[R-sig-ME] Mixed modelling and Species Area Relationship (SAR)

[Gitu wa Mbui]

Thanks @TO and @BB. Sounds like there is a consensus that adding area as a
covariate (log area) is the way to go, considering a variable area among
methods. A few clarifications:

1. @TO - under what circumstances would you add area 'as an offset, as a
(log)linear trend, as a smoother'? please clarify

2. Would it make a difference if the model is smoothed spline? (i.e such
that: gamm4(response ~ s(Area) + s(b1, k..) +...)

~Gitu







On Fri, Nov 27, 2015 at 12:21 AM, Thierry Onkelinx <thierry.onkelinx at inbo.be
> wrote:

> Dear Gitu,
>
> If the area is constant within each method, then the random effect of
> method will model the area effect. If not you can add area to the fixed
> effects of the model. You have several options: as an offset, as a
> (log)linear trend, as a smoother, ... Much will depend on your assumption
> on the relation between species richness and sample area.
>
> Best regards,
>
> ir. Thierry Onkelinx
> Instituut voor natuur- en bosonderzoek / Research Institute for Nature and
> Forest
> team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
> Kliniekstraat 25
> 1070 Anderlecht
> Belgium
>
> To call in the statistician after the experiment is done may be no more
> than asking him to perform a post-mortem examination: he may be able to say
> what the experiment died of. ~ Sir Ronald Aylmer Fisher
> The plural of anecdote is not data. ~ Roger Brinner
> The combination of some data and an aching desire for an answer does not
> ensure that a reasonable answer can be extracted from a given body of data.
> ~ John Tukey
>
> 2015-11-26 15:09 GMT+01:00 Gitu wa Mbui <gitumbui at gmail.com>:
>
>> How does one account for the species area relationship in a mixed model of
>> predicting species richness?
>>
>> Sampling was carried out using different methods - photoquadrats,
>> transects
>> etc ( five different methods).
>>
>> The area of the sampled plots differed and there were hundreds of plots. I
>> am constructing a glmm for predicting the species richness, overall, and
>> have configured the Method of sampling as a random intercept in the model.
>> I am wondering how I should construct the model such the influence of SAR
>> is taken into account - considering that SAR can not be a random factor.
>>
>> ~Gitu
>>
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>>
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