Glacial refugia: What are they? Where have they occured? What has their

impact been on the contemporary disribution and diversity of biota?

(An annotated bibliography compiled by Mark Ward)

Willis, K.J. 1996. Where did all the flowers go? The fate of temperate

European flora during glacial periods. Endeavour. 20:110-114.

This is the paper that we will be discussing in class. Although

there isnt a lot of original data presented in this paper, it looks at the

phenomena of isolated refugia south of the ice front in Europe. What I

liked about it is that it considers the degree to which the isolation of

these refugia may lead to speciation. And it also considers the

implications of these findings for conservation practices. I dont want to

give away too much on this paper since we will all be discussiong it, but

one of my reasons for choosing it was its "readability."

Whitehead, D.R. 1972. Approaches to disjunct populations: the

contributions of palynology. Ann Miss. Bot. Garden. 59:125-137.

This paper surveys a handful of examples of disjunct populations.

It is a good overview of the essential questions that are asked when

discontinuous distributions of species or communities are encountered.

Among these questions are: Do disjuncts represent relict populations? At

what time did the disjunction develop? How different are disjunct

populations to the presumed parent populations? The papers real strength

is that it addresses the degree to which palynological evidence can be

used to answer these questions and the need for interdisciplinary

approaches to this complex biogeographical problem.

Davis, M.B. 1980 Quaternary history and the stability of forest

communities. In Forest succession: concepts and applications ed. by D.C.

West, H.H. Shugart, and D.B. Botkin (pp 132-153), Springer-Verlag.

This paper provides a good overview of the changes in the

vegetation patterns in northeastern North America since the time of the

last glacial maximum. The author points to the likely presence of refugia

for white pine and hemlock on the east coast or in the foothills of the

Appalachians. All of the evidence for the reconstruction of vegetation

comes from dating pollen assemblages throughout the eastern U.S. The paper

compiles a lot of data from other sources into its broad analysis of the

northeast. It includes an excellent discussion of climatic change and the

rate at which tree species arrived and how they have grouped themselves on

the landscape over time. It calls into question the idea of natural

associations of plant community types.

Haffer, J. 1969. Speciation in Amazonian forest birds. Science.

165:131-137.

This paper is extremely speculative and frankly I was surprised to

find it in this journal. The main idea that the author proposes is that

the exceptional diversity of fauna in the Amazonian lowlands can be

accounted for by periodic shrinkages and reexpansions of the Amazonian

forest throughout the Pleistocene. The shrinkages of the forest into

refugia during dry climatic periods allowed speciation to occur more

rapidly because of the geographic isolation of these forest patches.

Haffer makes his case for climatic change by drawing on a handful of

sources, and he combines this with his own analysis of the current

distribution of birds to circumscribe nine presumed forest refuges in

South America during the dry periods of the Pleistocene. He argues that

the rate of speciation among birds was much more rapid during the

Quaternary than during the Tertiary.

Vuilleumier, B.S. 1971. Pleistocene changes in the flora and fauna of

South America. Science. 173:771-780.

This paper uses the Haffer paper as a springboard to try to

account for the changes not only in birds in Amazonia but of much of the

biota of South America. The author breaks the continent into six

geographically defined provinces and surveys the literature from each to

challenge the longheld notion that the continent remained relatively

stable throughout the climatic changes of the Quaternary. Once again the

argument is used that these changes can help account for the wealth of

species in the tropics. The real problem with both this paper and the

Haffer paper are that they fail to take into account the rate at which

speciation occurs in comparison to the duration of the periods of climate

change.

Colinvaux, P.A. et al. 1996. A long pollen record from lowland Amazonia:

Forest and cooling in glacial times. Science. 274:85-88.

This very recent paper looks at a 40,000 year pollen record from a

lake in the Amazonian rain forest. The authors use this pollen record to

argue that in fact glacial age forests did not differ significantly from

modern forests except that they included some species that are now only

found at higher elevations. They use the pollen evidence to suggest a

cooling of only 6C and no resulting breakup of the lowland forests into

refugia as a result of climate change. This paper is an attempt to refute

the arguments of Haffer, Vuillemier and others that climatic changes

fragmented the Amazonian forests. They nevertheless argue that the

scenario of a drop in temperature would cause an increase in diversity

without invoking the refugia argument. The greatest limitation of this

paper is that it examines the pollen record from only one lake in a vast

ecosystem. It makes it difficult to put too much faith in their

interpretation, but nevertheless presents preliminary evidence for a

reconsideration of the refugia hypothesis.

Latham, R.E. and R.E. Ricklefs. 1993. Continental comparisons of

temperate-zone tree species diversity. In Species Diversity in Ecological

Communities ed.

by R.E.Ricklefs and D. Schluter (pp.294-314) University of Chicago Press.

This is an extremely interesting paper which compares the relative

species diversity in the four major north temperate forests of the world

(eastern and western North America, Europe, and east Asia). The number of

species in the east Asian temperate forests greatly exceed those of all

other regions, and the authors are searching for an explanation to this

phenomenon. Unfortunately the way they go about it involves some pretty

heavy duty statistical analysis that is not always very easy to follow. By

combining contemporary distribution information with the fossil records

from different regions they conclude that most cosmopolitan taxa of

temperate trees originated in eastern Asia and dispersed to Europe and

North America. The overall point of the paper is to remind the reader of

the degree to which longer scale evolutionary processes (in contrast to

biogeographical or ecological processes) may control distributions of

temperate tree taxa.

Delcourt, P.A. and H.R. Delcourt. 1987. Long-term Forest Dynamics of the

Temperate Zone: A Case Study of Late-Quaternary Forests in Eastern North

America. Springer-Verlag.

This book is a classic treatise on the effects of glaciation on

the dynamics of temperate forests. It focuses primarily on eastern North

America, but there is an excellent chapter on the climatic history of

Europe that serves as a good comparison of temperate forests on the two

continents. One of the best parts of this book is that at the end of each

chapter the authors clearly state the draw from the data presented.

Hoppe, G. 1963. Some comments on the "ice-free refugia" of northern

Scandinavia. In North Atlantic Biota and their History. ed. by A. Love and

D. Love. (pp. 321-336) Pergamon Press.

This paper is fairly old, but it gives a decent overview of the

two types of proposed Scandinavian refugia--nunataks which remained above

the ice and foreland areas situated above and below the present shoreline.

The author points to the lack of good geological evidence to support the

refugia hypothesis, and cautions that the disjunct distributions of biota

may be explicable by earlier deglaciation than surrounding areas.

The book itself is an often quoted source especially in papers

which deal with the present day distribution of plants and animals in

Europe. Its greatest weeaknes is its age and the lack of use of

palynological evidence to support its arguments. Nevertheless it provides

good reading on the historical development of the idea of glacial

refugia. The titles of some of the other papers that it contains are

"Survival of plants on nunataks in Norway during the Pleistocene

Glaciation" and "Ice-age refugia in Iceland as indicated by the present

distribution of plant species."