Life-history variation within and between two closely related gull species
Bosman, D. (2016). Life-history variation within and between two closely related gull species. PhD Thesis. Ghent University, Faculty of Sciences: Gent. 103 pp.
Animal species differentially invest in growth, reproduction and survival throughout their lifetime and the balance between these conflicting demands in terms of time and energy is what we refer to as ‘life-history’. The life-history of an individual, includes all of the stages from birth to death, i.e. from early development and maturation, over the adult life-stage to senescence. Many long-lived species inhabit areas with strong seasonality where environmental conditions such as resource availability and temperature may change in a predictable manner within the year, and consistently from year to year within the period of a single lifespan. To cope with such temporal variability, individuals are likely to experience selection pressures to carry out different activities related to reproduction and survival at favorable times of the year, i.e. an optimal annual routine or cycle. These routines vary according to the annual pattern of environmental conditions individuals experience and show great variation in the timing, duration and sequence of major activities through the year. Breeding is a crucial stage in the annual cycle and in terms of energy requirements probably the most demanding. Logically, the timing of breeding takes precedence over other activities of the annual cycle that are then scheduled around it. Birds are remarkably consistent in their basic life-cycle. However, at all stages of this basic life-cycle, birds display a great deal of variation in the way these stages are realized and organized. Age- and sex-differences commonly explain a large part of the life-history variation between and within individuals. Understanding this variation requires examining the performance of individuals and changes in performance over life. Here, I studied life-history variation in Herring Gulls and Lesser Black-backed Gulls on an individual basis.
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