Species Concept

Biology 1

Carmela Española

Room 107, IB Main Building

M 10-12AM

TTh 10-12AM & 3-5PM

What is a species?

Why do we need to know what a species is?

Why do we need to know what a

species is?

• Utility

• Delimit groups of organisms along natural fault lines, so that

approximately the same groupings can be recovered by

independent observers

• Basic rank of classification

• Order and retrieve information on individual specimens

in collections or data banks

Why do we need to know what a

species is?

• Species are important in biodiversity issues

• Conservation, ecology, legislation concerns focus on this level

• Something quantifiable

Biology

The study of life.

What is a species?

It is actually controversial…

Species concepts

1. Biological species concept

2. Morphological species concept

3. Evolutionary species concept

4. Ecological species concept

What is a species?

Different definitions of the species concept


• A species is a population or group of

populations whose members have the potential

to interbreed and produce fertile offspring

• Reproductive barriers prevent gene flow

between 2 different species

Reproductive barriers between species


Prezygotic barriers

1. Geographical isolation—different areas with physical barrier

2. Ecological isolation—same area but different habitats

3. Temporal isolation—different mating times

4. Behavioral isolation—no sexual attraction

5. Mechanical isolation—incompatible mating organs

6. Gametic isolation—incompatible gametes



Postzygotic barriers

1. Hybrid inviability—hybrids do not survive

2. Hybrid sterility—hybrids do not produce

functional gametes

3. Hybrid breakdown—offspring of hybrids are

weak or infertile

What is a species?



• Difficult to apply on organisms which are not

known to undergo sexual reproduction or where

sexual barriers cannot be determined

What is a species?


2. Morphological species concept

• Used gaps in morphology to delimit species

• Criterion can be extended to ecology, behaviour

or genetics

Morphological

Diagnosis Limitation

• phenotypic plasticity

and genetic variability

• e.g. Eastern Reef EgretOkatopa 2006

• morphologically

cryptic taxa

overlooked

• e.g. Hermit Thrush

The barcode blog 2007

Morphological


• morphological

keys are life stage

and/or gender

selective

• e.g. Blue Rock-

thrush

Photo by Ding Carpio

Morphological


• demands high

level of

expertise

Morphological


What is a species?


3. Evolutionary species concept

• A species is a cluster of organisms that represent a genealogy or a lineage of descent.

• DNA barcoding—identifies unknown individuals through DNA sequences

DNA Barcoding

Methodology• DNA extraction

• PCR amplification

• DNA sequencing

DNA Barcoding

Applications

• Discovery of new species

• Biodiversity assessment

• Phylogenetic studies of closely

related taxa

• Regulation of export/import of

endangered species

What is a species?


4. Ecological species concept

• Proponents: van Valen, Mayr, George Evelyn Hutchinson

• Occupancy of an ecological niche = the entirety of environmental factors that tend to suit and allow an animal or plant species to survive in its habitat; the way of life of a species.

• It is where you are and what you are doing that matters.

Darwin’s Finches Objections to the species concept

• Species are not individual real objects but instead are

manmade constructs.

• They exist, but we don’t know how to measure or define

them.

• It is more useful to identify species using morphological

characters and genetic gaps rather than to try to infer

the underlying process of how they came about.

Objections to the species concept

• If organisms are a continuum of genes, then assigning

“points” become arbitrary.

• Species becomes a unit of measure

• 1 meter ~ 1 yard ~ 1 dipa

• But the diversity of life does not run on just one

straight line

Species as evolutionary units

• Species exist and are real in local communities, but only

within local communities

• If it does not exchange genes with a distant population,

it is fallacious to treat them as the same species.

Challenge for taxonomists

• Taxonomists are in the front line of species

identification

• If you were a taxonomist, how would you classify species?

Points to ponder

• Ecological and biodiversity studies tend to ignore

difficulties in classifying species and assume that species

are objectively real basal units

• Convention on Biological Diversity

• International Union for the Conservation of Nature

• Endangered species

• Whether an organism is species A or species B does not

change its biological characteristics

Points to ponder

• Classification is man-made

• Differences in opinion is to be expected

• Classification is arbitrary

• Changes are to be expected as taxonomists are able to gather

new information aout organisms

• Classification is not the basic biological concept,

DIVERSITY OF LIFE is.

Points to ponder

Hence, it is important to study the similarities and

differences of organisms so that they can be used

to better understand the changes that occurred

among organisms through time.

“

”

If we don’t know what species we have, how can we know what we’re losing and take practical steps to the loss of the world’s

plants and animals?

Dr. Richard LaneDirector of Science

Natural History Museum, London

Sources

• Slides were taken and modified from:

• Bio11 slides

• Bio12 slides

• Dr. Catherine Lagunzad

• Dr. Ma. Dolores Tongco

• Dr. Ian Fontanilla

• Main references:

• Mallet, J. 2007. Species, Concept of. Encyclopedia of Biodiversity

• Zimmer, C. 2008. What is a species? Scientific American

Next meetingMechanisms and evidences of evolution.

Documents

Species Concept