I just found an extremely relevant paper form 2001 where someone has actually implemented an agent-based model of panther movements to explore the feasibility of re-introducing panthers to a location in Northern Florida.
The paper doesn't explicitly acknowledge its agent-based modelling methodology, but it definitely uses ABMs to model panthers moving around a real landscape. There are many similarities to my work here. The exact methodology does differ but is essence they have panthers looking at neighbouring cells, choosing a location and moving to that location, based on habitat, prey resource, roads and human density, whilst simultaneously interacting with other panthers in the area.
This is THE paper to reference.
And I am one very happy camper! :)
Reference:
Cramer, P.C. & Portier, K.M. (2001) Modelling Florida panther movements in response to human attributes of the landscape and ecological settings. Ecological Modelling 140: 51-80
(available from ScienceDirect, or Mendeley).
1.11.11
Habitat preference and territory development
Getting jaguar agents to mimic real-life individuals and create territories is one of the most important features to try and get right in this type of agent-based model.
Exploring the way jaguars move through landscapes involves understanding how they interact with each other and with the environment. Territory formation and avoidance (or not) of conspecifics are integral to getting these interactions to be as close to mimicking those found in real populations as possible.
So.... some kind of pheromone seems that it should elicit an easy territory response in the agents. 'Marking' each cell with some level of pheromone as the agents move into and out of the cell and then allowing this 'pheromone' to degrade over time should allow territories to organically emerge during the simulation and with a bit of tweaking as to how quickly the pheromones should degrade and how 'strong' they should be to other individuals and to themselves.
The main idea is that individuals should not want to re-trace their steps too often, and that generally individuals should try and avoid each other - either due to possible conflicts between adults and due to resource depletion.
We know a bit about how large and flexible territories are in wild jaguar populations and so we settled on a maximum pheromone level of 100, with a degradation rate of 0.98, so that the pheromone reduced by 0.02% each timestep. This gave realistic territory sizes.
The strength of the pheromone is equal to its level, except for an agents own pheromone which is reduced to 0.15% of its current level; a deterrent to re-entering the cell but not enough to mean that the individual would not want to re-treat to its territory if meeting another individual or unsuitable habitat was the only other option.
The addition of pheromones, and the basic least-cost model idea of the simulation led to the following output, where clearly define territories (individuals in different colours) and habitat preferences can be seen:
Some individuals have been 'pushed' out of the forest area due to the population size. This is intentional. A higher number of individuals creates stress for any single individual. Without some level of stress, individuals will be content on remaining in fairly isolated areas. Some stress is needed in order for individuals to move and seek new areas in which lead a lifestyle of least-cost, so prompting the migration of individuals from one side of the landscape to the other.
Exploring the way jaguars move through landscapes involves understanding how they interact with each other and with the environment. Territory formation and avoidance (or not) of conspecifics are integral to getting these interactions to be as close to mimicking those found in real populations as possible.
So.... some kind of pheromone seems that it should elicit an easy territory response in the agents. 'Marking' each cell with some level of pheromone as the agents move into and out of the cell and then allowing this 'pheromone' to degrade over time should allow territories to organically emerge during the simulation and with a bit of tweaking as to how quickly the pheromones should degrade and how 'strong' they should be to other individuals and to themselves.
The main idea is that individuals should not want to re-trace their steps too often, and that generally individuals should try and avoid each other - either due to possible conflicts between adults and due to resource depletion.
We know a bit about how large and flexible territories are in wild jaguar populations and so we settled on a maximum pheromone level of 100, with a degradation rate of 0.98, so that the pheromone reduced by 0.02% each timestep. This gave realistic territory sizes.
The strength of the pheromone is equal to its level, except for an agents own pheromone which is reduced to 0.15% of its current level; a deterrent to re-entering the cell but not enough to mean that the individual would not want to re-treat to its territory if meeting another individual or unsuitable habitat was the only other option.
The addition of pheromones, and the basic least-cost model idea of the simulation led to the following output, where clearly define territories (individuals in different colours) and habitat preferences can be seen:
Some individuals have been 'pushed' out of the forest area due to the population size. This is intentional. A higher number of individuals creates stress for any single individual. Without some level of stress, individuals will be content on remaining in fairly isolated areas. Some stress is needed in order for individuals to move and seek new areas in which lead a lifestyle of least-cost, so prompting the migration of individuals from one side of the landscape to the other.
14.10.11
Jaguar vs Leopard Identification
I found this and thought it summed things up pretty well for anyone not sure on what the differences are between a jaguar and a leopard.
Jaguars also live in central and south America, whilst Leopards are found in central and southern Africa and parts of Asia.
Jaguars also tend to be heavier and stockier than their leopard cousins.
p.s. The Leopard scientific name should read Panthera Pardus.
Jaguars also live in central and south America, whilst Leopards are found in central and southern Africa and parts of Asia.
Jaguars also tend to be heavier and stockier than their leopard cousins.
p.s. The Leopard scientific name should read Panthera Pardus.
20.9.11
1st jaguar simulation model
With my case study involving complicated landscape structures and real-world scenarios, I needed to first get to grips with getting an agent-based model of jaguar movements up and running in a simplified landscape that would enable some interpretation of population dynamics without the need for an in-depth and overly detailed landscape.
After discussing several options, a very abstract and basic landscape structure was decided on to try to answer some fundamental questions important to my on-going research:
1) Can we get a model of jaguar movements working, with plausible daily movements and territory sizes close to those found in real world populations?
2) Does landscape structure seem to influence the way jaguars move around the landscape and does it affect the fitness of individuals and the population as a whole?
3) Can habitat corridors help to increase the connectivity of the landscape and facilitate movement of individuals between habitat patches?
9 landscape structures were defined to help explore these questions, including 3 control landscapes (top row), 3 connected corridors (middle row) and three non-connected corridors (bottom row) :
'Good' habitat here is forest (in green). This is where jaguars will prefer to be. Intermediate habitat is marked in blue, and represented edge habitat; the edge of the forest that meets the non-forest habitat. This is deemed to be less desirable than the forest itself but more desirable than the non-forest habitat. Non-forest (matrix) is coloured beige, and represents any habitat where the jaguar do not want to be; urban areas, agricultural land, roads etc etc.
Landscapes were designed to cover a range of potential options. All designs (bar the first two; the all forest and the 2 distinct habitat patches) have exactly the same amount of forest and matrix habitat. Edge habitat changes depending on the design of the landscape.
The model is designed as a grid, with individual jaguars occupying any one grid cell at a time. Least-cost methodologies are employed so that each habitat has a cost; forest of 1, edge of 5 and non-forest (or matrix) as 25. This represents the strength of the preference of jaguars to any habitat (lower cost equals a much stronger preference).
Next post - more information about jaguar movements and getting territories to develop.
After discussing several options, a very abstract and basic landscape structure was decided on to try to answer some fundamental questions important to my on-going research:
1) Can we get a model of jaguar movements working, with plausible daily movements and territory sizes close to those found in real world populations?
2) Does landscape structure seem to influence the way jaguars move around the landscape and does it affect the fitness of individuals and the population as a whole?
3) Can habitat corridors help to increase the connectivity of the landscape and facilitate movement of individuals between habitat patches?
9 landscape structures were defined to help explore these questions, including 3 control landscapes (top row), 3 connected corridors (middle row) and three non-connected corridors (bottom row) :
'Good' habitat here is forest (in green). This is where jaguars will prefer to be. Intermediate habitat is marked in blue, and represented edge habitat; the edge of the forest that meets the non-forest habitat. This is deemed to be less desirable than the forest itself but more desirable than the non-forest habitat. Non-forest (matrix) is coloured beige, and represents any habitat where the jaguar do not want to be; urban areas, agricultural land, roads etc etc.
Landscapes were designed to cover a range of potential options. All designs (bar the first two; the all forest and the 2 distinct habitat patches) have exactly the same amount of forest and matrix habitat. Edge habitat changes depending on the design of the landscape.
The model is designed as a grid, with individual jaguars occupying any one grid cell at a time. Least-cost methodologies are employed so that each habitat has a cost; forest of 1, edge of 5 and non-forest (or matrix) as 25. This represents the strength of the preference of jaguars to any habitat (lower cost equals a much stronger preference).
Next post - more information about jaguar movements and getting territories to develop.
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