The Concept of a Species
CLASSIFICATION - organisation of living organisms into groups, based on a number of accepted principles.
The concept of a species - members of a species have certain things in common:
- Similar to one another, different to others - similar genes, they physically and biochemically resemble each other, and they have similar patterns of development and immunological features (occupy the same ecological niche).
- Capable of breeding and producing living, fertile offspring - successfully able to produce more offspring. When species sexually reproduce, any genes can be combined (belong to the same gene pool).
The Binomial System
Binomial System (naming species) - Organisms are identified by 2 names. Its features are:
- Its a universal system based on Latin/Greek names.
- Its first name, Generic name, tells us which genus the organism belongs in.
- Its second name, Specific name, tells us which species the organism belongs in.
- The names are printed in italics. Or if handwritten, they are underlined to show they are scientific names.
- The first letter of the Generic name is UPPERCASE, the rest is lowercase.
- If the specific name isnt known, it is written as 'SP'.
Classification of species is constantly changing as our knowledge is increasing.
Grouping a Species
Why? It allows better communication between scientists and avoids confusion.
TAXONOMY - the theory and practise of biological classification.
There are two main forms:
- ARTIFICIAL CLASSIFICATION - divides organisms according to their differences. E.g. colour, size, number of legs (ANALOGUS characteristics). It is only temporary.
- NATURAL CLASSIFICATION - based on evolutionary relationships between organisms and their ancestors.
- Classifies species into groups based on their shared features derived from their ancestors.
- Arranges the group into a heirarchy, groups are contained within larger composite groups with no overlap.
Relationships in natural classification are based on HOMOLOGUS CHARACTERISTICS - similar evolutionary origins regardless of their functions as an adult of a species.
All systems of classificationa are human interventions, for our convenience.
TAXON - each group within a natural biological classification.
Taxonomy is the study of these groups, and their positions in the heirarchy, based on their evolutionary line of decent of the group members.
Taxonomic ranks - heirarchy.
- KINGDOM - largest group, and every organism is placed in one.
- PHYLUM - different bodyplan from organisms in other phylums.
- CLASS - due to diversity in phyla.
- ORDER - have additional features in common.
- FAMILY - the differences are less obvious.
Difficulty in Defining a Species
- Species are always changing/evolving - some may develop into a new species.
- Within a species, there can be incredible variation.
- Many species are extinct and have left no fossils.
- Some species rarely/never reproduce.
- Members of different groups in a species may have become isolated - may be classed as a different species.