MARCO NORMATIVO

Di↵erences between the aspatial closed model structure and the open and complete model structure varied between habitats. Both approaches reflected a high level of variability between the individual cells (Figure 5.1). With either approach, the density of adults in occupied cells in the forest creek and forest habitats appeared to grow in an almost linear fashion, and do not appear to have reached a maximum density by the end of the simulation. In contrast, the densities in the forest gap, alpine creek, scrub, and tussock habitats appeared to have reached a maximum density at lower levels than the forest or forest creek. The initial seeding density appears to have a slight influence on projections in the forest, forest creek, forest gap, and alpine creek habitats, while the densities in the scrub and tussock habitats appear to all converge at similar levels, regardless of their initial state. Overall, it appears that model structure (open or closed) does not have a significant influence on mean density after 100 years of population development, as trajectories from both structures are very similar, and comparisons of confidence interval reflecting one standard deviation above and below indicate a great deal of overlap between the two model structures (Figure 5.1). However, even though the standard deviations suggest this pattern was not significant, the closed system did consistently produce higher mean adult densities than the complete system.

The trajectories of total population size from the closed and complete model structures (measured as the total number of adults in the simulated landscape) appear to di↵erentiate in some, but not all of the habitats examined (Figure 5.2). In those habitats where di↵erences between the two model structures are evident, the complete system tends to result in larger populations compared to the closed model structure (forest creek, forest, and tussock habitats); population size in the remaining habitats appears to be nearly identical. The forest creek and forest habitats appear to be able to support the largest populations, followed by the alpine creek habitat. Populations in the tussock habitat, while relatively small, appear to be steady or increasing in size, in comparison to the forest gap or scrub habitats, which appear to exhibit negative growth throughout the simulation period, and appear to be headed for extinction. The initial conditions appear to have a strong influence over the population size after 100 years of simulated growth in most of the habitats, regardless of whether or not the population is stable by this time. In general, initial densities were positively correlated with population size at the end of the simulation run for most habitats (except scrub). However, the e↵ect of the initial density on the general trajectory is less clear; populations in forest gap and scrub appear to be headed for extinction regardless of the initial condition. In other habitats (forest, forest creek, and alpine creek), higher initial densities result in apparently self- sustaining populations, while lower initial densities seem destined for extinction. This result is further confounded by the influence of the di↵erent model structures as well. In general, the complete model almost always resulted in a higher occupancy rate at the

Figure 5.2: Projections of the population trajectories obtained from simulating the H. lep- idulum population over 100 time steps. The simulations were initiated with either 1, 10, or 50 adult individuals in each cell, and demographic models reflected either a closed model structure (in black) that did not incorporate dispersal between the cells, or a complete model structure (in red) that included interactions between cells driven by the dispersal of seed. As an aggre- gate measure of performance, there are no replicates at this level and therefore no measure of variability in these values.

Figure 5.3: Trajectories of the occupancy rates of cells by adults were obtained from simulating the H. lepidulum population over 100 time steps. The simulations were initiated with either 1, 10, or 50 adult individuals in each cell, and demographic models reflected either a closed model structure (in black) that did not incorporate dispersal between the cells, or a complete model structure (in red) that included interactions between cells driven by the dispersal of seed.

end of simulating 100 years of population growth (Figure 5.3). Di↵erences in model per- formance were barely perceptible in the scrub habitat, but in the remaining habitats the complete model clearly had higher occupancy rates at the end of the simulation. Patterns in the change of occupancy rates over time also emerged. Cell occupancy tended to decline in nearly all of the simulations immediately following the initial 100% occupancy. Beyond this, however, a distinction can be made between those simulations where occupancy rates recovered, and began to increase after the initial drop, those simulations where occupancy rates levelled out, and those simulations that continued to decrease. The occupancy rates of simulations using the closed model structure typically continued to decrease over time. Only in the forest creek habitat do occupancy rates of the closed model appear to level o↵; none of the simulations with the closed model showed any increases in occupancy during the simulations. Patterns of occupancy from the simulations using the complete model structure are more indicative of a self-sustaining population; while simulations from this model appear to continue to decline throughout the simulation in some habitats (forest gap and scrub), they appear to level out (alpine creek) or even increase in others (forest creek, forest, and tussock; Figure 5.3). Also notable is the apparent influence of initial starting densities; simulations with higher initial densities were not only more resilient in terms of the initial drop in occupancy (compared to comparable simulations with lower initial densities), but they also appear to approach a higher sustainable occupancy level in some habitats (i.e. forest and alpine creek habitats).