| 1. |
- Lindhe Norberg, Ulla, et al.
(författare)
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Evolutionary divergence of body size and wing and leg structure in relation to foraging mode in Darwin's Galapagos finches
- 2023
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Ingår i: Biological Journal of the Linnean Society. - 0024-4066. ; 140:2, s. 240-60
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Tidskriftsartikel (refereegranskat)abstract
- The wings, legs, and tail in Darwin's finches show many clear adaptations to different types of locomotion used during foraging. We use size scaling to analyse how various characters vary with body mass to clarify dimensional relationships. The selective advantage of a character is judged in terms of energy savings. The wing aspect ratio (4.6-4.9) is very low, so the energy costs for flight are high. Low body mass, low wing loading, and short arm wings in the warbler finch, small tree finch, and small ground finch promote agility and manoeuvrability among vegetation, along with short wings in the warbler finch. Evolution towards a shorter arm wing seems to be favoured in the smaller finch species. Long legs, long toes, and long curved claws are adaptations for climbing/clinging locomotion without tail support (woodpecker finch, small and large tree finches, cactus finch but having short legs). Selection for longer legs seems to act towards a lengthening of the tarsometatarsus. The climbing technique in the woodpecker finch is described. We discuss how the diversification in the beaks relates to the locomotion organs.
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| 2. |
- Andersson, Malte, 1941, et al.
(författare)
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”Minskande befolkning är inte problemet”
- 2020
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Ingår i: Dagens Nyheter. ; :1 augusti, DN-debatt
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Nätverket Population Matters Sweden: En uppmärksammad studie i The Lancet pekar mot en lägre befolkningsökning i världen än tidigare prognoser. Men en miljard människor till är fortfarande långt över vad jorden klarar. Befolkningstrenden måste snarare vända neråt, och det kräver åtgärder för att stärka kvinnors rättigheter världen över.
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| 3. |
- Norberg, Åke, 1939
(författare)
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Test of theory of foraging mode: Goldcrests, Regulus regulus, forage by high-yield, energy-expensive hovering flight when food is abundant but use low-yield, low-cost methods when food is scarce
- 2021
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Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 11:23, s. 16547-16561
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Tidskriftsartikel (refereegranskat)abstract
- Here, I describe foraging behavior of goldcrests, Regulus regulus, based on eight years of field observation in a coniferous forest dominated by Norway spruce Picea abies in southwestern Sweden. The aim was to test predictions from theory on the choice of optimal foraging modes in relation to food availability. Mortality from early November to early March amounts to 70-86% among goldcrests in the resident population, suggesting they are food-limited in winter. Food-limitation manifests itself as a shortage of time for foraging. It promotes the use of foraging methods that minimize the daily foraging time by maximizing the rate of net energy gain. It increases both individual survival and competitiveness. Elimination of competitors by exploitation occurs when an individual is able to support itself, while food density in the habitat is reduced to levels at which others cannot. Theory shows that when food is abundant, high-efficiency energy-expensive search and capture methods give shorter daily foraging times than low-efficiency low-cost methods, whereas the latter gives shorter daily foraging times at food shortages (Norberg 2021). Hovering flight is extremely expensive in energy but results in high foraging efficiency. Hover-foraging should therefore be used when food is abundant. In autumn, there were 85.3 arthropods per kilogram of branch mass, as opposed to 12.9 in spring. The numerical decline of arthropods, their fat metabolism, and size-biased predation by birds reduced the spring density of food for goldcrests to less than 15.1% of the autumn density. Hover-foraging occurred 5.29 times per minute in autumn but only 0.23 times per minute in spring, which is 4.4% of the autumn frequency. Foraging conditions are favorable at midsummer because of long days, high temperatures, and an abundance of arthropod prey. Parent birds that were feeding fledglings gathered food at a high rate and hovered 5.42 times per minute. But adults with no young to feed were not compelled to maximize the rate of net energy gain and only hover-foraged 0.52 times per minute, which is 10% of that of providers. These results are highly consistent from year to year and in qualitative agreement with theory.
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| 4. |
- Norberg, Åke, 1939
(författare)
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To minimize foraging time, use high-efficiency, energy-expensive search and capture methods when food is abundant but low-efficiency, low-cost methods during food shortages
- 2021
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Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 11:23, s. 16537-16546
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Tidskriftsartikel (refereegranskat)abstract
- Based on a mathematical model, I show that the amount of food in the habitat determines which among alternative methods for search of prey, respectively, for pursuit-and-capture give the shortest daily foraging time. The higher the locomotor activity, the higher the rate of energy expenditure and the larger the habitat space a predator can search for prey per time unit. Therefore, I assume that the more efficient a foraging method is, the higher its rate of energy expenditure. Survival selection favors individuals that use foraging methods that cover their energy needs in the shortest possible time. Therefore, I take the optimization criterion to be minimization of the daily foraging time or, equivalently, maximization of the rate of net energy gain. When time is limiting and food is in short supply, as during food bottleneck periods, low-efficiency, low-cost foraging methods give shorter daily foraging times than high-efficiency, energy-expensive foraging methods. When time is limiting, food is abundant and energy needs are large, as during reproduction, high-efficiency high-cost foraging methods give shorter daily foraging times than low-efficiency low-cost foraging methods. When time is not limiting, food is abundant, and energy needs are small, the choice of foraging method is not critical. Small animals have lower rates of energy expenditure for locomotion than large animals. At a given food density and with similar diet, small animals are therefore more likely than large ones to minimize foraging time by using high-efficiency energy-expansive foraging methods and to exploit patches and sites that require energy-demanding locomotion modes. Survival selection takes place at food shortages, while low-efficiency low-cost foraging methods are used, whereas reproduction selection occurs when food is abundant and high-efficiency energy-expensive foraging methods do better. In seasonal environments, selection therefore acts on different foraging methods at different times. Morphological adaptation to one method may oppose adaptation to another. Such conflicts select against foraging and morphological specialization and tend to give species-poor communities of year-round resident generalists. But a stable year-round food supply favors specialization, niche narrowing, and dense species packing.
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