If loading the libraries does result in an ERROR message, check to see that the libraries were installed properly. This is normal, and as long as none of the messages include “ ERROR”, you can just hum right through those messages. There is a good chance you might have seen some red messages print out to the screen, especially when loading the maptools or rgdal libraries. And of course adding a little bit of information at the very top of our script that says what the script does and who is responsible! # Species distribution modeling for saguaro We’ll start our script by loading those five libraries we need. Rather than downloading the data from WorldClim, we’ll use functions from the dismo package to download these data (see below). In this lesson we will focus on the 19 abiotic variables available from WorldClim. Environmental data: these are descriptors of the environment, and can include abiotic measurements of temperature and precipitation as well as biotic factors, such as the presence or absence of other species (like predators, competitors, or food sources).For this lesson, we will use the occurrence data of the saguaro that you downloaded earlier. Absence data are a bit harder to come by, but are required by some modeling approaches.
Some models also make use of ‘absence’ data, which are geographic coordinates of locations where the species is known to not occur. Occurrence data: these are usually latitude and longitude geographic coordinates where the species of interest has been observed.The basic idea behind species distribution models is to take two sources of information to model the conditions in which a species is expected to occur.
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