Editor´s choice - Territory quality and habitat heterogeneity in ravens
Submitted by avianbiology on 19 January 2014.
Territory quality affects the relative importance of habitat heterogeneity and interference competition in a long-lived territorial songbird
A common observation in avian population ecology is a density-dependent decrease in breeding success. Among territorial species this has been explained either as depending on habitat heterogeneity; low-quality territories are occupied in a higher frequency with density reducing overall breeding success or on individual adjustment; breeders in all territories suffers from reduced breeding success with increasing densities. These two hypotheses are seldom tested but in a recent paper in J. Avian Biol., Grünkorn and colleagues present data from an impressive long-term data-set on Ravens, breeding in northern Germany making it possible to disentangle the hypotheses. While a large part of the density-dependent decrease in Raven breeding success is due to habitat heterogeneity, also individual adjustment plays a role as breeding success decreases with density in all territories. The latter observation is suggested to be due to the special social system of Ravens where the number of non-breeding floaters increases with density. Furthermore, competition with the floaters seems to be stronger on low-quality territories as the breeding success on these territories were affected the most by density. This fascinating result may have wide implications in predicting that density-dependent effects on populations may differ according to the general level of food availability.
Jan-Åke Nilsson, Editor in Chief
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