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| 2. |
- Dahl, Jonas, et al.
(författare)
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Against the flow: chemical detection of downstream predators in running waters
- 1998
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Ingår i: Royal Society of London. Proceedings B. Biological Sciences. - : The Royal Society. - 1471-2954. ; 265:1403, s. 1339-1344
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Tidskriftsartikel (refereegranskat)abstract
- In running waters, chemical cues have generally been assumed to always come from upstream locations. Here, we present ¢eld and laboratory evidence that Gammarus pulex can use chemical cues from down- stream predators to adaptively adjust drifting behaviour. In the ¢eld, signi¢cantly fewer Gammarus migrated into stream enclosures where brown trout (Salmo trutta) were present than into control enclo- sures. In a subsequent laboratory experiment, Gammarus actively avoided live trout and trout chemicals placed downstream in an arti¢cial stream, whereas no e¡ects were found in response to control or visual cues.We suggest that the mechanism explaining the ability of Gammarus to detect downstream predators is use of back£ows, which locally transport ¢sh chemicals against the main £ow. Such back£ows are both created by the Gammarus itself and by surrounding substrate heterogeneity. These results profoundly a¡ect the way in which we view the chemical environment of running waters and have important implications for empirical and theoretical work evaluating predator e¡ects in running waters, as they demonstrate that prey immigration rates can depend on downstream predator densities.
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| 4. |
- Ekeberg, Örjan, 1954-, et al.
(författare)
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Simulations of neuromuscular control in lamprey swimming
- 1999
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Ingår i: Philosophical Transactions of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 354:1385, s. 895-902
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Tidskriftsartikel (refereegranskat)abstract
- The neuronal generation of vertebrate locomotion has been extensively studied in the lamprey. Models at different levels of abstraction are being used to describe this system, from abstract nonlinear oscillators to interconnected model neurons comprising multiple compartments and a Hodgkin-Huxley representation of the most relevant ion channels. To study the role of sensory feedback by simulation, it eventually also becomes necessary to incorporate the mechanical movements in the models. By using simplifying models of muscle activation, body mechanics, counteracting water forces, and sensory feedback through stretch receptors and vestibular organs, we have been able to close the feedback loop to enable studies of the interaction between the neuronal and the mechanical systems. The neuromechanical simulations reveal that the currently known network is sufficient for generating a whole repertoire of swimming patterns. Swimming at different speeds and with different wavelengths, together with the performance of lateral turns can all be achieved by simply varying the brainstem input. The neuronal mechanisms behind pitch and roll manoeuvres are less clear. We have put forward a 'crossed-oscillators' hypothesis where partly separate dorsal and ventral circuits are postulated. Neuromechanical simulations of this system show that it is also capable of generating realistic pitch turns and rolls, and that vestibular signals can stabilize the posture during swimming.
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| 5. |
- Ellegren, H, et al.
(författare)
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The genetical history of an isolated population of the endangered grey wolf Canis lupus : A study of nuclear and mitochondrial polymorphisms
- 1996
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Ingår i: Philosophical Transactions of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 351:1348, s. 1661-1669
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Tidskriftsartikel (refereegranskat)abstract
- The grey wolf was thought to have been exterminated in the Scandinavian peninsula when the sudden appearance of a few animals in southern Sweden was reported in 1980. These wolves founded a new Swedish population which currently numbers at least 25 individuals, one of the world's smallest populations of the species. The sudden occurrence of the founder animals caused speculation that these had not appeared by 'natural' means but rather were Swedish zoo animals deliberately released by man. To analyse if this was the case and to elucidate the genetic status bi; this small and isolated population, we assessed nuclear and mitochondrial (mt) genetic variability in wild and captive grey wolves, using microsatellite typing and sequence analysis of the mtDNA D-loop. The new population was found to be monomorphic for a mtDNA haplotype which also was present in the Swedish zoo population. A total of four different mtDNA haplotypes were found among all captive and wild wolves (including two animals from an occasional establishment of a few wolves in northern Sweden in the late 1970s), with a maximum sequence divergence of 3.1 %. Despite the mtDNA congruence, animals from the zoo population could most likely be excluded as founders for the wild population since the latter group of animals displayed several unique microsatellite alleles (i.e. alleles not found in the zoo population). Moreover, a phylogenetic analysis of individual wolves, using microsatellite allele sharing as distance measure, placed all wild animals on a branch separated from that of the captive animals. The average degree of nuclear variability as well as allelic diversity was similar in the wild and the captive populations, respectively, but was lower than that reported for North-American populations of grey wolves. Polymorphism has declined in wild wolves born in recent years suggesting that this small population is currently suffering from a loss of genetic variability due to inbreeding. Inbreeding depression is documented in captive wolves and the long-term survival of the wild Swedish population may therefore depend on immigration of animals from Russia. This study illustrates the usefulness of microsatellites for dissecting close genetic relationships and for addressing the genetic status of individuals.
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| 7. |
- Hansson, Lars-Anders, et al.
(författare)
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Consumption patterns, complexity and enrichment in aquatic food chains
- 1998
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Ingår i: Royal Society of London. Proceedings B. Biological Sciences. - : The Royal Society. - 1471-2954. ; 265:1399, s. 901-906
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Tidskriftsartikel (refereegranskat)abstract
- The interactions between consumers and prey, and their impact on biomass distribution among trophic levels, are central issues in both empirical and theoretical ecology. In a long-term experiment, where all organisms, including the top predator, were allowed to respond to environmental conditions by reproduction, we tested predictions from `prey-dependent' and `ratio-dependent' models. Prey-dependent models made correct predictions only in the presence of strong interactors in simple food chains, but failed to predict patterns in more complex situations. Processes such as omnivory, consumer excretion, and unsuitable prey-size windows (invulnerable prey) increased the complexity and created patterns resembling ratio-dependent consumption. However, whereas the prey-dependent patterns were created by the mechanisms predicted by the model, ratio-dependent patterns were not, suggesting that they may be right for the wrong reason'. We show here that despite the enormous complexity of ecosystems, it is possible to identify and disentangle mechanisms responsible for observed patterns in community structure, as well as in biomass development of organisms ranging in size from bacteria to fish.
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| 8. |
- Hardling, R., et al.
(författare)
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Experimental evidence for low intra-pair cache pilfering rates in European nuthatches
- 1995
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Ingår i: Proceedings of the Royal Society B: Biological Sciences. - : The Royal Society. - 0962-8452. ; 260:1358, s. 127-130
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Tidskriftsartikel (refereegranskat)abstract
- European nuthatches, Sitta europaea, live all year in permanent pair-territories. In winter, hoarded food is an important food source. To measure the rate of cache pilfering within pairs, each member of six pairs was supplied with either white- or dark-shelled sunflower seeds which the birds cached. When each bird had cached some 100-300 seeds, the feeder was removed and the birds were monitored during their normal foraging. For each sunflower seed that the nuthatches retrieved, the colour of the seed and the sex of the retrieving bird were recorded. In all pairs, each member almost exclusively retrieved seeds of the colour it had itself cached, pilfering amounting to less than 5%. As no clear differences in hoarding niches were detected between the sexes, these results suggest that caches were relocated with the aid of memory.
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| 9. |
- Hemborg, Christer, et al.
(författare)
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A sexual conflict in collared flycatchers, Ficedula albicollis : early male moult reduces female fitness
- 1998
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 265:1409, s. 2003-2007
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Tidskriftsartikel (refereegranskat)abstract
- A sexual conflict over levels of parental care occurs in most animals with biparental care, and studies of sexual differences in levels of parental care have usually focused on its intra-annual fitness consequences. We investigated inter-annual fitness consequences of a sexual difference in timing of feather replacement (moult) in collared flycatchers (Ficedula albicollis). In this study, males overlapped reproduction and moult more often than females, they also initiated their moult at an earlier stage of breeding than females. Females mated to males with a moult-breeding overlap had significantly lowered survival chances than females mated with males initiating moult after breeding. Furthermore, females mated with moulting males risked a lowered future fecundity in terms of a delayed start to breeding in the following season. However, early moulting males achieved a similar reproductive success as males initiating moult after breeding. Likewise, male survival probability to the following breeding season did not differ between early and late moulting individuals, nor was there any evidence that males gained or lost in future mating advantages by moulting early. These results show not only that a sexual conflict over timing of moult may operate, but also that it can impose severe fitness consequences, in terms of reduced future fecundity and survival probability, upon the 'losing' sex.
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