Invasive axis deer and wild boar in a protected area in Argentina, controlled hunting, and Taylor's law

Abstract

Context: Spatial and temporal variability in population density tends to increase with an increasing mean density, as widely documented by Taylor's law (TL) of fluctuation scaling. A management program based on local hunters has been used to control invasive wild boar and axis deer in a protected area of north-eastern Argentina since 2006. Aim: We determine the effects of species (boar or deer), hunting shift (diurnal, overnight), human disturbance (by comparing one section open for public use, one not) and time scale (one-versus three-month periods) on the values of the parameters of TL, and consider both its spatial and temporal forms. Methods: Park management collected data on the hunting efforts and harvest of 6104 hunting parties shooting from elevated blinds from 2006 to 2015. The log-transformed sample means and variances of four indices of relative abundance were computed for each period and blind, and analysed through least-squars linear regression and ANCOVA. Key results: Axis deer satisfied the spatial TL by all four indices, but wild boar had a significantly non-linear relationship for crude catch per unit effort (CP-UE) only. In the spatial TL, the slope b did not deviate significantly from 1 when using crude or standardised catch per hunting-party session or standardised CPUE, but b was substantially >1 for crude CPUE in both species (range, 1.307-1.434). Human disturbance, hunting shift, and time scale did not significantly modify the parameters of the spatial TL, except in two cases. All metrics at identified blinds over consecutive trimesters confirmed the temporal TL. Wild boar crude catch was 43% greater in the restricted zone of greater conservation value, whereas axis deer catch was 60% greater in the public-use zone. Conclusions: With rare exceptions, TL describes well the mean and variance of four metrics of abundance of wild boar and axis deer under sustained hunting pressure. This paper may be the first to demonstrate the connection of TL with any aspect of vertebrate pest control. Implications: TL identifies key zones with a high mean and high variance of ungulate density for targeted control, and can be used to attain fixed-precision estimates of abundance through sequential sampling.