1,721,093 research outputs found
Intrinsic Lévy behaviour in organisms – searching for a mechanism: Comment on “Liberating Lévy walk research from the shackles of optimal foraging” by A.M. Reynolds
Full text linkThe seminal papers by Viswanathan and colleagues in the late 1990s [1] and [2] proposed not only that scale-free, superdiffusive Lévy walks can describe the free-ranging movement patterns observed in animals such as the albatross [1], but that the Lévy walk was optimal for searching for sparsely and randomly distributed resource targets [2]. This distinct advantage, now shown to be present over a much broader set of conditions than originally theorised [3], implied that the Lévy walk is a search strategy that should be found very widely in organisms [4]. In the years since there have been several influential empirical studies showing that Lévy walks can indeed be detected in the movement patterns of a very broad range of taxa, from jellyfish, insects, fish, reptiles, seabirds, humans [5], [6], [7], [8], [9] and [10], and even in the fossilised trails of extinct invertebrates [11]. The broad optimality and apparent deep evolutionary origin of movement (search) patterns that are well approximated by Lévy walks led to the development of the Lévy flight foraging (LFF) hypothesis [12], which states that “since Lévy flights and walks can optimize search efficiencies, therefore natural selection should have led to adaptations for Lévy flight foraging”
Optimal foraging strategies: Lévy walks balance searching and patch exploitation under a very broad range of conditions
No full textWhile evidence for optimal random search patterns, known as Lévy walks, in empirical movement data is mounting for a growing list of taxa spanning motile cells to humans, there is still much debate concerning the theoretical generality of Lévy walk optimisation. Here, using a new and robust simulation environment, we investigate in the most detailed study to date (24×106 simulations) the foraging and search efficiencies of 2-D Lévy walks with a range of exponents, target resource distributions and several competing models. We find strong and comprehensive support for the predictions of the Lévy flight foraging hypothesis and in particular for the optimality of inverse square distributions of move step-lengths across a much broader range of resource densities and distributions than previously realised. Further support for the evolutionary advantage of Lévy walk movement patterns is provided by an investigation into the ‘feast and famine’ effect, with Lévy foragers in heterogeneous environments experiencing fewer long ‘famines’ than other types of searchers. Therefore overall, optimal Lévy foraging results in more predictable resources in unpredictable environments
Trade in mislabeled endangered sharks
Full text linkThe Conference of the Parties (CoP) of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), the global treaty that regulates wildlife trade, will meet in Sri Lanka later this year (1). Among the species to be proposed for Appendix II listing, as in previous CoPs, are globally endangered pelagic sharks, this time the shortfin (Isurus oxyrinchus) and longfin (I. paucus) makos (2). However, because species such as
sharks are often mislabeled (3, 4), the current CITES monitoring requirements (5) are not sufficient protection. In addition to listing these sharks on Appendix II, CITES signatory nations must invest in comprehensive genetic testing to ensure that listed species are not
disguised as legally traded products
Are critically endangered fish back on the menu? Analysis of U.K. fisheries data suggest post-ban landings of prohibited skates in European waters
Full text linkSkates (Rajidae) have been commercially exploited in Europe for hundreds of years with some species’ abundances declining dramatically during the twentieth century. In 2009 it became “prohibited for EU vessels to target, retain, tranship or land” certain species in some ICES areas, including the critically endangered common skate and the endangered white skate. To examine compliance with skate bans the official UK landings data for 2011–2014 were analysed. Surprisingly, it was found that after the ban prohibited species were still reported landed in UK ports, including 9.6 t of common skate during 2011–2014. The majority of reported landings of common and white skate were from northern UK waters and landed into northern UK ports. Although past landings could not be validated as being actual prohibited species, the landings’ patterns found reflect known abundance distributions that suggest actual landings were made, rather than sporadic occurrence across ports that would be evident if landings were solely due to systematic misidentification or data entry errors. Nevertheless, misreporting and data entry errors could not be discounted as factors contributing to the recorded landings of prohibited species. These findings raise questions about the efficacy of current systems to police skate landings to ensure prohibited species remain protected. By identifying UK ports with the highest apparent landings of prohibited species and those still landing species grouped as'skates and rays’, these results may aid authorities in allocating limited resources more effectively to reduce landings, misreporting and data errors of prohibited species, and increase species-specific landing compliance
Ontogenetic trends in resource partitioning and trophic geography of sympatric skates (Rajidae) inferred from stable isotope composition across eye lenses
No full textResource partitioning is expected in sympatric assemblages of predators as a mechanism that reduces competition between individuals of different species or age classes, which in turn can affect population and community interactions as well as resource distribution and availability. However, for species such as benthic skates (Rajidae), the juveniles of which are cryptic and not easily sampled by traditional survey methods, there is a knowledge gap concerning the spatial and trophic ecology during early life stages. The eye lenses of vertebrates grow over their lifetime providing a chronological biochemical record that can be used to infer differences in diet and/or foraging location (trophic geography) throughout the ontogeny of the animal. For the first time, eye lenses of 4 sympatric Rajidae species from the northeast Atlantic were successfully used to recover stable isotope life histories for individual skates. Isotopic separation among species and across life stages within species suggests that habitat partitioning and differences in trophic ecology are present throughout ontogeny. Isotopic data imply that adults are separated from juveniles both spatially and in terms of their diet and the 4 species appear to partition resources more than expected based on previous studies.</p
The spatial ecology of Rajidae from mark-recapture tagging and its implications for assessing fishery interactions and efficacy of Marine Protected Areas
No full textOften the ecology of a commercially fished species and the behaviour of the fishers are inextricably linked. An understanding of both species ecology and fisher behaviour are therefore fundamental for effective fisheries management. In Europe, Rajidae are commercially fished species that are vulnerable to overfishing, have historically been grouped in landings data and declines have been reported to the point of local extinction in some species. Management of these species is therefore important, however an understanding of species ecology and the way they interact with the fishery is lacking. Here we investigate how the differing ecology of four species affects interactions with the fishery by considering gear types, Marine Protected Areas, location of capture and geographic displacements. Our results demonstrate that the four species interacted differently with the fishery, for example Raja clavata were more commonly captured by static nets (69 % of recaptures) and Raja brachyura more commonly by trawlers (77 %). There were clear differences in the location of capture, depths and displacements of the four species resulting in differing interactions with existing management in the form of Marine Protected Areas. For example 53 % of R. clavata recaptures were within the boundaries of an MPA compared to 18 % for R. brachyura. These results provide important differences among species that are generally grouped by current management, emphasising the need for further species specific research to ensure effective management
Shark personalities? Repeatability of social network traits in a widely distributed predatory fish
Full text linkInterest in animal personalities has generated a burgeoning literature on repeatability in individual traits such as boldness or exploration through time or across different contexts. Yet, repeatability can be influenced by the interactive social strategies of individuals, for example, consistent inter-individual variation in aggression is well documented. Previous work has largely focused on the social aspects of repeatability in animal behaviour by testing individuals in dyadic pairings. Under natural conditions, individuals interact in a heterogeneous polyadic network. However, the extent to which there is repeatability of social traits at this higher order network level remains unknown. Here, we provide the first empirical evidence of consistent and repeatable animal social networks. Using a model species of shark, a taxonomic group in which repeatability in behaviour has yet to be described, we repeatedly quantified the social networks of ten independent shark groups across different habitats, testing repeatability in individual network position under changing environments. To understand better the mechanisms behind repeatable social behaviour, we also explored the coupling between individual preferences for specific group sizes and social network position. We quantify repeatability in sharks by demonstrating that despite changes in aggregation measured at the group level, the social network position of individuals is consistent across treatments. Group size preferences were found to influence the social network position of individuals in small groups but less so for larger groups suggesting network structure, and thus, repeatability was driven by social preference over aggregation tendency
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