Modelling the Presence-Absence of Multiple Species
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Predicting which species will be present (or absent) across a geographical region remains one of the key problems in ecology. Numerous studies have suggested several ecological forces that can determine species presence-absence: environmental factors (i.e. abiotic environments), interactions among species (i.e. biotic interactions), dispersal and demographic stochasticity. While various ecological forces have been considered, less attention has been given to the problem of understanding how dispersal processes, in interaction with other ecological factors, shape community assembly in the presence of priority effects (i.e. initial abundances determine the presence-absence of species). In this thesis, we investigate the consequences of different dispersal patterns and stochasticity on the occurrence of priority effects and species coexistence in multi-species competitive systems. By employing deterministic and stochastic models in one-dimensional space, our study shows the conditions under which priority effects occur and disappear as local dispersal strength changes. Without dispersal, priority effects emerge in the presence of intense biotic interactions, with only one species surviving at any given location (i.e. coexistence is impossible). For moderate dispersal levels, dispersal enhances priority effects and promotes multiple species coexistence. Further increasing dispersal strength leads to the disappearance of priority effects and causes extinction of some species. We also demonstrate contrasting observations of stochasticity on priority effects: while priority effects are more prevalent in the stochastic individual-based models (IBM) than in the deterministic models for large populations, we observe fewer occurrences of priority effects in IBM for small populations. When non-local dispersal is incorporated into the models, priority effects are more pronounced than in the local dispersal models. We also investigate the effects of different dispersal patterns on species coexistence: although very long-range dispersal leads to species extinctions, intermediate-range dispersal permits more outcomes where multispecies coexistence is possible than short-range dispersal (or purely local dispersal). Finally, we extend our model to consider community dynamics in two-dimensional space. We find that knowledge of species’ environmental requirements is also crucial to improving our ability to predict the occurrence of priority effects across heterogeneous environments.