Fenotipo, prospección y rasgos de vida en los individuos flotantes de estornino negro (Sturnus unicolor)

Abstract

Las poblaciones naturales animales a menudo poseen una porción de individuos sexualmente maduros no reproductores que reciben el nombre de flotantes. Estos flotantes conviven con los individuos reproductores en la población, pero a diferencia de estos, no defienden un recurso reproductivo como podría ser un territorio. Este carácter discreto y esquivo hace que la información de la que se dispone de ellos sea relativamente escasa en un gran número de especies. Existen dos hipótesis generales que tratan de explicar el origen del estatus flotante. La primera de ellas considera a los individuos flotantes como miembros de la población subordinados y de peor calidad que fracasan en la lucha por los recursos reproductivos; la segunda, en cambio, contempla el estatus flotante como un retraso u omisión de la reproducción para maximizar el éxito reproductor en el futuro. Para poder comprenderlas causas y las consecuencias de adquirir este estatus durante parte o totalidad dela vida es necesario investigar distintos aspectos de la vida de los flotantes como su morfología, su comportamiento o sus rasgos de vida...

In most animal wild populations there is fraction of individuals that are sexually mature but do no breed. These individuals receive the name of ‘floaters’.These floaters often cohabit with breeders in the population but do not defend any breeding resource such as a territory. Their secretive behaviour is one of the main reasons why we still lack a lot of information about their biology in a great number of species. There are two general proposed hypothesis that aim to explain the origin of floaters. The first of them considers floaters as subordinate and low-quality members of populations that fail in the fight for breeding resources; the second, in contrast, sees floating as a way to enhance reproduction in the future.To fully understand the causes and consequences of acquiring this status during part or totality of their life it is necessary to investigate several aspects of floaters such as their morphology, behaviour, and life-history traits. The aim of this thesis is to characterize the floating fraction of a wild population of spotless starling (Sturnus unicolor ) through the study of their phenotype, prospective behaviour, and life-history traits. The spotless starling is a relatively long-lived gregarious and semicolonial passerine that breeds in already excavated holes and whose populations can reach high local densities of individuals. This creates an intense competition for nesting-holes that leads to the formation of a surplus of floaters that can be detected in the colony during their visits to nest-boxes...