Jeff, Brian Cade (who responded earlier) and Barry Noon wrote a paper (Front Ecol Environ 2003; 1(8): 412-420) on quantile regression that discussed some of the issues that unmeasured limiting factors cause. Jason -----Original Message----- From: R-sig-ecology <r-sig-ecology-bounces at r-project.org> On Behalf Of Stratford, Jeff Sent: Sunday, October 30, 2022 5:06 PM To: Dixon, Philip M [STAT] <pdixon at iastate.edu> Cc: r-sig-ecology at r-project.org Subject: Re: [R-sig-eco] Modeling variability along a gradient using GAMLSS Thanks all. These are great suggestions. Someone much smarter than I am needs to write a paper on the ecology and statistical analysis of gradients. It seems that many response variables are closely tied to an environmental variable on one end of the gradient but not the other. For example, my work with migrant birds show that species richness declines with increasing urbanization and the relationship is tight past 30% urbanization but less than 30% the relationship isn't so clear. So many non-urban (not necessarily forested) sites have many more species than urban sites but a number of sites have very few species. So it seems a second variable kicks in when urbanization is low. My guess would be forest edge. But if you include forest edge in a regression model it would show up as insignificant because the overall pattern is driven by urban cover. Hope this all makes sense. Thanks for listening! ******************************************************** Jeffrey A. Stratford, PhD. Department of Biology and Earth System Sciences 84 W South Street Wilkes University, PA 18766 USA https://sites.google.com/a/wilkes.edu/stratford/ ******************************************************** On Sat, Oct 29, 2022 at 7:42 AM Dixon, Philip M [STAT] <pdixon at iastate.edu> wrote:
Jeff, And, if you don't want to dive into Bayesian methods, the GAMLSS package allows you to specify models for location, for scale (what you want) and/or for shape. Those models can be parametric or nonparametric, including multiple types of splines. https://linkprotect.cudasvc.com/url?a=https%3a%2f%2fwww.gamlss.com%2fb ooks-articles%2f&c=E,1,aQI7rQT0C1j9y2LKCn3SWDbP7XntqpLuu-WrmPjd6CcAUqw GCoKffo6NqOB7LVQU5i1F7DLf2wTkBV6Nj2LFZhJizmymEcNnMnSiaT0abTfmCd3i&typo =1 provides resources, including links to short course notes and a J. Stat Software article. Best, Philip [[alternative HTML version deleted]]
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