Posted by: oikosasa | October 18, 2013

Crowding effects on indfidelity

How density effects reproductive success and extra pair-paternity is studied in the new Early View paper “Form, function and consequences of density dependence in a long-distance migratory bird” by Ann E. McKellar and co-workers. Below is Ann’s summary of the study:

The negative effects of an increasing population density on reproductive output have long been recognized in many animals, including migratory birds. As breeding density increases, territory sizes generally decrease, causing crowding and increasing neighbour-neighbour interactions, which can lead to decreases in rates of foraging and chick feeding, and increases in rates of nest predation. Such density-dependent processes can thus produce negative feedbacks which contribute to population regulation and the general stability of population size, since periods of high population density will reduce overall breeding success, and vice versa.

Moreover, population density can affect mating tactics. Rates of extra-pair copulations often increase with population density, thus providing an additional challenge to the reproductive fitness of males residing in dense areas.

Interestingly, the density dependence of demography and behaviour are rarely studied simultaneously. And yet such a holistic view is important because individual behaviours can influence population demographics, which can then feed back into the success of individual behaviours. These types of behavioural-demographic loops are no trivial matter, as modeling exercises have shown that they may influence the probability of population extinction.

We examined the density dependence of reproductive success and extra-pair paternity at a long-term study site of breeding American redstarts in Ontario, Canada. We found that greater breeding density was associated with reduced reproductive success, likely as a result of increased nest predation, and increased rates of extra-pair paternity. Overall, these findings contribute to a broader understanding of the selective pressures and regulatory mechanisms acting on migratory birds, from the individual up to the population level.


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