Prevention of Population Cycles by Parasite Removal

Peter J. Hudson, Andy P. Dobson and Dave Newborn

Who remembers population cycles?

Parasites and the Red Grouse

Trichostrongylus tenuis Lagopus lagopus scoticus

Trichostrongylus tenius

Basic single host nematode life cycle

The affects that Trichostrongylus has on the Red Grouse

• Poor breeding in female grouse is caused by the nematode interfering with food intake.

• This interference will reduce the number of offspring in the population.

• This is how an increase in parasite intensity will lead to a decrease in red grouse populations.

• Breeding mortality is calculated as the clutch size of infected grouse compared to the average normal clutch size.

Treatment of the Grouse• Three conditions were observed to see how treatment of

grouse with Levamisole hydrochloride would affect the normal population cycles observed.

• The cycle was observed before treatments by two counts: number shot (dotted line) and visual counts (solid line)

The Test Results• A – Control groups: No

Treatment

• B – Treatment groups with only one round of treatment

• C – Treatment groups with two treatments to reduce worm burdens

Long Term Treatment of Grouse

Conclusion

• Population cycles in red grouse are a result of a single trophic interaction between Trichostrongylus and the grouse.

• In the classic case with the bobcat and hare there are at least three trophic levels involved.

• This was the first time that manipulations on a cyclic species have shown the cause of the population cycle on a large scale.

Reference

• Hudson, P.J., Dobson, A.P., and Newborn, D. (1998). Prevention of Population Cycles by Parasite Removal, Science, 282, 2256.

• http://www.dpd.cdc.gov/dpdx/html/imagelibrary/S-Z/Trichostrongylosis/body_Trichostrong ylosis_il1.htm