Dear list, I am relatively new to ArcGIS and its ecological applications, so please excuse me if this question seems naive or wrongheaded...
I have obtained all of the existing herbarium records for 29 aquatic weed species in Australia (approximately 1580 records total), as well as several GIS layers showing things like land use, dominant vegetation type, cover class, etc. Basically, I would like to be able to demonstrate that the spatial pattern I'm seeing is statistically valid, but I'm not sure how to do that. The principal spatial pattern I see from "selecting by" the various polygon features in my GIS layers is that the density of aquatic weed records is greater in "intensive" land use types (e.g. urban residential areas) than in other types. I derived density values by taking the total number of herbarium records (points) falling within those selected polygons and dividing by the total area (in km2) of the selected polygons. The problem is that this leaves me with only one density value for each land use type, which is, of course, not possibly to analyze statistically. How does one "replicate" when sampling from a map? I also went through the exercise of picking out each individual point (herbarium record, so each point is an individual of a particular species) and characterizing it in terms of the land use type, vegetation type, and cover class it sits in and whether or not it falls within 100 km of a city, but I am not really sure what I can do with that dataset. It is, at least, much bigger than the 5 density data points I have. If you can see an obvious solution to this or know of instructive texts or papers, please let me know. If you think there's nothing I can do with this dataset, I suppose that's good (but depressing) information too. If you have comments about the validity of using herbarium records to interpret distribution, I am somewhat aware of the issue already. Thank you. Lauren Quinn _________________________________________________________________ Making the world a better place one message at a time. http://www.imtalkathon.com/?source=EML_WLH_Talkathon_BetterPlace
