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Time stress, predation risk and diurnal-nocturnal foraging trade-offs in larval prey.
Stockholm University, Faculty of Science, Department of Zoology.
Stockholm University, Faculty of Science, Department of Zoology.ORCID iD: 0000-0002-4560-6271
2008 (English)In: Behavioral Ecology and Sociobiology, ISSN 0340-5443, E-ISSN 1432-0762, Vol. 62, no 10, 1655-1663 p.Article in journal (Refereed) Published
Abstract [en]

Insect larvae increase in size with several orders of magnitude throughout development making them more conspicuous to visually hunting predators. This change in predation pressure is likely to impose selection on larval anti-predator behaviour and since the risk of detection is likely to decrease in darkness, the night may offer safer foraging opportunities to large individuals. However, forsaking day foraging reduces development rate and could be extra costly if prey are subjected to seasonal time stress. Here we test if size-dependent risk and time constraints on feeding affect the foraging–predation risk trade-off expressed by the use of the diurnal–nocturnal period. We exposed larvae of one seasonal and one non-seasonal butterfly to different levels of seasonal time stress and time for diurnal–nocturnal feeding by rearing them in two photoperiods. In both species, diurnal foraging ceased at large sizes while nocturnal foraging remained constant or increased, thus larvae showed ontogenetic shifts in behaviour. Short night lengths forced small individuals to take higher risks and forage more during daytime, postponing the shift to strict night foraging to later on in development. In the non-seasonal species, seasonal time stress had a small effect on development and the diurnal–nocturnal foraging mode. In contrast, in the seasonal species, time for pupation and the timing of the foraging shift were strongly affected. We argue that a large part of the observed variation in larval diurnal–nocturnal activity and resulting growth rates is explained by changes in the cost/benefit ratio of foraging mediated by size-dependent predation and time stress.

Place, publisher, year, edition, pages
2008. Vol. 62, no 10, 1655-1663 p.
Keyword [en]
Predation risk - Growth rate - Life history theory - Body size - Seasonal constraints
URN: urn:nbn:se:su:diva-24852DOI: 10.1007/s00265-008-0594-4ISI: 000257912700013OAI: diva2:198422
Part of urn:nbn:se:su:diva-7498Available from: 2008-04-24 Created: 2008-04-16 Last updated: 2014-10-28Bibliographically approved
In thesis
1. Body Size Evolution in Butterflies
Open this publication in new window or tab >>Body Size Evolution in Butterflies
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Life history research deals with the scheme of resource partitioning to a wide spectra of processes and the trade-offs shaping these events. One of the most fundamental life history trade-offs is the one of at which age- and size an organism should start to reproduce; reaching a large size at maturity is often advantageous in terms of high adult survival and reproductive potential, while to attain a larger size the organisms must prolong juvenile development which is assumed costly in terms of mortality. In holometabolous insects, a larger size usually confers increased fitness to females in terms of fecundity. Moreover, insect larvae have the capacity for fast size increase. So, it seems that there are substantial fitness benefits associated with a choice to prolong development. Surprisingly, there is a great lack of empirical support for costs of such a choice and by incorporating these observations into a life history framework one arrives at the conclusion that insect body sizes should be several times larger than observed. I study body size evolution in butterflies by closely examining the fitness consequences of variation in the age- and size at maturity. By combining both laboratory and field measures of size-fitness relationships with standard life history modelling, I arrive at the main conclusions; 1: positive size dependent predation on larvae might a) significantly increase the cost of attaining a larger size at maturity, or b) induce risk sensitive foraging responses so to slow larval growth rates and thereby restrict size at maturity, 2: ecological factors might constrain female fecundity by inducing time limitation on large females that need more time to convert all their resources into offspring, making reproductive value increase at a slower rate than body size with increased larval growth effort. These mechanisms may help to explain the inconsistency between natural observations and theoretical predictions of life history variation in insects.

Place, publisher, year, edition, pages
Stockholm: Zoologiska institutionen, 2008. 120 p.
Body size evolution, age- and size at maturity, life history theory, fecundity, predation risk, juvenile growth rate, Lepidoptera
National Category
Biological Sciences
Research subject
Animal Ecology
urn:nbn:se:su:diva-7498 (URN)978-91-7155-635-6 (ISBN)
Public defence
2008-05-16, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 10:00 (English)
Available from: 2008-04-24 Created: 2008-04-16 Last updated: 2010-01-13Bibliographically approved

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