A comparison of model structures for the simulation of amphipod (Talitrus saltator) population dynamics.

A dynamic model is proposed in order to simulate sandhopper (Talitrus saltator) populationdynamics under various scenarios. It was built under the Stella simulation software and so far it has attainedthe calibration and verification stages. The basic structure of the model depends on the simulation of thenumber of animals in each age class (45 days). A von Bertalanffy growth curve has been adjusted to thetreated field data. From this equation another one expressing the instantaneous growth rate was extracted andused to calculate the growth. The number of individuals in each age class increases due to the ageing processi.e. new individuals coming from the previous age classes. The number of animals in the first age classincreases due to recruitment. Fertility is related to the weight of females, therefore the recruitment ispredicted by knowing the average weight and the number of females present. The outputs from each age classare the ageing and mortality. Three types of recruitment were tested: 1. A single and long reproduction periodonly dependent on the day of the year. 2. More than one reproduction period but also dependent on the day ofthe year. (2 and 3 periods). 3. Reproduction dependent on the temperature and day length. Each of these typesinvolved a different set of equations therefore the comparison of the results of each type acts (sensu lato) as aform of sensitivity analysis. Satisfactory results were accomplished by some of the model variants describedabove. A simple alternative approach to these model variants was also tested with the best results. No sizedependent fertility and no parallel structures to simulate growth in size or weight were considered. Inaddition the use of shorter age classes (28 days) was also experimented.