Date sent: Mon, 14 Sep 1998 21:07:10 -0700
From: Mike Fuller <mmfuller@UNM.EDU>
Subject: Re: niche occupation
To: ECOLOG-L@UMDD.UMD.EDU
Dear Thomas and Fred:
First of all, the species defines the niche, so if two organisms use
exactly the same niche (in all dimensions), they are the same species, by
definition. Second, niche as profession versus as multi-dimensional sphere
are not equivalent concepts -- you are talking about different things. The
first refers to function (a subset of a niche), and there is ample evidence
for functional redundancy of organisms in the more diverse ecosystems (not
so perhaps in systems of low diversity). The latter refers to a theoretical
object. From the perspective of theory, you certainly can define a niche
"to completeness" because it is a mathematical object. Also, the number of
dimensions is irrelevent -- the mathematics is the same. Thus one could
rigorously prove that two organisms can not occupy identical niches given
limited resources, unless they are the same species (given the above
definition of species). Now I agree completely with Fred that it is nigh
impossible to *measure* every dimension of species niches empirically. That
does not mean as an empirical issue niche is of no value -- empirical tests
of competition theory are useless unless certain dimensions dominate
fitness in a given set of conditions. That said, the original question
struck me as a theoretical problem.
Cheers,
Mike
>You cannot define any niche to completeness, therefore, is will always be
>impossible to falsify or even test for niche similarity in the absolute.
>So, the idea of niche breadth is, and always will be, theoretical and not
>open to experimentation. Sort of like the angels on the head of a pin,
>discussion or coming to the last number in an infinite series; can't be
>done. If you define a niche so that it fits your requirements.....well,
>that really isn't the same problem as the absolute biological niche any
>longer....now it is your niche, not natures.
>
>Fred Rickson
>
>----------
>> From: Thomas Schlemmermeyer <termites@usp.br>
>> To: ECOLOG-L@UMDD.UMD.EDU
>> Subject: niche occupation
>> Date: Monday, September 14, 1998 2:15 PM
>>
>>
>> Dear ECOLOG-L subscribers,
>>
>> my recent question on this topic provoked a lack of understanding.
>> I will reformulate my question in a somewhat more precise way:
>>
>> Intuitively, I always thought that two species never occupy the
>> same niche. The niche definition I had in mind, is the one
>> of a n-dimensional hyperspace.
>> Even if two species may be identical in, let's say, n-1 dimensions,
>> there still rests the n-th dimension where they may differ.
>> So, the very nature of niche definition results in the consequence
>> that two species never occupy the same niche (at least, in my
>> understanding).
>>
>> There are however other niche definitions as well. Let's define
>> niche as a profession of a species: Then one may conclude that
>> two species really occupy the same niche.
>> Because the relation "to have the same profession" is of weaker
nature
>> than the relation "to be identical in a infinite number of
dimensions".
>>
>> Now, let's go ahead: Once you have accepted that many species
>> occupy the same niche, you may look for evolutionay explanations
>> of this pattern and postulate quaternary or pre-quaternary
>> speciation cycles and so on.
>> Hypotheses which simply can be avoided by adopting the first, stronger
>> definition of niche.
>>
>> I still do not know whether my problem is personal, specific or
>> esotheric, but if there are any comments, I will greatly appreciate
>> it.
>>
>> Cheers Thomas
Michael M. Fuller
The Li Lab Group
Department of Biology
University of New Mexico
Albuquerque, New Mexico 87131-1091
