Details

Autor(en) / Beteiligte

• Evans, K. L.
• Duncan, R. P.
• Blackburn, T. M.
• Crick, H. Q. P.

Titel

Investigating Geographic Variation in Clutch Size Using a Natural Experiment

Ist Teil von

• Functional ecology, 2005-08, Vol.19 (4), p.616-624

Ort / Verlag

Oxford, UK: British Ecological Society

Erscheinungsjahr

2005

Link zum Volltext

Quelle

Access via Wiley Online Library

Beschreibungen/Notizen

• 1. Clutch sizes generally increase with latitude, and are smaller at southern latitudes compared with equivalent northern ones. 2. Descriptions of such patterns and attempts to identify their causal mechanisms are complicated as different species, with different ecological traits are often compared in different regions. We reduce such problems by using the introduction of 11 passerine species from the UK to New Zealand as a natural experiment to explore interspecific geographical variation in clutch size. 3. Nine species have significantly smaller clutches in New Zealand than the UK. Seasonality, measured both by climate and how birds respond to variation in resource availability, is also lower in New Zealand. Comparing across species, the magnitude of clutch size change is unrelated to the magnitude of reduced seasonality that each species experiences. 4. Such observations are partly compatible with Ashmole's hypothesis that areas with high seasonality have large clutch sizes (higher winter mortality results in a breeding population that is significantly lower than the environment's carrying capacity, and hence in extra resources for rearing chicks). However, additional data on seasonal changes in resource availability and population densities, combined with comparative data on survival and nest predation rates, are required to evaluate fully the mechanisms generating smaller clutches in the southern hemisphere. We discuss the potential determinants of geographical variation in the patterns of temporal variation in clutch size.