What is a species?

• The morphological concept of species uses the internal and external structure and appearance of organisms to determine a species. These characteristics are easy to observe, making species identification simple.
• The biological concept of species considers a species a population of organisms that can successfully interbreed but cannot breed with other groups. This characteristic is not easily observed, leading to disagreements in species identification.

Carolus Linnaeus is the Father of our modern system of scientific classification.

The major levels of classification, beginning with the largest group are:

• Kingdom
• Phylum
• Class
• Order
• Family
• Genus
• Species

 
Common vs Scientific:

You understand what I mean when I say, "I'm going to sit under a post oak tree by the creek and catch some perch". A biologist would want me to say, "I'm going to sit under a Quercus stellata by the creek and catch some Lepomis macrochirus". Why? Because not everyone attaches the same common names to the same organism. Actually, a perch is not a perch at all. It is a "sunfish". And many people call a post oak tree a "blackjack".

Binomial nomenclature: a two part system for scientific names.

• The genus name is written first and always capitalized.
   
• The species name is written second and never capitalized.
   
• Both names are italicized or underlined.
   
• "Formal" scientific names have a third part - the authority. It is written after the species name as an abbreviation of the last name of the person responsible for naming the organism and placed after the species name.
   
  • Example: Quercus alba L.
   
• The L. is common with plant names because Linnaeus was the first person to name many plants.

Click on the picture below to practice using "couplets" to identify the insect.

Morphology is the study of the body structure of organisms.

• Homologous structures are organs in different species that have the same basic structure.  
• Analogous structures are organs in different species that have different structure but perform the same function.

 
Physiology is the study of the internal workings of organisms - organ systems. The more complex the organism, the more complex its organ systems.

 
Evolution is the process by which living things change over a period of time.

NOTE: There is no doubt that living things change over time. The question is about speciation - one type of organism changing into another type of organism.

Phylogeny is the reconstruction of the evolutionary history of an organism. It is the cornerstone of a branch of biology called systematic taxonomy. Systematics, as it is commonly called, organizes the diversity of living things into the context of evolutionary relationships.

A phylogenetic tree is a family tree showing a hypothesis about the evolutionary relationships thought to exist among groups of organisms. It does not show a proven evolutionary history of the organisms.

The branches on a phylogenetic tree represent places where a gene pool is spearated.

Phylogenetic trees are usually based on a combination of these lines of evidence:

• The fossil record
• Morphology, body structure
• Embryological development
• Chromosomes and DNA

 
Cladistics is a system of phylogenetic classification that uses shared derived characters to establish evolutionary relationships. A derived character is a feature that apparently evolved only within the group under consideration.

Cladistics is based on three assumptions:

• Organisms within a group are descended from a common ancestor.
   
• There is a bifurcating (branching) pattern of cladogenesis.
   
• Change in characteristics occurs in lineages over time.