Hypotesis Testing In Biogeography

Opinion

Hypothesis testing in biogeography
Michael D. Crisp1, Steven A. Trewick2 and Lyn G. Cook3
1

Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia
Institute of Natural Resources, Massey University, Palmerston North, New Zealand
3
The University of Queensland, School of Biological Sciences, Brisbane, Qld 4072, Australia
2

Often,biogeography is applied only as a narrative addition to phylogenetic studies and lacks scientific rigour.
However, if research questions are framed as hypotheses, biogeographical scenarios become testable. In this
review, we explain some problems with narrative biogeography and show how the use of explicit hypotheses
is changing understanding of how organisms came to be
distributed as they are.Developing synergies between
biogeography, ecology, molecular dating and palaeontology are providing novel data and hypothesis-testing
opportunities. New approaches are challenging the classic ‘Gondwana’ paradigm and a more complicated history of the Southern Hemisphere is emerging, involving
not only general drivers such as continental drift and
niche conservatism, but also drowning andre-emergence of landmasses, biotic turnover and long-distance
colonization.

What is biogeography?
Biogeography is the study of the distribution and evolution
of organisms through space and time [1]. New methods
have given impetus to the discipline: for example, geographic information systems (GIS) for spatial analysis
[2]; Bayesian molecular phylogenetics for dating divergences between lineages [3];and integrative models for
reconstructing distributional change through evolutionary
time, using either maximum likelihood [4] or Bayesian
inference [5]. Above all, renewed recognition that ecological factors (e.g. climatic tolerance and dispersal limitation)
underlie deep historical events (i.e. speciation, extinction
and distributional change) [6,7] has rekindled interest in
old questions,such as ‘how do ecological factors influence
the processes of vicariance and long-distance dispersal and
establishment (LDDE)?’ (see Glossary) [6–8]. It has also
stimulated new questions, such as ‘what is the role of niche
conservatism in large-scale community assembly?’ [8–10].
In the beginning, with Wallace and Darwin, biogeography
was an exploration of evolution and it is popular todaybecause, with new methods, it can open windows on the
geographical dimensions of speciation. Although hypotheses about ancient ecological processes are not testable by
direct observation or experiment, their predictions about
present-day biota can potentially be tested. These include
predictions about distributional patterns, fossils, likelihoods of dispersal, and the shapes and timing ofphylogenies [11].
Corresponding author: Crisp, M.D. (mike.crisp@anu.edu.au).

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A purely inductive approach (‘pattern before process’) is
not science
Unfortunately, biogeography often lacks rigour when it is
presented as a geo-historical narrative for a single taxon,
commonly as an addendum to a phylogenetic analysis.
Biogeography deals with historical events that can neither
be observeddirectly nor manipulated experimentally, and
this limitation has been used to justify inductivism; that is,
the view that researchers should first observe and analyse
the present-day pattern and only then might explanations
emerge in terms of historical processes (‘pattern before
process’) [12,13]. In a commonly used inductivist approach,
Glossary
Area cladogram: a phylogeny in which thenames of the organisms at
the tips are replaced by those of the areas in which they occur (e.g.
[13,19]).
Ancestral area reconstruction (AAR): inference of hypothetical ancestral areas at the internal nodes (and root) of a phylogeny by ‘optimizing’ from known areas at the tips of an area cladogram. Several
methods are used for AAR, including parsimony and increasingly
complex models using...