Tiwi Buffalo Sim

This simulation has been developed to describe the distribution and dynamics of feral buffalo herds on Melville island and to illustrate possible outcomes of an eradication program.
The tool aims to:
• Be understood by both land managers and the broader community.
• Show scenarios of possible outcomes related to buffalo management.
• Support clear communication about the potential impacts of the proposed feral buffalo eradication program.

The simulation is an 'agent-based-model' using spatially explicit raster data to moderate agent (buffalo) movent. The model is purely descriptive, designed to illustrate some of the key factors related to buffalo management. It is not intended to predict outcomes.

HOW IT WORKS

Model set up.

The model is based around the Jessie creek region of northern Meliville island with the extents defined by TNRM. The landscape has been classified into broad landcover types using Sentinel-2 satellite imagery. These Landcover types moderate how the buffalo move through the landscape. In addition to the landcover classification, an NDVI (Greeness) layer was also produced and integrated into the model as a moderator of Buffalo movement. The correlation between Buffalo movement (grazing location) and NDVI has been described in work by Campbell et al (2020).

Buffalo herds initially appear in the landscape in locations identified by the TNRM air survey. For the purpose of the model, the buffalo operate as herds, so where single animals were seen in the survey they have been allocated a herd size of 5. Where small herds were recorded close together they were aggregated into single larger herds. This aggregation step results in an initial count of 14 herds made up of 114 buffalo. Each buffalo herd icon is size-scaled by the size of the herd it represents.

Buffalo movement.

The buffalo herds move between grazing sites in savannah woodlands and flood plain wallows sites. Wollow locations are based on where buffalo were recorded in floodplains. In addition, each herd has three additional potential wallow sites within a 5km radius of their current location. Buffalo move between wallowing and one of two hundred grazing sites in woodlands with high NDVI values.

Buffalo have three activity states; 1) grazing 2) wallowing 3) going to a wallow. The direction Buffalo herds move is based on their current state. If grazing they move between grazing sites. If wallowing they move in a small radius around a wallow site. If moving to a wallow they move to their closest wallow site. The activity state of each heard changes after a certain period (model cycles). Buffalo will wallow 40-120 model cycles before going to graze. Buffalo will graze between 200-300 model cycles before going to wallow. These pseudo-random time periods are designed to show that Buffalow spend quite a bit of time wallowing but more time wandering.

Buffalo reproduction

Buffalo herds grow at a rate set by a slider (default 0.32) in the interface approximately every 350 model cycles. Once a herd reaches a size of between 20-30 individuals it divides into two herds.

Buffalo landscape damage

Every landscape cell has a damage value. This value is initially set to 1000 (no damage). Each time a herd moves through a cell it causes damage equal to the herd size. Herds greater than 10 individuals inflict damage in a radius of one additional cell around the herd. The landscape 'recovers' at a rate of 1 per model cycle. The degree of damage to the landscape can be viewed using the 'view damage' button in the interface. If the 'show damage' switch is on the degree of damage will be automatically updated every 10 model cycles.

Buffalo culling

The 'Cull Buffalo' button reduces herd size proportionate to the herd size and the number of hours allocated to shooting using the following formula: hours-spent-on-shooting + herd-size / 5

This is designed to illustrate the cull rate based on time/$ spent and also that it would be easier to find/reduce the size of larger herds than small ones.

HOW TO USE IT

Press ‘set-up’ to load the model.
Choose a reproduction and shooting time setting.
Press 'Go' to run the model.
Press the Cull button to remove buffalo.
The Start Video button records the simulation run.
The 'Stop Video' button saves the simulation run.
The video format from NetLogo is cumbersome so it is recommended that you change the format to MP4 using the free video format editing software QWINFF available here: https://qwinff.github.io/

Download the model

First, make sure you have NetLogo installed then

Citations:

Campbell, H. A., Loewensteiner, D. A., Murphy, B. P., Pittard, S., & McMahon, C. R. (2020). Seasonal movements and site utilisation by Asian water buffalo (Bubalus bubalis) in tropical savannas and floodplains of northern Australia. Wildlife Research, 48(3), 230-239.

Download the model here.