Publisher Summary The chapter discusses an emerging area of study: that of applying self-organization theory to mobile vertebrate groups composed of many interacting individuals such as bird flocks, ungulate herds, fish schools, and human crowds in an attempt to improve our understanding of underlying organizational principles. Mathematical modeling is becoming increasingly recognized as an important research tool when studying collective behavior. The chapter presents the interaction dynamics among individuals result in the formation, internal structuring, and collective behaviors of vertebrate groups. The chapter explores the distribution of grouping individuals over larger spatial and temporal scales, and discusses how individual behaviors lead to population-level dynamics. Behavioral differences among individuals within a group may have an important internal structuring influence. By using simulation models, it can be shown how individuals can modify their positions relative to other group members without necessitating information about their current position within the group. In considering self-organization within vertebrate groups it is evident that the organization at one level, for example, that of the group relates to that at higher levels. For example, self-sorting processes that lead to internal structuring within groups also result in population-level patterns when such groups fragment, thus affecting the probability that an individual will be in a group of a given size and composition at any moment in time. These population properties then feed back to the individual interactions by changing the probability of encounters among different members of a population. The chapter concludes that to understand collective behaviors fully, these properties cannot necessarily be considered in isolation.

Self-Organization and Collective Behavior in Vertebrates

Signalling through dopamine D2 receptors governs physiological functions related to locomotion, hormone production and drug abuse1,2,3,4,5,6,7. D2 receptors are also known targets of antipsychotic drugs that are used to treat neuropsychiatric disorders such as schizophrenia8. By a mechanism of alternative splicing, the D2 receptor gene encodes two molecularly distinct isoforms9, D2S and D2L, previously thought to have the same function. Here we show that these receptors have distinct functions in vivo; D2L acts mainly at postsynaptic sites and D2S serves presynaptic autoreceptor functions. The cataleptic effects of the widely used antipsychotic haloperidol1 are absent in D2L-deficient mice. This suggests that D2L is targeted by haloperidol, with implications for treatment of neuropsychiatric disorders. The absence of D2L reveals that D2S inhibits D1 receptor-mediated functions, uncovering a circuit of signalling interference between dopamine receptors.

Distinct functions of the two isoforms of dopamine D2 receptors

A growing body of work suggests that breeding birds have a significant capacity to assess and respond, over ecological time, to changes in the risk of predation to both themselves and their eggs or nestlings. This review investigates the nature of this flexibility in the face of predation from both behavioural and reproductive perspectives, and also explores several directions for future research. Most available work addresses different aspects of nest predation. A substantial change in breeding location is perhaps the best documented response to nest predation, but such changes are not always observed and not necessarily the best strategy. Changes in nesting microhabitat (to more concealed locations) following predation are known to occur. Surprisingly little work addresses the proactive avoidance of areas with many nest predators, but such avoidance is probably widespread. Individual birds could conceivably adopt anti-predator strategies based on the nest predators actually present in an area, but such effects have yet to be demonstrated. In fact, the ways in which birds assess the risk of nest predation is unclear. Nest defence in birds has historically received much attention, but little is known about how it interacts with other aspects of decision-making by parents. Other studies concentrate on predation risk to adults. Some findings suggest that risk to adults themselves influences territory location, especially relative to raptor nests. An almost completely unexplored area concerns the sorts of social protection from predators that might exist during the breeding season. Flocking typical of the non-breeding season appears unusual while breeding, but a mated pair may sometimes act as a "flock of two". Opportunistic heterospecific sociality may exist, with heterospecific protector species associations more prevalent than currently appreciated. The dynamics of singing during the breeding season may also respond to variation in predation risk, but empirical research on this subject is limited. Furthermore, a few theoretical and empirical studies suggest that changes in predation risk also influence the behaviour of lekking males. The major influence of predators on avian life histories is undoubtedly expressed at a broad phylogenetic scale, but several studies hint at much flexibility on an ecological time scale. Some species may forgo breeding completely if the risk of nest predation is too high, and a few studies document smaller clutch sizes in response to an increase in nest predation. Recent evidence suggests that a female may produce smaller eggs rather than smaller clutches following an increase in nest predation risk. Such an increase may also influence decisions about intraspecific brood parasitism. There are no clear examples of changes in clutch/egg size with changes in risk experienced by adults, but parental responses to predators have clear consequences for offspring fitness. Changes in risk to adults may also influence body mass changes across the breeding season, although research here is sparse. The topics highlighted herein are all in need more empirical attention, and more experimental field work whenever feasible.

/pdf/predators-and-the-breeding-bird-behavioral-and-reproductive-378jghtgrm.pdf

Predators and the breeding bird: behavioral and reproductive flexibility under the risk of predation

The Visual Ecology of Avian Photoreceptors

Molecular evolution of vertebrate visual pigments.

IN northern Europe, broad four-year oscillations in small rodent and raptor populations are synchronous over hundreds of square kilometers1–6. Crashes in vole populations can induce wide emigration (> 1,000 km) of their predators7 –9, but almost nothing is known about how predators rapidly detect areas of vole abundance. Here we report on laboratory and field experiments on voles (Microtus agrestis) and kestrels (Falco tinnunculus). Voles mark their runaways with urine and faeces, which are visible in ultraviolet light. Wild kestrels brought into captivity were able to detect vole scent marks in ultraviolet light but not in visible light. In the field, kestrels hunted preferentially near experimental nest-boxes where artificial trails were treated with vole urine and faeces. We suggest that kestrels flying over an area can see and use vole scent marks to assess vole numbers. This ability would enable kestrels to 'screen' large areas in a relatively short time. Our results provide a novel explanation for how raptors detect patches of high vole densities without prior knowledge of local food resources.

Erkki Korplmäki

Papers

Attraction of kestrels to vole scent marks visible in ultraviolet light