I have a question about data analysis for the list: I'm working on a couple of endangered grouse species (capercaillie and = black grouse) in Scotland. Both species have declined markedly in over the last few decades and = although the data I have available isn't comprehensive, it is = potentially very valuable.
I have data on breeding success for both species that goes back as far = as 1989 from 11 different sites in northern Scotland. However, only two = different sites have the complete sequence of annual data. I'm interested in examining the effects of weather patterns and habitat = on breeding success of the two species.=20 Previous work has suggested that weather patterns during Spring are = important.=20 I therefore have temperature and rainfall data for Spring for all years = since 1989. However, weather data is not site specific and comes from = the nearest weather station. This essentially means that sites in one = catchment share the same weather data, which is then different from the = weather data shared by the remaining sites in a second catchment. I'm also interested in the interaction between weather patterns and = habitat quality. However, I only have comprehensive habitat data from = 1998. I intend therefore to assume that habitat hasn't changed markedly = across the years. To examine the effects of weather conditions, my initial approach has = been to use multiple linear regression (the variables are either normal = or readily transformed) with breeding success as my dependent variable = and the weather variables as my independent variables. My problem is = that over the 15 year period (1989 to 2004), the weather station data = shows that spring has become significantly warmer. Over the same period, = breeding success for the birds has declined. I therefore end up with a = model showing that colder spring temperatures are better for breeding = success, which works fine as a description of what has happened but = doesn't make biological sense. How do I take account of the spurious = pattern in the data in my model building? Essentially, if you like, I = wish to account for the effects of the changes in climate by year before = examining the effects of weather patterns. Additionally, is it sensible to examine any interactions between weather = and habitat variables given that there is no between year habitat = variation and no between site weather variation?=20 I'm working in R, so any specific help relating to that package would = also be welcome. Many thanks, Martin Dallimer Dr Martin Dallimer Woodland Grouse Scientist The Game Conservancy Trust Drumochter Lodge Dalwhinnie Inverness-shire PH19 1AF Scotland Phone: 01528 522300 Mobile: 07734 537654 email: [EMAIL PROTECTED]
