences of choice strongly influence preference. In contrast, evolutionary models emphasize the longer-term fitness consequences of choice. Building on recent work by Stephens & Anderson (2001, Behavioral Ecology12, 330-339), this study presents two experiments that address this conflict. Stephens & Anderson developed an alternative choice situation based on patch-leaving decisions and compared this to the binary choice, or self-control, situation typically used in psychological studies. They hypothesized that the same short-term choice rule could account for choice in both situations, maximizing long-term gains in the patch situation, but typically producing shortsighted results in the self-control case. Experiment 1 used captive blue jays, Cyanocitta cristata, to test this ‘same rule’ hypothesis. The results do not support this hypothesis, suggesting that if a single rule applies, it is probably a more complex rule. Stephens & Anderson also hypothesized that a rule based on the delay to the next meal could explain why the intertrial interval has little effect in binary choice studies, even though the analogous travel time strongly affects patch-leaving decisions. When an animal leaves a patch, it experiences a delay consisting of the travel time plus time spent searching in the patch until food is obtained. Experiment 2 tested the hypothesis that travel time and search time combine additively, behaving like a single delay. Using treatments that created the same combined delay via different combinations of travel and search time, we found no evidence of nonadditivity, suggesting that these two components may indeed be treated as a single delay. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.      

Toward an individual-level understanding of vigilance: the role of social information

A gregarious lifestyle affords the benefit of collective detectionof predators through the many-eyes effect. Studies of vigilanceare generally concerned with exploring the relationship betweenvigilance rates and group size. However, a mechanistic understandingof the rules individual animals use to achieve this group-levelbehavior is lacking. Building on a previous modeling approach,we suggest that individuals reconcile their own private informationagainst the social information they receive from their groupmates in order to decide whether to feed or be vigilant at anyone time. We present a novel modeling approach utilizing a Markovchain Monte Carlo process to describe the transition betweenvigilant and nonvigilant states. Many of our assumptions arebased qualitatively on recently published experimental observations.We vary the amount of social information and the fidelity withwhich individuals process this information and show that thishas a profound effect on the individual vigilance rate, theindividual vigilant bout length, and the proportion of vigilantindividuals at any one time. A wide range of group-level vigilancepatterns can be obtained by varying simple behavioral characteristicsof individual animals. We find that generally, increasing theamount of, and sensitivity to, social information generatesa more cooperative vigilance behavior. This model potentiallyprovides a theoretical and conceptual framework for examiningspecific real-life systems. We propose analyzing individual-baseddata from real animals by considering their group to be a connectednetwork of individuals, with information transfer between them.     

Social organization in Eulipotyphla: evidence for a social shrew

Shrews and their close relatives (order Eulipotyphla) are typically considered to be solitary. This impacts our understanding of mammalian social evolution: (i) the ancestor of mammals is believed to have been shrew-like, and even though Eulipotyphla are not more basal than other mammalian orders, this might have been one reason why the first mammals have been assumed to be solitary-living; (ii) Eulipotyphla are the third largest mammalian order, with hundreds of species entering comparative analyses. We review primary field studies reporting the social organization of Eulipotyphla, doing a literature research on 445 species. Primary literature was only available for 16 of the 445 species. We found 56% of the studied species to be social (38% were living in pairs), which is in sharp contrast to the 0.5 and 8% reported in other databases. We conclude that the available information indicates that shrews are more sociable than generally believed. An interesting alternative hypothesis is that the mammalian ancestor might have been pair-living. To understand the social evolution of mammals, comparative studies must be based on reliable and specific information, and more species of all orders must be studied in the field.     

A general rule for sensory cue summation: evidence from photographic, musical, phonetic and cross-modal stimuli

The Euclidean and MAX metrics have been widely used to model cue summation psychophysically and computationally. Both rules happen to be special cases of a more general Minkowski summation rule , where m = 2 and ∞, respectively. In vision research, Minkowski summation with power m = 3-4 has been shown to be a superior model of how subthreshold components sum to give an overall detection threshold. Recently, we have previously reported that Minkowski summation with power m = 2.84 accurately models summation of suprathreshold visual cues in photographs. In four suprathreshold discrimination experiments, we confirm the previous findings with new visual stimuli and extend the applicability of this rule to cue combination in auditory stimuli (musical sequences and phonetic utterances, where m = 2.95 and 2.54, respectively) and cross-modal stimuli (m = 2.56). In all cases, Minkowski summation with power m = 2.5-3 outperforms the Euclidean and MAX operator models. We propose that this reflects the summation of neuronal responses that are not entirely independent but which show some correlation in their magnitudes. Our findings are consistent with electrophysiological research that demonstrates signal correlations (r = 0.1-0.2) between sensory neurons when these are presented with natural stimuli.     

Evaluating the twin testosterone transfer hypothesis: A review of the empirical evidence

In this paper we review the evidence that fetuses gestated with a male co-twin are masculinized in development, perhaps due to the influence of prenatal androgens: the so-called twin testosterone transfer (TTT) hypothesis. Evidence from studies of behavioral, perceptual, cognitive, morphological and physiological traits in same- and opposite-sex human twins is considered. Apart from two studies reporting increases in aspects of sensation-seeking for females with a male rather than a female co-twin, there is sparse evidence supporting the TTT hypothesis in behavioral studies. Outcomes from studies of perception (in particular otoacoustic emissions) and cognition (in particular vocabulary acquisition and visuo-spatial ability) provide more consistent evidence in support of masculinized performance in twins with a male co-twin compared to twins with a female co-twin. The outcomes favorable to the TTT hypothesis for otoacoustic emissions and visuo-spatial ability are restricted to females. Studies of physiology and morphology (e.g., brain volume, tooth size and 2D:4D ratio) also show some influence of co-twin sex, but again these effects are often restricted to female twins. Because females produce little endogenous testosterone, the effects of gestation with a male co-twin may be more pronounced in females than males. Thus, while uneven, the evidence for the TTT hypothesis is sufficient to warrant further investigation, ideally using large samples of same- and opposite-sex twins, along with control groups of same- and opposite-sex siblings when the characteristics assessed are potentially open to social influences.