Antonio >From what you have given us I cannot see any problem with your original use of >'density'. Population density may be defined as the surface got by summing >individual 2-D activity (utilization) distributions, each of which is >technically a 2-D probability density. This assumes you have information on >all individuals in the area. At the broad scale, the average height of the >surface is what we conventionally understand as 'population density'. At a >fine scale, the density surface is affected by the behaviour of individuals >within their home ranges, which may be what is disturbing your critic, but it >is just the biological reality, as I see it. 'Occupancy' seems irrelevant, and >'usage' is perhaps just a (loose) reference to 2-D utilization.
In another context (spatially explicit capture-recapture) it is useful to define density differently, as a point process where each point is a home range centre or similar, but this need not bother you. I'm sorry I can't put my finger on a reference - it has long seemed 'obvious' to me! Perhaps others can help. Murray Efford ________________________________________ From: Ecological Society of America: grants, jobs, news [[email protected]] On Behalf Of Antonio Uzal Fernandez [[email protected]] Sent: Saturday, 20 March 2010 8:27 a.m. To: [email protected] Subject: [ECOLOG-L] density or usage? Dear Ecolog users, I am a PhD candidate working on the impact of a wild herbivore on the plant and animal communities of a protected habitat. My work has involved the spatial interpolation of animal occurrences to model what I called 'the spatial variation of densities'. However, recent comments about that piece of work said “the scale at which the study was undertaken was too fine to model density........what is modelled is occupancy, or usage...” and "...you are not measuring population density, but usage of the environment... and thus technically you are deriving a surrogate for relative patterns of habitat use/preference, not population density as such". I thought that 'usage' was related to two components: 'intensity' and 'time', instead it seems that using 'density' or 'usage' is dependant on the spatial scale (landscape vs. local) at which the analysis is conducted. I have tried to find a good reference to support the idea that because I am measuring occurrences at a fine spatial scale I cannot use the term 'density' and instead I should use 'usage' or even 'occupancy' but I have not been able to find anything yet. I was wondering if you could share your thoughts about these two terms, maybe you have been faced with the same dilemma? also a reference to support the use of the term 'usage' instead of 'density' would be just fantastic...as my mum always says 'you can only ask...' :-) Thank-you for your time, Regards Antonio + Antonio Uzal Fernandez Postgraduate Researcher Bournemouth University UK BU - the UK's Number One New University The Guardian University Guide 2009 & 2010 This email is intended only for the person to whom it is addressed and may contain confidential information. If you have received this email in error, please notify the sender and delete this email, which must not be copied, distributed or disclosed to any other person. Any views or opinions presented are solely those of the author and do not necessarily represent those of Bournemouth University or its subsidiary companies. Nor can any contract be formed on behalf of the University or its subsidiary companies via email.
