About the developers of the BIOCLIM/GARP MOSAIC tool
Phone: +61-6-274 1134
Fax : +61-6-274 1333
The idea of BIOCLIM is to find a single rule that identifies all areas with a similar climate to the locations of the species. To do this, the basic BIOCLIM algorithm (Nix 1986, Busby 1991, McMahon et al. 1996) finds the climatic range of the points for each climatic variable. The Climatic Envelope Model is a GARP-simulation of the bounding box, climate envelope method as used in BIOCLIM. It uses the concept of a bounding box to enclose the data points formed from a number of climate variables derived from climate surfaces (see below). It differs from the BIOCLIM program in the rule-based algorithm it uses to derive the predictions.The rules used here, consisting of ranges of climate for all climate variables, then encloses all points, within statistically defined limits. For example, the following rule was formed from the ranges of climate variables that enclose 90% of the data points as determined by calculating the mean and the standard deviation of the points.
IF TANN=(23,29]degC AND TMNCM=(10,16]degC AND TMXWM=(35,38]degC AND TSPAN=(19,27]degC AND TCLQ=(21,23]degC AND TWMQ=(29,30]degC AND TWETQ=(24,32]degC AND TDRYQ=(19,26]degC AND RANN=(609,1420]mm AND RWETM=(156,319]mm AND RDRY=(1,1]mm AND RCV=(101,123]mm2 AND RWETQ=(460,874]mm AND RDRYQ=(0,9]mm AND RCLQ=(1,16]mm AND RWMQ=(272,532]mm AND TMEL=(17,263]masl AND TMXEL=(40,303]masl AND TMNEL=(4,230]masl AND TREL=(0,105]masl AND LONG=(128,136]deg AND LAT=(-12,-15]deg THEN SP=PRESENTCentral assumptions are used in Climate Envelope Model are: the distribution of the species is determined by climate, the distribution of the climatic variables is standard normal, and all variables with restricted ranges influence the species of interest. With all modelling systems if the assumptions of a method are not satisfied then the results will be unreliable, or simply quite wrong. While Bioclim has been shown to give satisfactory results for many species, there was a percieved need to develop a system with less restrictive assumptions. Thus GARP (Genetic Algorithm for Rule-set Production) was developed with aims to develop models with:
IF TCLQ=(6,19]degC THEN SP=ABSENT IF GEO=(28,241]c AND SRT=(3,4]c AND TMNEL=(-19,308]masl AND LAT=(-13,-39]deg THEN SP=ABSENT IF RWMQ=(107,1176]mm THEN SP=PRESENT IF GEO=(6,244]c AND TMNEL=(285,1480]masl THEN SP=ABSENTThe production of a set of rules raises the problem of conflict. For example, at a given point, one rule might predict the presence of a species and another the absence. In these cases GARP predicts using the rule with the highest expected accuracy. GARP has a number of other features for increasing the rigour, reliability, and flexability when modelling species distributions. In the context of this application GARP can be seen as value-adding to the BIOCLIM method by increasing the accuracy and suggesting causal factors. This can be seen by comparing the predictive accuracy and the rules generated by the two methods.