Humphries, Nicolas E.Schaefer, Kurt M.Fuller, Daniel W.Phillips, Grace E. M....
189-201页
查看更多>>摘要：Rhythmic activity patterns are ubiquitous in animals and in the marine environment a dominant rhythmic activity is the diel vertical migration (DVM) of pelagic organisms, moving or 'migrating' from deep waters during the day to shallower waters at night. While this overall pattern of movement is well understood, the cryptic nature of the marine environment has limited the study of fine-scale movements within each phase. Active pelagic predators, such as tuna, perform consistent, predictable large-scale vertical movements; however, the fine-scale movements nested within these larger movements have not previously been investigated in detail. Further, the prey field densities are known to differ significantly between day and night, presenting an opportunity to study differences in foraging patterns between these two phases. Here, using long-term depth time series recorded from 93 bigeye tuna, Thunnus obesus, with electronic tags (18 003 days of data), fine-scale changes in vertical movement patterns between day and night time phases were investigated in the context of the Levy foraging hypothesis, which predicts a Levy distribution of move steps during foraging when prey is scarce, but an exponential distribution when prey is abundant and searching is not required. During the day, T. obesus were found to exhibit scale-free movements well fitted by a Levy distribution indicating optimized searching for sparsely distributed prey. During night-time hours, however, exponentially distributed scale-dependent move step lengths were found to be dominant, supporting a simple, Brownian, movement pattern sufficient where prey is abundant. This study not only confirms the predictions of the Levy foraging hypothesis but suggests that the identification of Levy patterns in movement data can be a useful indicator of foraging activity in animals that are difficult to observe directly. (C) 2016 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
查看更多>>摘要：Reproductive and agonistic behaviours typically diverge between individuals pursuing alternative reproductive tactics (ARTs). When tactics are fixed for life, evolutionary theory predicts that the relative frequencies of alternative male genotypes are stabilized in a population by negative frequency dependence. This implies that competition is greatest between males pursuing the same tactic. The cichlid fish Lamprologus callipterus exhibits three male ARTs involving fixed and flexible tactics, and an extreme intrasexual size dimorphism determined by Mendelian inheritance. Large nest males defend territories and construct nests of empty snail shells in which females breed. In contrast, dwarf males pursuing a genetically fixed parasitic tactic enter shells surreptitiously during spawning in order to steal fertilizations. Sneaker males using another parasitic tactic, which is plastic and conditional, steal fertilizations opportunistically during spawning by quick intrusions into the nest. The variation in tactic origin and reproductive behaviour and the substantial asymmetry in body size render L. callipterus an ideal model system to study theoretical predictions regarding the types and intensity of contest behaviours among conspecific competitors pursuing ARTs. In an experiment exposing males to competitors using either the same or a different tactic, within-tactic competition was much more intense than between-tactic competition in bourgeois males, as predicted by evolutionary theory. In addition, the level of aggression displayed by bourgeois males against male intruders was apparently triggered by perceived differences in body size. In contrast to bourgeois males, parasitic males showed hardly any aggressive behaviour against other males, indicating that their contests follow the pattern of scramble competition. The conditions characterizing parasitic reproduction apparently select for rapid responsiveness when opportunities arise to fertilize eggs, whereas attacking other males in this situation seems inappropriate. Our results show that males pursuing ARTs diverge in the way they react to reproductive competition, mainly dependent on their overall resource defence strategy. (C) 2016 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
Rankin, Robert W.Mann, JanetSingh, LisaPatterson, Eric M....
215-228页
查看更多>>摘要：Network null models are important to drawing conclusions about individual- and population-(or graph) level metrics. While the null models of binary networks are well studied, recent literature on weighted networks suggests that: (1) many so-called 'weighted metrics' do not actually depend on weights, and (2) many metrics that supposedly measure higher-order social structure actually are highly correlated with individual-level attributes. This is important for behavioural ecology studies where weighted network analyses predominate, but there is no consensus on how null models should be specified. Using real social networks, we developed three null models that address two technical challenges in the networks of social animals: (1) how to specify null models that are suitable for 'proportion-weighted networks' based on indices such as the half-weight index; and (2) how to condition on the degree-and strength-sequence and both. We compared 11 metrics with each other and against null-model expectations for 10 social networks of bottlenose dolphin, Tursiops aduncus, from Shark Bay, Australia. Observed metric values were similar to null-model expectations for some weighted metrics, such as centrality measures, disparity and connectivity, whereas other metrics such as affinity and clustering were informative about dolphin social structure. Because weighted metrics can differ in their sensitivity to the degree-sequence or strength-sequence, conditioning on both is a more reliable and conservative null model than the more common strength-preserving null-model for weighted networks. Other social structure analyses, such as community partitioning by weighted Modularity optimization, were much less sensitive to the underlying null-model. Lastly, in contrast to results in other scientific disciplines, we found that many weighted metrics do not depend trivially on topology; rather, the weight distribution contains important information about dolphin social structure. (C) 2015 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
查看更多>>摘要：In many species, aggressive individuals outcompete their less aggressive conspecifics for resources such as food and access to mates. Nevertheless, variation in aggression is maintained in populations, but the underlying mechanisms are not well understood. Here we tested the hypothesis that aggressive behaviours compromise the antipredator behaviour of prey, which would link aggressive behaviours to a cost of predation. We presented computer-animated images of predators to the cooperatively breeding cichlid fish Neolamprologus pulcher either during territorial contests with a group of territory intruders or when the test fish were alone. We investigated their response latencies and the behaviour directed towards predator images. We found that test fish responded to the predator images significantly later during territorial contests than when they were alone. Moreover, during territorial contests, response latencies of test fish increased with increasing levels of aggression towards conspecifics. Test fish also responded more aggressively to the predator images during territorial contests than when they were alone. During territorial contests, fish that responded later to the predator images were more aggressive towards these images. Our findings suggest that territorial contests compromised the ability of prey to respond quickly to predators. However, we propose that increased aggression towards predators might increase survival chances of prey during predator encounters in nature, and it may thus compensate for costs incurred by delayed predator responses during territorial contests. To test this hypothesis experiments under natural predation regimes that examine the relationship between predation risk, territorial and antipredator aggression are required. (C) 2016 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
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Elsevier