Age-dependent toxicity in plant chemical defences and herbivore feeding behaviour
- When?
- Friday 28 October 2011, 16:00 to 17:00
- Where?
- 22AA04
- Open to:
- Students, Staff
- Speaker:
- Stephen Gourley (Surrey)
Abstract: Plants defend themselves using chemical toxins the concentration of which often varies with the age of twig segments. In boreal forests, woody internodes of the youngest segments of the twigs of the deciduous angiosperm species that herbivores such as hares prefer to eat are more defended by toxins than the woody internodes of the older segments that subtend and support the younger segments. Thus, the per capita daily intake of the biomass of the older segments of twigs by herbivores is much higher than their intake of the biomass of the younger segments of twigs.
This age-dependent toxicity of twig segments is modelled using age-structured model equations which are reduced to a system of delay differential equations involving multiple delays. The model accounts for mortality of non-consumed younger twig segment biomass when older twig biomass was bitten off and consumed. Necessary and sufficient conditions can be found for the linear stability of the equilibrium in which the herbivore is extinct, and sufficient conditions found for the global stability of this equilibrium. Numerical simulations demonstrate the existence of limit cycles over ranges of parameters reasonable for hares browsing on woody vegetation in boreal ecosystems. This shows that age dependence in plant chemical defenses has the capacity to cause hare - plant population cycles, a new result.
This is joint work with Rongsong Liu, Donald DeAngelis and John Bryant.
