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31.
32.
The relationship between ecological segregation and sexual body size dimorphism in large herbivores 总被引:4,自引:0,他引:4
A. Mysterud 《Oecologia》2000,124(1):40-54
Ecological segregation (sexual differences in diet or habitat use) in large herbivores has been intimately linked to sexual
body size dimorphism, and may affect both performance and survival of the sexes. However, no one has tested comparatively
whether segregation occurs at a higher frequency among more dimorphic species. To test this comparatively, data on sex-specific
diet, habitat use and body size of 40 species of large herbivores were extracted from the literature. The frequency of ecological
segregation was higher among more dimorphic herbivores; however, this was only significant for browsers. This provides the
first evidence that segregation is more common among more dimorphic species. The comparative evidence supported the nutritional-needs
hypothesis over the incisor breadth hypothesis, as there was no difference in frequency of segregation between seasons with
high and low resource levels, and since segregation was also evident among browsers. Whether the absence of a correlation
between ecological segregation and level of sexual body size dimorphism for intermediate feeders and grazers is due to biological
differences relative to browsers or to the fact that the monomorphic species included in the analysis were all browsers is
discussed.
Received: 18 August 1999 / Accepted: 31 January 2000 相似文献
33.
J. MOYA‐LARAÑO D. VINKOVIĆ C. M. ALLARD M. W. FOELLMER 《Journal of evolutionary biology》2009,22(5):954-963
Several hypotheses have been put forward to explain the evolution of extreme sexual size dimorphism (SSD). Among them, the gravity hypothesis (GH) explains that extreme SSD has evolved in spiders because smaller males have a mating or survival advantage by climbing faster. However, few studies have supported this hypothesis thus far. Using a wide span of spider body sizes, we show that there is an optimal body size (7.4 mm) for climbing and that extreme SSD evolves only in spiders that: (1) live in high‐habitat patches and (2) in which females are larger than the optimal size. We report that the evidence for the GH across studies depends on whether the body size of individuals expands beyond the optimal climbing size. We also present an ad hoc biomechanical model that shows how the higher stride frequency of small animals predicts an optimal body size for climbing. 相似文献
34.
Claude Courties Roland Perasso Marie-Josèphe Chrétiennot-Dinet Manolo Gouy Laure Guillou Marc Troussellier 《Journal of phycology》1998,34(5):844-849
Ostreococcus tauri Courties et Chrétiennot-Dinet is the smallest described autotrophic eukaryote dominating the phytoplanktonic assemblage of the marine Mediterranean Thau lagoon (France). Its taxonomic position was partly elucidated from ultrastructure and high-pressure liquid chromatography (HLPC) pigment analysis. The sequence analysis of the 18S rDNA gene of O. tauri measured here is available in EMBL Nucleotide Sequence Database (accession number: Y15814) and allowed to clarify its phylogenetic position. O. tauri belongs to the Prasinophyceae and appears very close to Mantoniella, a typical scaly Prasinophyceae, morphologically very different from the naked and coccoid Ostreococcus. An electrophoretic analysis of O. tauri shows that the nucleus contains 10.20 mbp. This small genome, fragmented into 14 chromosomes ranging in size from 300 to 1500 kbp, confirms the minimalist characteristics of Ostreococcus tauri. 相似文献
35.
Mayumi YOSHIMURA 《Entomological Science》2012,15(2):145-154
Natural and human‐made disasters such as floods and logging occur in and around rivers. Stream‐dwelling aquatic insects respond to these disturbances in various ways. Primary consumers among them rely greatly on algae and leaf litter from riparian vegetation as food. Therefore, once a disturbance such as a flood has occurred, insects may find it difficult to find food in a stream, and the aquatic insect assemblage can be impacted greatly as a result. Disturbances in riparian areas also increase fine sediment loads into streams, damaging habitat and altering the aquatic insect assemblage. Deforestation impacts not only terrestrial but also aquatic animals. In this review paper, aquatic insect assemblages are assessed according to alterations in land use in and around streams. Following this paper, it is expected that clarification of aquatic insect fauna and their life cycles will progress and that the distribution and habitat use of aquatic insects will be afforded greater attention in forest management. 相似文献
36.
The allometric relationships between canine base area, first molar and summed molar crown area, and the glabella–opisthocranion distance, and the direct allometric relationships between canine and molar size have been established in five primate taxa. Separate sex and combined sex ‘intraspecific’, and ‘interspecific’ regression and ‘best fit’ allometry coefficients were computed. This analysis showed that for any increase in glabella–opisthocranion length, the rate of increase in canine size exceeds the rate of increase in molar area, and ‘best fit’ solutions indicate that canine base area is positively allometric when related directly to molar crown area. These results were compared with data available for the ‘gracile’ australopithecine, A. africanus, and two ‘robust’ australopithecine taxa, A. boisei and A. robustus. The differences in canine and molar size which occur between the ‘gracile’ taxon and the two ‘robust’ taxa do not correspond to any of the trends in the comparative allometric models. Data on glabella–opisthocranion length for the fossils, meagre though they are, show that while the proportional increase in molar crown area between the taxa corresponds to comparative allometry models, the reduced canine size in the ‘robust’ taxa is against comparative allometric trends. These results indicate that, at least in terms of canine/molar proportions, the differences between the ‘gracile’ and ‘robust’ australopithecines are not merely allometric and may indicate significant dietary or behavioural differences. 相似文献
37.
F. C. Neat 《Journal of fish biology》1998,53(4):890-892
In Tilapia zillii , the outcome of fights is closely related to difference in testis weight between opponents rather than differences in body weight. Testes size was predictable statistically on the basis of the size of the mouth in relation to body size, suggesting that among other functions mouth morphology may have evolved to facilitate assessment during fighting. 相似文献
38.
The survival of primates in moderately disturbed forests is determined by a complex of variables. Correlation analyses suggest
that ecological features of a species may confer a basal survival ability but that details of the form of disturbance may
be crucially important. Correlation analyses reveal that body size alone is a poor predictor of primate response to moderate
forest disturbance. However, when the effects of diet variables are held constant, body size more strongly correlates with
survival ability (smaller species surviving better). Degree of frugivory shows a significant negative correlation with survival
ability at both univariate and multivariate levels of analysis. In contrast, dietetic diversity is not correlated with survival
ability at either level of analysis. Together, body size and percentage frugivory explain 44% of the variation in species’
responses to moderate habitat disturbance. Idiosyncratic responses of species can usually be traced to specific features of
the changing environment, such as selective elimination of important food sources and, conversely, the presence of increased
densities of particular food sources arising from the disturbance. 相似文献
39.
G. Pellegrino D. Caimi M. E. Noce A. Musacchio 《Plant Systematics and Evolution》2005,251(2-4):119-129
The rewardless orchid Dactylorhiza sambucina shows a stable flower colour polymorphism, with both yellow- and red-flowered morphs growing sympatrically. Pollination biology and breeding system were investigated to examine the effects of density of plants, colour polymorphism, inflorescence dimension, and flower position within inflorescence on male and female reproductive success in three natural populations of D. sambucina. There were significant differences among sites in the number of pollinia removed and in fruit set per inflorescence. Number of removed pollinia and capsule production in D. sambucina were independent from flower and inflorescence size or flower position. As a whole, the red morphs showed the highest number of capsules produced, while the yellow morphs had the greatest male success. The relative male and female reproductive success were independent from plant density but were significantly correlated with the yellow morph frequency at the population level. Overall, our findings show that the contribution to the total reproductive success deriving from the two colour morphs does not conform with the predictions of negative frequency-dependent selection. 相似文献
40.
Summary Maximum penetrometer pressure was measured on artificial soil aggregates of finite size (2–29 mm) using blunt probes (total
cone angle 60°) driven at 3 mm min−1. Maximum penetrometer pressure increased asymptotically with increase in dimensionless aggregate radius,b/a, wherea andb are the probe and aggregate radii, respectively. A theory was developed for penetration of blunt probes into soil aggregates
of finite size. The theory assumed that plastic failure occurs out to a radius,R, and that beyond this only elastic straining occurs. This theory can be applied to estimate the radial and tangential stresses
adjacent to a blunt probe. The estimated radial and tangential stresses increased with increase in dimensionless aggregate
radius,b/a. The radius of the plastic front,R, around the probe is predicted to increase with increased aggregate size. The results also demonstrate the effect of soil
shear cohesion and internal friction angle onR. The results are discussed with reference to root penetration. 相似文献