Case Studies - Population Models & Invasive Species Management
We would now like you to explore NT case studies in weed management. The modelling focus in these case studies will be on regression modelling, as the case study on Mimosa employed. This is only one of many modelling approaches.
This introduction to modelling, through case studies, serves to make you aware of limitations of this one approach and to help you to critically appraise other approaches in light of what you learn here.
Activity 3.2
MImosa pigra
Mimosa (Mimosa pigra) is a small spindly shrub, less than 1m tall in its home range. In the NT it is a vigorous woody plant up to 3 m tall. In Australia is it confined to the NT, where it is well established on a number of river systems. It has the potential to spread across the savanna wetlands of northern Australia. An outbreak was located and eradicated in QLD in 2001.
Mimosa infestation
Vast sums have been spent on containing and eradicating populations - using both chemical and biological control methods. In its home range in central America, Mimosa has some 120 predators, 20 of which are specific to Mimosa, one of which has been observed to kill a mimosa plant. Clearly this plant has a terrific potential for growth and reproduction. For example, Mimosa is a prolific seed producer, and large seed banks have been recorded under mimosa stands. Even if all shrubs were removed tomorrow, the seed bank would remain.
So when will the seed-bank be depleted?
To explore this question, we'd like you to read an article by Londsdale et al. (1988) (Reading 3.11), in which the seed-bank dynamics have been modelled, in order to predict the likely reduction in seed-bank size over time.
Read the whole article and then answer the questions below.
- How did the mimosa seed in the seed-bank behave over time?
- What factors affected the mimosa seed-bank decline?
- What type of model is this (using the classification provided in Higgins & Richardson 1996)?
- What is the prognosis for seed-bank longevity for mimosa?
- How can the results of this study be used for the conrol of mimosa? Can you identify any limitations of the study?
Reading 3.11 Lonsdale W.M., Harley K.L.S. and Gillett J.D. (1988). Seed bank dynamics in Mimosa pigra, an invasive tropical shrub. Journal of Applied Ecology25: 963-976.