Hi Chris and other interested Ecologgers, I deal with a lot of microclimate data in terrestrial systems in the context of predicting the impacts of winter climate change on insects and other ectotherms. Although a comparison of means will surely be useful, there are many other parameters that may be as important or more important. As you say, it is vitally important to consider thermal variability in addition to mean temperatures, due to the non-linearity of many biological processes and the effects of Jensen's inequality (See Ruel and Ayres 1999 TREE for a nice explanation of the biological impacts of this mathematical phenomenon, and Williams et al. 2012 PLoS ONE 7(3)e34470 for an example of how to use hourly temperature data to predict organismal metabolism). In addition you may want to consider the proximity of extreme temperatures under the rocks to physiological limits (e.g. CTmin or max, LLT or ULT, developmental thresholds). Brent Sinclair has Excel macros that are very easy to use for extracting information from microclimate recordings (Sinclair 2001 Cryo Letters) that are available upon request from the author (now at Western University, bsinc...@uwo.ca) or I can provide you a copy if you email me). I now do most of my microclimate processing in R and I have some scripts I can provide if you want them. You could look at parameters such as number of times temperatures exceed a threshold, duration spent over a threshold etc etc. See our recent paper on freezing frogs for another example of how to use temperature data to predict threshold events (Sinclair et al. 2013 Journal of Experimental Biology doi: 10.1242/jeb.076331).
Cheers, Caroline (carolinewilli...@ufl.edu) -----Original Message----- From: Ecological Society of America: grants, jobs, news [mailto:ECOLOG-L@LI= STSERV.UMD.EDU] On Behalf Of Christopher Brown Sent: Wednesday, February 06, 2013 13:16 To: ECOLOG-L@LISTSERV.UMD.EDU Subject: [ECOLOG-L] Statistical Question on Temperature Profiles Ecologgers, =20 I have a master's student who is examining thermal preferences of two speci= es of scorpions in the Sky Islands of southeastern Arizona. She has gathere= d some field temperature data as part of her thesis, but we are unsure how = best to analyze the data (or perhaps more specifically, what data to analyz= e). I've given some details below, if you have some insight for us! =20 The short version of the experiment: these scorpions are found under rocks = during the day, and we have determined thermal profiles for 15 rocks under = which scorpions were found and 15 rocks under which scorpions were not foun= d. For both sets of rocks, we measured length and width and selected a rang= e of sizes based on binning the rocks into three categories (small, interme= diate, and large) and then choosing 5 rocks in each size range. Each rock h= ad an iButton placed under it, and temperatures were recorded every 30 minu= tes for 48 hours. =20 Her basic question is then, do the thermal characteristics of chosen rocks = differ from the thermal characteristics of non-chosen rocks? Our problem is= , what data should we use? Our first though is at a simple level: we could calculate mean temps for the two rock categories and compar= e them with a t-test, and/or we could compare variances or ranges (max-min) with a t-test to determine if variability differs between rocks. = We've found a couple of different variations of this kind of analysis in th= e literature, but we'd like to know if this is the best (or "best") way to = analyze the data, or are there more sophisticated techniques that involve a= nalysis of the whole profile? If we do use a fairly simple analysis based o= n some type of summary variable, what is the best summary variable to use (= mean? Variance? Range? Something else?) and the best analysis to do? =20 If anyone has any experience in analyzing this type of data and has some suggestions, we'd be happy to hear from you! =20 Thanks, CAB *********************************** Chris Brown Associate Professor Dept. of Biology, Box 5063 Tennessee Tech University Cookeville, TN 38505 email: cabr...@tntech.edu website: iweb.tntech.edu/cabrown =20 ------------------------------ __________________________________________________ Caroline Williams, PhD Postdoctoral Associate, Hahn lab Department of Entomology and Nematology University of Florida Gainesville, FL Cell: (352) 262-2908 Office: (352) 273-3949 Email: carolinewilli...@ufl.edu Website: plaza.ufl.edu/carolinewilliams __________________________________________________
