Influence of recruitment on population persistence in open and closed systems

This thesis examines the influence of recruitment on the persistence of populations in open and closed systems. Three systems were modelled, addressing questions concerning the influences on consumer dynamics of prey recruitment, consumer behaviour, and prey behaviour. Theoretical concepts were developed with mathematical models, and tested on observations from field experiments and empirical data collected from the literature. The following focal questions were addressed:1. How do consumer populations respond to migration of their limiting prey into or out of the system? A Lotka-Volterra type model revealed that even a small prey outflux had catastrophic consequence for predator persistence. In contrast, the predator population was stabilised by subsidising it with prey influx. These outcomes for prey subsidy were compared to those for prey enrichment, which is known to destabilise populations (Rosenzweig's 'paradox of enrichment'). This research has implications for conservation and pest management. An influx to conserve a threatened population or an outflux to eliminate a pest population may have more effect when applied to the limiting resource than to the focal species itself.2. How do populations of colonists respond to conspecifics in an open system? Recruitment of barnacles to rocky shores was monitored in experimental tests of alternative models for recruitment dynamics.3. How do prey respond to dietary switching by their predators? A two-prey model was applied to tundra microtine populations (the 'predators') eating vegetation (the 'prey') with wound-induced toxic defences to predation. Parameter values were gathered from the literature, and model outputs were tested against five empirically derived criteria that characterise population cycles in this group. For plants without chemical defences the model met only four of these criteria.