student profile: Mr Greg Clarke


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Thesis work

Thesis title: The effects of invasion history on intraspecific competition in a rapidly evolving invasive alien

Supervisors: Benjamin PHILLIPS, Rick SHINE

Thesis abstract:

Over the course of my Ph D, I am investigating the effects of invasion history on the intraspecific competitive ability of cane toads Rhinella marina. Since their introduction to Queensland in 1935, cane toads have spread across much of northern Australia. Over this period, we have observed rapid evolution of traits that improve their ability to colonise. How, then, has this rapid evolution of phenotypes affected intraspecific competition? To explore this, I am conducting trials where offspring from invasion-front (WA) and established (QLD) populations are placed in direct competition for resources. While adult toads at the invasion front are exposed to lowered densities, this may not be the case for other life stages and as such, I am conducting competition trials on each life stage, pairing specific traits with growth and survival.
So far, I have collected datasets on competition in toad tadpoles and the early terrestrial stages, and pilot experiments on mate competition. Over the coming months, I plan to finalise these datasets and analyse them ready for publication. The initial analyses suggest that there are significant differences in the competitive ability of both larval and early terrestrial toads from either end of their invasion range. As predicted, Larval toads from established populations outcompete frontal populations, metamorphosing larger in size and more rapidly. However, early terrestrial toads show the opposite trend, with front populations outcompeting core populations. These findings lead to the next part of my project, where I plan to use population models to predict the outcome of mixing high dispersal (frontal) and low dispersal (established) populations from an adult, right through to their offspring recruiting into the population. Building these models will help to show the flow on effects of competition at each life stage.

Selected publications

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Journals

  • Clarke, G., Crossland, M., Shine, R. (2016). Can we control the invasive cane toad using chemicals that have evolved under intraspecific competition? Ecological Applications, 26(2), 463-474. [More Information]
  • Clarke, G., Crossland, M., Shilton, C., Shine, R. (2015). Chemical suppression of embryonic cane toads Rhinella marina by larval conspecifics. Journal of Applied Ecology, 52(6), 1547-1557. [More Information]

2016

  • Clarke, G., Crossland, M., Shine, R. (2016). Can we control the invasive cane toad using chemicals that have evolved under intraspecific competition? Ecological Applications, 26(2), 463-474. [More Information]

2015

  • Clarke, G., Crossland, M., Shilton, C., Shine, R. (2015). Chemical suppression of embryonic cane toads Rhinella marina by larval conspecifics. Journal of Applied Ecology, 52(6), 1547-1557. [More Information]

Note: This profile is for a student at the University of Sydney. Views presented here are not necessarily those of the University.