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What keeps insects small? - Size dependent predation on two species of butterfly larvae
Stockholm University, Faculty of Science, Department of Zoology. Zoologisk Ekologi. (Gotthard)
Stockholm University, Faculty of Science, Department of Zoology. Zoologisk Ekologi. (Gotthard)
Stockholm University, Faculty of Science, Department of Zoology. Zoologisk Ekologi. (Gotthard)ORCID iD: 0000-0002-4560-6271
2006 (English)In: Evolutionary Ecology, ISSN 0269-7653, Vol. 20, no 6, 575-589 p.Article in journal (Refereed) Published
Abstract [en]

Insect size usually increases greatly in the latter stages of development, while reproductive value increases strongly with adult size. Mechanisms that can balance the benefits associated with increased growth are poorly understood, raising the question: what keeps insects from becoming larger? If predation risk was to increase with juvenile size, it would make an extension of development very risky, favouring smaller final sizes. But field measures of juvenile mortality seldom show any general patterns of size dependence. We here therefore try to estimate a mechanistic relationship between juvenile size and predation risk by exposing the larvae of two closely related butterflies to a generalist invertebrate predator in a laboratory experiment. Predation risk increased with larval size but was not affected by the species-specific growth rate differences. These results indicate that predation risk may increase with the size of the juvenile even when predators are relatively small. By basing a model simulation on our data we also show that size dependent predation of the kind found in this study has potential to stabilise selection on body size in these species. Thus, these findings suggest that more detailed studies of the size dependence of predation risk on juvenile instars will increase the understanding of what it is that keeps insects small.

Place, publisher, year, edition, pages
2006. Vol. 20, no 6, 575-589 p.
Keyword [en]
life history; body size; growth rate; juvenile mortality; age- and size at maturity; predation risk; lepidoptera; model
National Category
Ecology Ecology
URN: urn:nbn:se:su:diva-14396DOI: doi:10.1007/s10682-006-9118-8OAI: diva2:180916
Available from: 2008-09-12 Created: 2008-09-12 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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Berger, DavidGotthard, Karl
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