| Abstract: |
| Recently, many ungulate populations become overabundant worldwide.
Overpopulated ungulates often extirpate preferred plants and alter plant
communities into those dominated by less palatable ones.
We study effects of herbivory and nutrient recycling on
dynamics of nutrient, plants and herbivore.
We consider a simple dynamical model of a nutrient, palatable and
unpalatable plants, and an herbivore, assuming that (i) the nutrient
is supplied from outside at a constant rate; (ii) the unpalatable plant
is less efficient in resource acquisition; (iii) the herbivore preferentially
feeds on palatable plant; (iv) nutrient recycling is accelerated
by excretion of the herbivore. If nutrient inflow and herbivore
grazing rates on palatable plant are low, unpalatable plant becomes
extinct. Although unpalatable plant can survive and two plant species and
herbivore coexist if these rates are high, further increases
in the rates destabilize the coexistence and population oscillations occur.
Rapid mineralization of nutrients also makes the system unstable, but
it causes very different types of oscillations from those driven by differences in palatability of plants.
We also show that improvement in quality of less palatable plants
and subsequent increase in grazing intensity on the plant may
cause extirpation of not unpalatable but more palatable plants. |
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