refugia

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Several weeks ago, a brief review of Wignall's comment appeared here.  
For those on the net who don't receive the circulars from IGCP 335 (Biotic 
Recoveries from Mass Extinction) led by Dr. Douglas H. Erwin and Prof. 
Erle G. Kauffman, we have decided to retype Wignall's original piece as 
it appeared in the Fourth Circular, followed by our (Erle Kauffman 
and Peter Harries) response to it which will appear in the Fifth Circular.

DO REFUGIA REALLY EXIST?  by Paul Wignall, University of Leeds
	The recent meeting of Project 335 at Plymouth highlighted the 
rather varied and generally vague use of the term refugia.  In reality 
refugia (in the sense used at Plymouth) probably do not exist.  In the 
context of mass extinctions, a refugium is considered a place that 
remains habitable whilst all around is uninhabitable.  Populations of 
species which disappear from everywhere else in the world remain as lucky 
survivors on their refuge.  Why?  Presumably because their local 
environment is somewhow immured from the global perturbations.  Just how 
this could come about is never explained.  Most taxa are in fact Lazarus 
taxa because we haven't yet found them, the refugia are therefore 
intrinsically hypothetical.
	Essentially refuge/Lazarus taxa are a product of inadequate 
sampling.  But consider what happens when we collect this missing taxa in 
some previously sampled part of the world.  Do we call this area the 
refuge?  What happens when they are collected from a second area, does that 
become another refuge?  In fact, refugia are impossible to prove, because 
with further testing (collecting), they gradually cease to exist.  
Refugia are just an indirect admittal of an inadequate database for which 
we already have the far more useful concept of Lazarus taxa - a term 
which has no connotations of hypothetical paradise.
	Many of the supposed refugia taxa proposed recently have been 
discovered in China - an area that has only been well known to western 
paleontologists for a decade or so.  Thus the refugia taxa are new to us 
and in many cases that is the only reason for calling them such.  But, 
consider how we would perceive such fossils if they had been discovered 
neraly two centuries ago at the time that many of the familiar British 
fossils were first being found.  Such fossils would be familiar to us, 
they would probably feature in textbooks and generally there would be no 
tendency to consider them unusual or at all special.
	Thus refugia as geographic entities do not exist.  Most 
references to such areas rely on the circular reasoning that the area is 
a refugium because it contains refuge species.  I would suggest that a 
refuge can only exist in an environmental sense.  For example, if an 
anoxic event wipes out shallow-marine faunas whilst leaving the deep 
ocean untouched then the deep ocean abyssal zone becomes a refuge for 
that particular event.  In order to define a refuge environment we must 
be able to demonstrate two things:
	i) the taxa in that environment show preferential survival during 
mass extinction.
	ii) there must be independent sedimentary/geochemical criteria 
for defining a refuge environment.  The presence of so-called refuge 
species has no diagnostic value.
	Thus, in summary, there is no validity to the concept of 
geographic refugia, but, within anygiven region, there could be an 
environmental refuge.  Defining such environments is fundamental to our 
understanding of mass extinctions and their aftermath.


YOU CAN'T HIDE FROM REFUGIA: A REPLY TO WIGNALL

	Paul Wignall's comment on refugia in the last IGCP 335 newsletter
is not well argued, without data, and misrepresents the sense of the 
discussion at the Plymouth meeting. Whereas none of us would debate 
that some Lazarus Taxa are artifacts of inadequate sampling, especially 
among rare species, others have held up under the rigors of even the most
highly resolved, cm-scale stratigraphic data, and the focused efforts of
numerous international scientists, e.g., across the Frasnian-Famennian, 
Cenomanian-Turonian, and Cretaceous-Tertiary boundary intervals. Without 
evidence to the contrary, there remains a high probability that effective 
refugia existed for these Lazarus Taxa. 
	Wignall's separation of geographic from environmental and ecologic 
aspects of refugia or protected habitats is artificial: clearly these are 
interrelated aspects of all habitats; geography strongly influences local 
environments, the nature and diversity of habitats, and biological response
to them. To further state that all refugia are "hypothetical paradises" 
which cannot be defined by their constituent organisms, ignores the facts 
of biology and paleobiology, as well as widely utilized concepts of refugia 
and refugia species. Many modern refugia are documented and well-studied, 
including specific deep-sea habitats, reef caves and other cryptic 
sites, cold artesian springs and bogs with periglacial biotas in more 
temperate climate zones, isolated valleys with tropical microclimates within 
arid and/or temperate mountain ranges, mountain-top microhabitats with 
Pleistocene-style climates and biotas, situated well south (or north) of 
the present glacial margin, and many others. We further imagine that cryptic 
sclerosponges, deep-sea monoplacophorans, stalked crinoids and hexactinellids,
coelocanths, and Austral marsupials would be surprised to learn that their
survival in these isolated and/or secondary habitats were not evidence of 
refugia. Pervasive negativism is not the way to unravel the the complex
phenomena of survival and recovery from mass extinction: rather it is an 
excuse not to look for answers and test hypotheses with comprehensive data 
sets.	In an attempt to be more objective in this debate, and avoid semantic 
arguments, we broadly define the nature and scope of refugia and refugia 
species below, culled from diverse published literature and the advice of 
numerous colleagues, and request your constructive comments to help us arrive 
at a generally acceptable set of concepts for IGCP 335 studies. In making 
this proposal, we assume that there were protected habitats for fossil taxa, 
as there are for modern refugia species, to which (a) organisms could migrate,
by design or chance, (b) in which they have been stranded by long-term 
environmental changes around them, or emigration of their primary habitats, 
or (c) which they marginally occupied during background conditions, 
collectively allowing at least limited populations to survive the rigors of 
mass extinction. These refugia taxa would thus be available to return to 
former primary habitats (or post-extinction variations of these) and thus 
to partially seed the recovery of ecosystems following biotic crises. 
	The origins of the concept of a refuge are relevant, and rooted in 
human history. Refuge (from the Latin refugium) means to flee, and seek 
shelter and protection from danger and distress; a refuge (or refugium) is 
a shelter or protection from danger, distress, and calamity; any place 
where one is out of the way of danger. The meaning of refuge or refugium 
seems obvious, and it is also relevant that dictionary definitions, from 
which the above was culled, implies migration from an organisms' primary 
habitat to a new or secondary habitat, even over a short distance. We present 
below, to focus discussion, a broad paleobiologic/biologic definition of 
refugia from our paper recently submitted to the research volume stemming 
from the IGCP 335 Plymouth, UK, meeting in September, 1994. 
	Refugia are very small (e.g. reef cavities, artesian springs) to very
large (e.g., the deep ocean) protected habitats which (a) have been isolated 
or left-behind by long-term deterioraton or shifts in once-prominent Earth 
environments (e.g., glacial retreat), (b) to which organisms have 
emigrated from primary habitats during times of severe environmental 
stress, and/or (c) to which local species populations have adapted, and 
ultimately become restricted, at the margins of their primary species range. 
Primary habitation of refugia by surviving species populations commonly 
results from environmental deterioration and/or competitive displacement 
in their original preferred habitat. Refugia effectively protect species 
from the severe environmental perturbations that lead to a significant 
decline in biomass, mass death, and mass extinction of taxa in more 
perturbed primary habitats. The character of these refugia may vary 
among organisms and different mass extinction events, depending on the 
nature of forcing mechanisms and their environmental feedback loops. Many 
refugia taxa probably retain their ability to reoccupy primary habitats 
from which they have been environmentally and/or biologically displaced, 
as Immigrant Survivors, as those environments stabilize or themselves
immigrate back into the area of the refugium; refugia species may thus 
comprise Lazarus Taxa. Their ability to do this, however, may decline as 
the evolutionary time in the refugium lengthens. Two types of refugia 
species have been recognized in the biostratigraphic record of mass 
extinctions: Short- and Long-term Refugia Species (or taxa, clades).
	Short-term Refugia Species are those taxa which were forced into 
refugia habitats they did not previously occupy, or which they sparsely 
occupied as small populations at the margins of their adaptive range, 
by highly stressful environmental conditions during regional biological 
crises or mass extinctions. As post-crisis environmental conditions 
normalize, these taxa may rapidly return to occupy their primary habitats, 
through active or passive dispersion, usually without having undergone 
speciation. They thus become short-term Lazarus Taxa or early immigrant 
survivors.  Stratigraphically, short-term refugia taxa have relatively 
continuous biostratigraphic ranges, though with diminishing abundance 
and dispersion, into early phases of a mass extinction interval, at which 
time they essentially disappear from the fossil record or have very rare 
scattered occurrences (possibly representing immigration episodes during 
short, less stressful environmental intervals), during the major interval 
of environmental decline. After a geologically short interval of non-
occurrence, they then return abundantly as immigrant Lazarus Taxa within 
the survival and early recovery intervals.
	Long-term Refugia Species comprise those taxa which have been 
displaced from their primary habitat (usually through biological 
competition or long-term emigration or destruction of their primary 
habitat) long before the onset of stressed environments associated with 
biodiversity crises and mass extinction. These refugia taxa may further 
have evolved new taxa and adapted to their refugia habitats, while still 
retaining their dispersal potential. If the original displacing mechanism 
or competitor no longer exists after the crisis event, or their prior 
habitat re-develops in a region,  these long-term refugia taxa may expand 
their range to include their original or related niches, either as the 
same species (in slowly evolving lineages) or as new, phylogenetically 
related species with similar habitat requirements. Conceivably, long-term 
refugia species could have evolved characteristics that would allow them to 
occupy a different primary habitat after a mass extinction than that which 
they originally inhabited. Stratigraphically, these long-term refugia taxa 
become rare or disappear from the fossil record in their primary habitats
before the first perturbations associated with mass extinction intervals. 
After long stratigraphic intervals of non-occurrence, they reappear as late 
immigrants, or long-term Lazarus Taxa, during ecosystem recovery.
	Some workers have a more expanded view of refugia species, suggesting 
that the term also applies to species whose populations are greatly reduced 
and temporarily restricted to within a small portion of their original
primary habitat by a short-term environmental crisis, and which may 
subsequently reoccupy much of their original prime ecospace as environmental 
conditions ameliorate. Because this example does not involve significant 
migration of either the habitat (away from the refugium), or of the main 
surviving species population(s) (away from the perturbation) to new or 
marginal habitats (i.e. refugia) that are more protected from these 
perturbations, it does not strictly fit the original definition of a 
refugium species (or population). We have termed these types of survivors 
"stranded populations."	We invite your comments on these concepts in future 
IGCP 335 newsletters.

Erle G. Kauffman, Department of Geological Sciences, University of Colorado, 
Boulder, CO 80309-0250, and Peter J. Harries, Department of Geology, 
University of South Florida, Tampa, FL 33620-5200, U. S. A.