Hi

This has been documented for many groups and has to do principally with
competition and niche theory. We can consider the simplest explanatory model
with the fundamental niche that is the whole multidimensional space
representing the whole range of conditions (abiotic factors, resources etc.)
within which an organism is able to function and which it could occupy if
there were no competitors or interacting species; and the realized niche
which is that part of the fundamental niche that a species actually occupies
in the presence of competitors and/or interacting species. The loss of a
species may result in other species increasing their realized niches in the
absence of  competition, or decrease in competiton. Niche and competition
theory is widely researched but was a particularly 'hot' topic in ecology in
the late '70s to 80s.

Alex

-----Original Message-----
From: Conchologists of America List [mailto:[log in to unmask]]On
Behalf Of Ross Mayhew
Sent: 15 February 2004 11:07
To: [log in to unmask]
Subject: Extinctions and what happens to "empty niches"


The Lottia alveus extinction is quite interesting for a variety of
reasons - one of which is the way its former niche has been taken up by
a similar species at some localities.   In at least two large stands of
Zostera, i have found Lottia testudinalis specialized to inhabit the
eel-grass blades: they are considerably more elliptical - long and
narrow -  than the normal form, and seem to be filling essentially the
same niche that alveus Conrad occupied before the catastrophe that wiped
it out.  I have no idea if these are a genetically distinct population,
or whether some juveniles grow up on the blades, and their shells adapt
to the situation where they live - or whether only the individuals in a
local population whose shells are the required shape (and weight - they
are ligher than their cousins on the ocean floor beside the eel-grass
blades) to remain on the eel-grass, actually manage to do so.  Does
anyone know of a study of this matter, or of similar instances where a
species' niche has begun to be taken over after an extinction or local
expatriation?

From the Early Spring pleasantness of the Great Still-White North.