Lecture 4 –
Speciation and Islands

Islands: Ecology, Evolution, & Conservation

Dr. James A. Danoff-Burg

Department of Ecology, Evolution, & Environmental Biology

Columbia University

Today

• Base requirement for understanding speciation

• Species concepts

• Geography and speciation

• Speciation mechanisms

• Phylogeny and speciation inference

Understanding Speciation

• Necessary information for understanding speciation:

– Morphology of species

– Basic biology of species

• Reproductive, consumptive, productive, habitat requirements

– Basic biology of symbionts and “antibionts”

– Impact of abiotic changes on species under study

• In short – Know your Species!

Downfalls of Incomplete Knowledge

• Incorrect inferences

– Geographical distribution

– Impact of abiotic factors

– Impact of biotic factors

– Biological responses

– Reproductive responses

– Functional significance of morphological changes

• All contribute to understanding species limits

– Know your species!

Species Concepts

• Derived from specialists in many taxonomic fields

– Each striving to best understand the world

• Given their experiences

– Great acrimony

• Attempt to create a single, universally applicable species concept

Species Concepts

• Everyone knows what is a species

– No one agrees on what is a species

• Importance of accurately defining species

– Invoking comparable units

– Side note:

• Can higher taxonomic levels be comparable units?

• Definition(s)?

Defining Species

• Biological Species Concept

– Groups of actually or potentially interbreeding natural populations that are reproductively isolated from others

– Mayr 1942, using birds

• Problems with the BSC?

Other Species Concepts

• Proliferation in the 1990s

– As many as 7 or 8 currently advocated

• Examples

– Phylogenetic species concept

– Evolutionary species concept

– Morphological species concept

• How to resolve this issue?

Species Concepts – A Possible Resolution?

• A diversity of species concepts

– Dependent on the situation

• Taxon differences

– Birds vs. beetles, vs. bees vs. plants

• Taxonomist differences

• Temporal isolation

• Geographic isolation?

• A pragmatic nod to reality

– This is essentially what taxonomists do at present anyway

– Darwin’s definition: “well-marked varieties”

Geography and Speciation

• Two main contexts for isolating incipient species (Whittaker 1998)

– Distributional – degree of geographical overlap between populations / incipient species

• Sympatry

• Allopatry

• Parapatry

– Locational – geography of where evolution is occurring

• Neo-endemicity

• Paleo-endemicity

Distributional Context

• Sympatry

• Allopatry

• Parapatry

Locational Context

• Neo-endemicity

• Paleo-endemicity