No experimental evidence for local competition in the nestling phase as a driving force for density-dependent avian clutch size

1. In birds, local competition for food between pairs during the nestling phase may affect nestling growth and survival. A decrease in clutch size with an increase in breeding density could be an adaptive response to this competition. To investigate whether breeding density causally affected the clutch size of great tits (Parus major), we manipulated breeding density in three out of eight study plots by increasing nest-box densities. We expected clutch size in these plots to be reduced compared to that in control plots. 2. We analysed both the effects of variation in annual mean density (between-year comparisons) and experimental density (within-year comparison between plots) on clutch size variation, the occurrence of second broods and nestling growth. We examined within-female variation in clutch size to determine whether individual responses explain the variation over years. 3. Over the 11 years, population breeding density increased (from 0·33 to 0·50 pairs ha–1) while clutch size and the occurrence of second broods decreased (respectively from 10·0 to 8·5 eggs and from 0·39 to 0·05), consistent with a negative density-dependent effect for the whole population. Nestling growth showed a declining but nonsignificant trend over years. 4. The decline in population clutch size over years was primarily explained by changes occurring within individuals rather than selective disappearance of individuals laying large clutches. 5. Within years, breeding density differed significantly between manipulated plots (0·16 pairs ha–1 vs. 0·77 pairs ha–1) but clutch size, occurrence of second broods and nestling growth were not affected by the experimental treatment, resulting in a discrepancy between the effects of experimental and annual variation in density on reproduction. 6. We discuss two hypotheses that could explain this discrepancy: (i) the decline in breeding performance over time was not due to density, but resulted from other, unknown factors. (ii) Density did cause the decline in breeding performance, but this was not due to local competition in the nestling phase. Instead, we suggest that competition acting in a different phase (e.g. before egg laying or after fledgling) was responsible for the density effect on clutch size among years.

Gegenwärtigen Probleme der Theorie des volkswirtschaftlichen Wohlstands

Die Veröffentlichung des Aufsatzes von Prof.Tinbergen im Fachjournal des Zentralen Instituts für Wirtschaftsmathematik der Akademie der Wissenschaften der UdSSR zeigt, in welchem Bereich und auf welchem Niveau Sozialwissenschaftler aus Ost- und Westeuropa heute zusammenarbeiten können. Dieser Bereich gemeinsamen Interesses ist durch die Frage nach der optimalen Organisation der Gesellschaft charakterisiert. Prof.Tinbergen faßt die Bedürfnisbefriedigung als allgemeinen Inhalt der gesellschaftlichen Zielfunktion auf, geht jedoch insofern über die traditionelle Interpretation hinaus, als die gesellschaftlichen Institutionen nicht Daten, sondern Variable der Optimierungsaufgabe sind. Besondere Aufmerksamkeit verdienen die Einbeziehung der Arbeitsanstrengung in die Nutzenfunktion und die Behandlung der Häufigkeitsverteilung von Arbeitsqualitäten im Rahmen der Produktionsfunktion; abschließend verweist der Autor auf die Notwendigkeit empirischer Forschung zur Aufstellung einer volkswirtschaftlichen Bildungsfunktion. The publication of the article by ProfessorTinbergen in the Journal of the Central Institute for Mathematical Economics of the Academy of Sciences of the USSR indicates both the field and the level on which social scientists from eastern and western Europe can cooperate today. The field of joint interest is characterized by the search for an optimal organization of society. According to ProfessorTinbergen the satisfaction of wants is the general content of the social optimum; yet, he goes beyond traditional interpretation in that he does not consider social institutions to be data but variables of the optimization problem. Furthermore, the inclusion of productive effort into the utility function and the treatment of the frequency distribution of labour qualities in the framework of the production function are of special interest; in conclusion, the author points to the necessity of empirical research for the development of a social education function. In Polish: Sovremennye Problemy Teorii Naradnochzjajstvennogo Blagosostojanija, in: Ekonomika i Matematicheski Metody, Vol. 3, No.3, 1967, pp. 348-35

What might the Soviet Union learn from the OECD countries in economics and politics ? An article from 1991 with some comments from 2005

When cleaning up my archives I came across a short article of April 1991 co-authored with Jan Tinbergen, on what the Soviet Union might learn from OECD countries in economics and politics. The article apparently never got published, partly since the Soviet Union collapsed in December 1991. Jan Tinbergen died in 1994. Reading the article again in 2005 shows that some arguments still have value. In 2005, an advice, purely my own now, would be that Russia and the other republics of the former Soviet Union apply for membership of the European Union.