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- Nilsson, Jan-Åke
(författare)
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Energetic constraints on hatching asynchrony
- 1993
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 141:1, s. 158-166
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Tidskriftsartikel (refereegranskat)abstract
- At least nine hypotheses have been advanced to account for why many passerine species hatch their clutches asynchronously: 1) The brood reduction hypothesis; 2) The peak load reduction hypothesis; 3) The sibling rivalry reduction hypothesis; 4) The hurry-up hypothesis; 5) The egg viability hypothesis; 6) The sexual conflict hypothesis; 7) The equal investment hypothesis; 8) The nest failure hypothesis; 9) The adult survival hypothesis; This study measured the effect of experimentally increased food availability on the incubation pattern during egg laying, predicting that the degree of hatching asynchrony (measured by onset of incubation, hatching spread, and variation in the size of nestlings) would increase with increased food levels, because of the costs of hatching asynchrony, irrepective of possible benefits, are alleviated by the extra food. However, the hypothesized benefits also may be influenced by extra food. Hypotheses 1-3 are adaptations to varying or low food resource levels during the nestling phase, thus in contrast to the experimental situation. According to these three hypotheses, both benefits and costs will decrease with an increase in food availability. The benefits predicted by hypotheses 4-8 are unrelated to food level. Thus, following experimental provisioning of food, costs will decrease whereas benefits will remain unaltered, which will lead to increased levels of hatching asynchrony. The last hypothesis, 9, predicts no influence of food, on either costs or benefits. -from Author
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- PART, T, et al.
(författare)
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TERMINAL INVESTMENT AND A SEXUAL CONFLICT IN THE COLLARED FLYCATCHER (FICEDULA-ALBICOLLIS)
- 1992
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Ingår i: American Naturalist. - : University of Chicago Press. - 0003-0147 .- 1537-5323. ; 140:5, s. 868-882
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Tidskriftsartikel (refereegranskat)abstract
- When the expectation of future reproduction is reduced by senescence, life-history theory predicts that reproductive effort will increase with increasing age. This idea was examined in the collared flycatcher by estimating whether reproductive costs increase with female age, comparing feeding rates and weight losses of old, "senescent" females (i.e., greater-than-or-equal-to 5 yr old) and middle-aged females (2-3 yr old) with the same breeding phenology and the same brood size, and testing whether feeding rate was correlated with daily energy expenditure and with weight loss of females during the nestling period. There was a negative relationship between fledgling production and subsequent survival among old females (greater-than-or-equal-to 5 yr old), but not among younger age classes, which suggests that reproductive effort increases with age. Also, old females fed their nestlings more often and lost more weight during the nestling period than did middle-aged females. Observed feeding rates were positively correlated with daily energy expenditure and weight loss. Since there was no evidence that individuals that survived to old ages were better at all ages, the results strongly suggest that old collared flycatcher females increase their reproductive effort at the cost of a decreased probability of surviving to the next year. However, the payoff of the increased reproductive effort of old females seemed to be small. We suggest that this is a consequence of a conflict between the sexes over the division of work, because old females generally are mated to younger males that probably have better future prospects. Data on male feeding rates in relation to female feeding rates support this idea.
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- von Schantz, Torbjörn, et al.
(författare)
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Intersexual selection and reproductive success in the pheasant Phasianus colchicus
- 1994
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Ingår i: American Naturalist. - 0003-0147. ; 144:3, s. 510-527
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Tidskriftsartikel (refereegranskat)abstract
- Some recent sexual selection models predict that female choice in species without paternal care may function to discriminate among males in order to pass ''good genes'' to offspring. Data quantifying the relationship between female mate choice and reproductive success are scarce. In a Swedish population of pheasants females prefer to mate with long-spurred males. Male viability also correlates with male spur length. We used DNA fingerprinting to measure individual pheasants' reproductive success in terms of both hatchlings and surviving offspring. The data show that long-spurred males sired more hatchlings and surviving offspring and also that the females' production of surviving offspring correlated with their mate's spur length. The analyses also indicate that offspring of females who mated with long-spurred males experienced an increased survival rate.
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