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Size Hierarchies (size + hierarchy)
Selected AbstractsThe Process and Causes of Fledging in a Cavity-Nesting Passerine Bird, the House Wren (Troglodytes aedon)ETHOLOGY, Issue 9 2004L. Scott Johnson Little is known about the process or causes of fledging or nest-leaving in passerine birds because researchers can rarely predict when fledging will occur in a given nest. We used continuous videotaping of nests to both document the process of fledging in the house wren, Troglodytes aedon, a small, cavity-nesting songbird, and test hypotheses as to what might cause fledging to begin. Fledging began any time from 14 to 19 d after hatching commenced. Slower-developing broods fledged later than faster-developing broods. Fledging typically began within 5 h of sunrise and over 80% of all nestlings fledged before noon. All nestlings fledged on the same day at 65% of nests and over two consecutive days in most other nests. We found no evidence that fledging was triggered by changes in parental behaviour. Parental rate of food delivery to nestlings did not decline during a 3-h period leading up to the first fledging, nor was the rate of feeding just prior to the first fledging lower than the rate at the same time the day before. Moreover, parents did not slow the rate of food delivery to nests after part of the brood had fledged. Hatching is asynchronous in our study population which creates a marked age/size hierarchy within broods. At most nests, the first nestling to fledge was the most well-developed nestling in the brood or nearly so (as measured by feather length). This suggests that fledging typically begins when the most well-developed nestlings in the brood reach some threshold size. However, at about one-fifth of nests, the first nestling to fledge was only moderate in size. At these nests, severe competition for food may have caused smaller, less competitive nestlings to fledge first to increase their access to food. We found no strong support for the suggestion that the oldest nestlings delay fledging until their least-developed nestmate reaches some minimum size, although further experimental work on this question is warranted. [source] Reproductive Allocation Patterns in Different Density Populations of Spring WheatJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 2 2008Jing Liu Abstract The effects of increased intraspecific competition on size hierarchies (size inequality) and reproductive allocation were investigated in populations of the annual plant, spring wheat (Triticum aestivum). A series of densities (100, 300, 1 000, 3 000 and 10 000 plants/m2) along a gradient of competition intensity were designed in this experiment. The results showed that average shoot biomass decreased with increased density. Reproductive allocation was negatively correlated to Gini coefficient (R2 = 0.927), which suggested that reproductive allocation is inclined to decrease as size inequality increases. These results suggest that both vegetative and reproductive structures were significantly affected by intensive competition. However, results also indicated that there were different relationships between plant size and reproductive allocation pattern in different densities. In the lowest density population, lacking competition (100 plants/m2), individual reproductive allocation was size independent but, in high density populations (300, 1 000, 3 000 and 10 000 plants/m2), where competition occurred, individual reproductive allocation was size dependent: the small proportion of larger individuals were winners in competition and got higher reproductive allocation (lower marginal reproductive allocation; MRA), and the larger proportion of smaller individuals were suppressed and got lower reproductive allocation (higher MRA). In conclusion, our results support the prediction that elevated intraspecific competition would result in higher levels of size inequality and decreased reproductive allocation (with a negative relationship between them). However, deeper analysis indicated that these frequency- and size-dependent reproductive strategies were not evolutionarily stable strategies. [source] The significance of small herbivores in structuring annual grasslandJOURNAL OF VEGETATION SCIENCE, Issue 2 2007Halton A. Peters Abstract Question: Herbivores can play a fundamental role in regulating the composition and structure of terrestrial plant communities. Relatively inconspicuous but nevertheless ubiquitous gastropods and small mammals are usually considered to influence grassland communities through distinct modes. 1. Do terrestrial gastropods and small mammals, either alone or in combination, influence plant community composition of an intact annual grassland? 2. Do these herbivores influence the plant size structure of the dominant grass Avena? Location: Jasper Ridge Biological Preserve (37°24' N, 122° 13' W, elevation 150 m) in northern California. Methods: Animal exclosures were used to examine the single and combined influences of these herbivores on annual grassland production, community composition, and plant size structure during the growing season of an intact annual grassland. Results: The removal and exclusion of the herbivores increased the prevalence of grasses relative to legumes and non-legume forbs; increased total production of above-ground plant biomass; and increased mean plant size and exacerbated size hierarchies in populations of Avena. The effect of both gastropods and small mammals, alone and in combination, was characterized by temporal oscillations in the relative dominance of grasses in plots with vs. without herbivores. Conclusions: Both groups of herbivores are important controllers of California annual grassland that exert similar influences on production and composition. While other factors appear to determine the absolute number of individuals in this plant community, selective consumption of grasses by gastropods and small mammals partially offsets the competitive advantages associated with their early germination. [source] Hatching asynchrony and growth trade-offs within domesticated and wild zebra finch, Taeniopygia guttata, broodsBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2010MARK C. MAINWARING The Australian zebra finch, Taeniopygia guttata, is a widely used model organism, yet few studies have compared domesticated and wild birds with the aim of examining its relevance as an evolutionary model species. Domestic and wild broods hatch over approximately 4 and 2 days, respectively, which is important given that nestlings can fledge after as little as 12 days, although 16,18 days is common. We aimed to evaluate the extent to which the greater hatching asynchrony in domestic stock may effect reproductive success through greater variance in size hierarchies, variance in within-brood growth rates, and partial brood mortality. Therefore, by simultaneously controlling brood sizes and experimentally manipulating hatching intervals in both domesticated and wild birds, we investigated the consequences of hatching intervals for fledging success and nestling growth patterns, as well as trade-offs. Fledging success was similarly high in domestic and wild broods of either hatching pattern. Nonetheless, between-brood analyses revealed that domestic nestlings had significantly higher masses, larger skeletal characters, and longer wings than their wild counterparts, although wild nestlings had comparable wing lengths at the pre-fledging stage. Moreover, within-brood analyses revealed only negligible differences between domestic and wild nestlings, and larger effects of hatching order and hatching pattern. Therefore, despite significant differences in the hatching intervals, and the ultimate size achieved by nestlings, the domestication process does not appear to have significantly altered nestling growth trade-offs. The present study provides reassuring evidence that studies involving domesticated zebra finches, or other domesticated model organisms, may provide reasonable adaptive explanations in behavioural and evolutionary ecology. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 763,773. [source] Maternal yolk testosterone does not modulate parasite susceptibility or immune function in great tit nestlingsJOURNAL OF ANIMAL ECOLOGY, Issue 4 2005BARBARA TSCHIRREN Summary 1Maternal yolk hormones can enhance the development and phenotypic quality of nestling birds. Nevertheless, within species large differences in yolk androgen concentrations among clutches are observed. This differential allocation of maternal yolk hormones might be explained by a trade-off between beneficial effects of yolk androgens and their associated costs. 2Potential costs include an increased susceptibility to parasites in nestlings exposed to high concentrations of yolk androgens during embryonic development, weaker immune response or increased levels of circulating corticosterone that indirectly reduce immune function. 3In a field study, we manipulated yolk testosterone in great tit (Parus major) eggs and tested the nestling's susceptibility to ectoparasites as measured by the parasites' effect on growth, the cellular immune response, and the levels of circulating corticosterone. 4At the end of the nestling period, nestlings originating from testosterone-injected eggs were heavier than control nestlings. This effect was strongest in nestlings at the end of the size hierarchy, as shown by a significant interaction between hormone treatment and the nestlings' size rank within nests. 5High levels of yolk testosterone promoted growth of the nestling's body mass similarly in parasite-infested and parasite-free nests, and neither affected the levels of plasma corticosterone, nor the nestling's cell-mediated immune response. 6In summary, our results do not show negative short-term effects of high concentrations of yolk testosterone on immune function or parasite susceptibility, but emphasize that maternal investment via deposition of yolk testosterone can promote fitness-related growth and development of nestlings. [source] | ||||||||||