I think you need to consider the biological reality of the community of
interest. You need a model of the species-abundance curve for this
particular community, where the relative abundance of each species on the
reef is known. So, instead of writing "Sample 1, 6 Fish, 3 Species" you need
to determine how many of each species there are. Simply noting how many
species in a catch doesn't help. You can then use the resulting
species-abundance curve to determine the probability of getting one fish of
each of the seven species in any one sample.
Dan
____________________________
Mr. Daniel P. Bebber
Department of Plant Sciences
University of Oxford
South Parks Road
Oxford OX1 3RB
Tel. 01865 275000
Fax. 01865 275074
> -----Original Message-----
> From: [log in to unmask]
> [mailto:[log in to unmask]]On Behalf Of Coomaren Pillay
> Vencatasawmy
> Sent: 18 August 1999 13:21
> To: [log in to unmask]
> Subject: Help with a probability question
>
>
> Dear all
>
> I got this request from a friend:
>
> In theory, the more fish there is on a reef, the more species are
> expected
> to exist by chance (if fish of different species have a random chance of
> joining the community). My own hypothesis is different so I am trying to
> disprove the hypothesis that different fish species appear at random in
> a
> fish community.
>
> So he took 150 samples, each containing up to 12 fishes.
>
> For example he has (out of a maximum of 7 species)
>
> sample 1 6 fish 2 species
> sample 2 4 fish 1 species
> sample 3 8 fish 5 species
>
> He needs to determine the expected number of species in each sample or
> the probability of observing sample 1.
>
> According to me (and him) he is testing the hypothesis prob(getting
> species i)=1/7. So in principle in a sample of 6, he should get 6
> species.
>
> This seems intuitively wrong.
>
> Can anyone help please?
>
> Coomaren
>
>
> ........................................................................
> ........................................................
> Dr Coomaren P Vencatasawmy
> Senior Research Fellow
> Spatial Modelling Centre (SMC)
> P.O. Box 839
> S-981 28
> Kiruna
> Sweden
> [log in to unmask]
> Telephone: 46 980 67013
> Fax : 46 980 67190
> "Perfection is achieved, not when there is nothing more to add, but when
> there is nothing left to take away." - Antoine de Saint Exupery
> ........................................................................
> ........................................................
>
>
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