The Spoonbill Platalea leucorodia population of the Wadden sea islands :does population growth level off?

Na een dieptepunt van ca. 150 broedparen in 1968 is het aantal Lepelaars in Nederland gestaag gaan toenemen. In het broedseizoen van 2008 werden 1907 paren geteld, waarvan 1179 op de Waddeneilanden. Hier bekijken we de groei van de populatie op de Wadden eilanden in meer detail en proberen we te voorspellen hoe lang deze groei nog zal voortduren. We doen dat door op grond van de resultaten van een langlopend kleurringproject en waarnemingen aan het broedsucces een populatiemodel op te stellen. Het model voorspelt dat het aantal broedparen op de Wadden eilanden zal stabiliseren rond 1375, doordat de jaarlijkse overleving van volwassen Lepelaars afneemt naarmate de populatie groeit.After a minimum of c. 150 breeding pairs in 1968, the Dutch breeding population of Spoonbills has increased steadily. In 2008, 1907 breeding pairs were counted, of which 1179 (2358 breeding birds) on the Wadden Sea Islands. Here we investigate the population growth on the Wadden islands in more detail, and try to predict to what size the population will eventually grow. The population growth since 1985 appears to fit best to a logistic growth curve with an asymptotic population size of 2780 breeding birds. To understand the underlying processes in more detail, we developed a population model based on our data on survival probabilities and recruitment ages of colour-marked birds and on breeding success. We investigated whether these parameters depend on population size, which could explain the observed reduction in population growth. Adult survival was related to the size of the total Dutch population, and decreased from 90% to 78% when population size increased from 800 to 3600 breeding birds between 1990 and 2007. On Schier monnikoog, breeding success was negatively related to colony size. However, due to lack of data, we could not verify this observation for the other islands. Therefore, we used the mean breeding success of 1.67 young per breeding pair as a model parameter. Neither survival nor return age of subadults were density dependent: 42% of the colour-ringed juveniles were resighted in the breeding area as adult. The average age at which Spoonbills returned to the breeding area was 4.0 years, and the annual survival probability of subadult birds was 80.5%. The model predicts that the population on the Wadden Sea islands will grow to a population size of 2750 breeding adults (1375 breeding pairs), a number closely resembling the prediction of the logistic growth curve. Further research is needed to investigate whether the density dependent effect on adult survival arises in the breeding or wintering areas

Recurrent and dissipative sets for the Markov shift

No abstract

Ageing and Technology

This thesis aims to explore whether Dutch middle aged internet users, in this study referred to as Dutch mediors, have different behaviour, needs, preferences and motivation when going online compared to older and younger internet users. Even though Dutch mediors were not born as digital natives, the current digital era might be forcing them to increasingly make use of computer and internet technologies in order to keep up with society. Although older internet users are often perceived as less active users who experience both physical as cognitive difficulties when trying to make use of new technologies, middle aged users might be more experienced and active internet users regarding their place in the work force and their close bonds with children and teenagers. In many societies the middle aged part of the population is increasing, creating a large and economically strong market for many products and services, including e-business. The central question in this study is: “Do Dutch mediors have inherently different behaviours, needs and perceptions when making use of the internet than digital natives or older internet users in this information and social media age?”. By combining quantitative research methods (online survey) with qualitative research methods (focus groups), both general patterns in the behaviour and digital needs of Dutch mediors are explored and explained by retrieving in-depth information about their preferences and motivations. This study reveals that Dutch mediors in general are very practical internet users, mostly explained by their mainly utilitarian approach towards this type of technology. Remarkably, even hedonic features of the internet such as shopping online and communicating with friends and family through social networking sites are by Dutch mediors perceived as a practical internet activities. In order to appeal to the needs and preferences of Dutch mediors, websites should be mainly utilitarian with clear directions, a logical structure and valuable and newsworthy information