Stable isotopic niche predicts fitness of prey in a wolf–deer system

Interindividual variation in niche presents a potentially central object on which natural selection can act. This may have important evolutionary implications because habitat use governs a suite of selective forces encountered by foragers. In a free-living native black-tailed deer, Odocoileus hemionus , population from coastal British Columbia, we used stable isotope analysis to identify individual variation in foraging niche and investigated its relationship to fitness. Using an intragenerational comparison of surviving and nonsurviving O. hemionus over 2 years of predation by wolves, Canis lupus, we detected resource-specific fitness. Individuals with isotopic signatures that suggested they foraged primarily in cedar ( Thuja plicata )-dominated and low-elevation hemlock ( Tsuga heterophylla )-dominated forest stands were more likely to be killed by C. lupus . High-quality forage in T. plicata stands, as indexed by protein content, may be involved in maintaining this foraging phenotype. Moreover, nonsurvivors diverged more than survivors from median isotopic signatures, suggesting selection against foraging specialization. Stable isotope analysis provides a novel opportunity to integrate ecological and selective landscapes in order to identify underlying ecological mechanisms of selection and provide insight into the maintenance of variability.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 125–137.     

Morphological differentiation and resource polymorphism in three sympatric whitefish Coregonus lavaretus(L.) forms in a subarctic lake

Three field‐identified whitefish Coregonus lavaretus forms in Lake Muddusjärvi, Finland, were compared in morphology, diet and prey size. First, these forms were studied with univariate and multivariate analysis to assess morphological divergence at a higher resolution level than in the field. Second, stomach contents were analysed to estimate diet‐overlap among forms. Finally, the relationship between prey size and morphology was examined. The whitefish were assigned to the initial field‐classification with 99·2% and 98·8% accuracy for morphologic and meristic traits, respectively. The small sparsely‐rakered form (SSR) had the shortest rakers and largest gillraker space, followed by the large sparsely‐rakered form (LSR) with intermediate gillraker length and gillraker space, while densely‐rakered whitefish (DR) had the longest rakers and smallest gillraker space. The two sparsely‐rakered whitefish forms (LSR and SSR), consumed mainly benthic macroinvertebrates, while densely‐rakered whitefish (DR), utilized pelagic food items. Average diet‐overlaps between whitefish forms were low in June‐September (Schoener's α = 0·02 − 0·23). Gillraker number and length were negatively correlated to prey length in the diet ( r  = −0·73, and r  = −0·60), while gillraker space was positively correlated with prey length ( r  = 0·81). The fact that these whitefish forms were morphologically and ecologically segregated, and that gillraker traits probably have a functional value in food selection, further suggests that natural selection has been important in structuring life‐history trajectories into divergent niche use.     

Resource partitioning in a guild of aphid species associated with creeping thistle Cirsium arvense

Four aphid species (Aphis fabae cirsiiacanthoidis Scop., Brachycaudus cardui (L.), Capitophorus carduinus Walker and Uroleucon cirsii (L.)) feed on the creeping thistle Cirsium arvense. They utilize different parts of their host plant and at different times. A wide niche is typical of C. carduinus and U. cirsii, whereas A. f. crisiiacanthoidis and B. cardui, show narrower but overlapping niches. Morphological features such as stylet length and body size as well as colony size and density are associated with the choice of feeding site. C. carduinus, the smallest species with the shortest stylets was able to use leaf veins and lamina, while the other species mainly used the stem and peduncles. Within this group, A. f. cirsiiacanthoidis and B. cardui are restricted to the upper part of the stem because of their short stylets, but adult U. cirsii, the species with the longest stylets, can also feed at the base of the stem.

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Räumliche und zeitliche ressourcenaufteilung in der blattlausgilde an der ackerkratzdistel cirsium arvense

Zusammenfassung An der Ackerkratzdistel leben vier Blattlausarten (Aphis fabae cirsiiacanthoidis Scop., Brachycaudus cardui (L.), Capitophorus carduinus Walker und Uroleucon cirsii (L.)), die im Verlauf der Vegetationsperiode verschiedene Strukturen ihrer Wirtspflanze nutzen. Eine breite Nische ist für U. cirsii und C. carduinus typisch, während A. f. cirsiiacanthoidis und B. cardui engere Nischen besitzen, die sich nahezu überlappen. Die Nahrungsplatzwahl wird sowohl durch morphologische Parameter wie Stilettlänge und Körpergewicht als auch durch Koloniegröe und Dispersion innerhalb der Kolonie beeinflut. Die kleinste Art, C. carduinus, die auch das kürzeste Stilett besitzt, ist in der Lage, an Blattadern und auf der Blattspreite zu saugen. Die anderen Arten bevorzugen Stengel, Seitenstengel und Blütenstiele. Innerhalb dieser Gruppe können A. f. cirsiiacanthoidis und C. carduinus wegen ihrer kürzeren Stilette nur am oberen Teil des Stengels saugen, während adulte U. cirsii aufgrund ihrer längeren Stilette auch an der Stengelbasis leben können.

     

Guild structure in solitary spider-hunting wasps (Hymenoptera: Pompilidae) compared with null model predictions

Abstract.

• 1 Three aspects of prey utilization are documented in a guild of spider-hunting pompilid wasps at a Breckland heath site: female phenology, size, and microhabitat utilization.
• 2 Twenty-four species were present at the site, 59% of the British fauna. Ten species individually represented more than 1% of the guild.
• 3 Pompilid abundance peaked in early July and mid-late August. Anoplius viaticus had a different life-history from other common guild members, making its inclusion in the guild questionable.
• 4 Most species represented by large samples occurred in all microhabitats and time intervals, and all species overlapped in size with all other species except A. viaticus. Arachnospila anceps was numerically dominant in all microhabitats and most time intervals.
• 5 Mean pair-wise overlaps in phenology and microhabitat utilization were significantly lower than predicted by null models, consistent with the idea that interspecific competition has been important in determining guild structure.
• 6 Female size is highly correlated with prey size, but the distribution of mean female sizes did not generally differ from null expectations.
• 7 Interpretation of comparisons with null models is problematic, particularly because it is difficult to quantify evolutionary ‘favourability’ of different resource states. Null models are currently of limited use because the patterns expected to result from key processes such as competition are uncertain in multi-dimensional systems.

     

神农架金丝猴的生态学观察

金丝猴(Rhinopithecus roxellanae)仅产于我国,属国家Ⅰ级保护动物,自然分布于四川、陕西、甘肃的部分地区和湖北省神农架自然保护区。1983年以来,笔者对神农架金丝猴生存环境生态习性等作了长期观察研究,结果报道如下。     

Coexistence of Banksia species in southwestern Australia: the role of regional and local processes

Abstract. 60 of the 75 Banksia species are confined to southwestern Australia where five or six species often coexist. We explored the role of regional species richness, niche differentiation, and habitat specialization in structuring banksia assemblages. The diversity of growth forms and categories of seed production and response to fire were assessed in actual assemblages at 40 sites throughout southwestern Australia. Diversity indices at each site were compared with those from null communities assembled on the basis of the abundance and sociability of taxa in regional species pools. The relationship between local and regional species richness suggests that processes at the scale of 100-m² quadrats limit local richness and therefore coexistence. However, there was no consistent evidence that taxa are differentiated by growth form or regeneration strategy. No particular biological profile makes a banksia adept at coexisting with a wide range of other taxa. Habitat specialization is an important factor contributing to lower local richness than would be predicted from niche differentiation of taxa in regional pools. There is recent empirical evidence of several mechanisms whereby the number of coexisting banksias is increased beyond the limits suggested by simple niche theories. Variability in the fire regime also provides a mechanism for maintaining local species richness because different fires favour recruitment of different taxa.     

Responses to recent climatewarming of Pinus sylvestris and Pinus cembra within their montane transition zone in the Swiss Alps

Abstract. Altitudinal and latitudinal distribution limits of trees are mainly controlled by temperature. Therefore climate warming is expected to induce upslope or poleward migrations. In the Swiss Central Alps, summers in the period 1982-1991 were on average 0.8 °C warmer than those of the period 30 yr before. We investigated whether populations of conifers at the montane Pinus sylvestris-Pinus cembra ecocline exhibit demographic trends in response to that warming. We found no evidence for this. Young seedlings of Pinus sylvestris, the species which is expected to expand its range upward in a warmer climate, were virtually absent from all sites, whereas large fractions of Pinus cembra populations were observed in the seedling and juvenile categories even below the present lower distribution limit of adult trees. This suggests that there are no major altitudinal shifts in response to the recent sequence of warmer summers. Germination and seedling survival trials with Pinus sylvestris suggest that temperature per se would not exclude this species even from establishing at the current treeline in the Swiss Central Alps. Similar results were found at the polar treeline. Phytotron tests of seedling survival showed much less drought resistance in Pinus sylvestris than in Pinus cembra which is in contrast to their phytogeographic distributions. Thus, the montane pine ecocline in the Swiss Central Alps seems to be stabilized by species interactions and may not be directly responsive to moderate climatic change, which needs to be taken into account in predictive attempts.