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Search Results: 1 - 10 of 6717 matches for " Tom Tregenza "
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Spatial and Temporal Habitat Use by GPS Collared Male Cheetahs in Modified Bushland Habitat  [PDF]
Matti Nghikembua, Jacob Harris, Tom Tregenza, Laurie Marker
Open Journal of Forestry (OJF) , 2016, DOI: 10.4236/ojf.2016.64022
Abstract: Cheetahs and other apex predators are threatened by human-wildlife conflict and habitat degradation. Bush encroachment creates one of the biggest forms of habitat change, thus it is important to understand the impact this has on habitat use. We investigated habitat preferences of five male cheetahs in Namibian farmlands degraded by bush encroachment. Cheetahs were tracked using satellite based Global System for Mobile (GSM) collars providing a higher resolution on ranging behavior. We aimed to investigate: 1) habitat characteristics; 2) evidence for habitat selection; 3) temporal activity partitioning; and 4) whether revisits to locations were related to habitat type. There were differences in habitat characteristics, showing that cheetahs were able to utilise different habitats. Fecal pellet counts revealed that warthog, oryx, scrub hare and kudu were most abundant. The cheetahs spent more time in high visibility shrubland, suggesting they selected rewarding patches within predominantly bush-encroached landscapes. The usage in marginal habitat was strikingly influenced by habitat type, with both previously cleared and open vegetated areas showing high proportions in edge use. Individuals exhibited significant temporal activity partitioning, showing peaks between late afternoon and early morning hours. This finding could be key to managing human-wildlife conflict by showing that increased protection such as the use of herders and livestock guarding dogs should be used as mitigation methods to minimize the impact of cheetah specific temporal patterns at all times as defined in this research. Visits to the same locations were not correlated to habitat type; revisits may be dictated by other reasons such as social interaction, prey density or avoidance of other predators. Findings from this study will help build existing knowledge on the effects bush encroachment has on cheetah habitat preference.
Preparing the Perfect Cuttlefish Meal: Complex Prey Handling by Dolphins
Julian Finn,Tom Tregenza,Mark Norman
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0004217
Abstract: Dolphins are well known for their complex social and foraging behaviours. Direct underwater observations of wild dolphin feeding behaviour however are rare. At mass spawning aggregations of giant cuttlefish (Sepia apama) in the Upper Spencer Gulf in South Australia, a wild female Indo-Pacific bottlenose dolphin (Tursiops aduncus) was observed and recorded repeatedly catching, killing and preparing cuttlefish for consumption using a specific and ordered sequence of behaviours. Cuttlefish were herded to a sand substrate, pinned to the seafloor, killed by downward thrust, raised mid-water and beaten by the dolphin with its snout until the ink was released and drained. The deceased cuttlefish was then returned to the seafloor, inverted and forced along the sand substrate in order to strip the thin dorsal layer of skin off the mantle, thus releasing the buoyant calcareous cuttlebone. This stepped behavioural sequence significantly improves prey quality through 1) removal of the ink (with constituent melanin and tyrosine), and 2) the calcareous cuttlebone. Observations of foraging dolphin pods from above-water at this site (including the surfacing of intact clean cuttlebones) suggest that some or all of this prey handling sequence may be used widely by dolphins in the region. Aspects of the unique mass spawning aggregations of giant cuttlefish in this region of South Australia may have contributed to the evolution of this behaviour through both high abundances of spawning and weakened post-spawning cuttlefish in a small area (>10,000 animals on several kilometres of narrow rocky reef), as well as potential long-term and regular visitation by dolphin pods to this site.
Nuptial gifts fail to resolve a sexual conflict in an insect
Nina Wedell, Tom Tregenza, Leigh W Simmons
BMC Evolutionary Biology , 2008, DOI: 10.1186/1471-2148-8-204
Abstract: We show that receiving multiple ejaculates reduces longevity in female R. verticalis, indicating a cost of male derived receptivity-suppressing compounds. Consumption of male nutrient donations does not appear to ameliorate this longevity cost, and there was no effect of nutrient provisioning on female lifetime fecundity.These results indicate that nutrient provisioning does not provide a resolution to sexual conflict over female receptivity in this bushcricket species.The reproductive interests of mates rarely coincide, resulting in sexual conflict over most aspects of reproduction [1,2]. There is frequent conflict over female remating, as males will have to endure sperm competition and reduced fertilization success when females mate again [3]. The risk of sperm competition has promoted a variety of male adaptations, often associated with female costs [4]. Males frequently transfer compounds in the ejaculate that manipulate female reproductive physiology to increase male reproductive success. For example, Drosophila melanogaster males transfer a cocktail of >80 different proteins in the ejaculate that (amongst other things) stimulate oviposition and reduce female receptivity, thereby increasing male fertilization success [5,6]. However, these male-derived molecules have a negative effect on female fitness by reducing lifespan [7]. It has even been suggested that male harm could evolve as a means to manipulate females to increase their terminal investment in immediate reproductive output, due to reduced residual reproductive value, which then results in higher male reproductive success [8,9].Not all compounds transferred to the female at mating have a negative effect on female fitness. Males of several insects transfer nutrients at mating, either in the ejaculate or together with the sperm packet, that increase female reproductive success by enhancing fecundity and/or offspring survival [10-13]. As a consequence, male nutrient donations create an additional conflict
The evolution of body size under environmental gradients in ectotherms: why should Bergmann's rule apply to lizards?
Daniel Pincheira-Donoso, David J Hodgson, Tom Tregenza
BMC Evolutionary Biology , 2008, DOI: 10.1186/1471-2148-8-68
Abstract: Our results fail to support Bergmann's rule in Liolaemus lizards. Non-phylogenetic and phylogenetic analyses showed that none of the studied clades experience increasing body size with increasing latitude and elevation.Most physiological and behavioural processes in ectotherms depend directly upon their body temperature. In cold environments, adaptations to gain heat rapidly are under strong positive selection to allow optimal feeding, mating and predator avoidance. Therefore, evolution of larger body size in colder environments appears to be a disadvantageous thermoregulatory strategy. The repeated lack of support for Bergmann's rule in ectotherms suggests that this model should be recognized as a valid rule exclusively for endotherms.Geographical variation in environmental conditions is a major ecological factor involved in evolutionary diversification [1,2]. Since thermal regimes are particularly sensitive to latitude and altitude, geographical location imposes profound selection on organisms' metabolism, morphology and behaviour [3-5], leading to covariation between phenotypic traits and geographical gradients [5-7]. Body size is known to exhibit substantial variation in relation to thermal differences among habitats [4,8,9]. However, factors other than environmental temperature (e.g. sexual selection, predation) may also impose selection on body size [2,10-16]. As a result, models predicting patterns of evolutionary change in body mass in response to thermal variation are controversial [17-20]. One such example is Bergmann's rule [18], which suggests that species body size increases with increasing latitude and elevation, and hence, with decreasing environmental temperatures [6,21-23].Different hypotheses have attempted to elucidate the causal factors promoting the pattern predicted by Bergmann's rule [18,24-26]. Potential explanations have focused on heat-conservation strategies [4,6,20,27], later maturation to larger body size [28,29], phylogenetic constraint
Premating Reproductive Barriers between Hybridising Cricket Species Differing in Their Degree of Polyandry
Thor Veen,Joseph Faulks,Rolando Rodríguez-Mu?oz,Tom Tregenza
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0019531
Abstract: Understanding speciation hinges on understanding how reproductive barriers arise between incompletely isolated populations. Despite their crucial role in speciation, prezygotic barriers are relatively poorly understood and hard to predict. We use two closely related cricket species, Gryllus bimaculatus and G. campestris, to experimentally investigate premating barriers during three sequential mate choice steps. Furthermore, we experimentally show a significant difference in polyandry levels between the two species and subsequently test the hypothesis that females of the more polyandrous species, G. bimaculatus, will be less discriminating against heterospecific males and hence hybridise more readily. During close-range mating behaviour experiments, males showed relatively weak species discrimination but females discriminated very strongly. In line with our predictions, this discrimination is asymmetric, with the more polyandrous G. bimaculatus mating heterospecifically and G. campestris females never mating heterospecifically. Our study shows clear differences in the strength of reproductive isolation during the mate choice process depending on sex and species, which may have important consequences for the evolution of reproductive barriers.
Does Publication in Top-Tier Journals Affect Reviewer Behavior?
Lonnie W. Aarssen, Christopher J. Lortie, Amber E. Budden, Julia Koricheva, Roosa Leimu, Tom Tregenza
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0006283
Abstract: We show that when ecologists act as reviewers their reported rejection rates recommended for manuscripts increases with their publication frequency in high impact factor journals. Rejection rate however does not relate to reviewer age. These results indicate that the likelihood of getting a paper accepted for publication may depend upon factors in addition to scientific merit. Multiple reviewer selection for a given manuscript therefore should consider not only appropriate expertise, but also reviewers that have variable publication experience with a range of different journals to ensure balanced treatment. Interestingly since age did not relate to rejection rates, more senior scientists are not necessarily more jaded in reviewing practices.
Systematic Variation in Reviewer Practice According to Country and Gender in the Field of Ecology and Evolution
Olyana N. Grod, Amber E. Budden, Tom Tregenza, Julia Koricheva, Roosa Leimu, Lonnie W. Aarssen, Christopher J. Lortie
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0003202
Abstract: The characteristics of referees and the potential subsequent effects on the peer-review process are an important consideration for science since the integrity of the system depends on the appropriate evaluation of merit. In 2006, we conducted an online survey of 1334 ecologists and evolutionary biologists pertaining to the review process. Respondents were from Europe, North America and other regions of the world, with the majority from English first language countries. Women comprised a third of all respondents, consistent with their representation in the scientific academic community. Among respondents we found no correlation between the time typically taken over a review and the reported average rejection rate. On average, Europeans took longer over reviewing a manuscript than North Americans, and females took longer than males, but reviewed fewer manuscripts. Males recommended rejection of manuscripts more frequently than females, regardless of region. Hence, editors and potential authors should consider alternative sets of criteria, to what exists now, when selecting a panel of referees to potentially balance different tendencies by gender or region.
Environmental Conditions during Breeding Modify the Strength of Mass-Dependent Carry-Over Effects in a Migratory Bird
Xavier A. Harrison, David J. Hodgson, Richard Inger, Kendrew Colhoun, Gudmundur A. Gudmundsson, Graham McElwaine, Tom Tregenza, Stuart Bearhop
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0077783
Abstract: In many animals, processes occurring in one season carry over to influence reproductive success and survival in future seasons. The strength of such carry-over effects is unlikely to be uniform across years, yet our understanding of the processes that are capable of modifying their strength remains limited. Here we show that female light-bellied Brent geese with higher body mass prior to spring migration successfully reared more offspring during breeding, but only in years where environmental conditions during breeding were favourable. In years of bad weather during breeding, all birds suffered reduced reproductive output irrespective of pre-migration mass. Our results suggest that the magnitude of reproductive benefits gained by maximising body stores to fuel breeding fluctuates markedly among years in concert with conditions during the breeding season, as does the degree to which carry-over effects are capable of driving variance in reproductive success among individuals. Therefore while carry-over effects have considerable power to drive fitness asymmetries among individuals, our ability to interpret these effects in terms of their implications for population dynamics is dependent on knowledge of fitness determinants occurring in subsequent seasons.?
Interactive Television in Schools: An Australian study of the tensions of educational technology and change
Terry Evans,Elizabeth Stacey,Karen Tregenza
International Review of Research in Open and Distance Learning , 2001,
Abstract: This paper outlines some key issues that arose from several projects that investigated the use of interactive television in schooling. In this paper we draw on these projects, to illustrate and discuss how a (then) new form of distance education – satellite-based, narrowcast ITV – was designated for use in primary (elementary) and secondary (high school) classroom settings, how it was implemented, and how it collapsed as an endeavour. Issues raised by students, teachers, and administrators are related to each to illustrate how ITV slowly declined over several years, despite its usefulness for some and strong support from those involved.
What’s Wrong with Requirements Specification? An Analysis of the Fundamental Failings of Conventional Thinking about Software Requirements, and Some Suggestions for Getting it Right  [PDF]
Tom Gilb
Journal of Software Engineering and Applications (JSEA) , 2010, DOI: 10.4236/jsea.2010.39096
Abstract: We know many of our IT projects fail and disappoint. The poor state of requirements methods and practice is frequently stated as a factor for IT project failure. In this paper, I discuss what I believe is the fundamental cause: we think like programmers, not engineers and managers. We do not concentrate on value delivery, but instead on functions, on use-cases and on code delivery. Further, management is not taking its responsibility to make things better. In this paper, ten practical key principles are proposed, which aim to improve the quality of requirements specification.
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