New Zealand Journal of Ecology (2006) 30(1): 13- 23

Linking pasture, livestock productivity and vertebrate pest management

Research Article
Jim Hone  
  1. Institute for Applied Ecology, University of Canberra, ACT 2601, Australia

The study of pastures, pests (rabbits and caterpillars) and sheep productivity by Barlow (1987; New Zeal J Ecol 10: 43–55) is reviewed, updated and extended. Pasture growth was modelled as a dynamic process, though sheep and rabbit abundance were not dynamic. The model predicted that there was a parabolic relationship between sheep productivity and sheep stocking rate with the effects of rabbits being to shift the relationship lower and to the left. The relationship is analogous to a model of sustained harvest of a wild population, and the shape parameter of each has similar numerical values (2 to 3). The Barlow model also predicted a negative relationship between sheep productivity and rabbit abundance, with the relationship being curved with fixed stocking rates. Analysis of data from an independent experimental study shows more support for a negative quadratic (concave down, R2 = 0.509) than a negative linear (R2 = 0.416, ΔAICc = 2.770) relationship. The Barlow (1987) study assumed a positive linear relationship between the area of denuded pasture and pest abundance. A model selection analysis of a priori models of disturbance by feral pigs provides support for a positive curved relationship (R2 = 0.854) and a positive linear relationship (R2 = 0.357; ΔAICc = 0.03) between the area of denuded pasture (as disturbed ground) and pig abundance. The general results and their implications are discussed.