BDE 244: Species Concepts & Speciation
Lecture Notes by Tegan Gibaud
Species Concepts: Introduction & Phenetic Species Concept
Definitions Allopatric: Taking place as a result of allopatric separation - the
separation due to non-overlapping geological areas.
Holotype: A single type specimen upon which the description and
name of a new species is based.
Species Concepts There are several ways to categorize species such as the
morphological species concept, phenetic species concept, biological
species concept,
The Dilemma When Categorizing Species
➔ It is easy to categorize a species when they occur together in a
community and when there is little disagreement about where
the species boundaries lie.
➔ However, when there are differences among allopatric
populations, the taxonomic rank becomes subjective.
➔ If gradual evolution occurs, populations would have
intermediates which may complicate the taxonomic process.
“Variety”
● In taxonomic ranking, “variety” is seldomly used.
● It is considered below the ranking of “species” and “subspecies”
but above “form”.
● The variety rank is used if the taxon is seen throughout the
geographic range of the species.
“Lumpers” vs “Splitters”
● Taxonomists are often categorized as “lumpers” or “splitters”.
● Ted Oliver - the leading Erica taxonomist - is a lumper.
● Splitters would say that each of his Erica species contain many
species.
Species Concepts
→ There are many different species concepts that perform different
functions.
1. Phenetic (morphological/phenotypic)
2. Biological
3. Phylogenetic
Morphological Phenetic includes morphological, physiological and behavioural traits.
(Phenetic) Species Phenetic = phenotypic.
Concept
The morphological species concept is based on the idea that a group
1
,of individuals that are more similar to each other than to individuals of
other species.
Darwin (1859) stated that “...varieties have the same general
characters as species, for they cannot be distinguished from species, -
except, firstly, by the discovery of intermediate linking forms...; and
except, secondly, by a certain amount of difference, for two forms, if
differing very little, are generally ranked as varieties.… the complete
absence, in a well-investigated region, of varieties linking together any
two closely-allied forms, is probably the most important of all the
criterions of their specific distinctness.”
This concept requires morphological discontinuity between species as
well as consistent difference which is not always the case.
➔ It is pattern based rather than process based.
Image: https://slidetodoc.com/identifying-naming-and-classifying-species-sbu-3-u/
Prof Pauw’s Work: Species Amount Determination
● An analysis of the W. nodiflora showed that an individual could
resprout (if burnt) into a different morphology as a response to a
different niche.
● Ecological differences can thus inform the morphological
species concept.
● It is important to consider allometry when comparing
individuals. Example: the bark thickness of two individuals
cannot be compared without considering how thick the trunks
are. Instead, an allometric scaling relationship must be
constructed.
● Note: Histograms are useful for detecting groups. (See below)
In this diagram, bimodality suggests the existence of two
species.
2
, Image: Lecture Slides
● A multivariate analysis (in the below case, a Principal
components analysis) considers many traits together and
objectively defines clusters. Each point on the graph is an
individuals. It is expected that the different species should form
discrete clusters.
Image: Lecture Slides
● It was found that two species are very similar, but variation is
not continuous - there are some discontinuities. Example: the
length of branchlets are different. These differences clearly
separate individuals into species. There are no intermediates.
Dichotomous Keys Dichotomous keys help you to identify an individual that has been
captured. It is called this as it utilizes dividing concepts into two
branches.
3
, Simple Dichotomous Key Example:
Image: https://www.nagwa.com/en/explainers/842173734891/
Example of University Versions:
Image: Lecture Slides
The first specimen listed is the type specimen or holotype. This is the
individual that represents the species name and therefore these are
very valuable specimens – they generally get red labels.
→ The other specimens listed here are individuals that are considered
by the authors to fall into this species. The species name is followed by
the name of the author and the date, to reflect the subjective nature of
species delimitations.
4
Lecture Notes by Tegan Gibaud
Species Concepts: Introduction & Phenetic Species Concept
Definitions Allopatric: Taking place as a result of allopatric separation - the
separation due to non-overlapping geological areas.
Holotype: A single type specimen upon which the description and
name of a new species is based.
Species Concepts There are several ways to categorize species such as the
morphological species concept, phenetic species concept, biological
species concept,
The Dilemma When Categorizing Species
➔ It is easy to categorize a species when they occur together in a
community and when there is little disagreement about where
the species boundaries lie.
➔ However, when there are differences among allopatric
populations, the taxonomic rank becomes subjective.
➔ If gradual evolution occurs, populations would have
intermediates which may complicate the taxonomic process.
“Variety”
● In taxonomic ranking, “variety” is seldomly used.
● It is considered below the ranking of “species” and “subspecies”
but above “form”.
● The variety rank is used if the taxon is seen throughout the
geographic range of the species.
“Lumpers” vs “Splitters”
● Taxonomists are often categorized as “lumpers” or “splitters”.
● Ted Oliver - the leading Erica taxonomist - is a lumper.
● Splitters would say that each of his Erica species contain many
species.
Species Concepts
→ There are many different species concepts that perform different
functions.
1. Phenetic (morphological/phenotypic)
2. Biological
3. Phylogenetic
Morphological Phenetic includes morphological, physiological and behavioural traits.
(Phenetic) Species Phenetic = phenotypic.
Concept
The morphological species concept is based on the idea that a group
1
,of individuals that are more similar to each other than to individuals of
other species.
Darwin (1859) stated that “...varieties have the same general
characters as species, for they cannot be distinguished from species, -
except, firstly, by the discovery of intermediate linking forms...; and
except, secondly, by a certain amount of difference, for two forms, if
differing very little, are generally ranked as varieties.… the complete
absence, in a well-investigated region, of varieties linking together any
two closely-allied forms, is probably the most important of all the
criterions of their specific distinctness.”
This concept requires morphological discontinuity between species as
well as consistent difference which is not always the case.
➔ It is pattern based rather than process based.
Image: https://slidetodoc.com/identifying-naming-and-classifying-species-sbu-3-u/
Prof Pauw’s Work: Species Amount Determination
● An analysis of the W. nodiflora showed that an individual could
resprout (if burnt) into a different morphology as a response to a
different niche.
● Ecological differences can thus inform the morphological
species concept.
● It is important to consider allometry when comparing
individuals. Example: the bark thickness of two individuals
cannot be compared without considering how thick the trunks
are. Instead, an allometric scaling relationship must be
constructed.
● Note: Histograms are useful for detecting groups. (See below)
In this diagram, bimodality suggests the existence of two
species.
2
, Image: Lecture Slides
● A multivariate analysis (in the below case, a Principal
components analysis) considers many traits together and
objectively defines clusters. Each point on the graph is an
individuals. It is expected that the different species should form
discrete clusters.
Image: Lecture Slides
● It was found that two species are very similar, but variation is
not continuous - there are some discontinuities. Example: the
length of branchlets are different. These differences clearly
separate individuals into species. There are no intermediates.
Dichotomous Keys Dichotomous keys help you to identify an individual that has been
captured. It is called this as it utilizes dividing concepts into two
branches.
3
, Simple Dichotomous Key Example:
Image: https://www.nagwa.com/en/explainers/842173734891/
Example of University Versions:
Image: Lecture Slides
The first specimen listed is the type specimen or holotype. This is the
individual that represents the species name and therefore these are
very valuable specimens – they generally get red labels.
→ The other specimens listed here are individuals that are considered
by the authors to fall into this species. The species name is followed by
the name of the author and the date, to reflect the subjective nature of
species delimitations.
4
