Invader–invader mutualism facilitates secondary invasions in rainforest on Christmas Island.

O’Loughlin, Luke S.

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Title: Invader–invader mutualism facilitates secondary invasions in rainforest on Christmas Island.
Creator: O’Loughlin, Luke S.
Contributor: La Trobe University. College of Science, Health and Engineering.
Contributor: La Trobe University. School of Life Sciences.
Contributor: La Trobe University. Department of Ecology, Environment and Evolution.
Date: 2015
Publisher: La Trobe University.
Description: Thesis (Ph.D.) - La Trobe University, 2015
Description: Submission note: A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy [to the] Department of Ecology, Environment and Evolution, School of Life Sciences, College of Science, Health and Engineering, La Trobe University, Bundoora.
Description: Mutualistic interactions between successful ‘primary’ invaders can produce reciprocal, positive population-level effects that amplify their impacts. These impacts may alter key properties of the recipient community to facilitate ‘secondary’ invaders. On Christmas Island, mutualism between the exotic yellow crazy ant Anoplolepis gracilipes and a variety of introduced honeydew-producing scale insects results in the formation of high-density crazy ant super colonies that cause local extinctions of the dominant omnivore-detritivore, the red land crab Gecarcoidea natalis. Occurring at naturally high densities, these crabs could provide the rainforest community with considerable biotic resistance against invaders through their activities both as predators, and by limiting key resources such as leaf litter and seedlings. In this project I asked whether the ant-scale mutualism indirectly facilitated the success of secondary invaders – exotic land snails – by altering these key attributes of the recipient community. Land snails are common invaders on islands, and on Christmas Island 22 of the 38 species are introduced, including the notorious Giant African Land Snail Achatina fulica. Where red crabs were absent, exotic land snails were an order of magnitude more abundant and the community differed compositionally from the uninvaded state. Field experiments that manipulated red crab density and leaf litter biomass, either singly or in combination, showed that increased land snail abundance was due to the augmentation of habitat and resources, rather than the creation of enemy-free space. This represents a ‘population-release’ model of secondary invasion, defined as the facilitation of invasive species from very low to very high densities. However, high density does not necessarily mean high impact. An exclusion experiment demonstrated that high densities of A. fulica had no detectable impact on seedling recruitment or leaf litter decomposition. This research demonstrates the importance of properties of the recipient community in determining invasion success and highlights the role of invasive species themselves in altering those properties.

Language: en
Rights: This thesis contains third party copyright material which has been reproduced here with permission. Any further use requires permission of the copyright owner. The thesis author retains all proprietary rights (such as copyright and patent rights) over all other content of this thesis, and has granted La Trobe University permission to reproduce and communicate this version of the thesis. The author has declared that any third party copyright material contained within the thesis made available here is reproduced and communicated with permission. If you believe that any material has been made available without permission of the copyright owner please contact us with the details.
Type: Thesis

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