Welcome to the HexSim Project
HexSim is a spatially-explicit, individual-based computer model designed for simulating terrestrial wildlife population dynamics and interactions. HexSim is a modeling framework within which plant and animal population models are constructed. Users define the model structure, complexity, and data needs. Every HexSim function can be accessed through a sophisticated graphical user interface (GUI). HexSim uses spatial data to capture landscape structure, habitat quality, stressor distribution, and other types of information. HexSim’s design makes it ideal for exploring the cumulative impacts to wildlife populations and plants resulting from multiple interacting stressors.
HexSim simulations are built around a user-defined life cycle. This life cycle is the principal mechanism driving all other model processing and data needs. Users develop the life cycle when setting up a simulation (but it can be modified at any time). The life cycle consists of a sequence of life-history events that are selected from a list. This event list includes survival, reproduction, movement, resource acquisition, species interactions, and many other actions. Through the creative use of events, the user can impose yearly, seasonal, daily, or other temporal cycles on the simulated population. Each event can work with all, or just a segment of a population, and events can be linked to static or dynamic spatial data layers. Each life-cycle event has its own data requirements. Simple scenarios may use few events with minimal parametrization and little spatial data. But when more complexity is warranted, HexSim allows a great deal of data and behavior to be added to its simulations.
HexSim scenarios include descriptions of one or more populations, spatial data needs, life cycle structure, event data, and basic simulation criteria such as the length of each simulation. Each population is composed of individuals, and individuals have traits that can change probabilistically, or based on age, resource availability, disturbance, competition, etc. HexSim also includes genetics and heritable traits. The use of traits allows individuals to have unique properties that change in time and space. Traits also allow populations to be segregated into classes, such as males and females, fitness levels, disease categories, etc. Combinations of trait values can be used to stratify events such as survival, reproduction, movement, and so on.
Traits are a fundamental part of HexSim scenarios. HexSim traits are defined at the population level, but they are implemented on an individual basis. HexSim’s traits can be used to control most life cycle events. Traits influence events because events can be stratified by trait combinations. For example, a movement event might be set up to operate only on a fledgling stage class. Or a survival event might specify mortality based on the values of a trait that reflects resource acquisition. In addition, one trait’s values can be influenced by multiple other traits, which makes it possible to set up stressor interactions and complex feedback loops. Traits can also be used to capture species’ interactions such as parasitism, competition, mutualism, breeding, etc.
A number of different data analysis tools are built into the HexSim model. These include reports, output maps that illustrate model dynamics, and an animated simulation viewer. In addition, the HexSim Census events can be used to track population size, stratified by any combination of traits. The HexSim reports are written as comma separated variable (CSV) files, and can be opened with a spreadsheet. The output maps are easily converted to raster images or ESRI Shapefiles. Other usability-related features include a batch processing tool, a sensitivity analysis module, the ability to change color schemes, to name a few.
Examples of HexSim applications include population viability analysis for one or more wildlife species, studying the consequences for wildlife of multiple interacting disturbances, assessing which habitat components are most critical for population maintenance, quantifying the consequences of species invasions or competition, designing restoration, mitigation, or reintroduction strategies, determining the impacts that roads and other barriers may be having on viability, measuring the consequences for wildlife of changes to landscape connectivity, exploring mechanisms linking human activities to patterns of disease spread, adding realism to the study of landscape genetics, and more.
HexSim only runs on Microsoft's Windows operating system. However, the model engine is written in C++, so porting it to another platform is a possibility. The HexSim GUI is written in C#, and would have to be completely rewritten for non-Windows computers. The HexSim model engine has been compiled for both 32-bit and 64-bit computers, and the HexSim interface will automatically launch the appropriate version.
HexSim does not use an installer -- you simply download the program and run it. This means it is not necessary to have administrative permissions on your computer to use HexSim. When you download HexSim, you get the model itself, a User's Guide, an example workspace including spatial data and ready-to-run scenarios, and a few accessories. The HexSim User's Guide is complete, but will be improved over time.