The design and implementation of an individual-based predator–prey model for a distributed computing environment¹

Abstract

A distributed implementation of the Spatially-Explicit Individual-Based Simulation Model of Florida Panther and White-Tailed Deer in the Everglades and Big Cypress Landscapes (SIMPDEL) model is presented. SIMPDEL models the impact of different water management strategies in the South Florida region on the white-tailed deer and the Florida panther populations. SIMPDEL models the interaction of the four interrelated components – vegetation, hydrology, white-tailed deer and Florida panther, over a time span up to several decades. Very similar outputs of bioenergetic and survival statistics were obtained from the serial and distributed models. A performance evaluation of the two models revealed moderate speed improvements for the distributed model (referred to as DSIMPDEL). The 4-processor configuration attained a speed improvement of 3.83 with small deer populations on an ATM-based network of SUN Ultra 2 workstations over the serial model executing on a single SUN Ultra 2 workstation.

Introduction

The landscape of South Florida is a complex environment that has been subjected to years of environmental stress. Disruptions in the natural water flows have been the catalyst for profound changes in the vegetation and animal life in the region. Attempts are now being made to repair the devastating effects of these changes in the water flow on the ecosystem of the South Florida region [10]. The effects of these corrections must be modeled to ensure that these new changes do not further harm the fragile region. The most effective way to evaluate the effects of changes on this complex environment is through computer modeling [5]. The Across Trophic Levels System Simulation for the Everglades and Big Cyprus Swamp (ATLSS) [5]family of models was developed to address modeling the impacts of environmental changes on this region. The Spatially-Explicit Individual-Based Simulation Model of Florida Panther and White-Tailed Deer in the Everglades and Big Cypress Landscapes (SIMPDEL) model [4]is one component of the ATLSS model. SIMPDEL was developed to model the interaction of the vegetation, hydrology, white-tailed deer and Florida panther in the region.

The serial SIMPDEL model demanded extensive computer resources in the form of memory requirements and execution time. To address these memory and time requirements, a parallel implementation (PSIMPDEL) was developed for the Thinking Machines CM-5 [1]. PSIMPDEL incorporated the vegetation, hydrology, and deer components of the SIMPDEL model [2]and provided outputs comparable to the serial SIMPDEL model. The limitation to the PSIMPDEL implementation was that the model was developed specifically for the Thinking Machines CM-5, and did not include the panther component of SIMPDEL. This need for a model that incorporated the panther component and could be executed on a network of workstations was the motivation for the development of the DSIMPDEL model. The following sections briefly describe the background work of the SIMPDEL and PSIMPEL implementations followed by a more detailed description of the DSIMPDEL implementation (Section 3), model verification and performance (Section 4). Conclusions to this modeling effort are provided in Section 5.

In the following sections, m denotes meters and the notation 500 m grid cell is used to refer to a grid cell that contains information about an area that is $\text{500}\text{m}\text{×500}\text{m}$. A $\text{100}\text{m}\text{×100}\text{m}$ grid cell is referred to as a 100 m grid cell. P_i, P_j, and P_k are used to represent processor ID numbers of the machines used in the simulation. The notation P_i is always used to represent the current processor. P_j and P_k are used to represent any other processors participating in the simulation.