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Existing Hypotheses (existing + hypothesis)
Selected AbstractsFrom small-scale habitat loopholes to decadal cycles: a habitat-based hypothesis explaining fluctuation in pelagic fish populations off PeruFISH AND FISHERIES, Issue 4 2004Arnaud Bertrand Abstract The Peru-Humboldt Current system (HCS) supports the world's largest pelagic fisheries. Among the world's eastern boundary current systems, it is the most exposed to high climatic stress and is directly affected by El Niņo and La Niņa events. In this volatile ecosystem, fish have been led to develop adaptive strategies in space and time. In this paper, we attempt to understand the mechanisms underlying such strategies, focusing on the El Niņo 1997,98 in Peru from which an extensive set of hydrographic, capture and acoustic survey data are available. An integrated analysis of the data is crucial, as each has substantial shortcomings individually; for example, both catch data and acoustic surveys may easily lead to wrong conclusions. Existing hypotheses on anchovy and sardine alternations lead us to a ,habitat-based' synthetic hypothesis. Using our data, an integrated approach evaluated how fish responded to habitat variation, and determined the consequences in terms of fish-population variability. Various factors occurring at a range of different spatio-temporal scales were considered: interdecadal regime (warm ,El Viejo'/cool ,La Vieja' decadal scale); strength and the duration of the El Niņo Southern Oscillation event (interannual scale); population condition before the event (interannual scale); fishing pressure and other predation (annual scale); changes in reproductive behaviour (intra-annual scale); presence of local upwelling (local scale). During El Niņo 1997,98, anchovy was able to exploit a small-scale temporal and spatial ,loophole' inside the general unfavourable conditions. Moreover, sardine did not do better than anchovy during this El Niņo and was not able to take advantage of the ,loophole' opened by this short-term event. Our results question the traditional view that El Niņo is bad for anchovy and good for sardine. [source] Gut content analysis and a new feeding group classification of termitesECOLOGICAL ENTOMOLOGY, Issue 4 2001S. E. Donovan Summary 1. Gut content analysis of termites was undertaken using microscopical techniques. The 46 study species covered the entire range of taxonomic and feeding forms within the Order. 2. Inter-specific gut contents data were analysed using principal components analysis, placing species along a clear humification gradient based on variations in the amount of silica and plant tissue fragments in the gut. 3. Redundancy analysis was used to find morphological correlates of the observed variation in gut contents. A total of 22 morphological characters (out of 45 candidate characters) were correlated significantly with the gut contents. 4. Three of the 22 significantly correlated characters unambiguously defined feeding groups, which were designated groups I to IV in increasing order of humification of the feeding substrate. Group I contains lower termite dead wood and grass-feeders; group II contains Termitidae with a range of feeding habits including dead wood, grass, leaf litter, and micro-epiphytes; group III contains Termitidae feeding in the organic rich upper layers of the soil; group IV contains the true soil-feeders (again all Termitidae), ingesting apparently mineral soil. These groupings were generally supported statistically in a canonical covariance analysis, although group II apparently represents termite species with a rather wide range of feeding habits. 5. Using existing hypotheses of termite phylogenetic relationships, it seems probable that group I feeders are phylogenetically basal, and that the other groupings have arisen independently on a number of occasions. Soil-feeding (i.e. group III and group IV feeding) may have evolved due to the co-option of faecal material as a fungal substrate by Macrotermitinae-like ancestral forms. As a consequence, these forms would have been constrained to build nest structures from soil and would therefore have passed at least some soil through their guts. [source] Fly or die: the role of fat stores in the growth and development of Grey-headed Albatross Diomedea chrysostoma chicksIBIS, Issue 2 2000KEITH REID Chicks of albatrosses, like other Procellariiformes, become independent at a mass similar to their parents but during growth attain a peak mass some 30% or more greater, before losing mass prior to fledging. The current views are that this high peak mass represents chicks storing fat reserves as an energy sink, or as an insurance against periodic food scarcity, or as a Consequence of natural stochastic variation in provisioning rate. We analysed growth and body composition of Grey-headed Albatross Diomedea chrysostoma chicks at Bird Island, South Georgia in 1984 and 1986, two years of very different food availability. In 1984 when overall breeding success was only 28% (the lowest in 20 years and less than halt that in 1986), chicks were significantly smaller in terms of peak mass (by 37%), primary length (by 25%), liver, lung, heart and kidney size (by 18,34%) and fat (by 75,80%) but not significantly different in terms of skeletal (tarsus, culmen, ulna, sternum) or muscle (pectoral, leg) size. Despite these differences, there were some important similarities in the patterns of growth in both years. Up to the attainment of peak mass, most of the growth of organs and of skeletal structures was completed and little fat was deposited. In the remaining part of the chick-rearing period, feather growth and acquisition of fat stores were undertaken. Thus Grey-headed Albatross chicks begin to acquire substantial fat stores only during the later part of the development period; this is contrary to the predictions of any of the existing hypotheses concerning provisioning patterns and the role of fat stores in Procellariiformes. We propose that the deposition of fat in the later stages of chick growth is an adaptation to: (a) ensure against energy demands and/or nutritional stress affecting the quality of flight feathers (many of which are not renewed for up to three years after fledging); and (b) provide an energy reserve for chicks to use in the critical period immediately after independence. [source] What does the stress-gradient hypothesis predict?OIKOS, Issue 10 2010Resolving the discrepancies In recent years the importance of facilitative interactions in ecological communities is increasingly recognized. This phenomenon has been observed repeatedly, particularly in vegetation communities, in a wide range of environmental conditions. The current hypothesis predicts that the role of facilitation becomes increasingly important in conjunction with increasing stress. Several empirical studies, however, failed to detect such patterns, particularly at the extreme ends of the stress gradients. Herein, we present a conceptual model that may resolve discrepancies between expected and observed and provides a more precise framework of the existing hypotheses. By relaxing two common assumptions commonly used by the stress-gradient hypothesis (SGH) we are able to demonstrate that under some circumstances the importance of facilitation may be less at the extreme ends of these gradients. Namely, we first re-emphasize the notion that physiological response is not linear with respect to environmental changes along stress gradients. Second, it is argued that the net outcome of facilitative and competitive interactions is reflected in the fitness of individuals as a product of these two processes, in contrast to the commonly applied assumption of additivity. Accordingly, a synthesis of the concepts of population biology (measures of fitness) and plant physiology (nonlinear responses) with the stress gradient hypothesis while retaining the original simplicity of the SGH model contributes to a better specification of the predictions of the stress-gradient hypothesis and the resolution of observed contradictions. [source] Molecular and morphological supertree of stony corals (Anthozoa: Scleractinia) using matrix representation parsimonyBIOLOGICAL REVIEWS, Issue 4 2005Alexander M. Kerr ABSTRACT The supertree algorithm matrix representation with parsimony was used to combine existing hypotheses of coral relationships and provide the most comprehensive species-level estimate of scleractinian phylogeny, comprised of 353 species (27% of extant species), 141 genera (63%) and 23 families (92%) from all seven suborders. The resulting supertree offers a guide for future studies in coral systematics by highlighting regions of concordance and conflict in existing source phylogenies. It should also prove useful in formal comparative studies of character evolution. Phylogenetic effort within Scleractinia has been taxonomically uneven, with a third of studies focussing on the Acroporidae or its most diverse genera. Sampling has also been geographically non-uniform, as tropical, reef-forming taxa have been considered twice as often as non-reef species. The supertree indicated that source trees concur on numerous aspects of coral relationships, such as the division between robust versus complex corals and the distant relationship between families in Archaeocoeniina. The supertree also supported the existence of a large, taxonomically diverse and monophyletic group of corals with many Atlantic representatives having exsert corallites. Another large, unanticipated clade consisted entirely of solitary deep-water species from three families. Important areas of ambiguity include the relationship of Astrocoeniidae to Pocilloporidae and the relative positions of several, mostly deep-water genera of Caryophylliidae. Conservative grafting of species at the base of congeneric groups with uncontroversial monophyletic status resulted in a more comprehensive, though less resolved tree of 1016 taxa. [source] INSIGHTS INTO NORTH MESOPOTAMIAN ,METALLIC WARE'*ARCHAEOMETRY, Issue 2 2006T. BROEKMANS With the aim of shedding new light on the still poorly understood North Mesopotamian metallic ware, ceramic and soil samples from Tell Beydar (northeastern Syria, third millennium bc) were investigated using a range of analytical techniques, including optical microscopy, SR,XRD and SEM,EDX. The objective of this work was to differentiate calcareous metallic ware from non-calcareous ware without the aid of chemical analyses and to find further validation of the existing hypothesis that the former group is an imitation of the latter. A third group of metallic wares from Tell Beydar is believed to be of non-local, still regional origin. [source] Differentiation among disjunct populations of agamospermous species of Hieracium section Cernua (Asteraceae) in Central European subalpine habitatsBOTANICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2008MICHA, RONIKIER A morphological survey and assessment of genetic diversity using amplified fragment length polymorphism (AFLP) were applied to study the variability of two agamospermous species of Hieracium section Cernua R. Uechtr. characterized by disjunct, subalpine distributions: H. silesiacum (Western Carpathians and Eastern Sudetes) and H. vierhapperi (Western Carpathians and Eastern Alps). Contrasting patterns were revealed. In H. silesiacum, no genetic or morphological differences were found between its remote populations from the Sudetes and the Tatry mountains, suggesting a recent dispersal. In contrast, distinct morphological differentiation of population in the Nízke Tatry mountains was confirmed by high genetic differentiation; the analysis indicated independent origin of this population and gave grounds for taxonomic separation and description of a new species, H. austrotatricum. In H. vierhapperi, genetic differentiation and slight morphological difference (colour of achenes) was observed between disjunct populations from the Carpathians and the Alps. The data suggest long-term isolation of these populations resulting in pronounced independent history. High number of markers monomorphic for all populations supports the existing hypothesis of common sexual ancestors from H. section Cernua involved in the origin of these polyploid taxa. No or only minor morphological differentiation within the taxa indicates high stability of apomictic populations of Hieracium. Š 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158, 93,105. 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