Democracy in animals: the evolution of shared group decisions

A 'consensus decision' is when the members of a group choose, collectively, between mutually exclusive actions. In humans, consensus decisions are often made democratically or in an 'equally shared' manner, i.e. all group members contribute to the decision. Biologists are only now realizing that shared consensus decisions also occur in social animals (other than eusocial insects). Sharing of decisions is, in principle, more profitable for groups than accepting the 'unshared' decision of a single dominant member. However, this is not true for all individual group members, posing a question as to how shared decision making could evolve. Here, we use a game theory model to show that sharing of decisions can evolve under a wide range of circumstances but especially in the following ones: when groups are heterogeneous in composition; when alternative decision outcomes differ in potential costs and these costs are large; when grouping benefits are marginal; or when groups are close to, or above, optimal size. Since these conditions are common in nature, it is easy to see how mechanisms for shared decision making could have arisen in a wide range of species, including early human ancestors.     

The empirical question of thresholds and mechanisms of mate choice

Summary Theoretical discussions concerning how animals might best sample and select mates have suggested that individuals could base decisions either on a sample of mates (sampled-based decisions) or on a threshold of comparison (threshold-based decisions). Recent theoretical work demonstrates that threshold-based mating decisions generate higher expected fitness than sample-based mating decisions when search costs exist. Empirical results from most unmanipulated systems, however, either conclude that females make sample-based decisions or are inconclusive. A few experimental studies designed to detect mating thresholds purport to demonstrate threshold-based choice but an examination of these studies indicates such conclusions were premature. We believe that few examples of threshold-based choice exist because protocols designed to identify mating thresholds were often inconsistent with models of threshold choice. We suggest that future empirical work strive not to document mating thresholdsper se. Rather, future work might best reveal decision rules by manipulating the distribution of quality among potential mates; such manipulations predict uniquely how females using sample-based and threshold-based decision rules should behave.     

Host discrimination and superparasitism in wild and mass-reared Diachasmimorpha longicaudata (Hym.: Braconidae) females

We compared the oviposition behavior and host discrimination ability of wild and mass-reared Diachasmimorpha longicaudata (Hymenoptera: Braconidae) females parasitizing Anastrepha ludens (Diptera: Tephritidae) larvae. Both kinds of parasitoid females were presented simultaneously with parasitized and non-parasitized larvae in choice tests, and their superparasitism performance was evaluated under a mass-rearing situation. At the time of the test, D. longicaudata had 156 generations under mass-rearing conditions. Our goal was to determine the effect of the mass-rearing process on the foraging decisions of this species. One of the primary findings was the apparent ubiquity of superparasitism by D. longicaudata females. Both types of females showed similar patterns in each of the phases of oviposition behavior evaluated. The only notable differences were among the percentages of transition between behaviors, mainly related to the intensity with which each activity was performed. Under a mass-rearing situation, both strains of females had a similar tendency to increase superparasitism (i.e., number of oviposition scars per puparium and the proportion of superparasitized larvae) over time. The mass-rearing process appears to have induced the selection of more aggressive, fertile and precocious females. Despite these observations, we concluded that the process of adaptation to mass-rearing conditions has not substantially influenced the foraging and ovipositional behaviors in this species.     

On the Assessment of the Performance of Multiple Test Procedures

Based on the concept of the multiple level of significance two criteria for assessing the performance of multiple tests are proposed: The simultaneous power is defined as the probability of rejecting all false null hypotheses. The probability of a correct decision is defined as the probability of correctly rejecting all false null hypotheses and accepting all true ones. Both criteria are discussed for nonstagewise and stagewise procedures in case of independent test statistics. For the example of 5 independently and normally distributed test statistics the values of the two criteria are calcutated under reasonably simple alternatives.     

State-dependent ideal free distributions

Summary The standard ideal free distribution (IFD) states how animals should distribute themselves at a stable competitive equilibrium. The equilibrium is stable because no animal can increase its fitness by changing its location. In applying the IFD to choice between patches of food, fitness has been identified with the net rate of energetic gain. In this paper we assess fitness in terms of survival during a non-reproductive period, where the animal may die as a result of starvation or predation. We find the IFD when there is a large population that can distribute itself between two patches of food. The IFD in this case is state-dependent, so that an animal's choice of patch depends on its energy reserves. Animals switch between patches as their reserves change and so the resulting IFD is a dynamic equilibrium. We look at two cases. In one there is no predation and the patches differ in their variability. In the other, patches differ in their predation risk. In contrast to previous IFDs, it is not necessarily true that anything is equalized over the two patches.     

Effects of resource distribution, patch spacing, and preharvest information on foraging decisions of northern bobwhites

We investigated patch assessment by northern bobwhites (Collinusvirginianus) in an experimental arena where the distributionof resources in patches, preharvest information about thesepatches, and spacing of patches varied. We found that preharvestinformation about patch quality and a bimodal distribution ofpatch rewards allowed birds to selectively exploit patches highin resources. In contrast, uniform distribution of patch qualitiesand lack of preharvest information caused birds to forage nonselectivelyamong patches. Birds distinguished among patches of differentquality when these patches were spaced 13 m apart, but failedto react to patch quality differences when patches were 0 or3 m apart We also found a strong effect of the level of patchdepletion on foraging decisions: as resources in die arena becamescarce, birds increasingly foraged selectively in die most profitablepatches. Foraging decisions of bobwhites are biased by die waythey experience and memorize a spatially and temporally variableenvironment. The relative cost of this cognitive bias (i.e.,lost opportunity) is nonlinearty related to die mean resourcedensity in die environment and to die difference between thismean density and die resource density in die exploited patch.Cognitive bias should be considered when evaluating patch assessmentcapabilities of foragers in complex environments.     

Decision to superparasitize based on larval survival: competition between aphid parasitoids Aphidius ervi and Aphidius smithi

Oviposition by a parasitoid wasp in an already parasitized host (= superparasitism) may result in larval competition and the loss of offspring. Consequently, in solitary species, the decision to superparasitize should be based on the probability of offspring survival. Females of Aphidius ervi Haliday and A. smithi Sharma & Subba Rao (Hymenoptera: Aphidiidae), two parasitoids of the pea aphid, discriminated between conspecific-and heterospecific-parasitized hosts. Both species showed partial preference for aphids previously attacked by A. smithi, a result predicted from the fact that A. ervi is superior to A. smithi in larval competition under most conditions. Females of A. smithi selectively attacked conspecific-parasitized pea aphids when given a choice between these and self-parasitized hosts. Results indicated that females of both species responded to an external pheromone-like marker to discriminate between selfconspecific-and heterospecific-parasitized aphids. In addition, A. smithi may use internal cues to recognize, and avoid oviposition in, aphids previously parasitized by A. ervi.

---

Résumé L'oviposition par une guêpe parasite dans un hôte qui a déjà été parasité (= superparasitisme) pourrait conduire à une compétition entre larves et à une perte de progéniture. Par conséquent, dans les espèces solitaires, la décision de superparasiter devrait être basée sur la probabilité de survie de la progéniture. Les femelles de Aphidius ervi Haliday et de A. smithi Sharma & Subba Rao (Hymenoptera: Aphidiidae), deux parasites du puceron du pois, ont discriminé entre les hôtes parasités par des individus de la même espèce et ceux parasités par des individus d'une espèce différente. Les deux espèces de parasite ont montré une préférence partielle pour les pucerons préalablement parasités par A. smithi, résultat qui était prévisible du fait que, dans la majorité des cas, A. ervi est supérieur à A. smithi dans la compétition entre larves. Les femelles de A. smithi ont sélectivement attaqué les pucerons parasités par un individu de la même espèce lorsqu'il leur était donné de choisir parmi ceux-ci et ceux parasités par les même individu. Les résultats indiquaient que les femelles des deux espèces répondaient à une sorte de phéromone externe pour distinguer les pucerons parasités par le même individu de ceux parasités par un individu de la même espèce et ceux parasités d'une autre espèce. En plus, A. smithi pourrait utiliser des signaux internes pour reconnaître et éviter l'oviposition dans les pucerons préalablement parasités par A. ervi.

     

Comparative Risk Assessment Methods and Their Applicability to Dredged Material Management Decision-Making

This article reviews the status of comparative risk assessment within the context of environmental decision-making; evaluates its potential application as a decision-making framework for selecting alternative technologies for dredged material management; and makes recommendations for implementing such a framework. One of the most important points from this review for decision-making is that comparative risk assessment, however conducted, is an inherently subjective, value-laden process. There is some objection to this lack of total scientific objectivity (“hard version” of comparative risk assessment). However, the “hard versions” provide little help in suggesting a method that surmounts the psychology of choice in decision-making schemes. The application of comparative risk assessment in the decision-making process at dredged material management facilities will have an element of value and professional judgment in the process. The literature suggests that the best way to incorporate this subjectivity and still maintain a defensible comparative framework is to develop a method that is logically consistent and allows for uncertainty by comparing risks on the basis of more than one set of criteria, more than one set of categories, and more than one set of experts. It should incorporate a probabilistic approach where necessary and possible, based on management goals.