Rats in the ranks; demographic responses of an invasive species, rattus rattus, to pest control in urban bush land remnants
Pest control has the potential to disrupt the local social structure of the pest population, influencing the timing and mechanisms of reinvasion and thus the effectiveness of long-term management. Yet, little is known about the behavioral and demographic attributes of the re-invaders or the conseque...
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| Format: | Master Thesis |
| Language: | English |
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UNSW, Sydney
2011
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| Online Access: | http://hdl.handle.net/1959.4/51601 https://unsworks.unsw.edu.au/bitstreams/1dd29846-e065-428e-a342-04f55b2252a9/download https://doi.org/10.26190/unsworks/15223 |
| Summary: | Pest control has the potential to disrupt the local social structure of the pest population, influencing the timing and mechanisms of reinvasion and thus the effectiveness of long-term management. Yet, little is known about the behavioral and demographic attributes of the re-invaders or the consequent population responses following depopulation. Here, I study the demographic changes, movements and activity patterns associated with reinvasion of the feral black rat, Rattus rattus, using gradients of localised pest control in urban bush land remnants within Sydney, Australia. In doing so, I test three main theories of the mechanisms of reinvasion: ‘The Founding effect’, the ‘Trickle effect’ and the ‘Vacuum effect’. Firstly, I examined the demographic and reproductive responses of two populations of black rats within two successive harvesting scenarios: an imposed harvested population (subjected to localized regular removal associated with management) and a non-harvested population (no previous rat removal). Rats were dissected to estimate body condition, size, age (via eye lens weight) and breeding activity. Individuals captured within the harvested population had similar reproductive activity to those in the non-harvested population. However, no juveniles were captured in the harvested sites, suggesting that harvesting disrupted reproductive success with consequences for long term population dynamics of black rats. These results also suggest that the stable social system in the non-harvested population is more conducive to juvenile survivorship. I then examined the potential short and long term recovery responses by experimentally removing individuals from 1ha plots and monitoring reinvasion success and the types of subsequent re-invaders. Mixed responses were observed from the differing gradients of removal. There was no net influx of individuals four weeks after the initial targeted removal (from half the grid), possibly due to social blocking of reinvasion by residual animals. However, a larger scale removal ... |
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