What is a species

Biological Terminology

  • Species: [ \text{species} ] - A basic unit of biological classification.

  • Demes:

    • Defined as a small local population where individuals are not identical but resemble each other more than other demes.

    • Exhibit genetic similarity, akin to a family group or “tribe”.

    • Share similar environmental influences.

    • Not considered permanent units.

Cline Formation

  • Cline: A gradient of variation among species across a geographical area.

  • Example of Cline:

    • Altitudinal Clines:

    • Observed in the height of milfoil, Achillea lanulosa.

    • Variation not due to physiological stress responses, since traits are heritable.

Human Clines

Skin Colour Variation:

  • Human skin displays extensive variations in pigmentation.

  • Linked to adaptation from hairlessness; with reduced body hair, enhanced skin protection is necessary.

  • Melanin serves as sunscreen for the skin.

  • Clear cline in skin pigmentation among human demes.

Implications of Skin Pigmentation

  • Health Effects of Skin Pigmentation:

    • Light-skinned individuals exposed to strong sunlight risk a 50% loss in folate levels within one hour.

    • Increased risk of neural tube defects such as spina bifida- a condition where the arches of the spinal cord fail to close.

    • Decreased spermatogenesis, with folate being essential for DNA synthesis in dividing cells.

Vitamin D and Folate Balance

  • Vitamin D Deficiency:

    • Folate levels must be balanced with the UV-B rays needed for vitamin D synthesis.

    • Vitamin D is crucial for calcium absorption.

    • A deficiency in vitamin D leads to conditions like "Rickets".

Adaptive Solutions Based on Skin Colour

  • Locations with different skin colours adapt in distinct ways based on environmental factors:

    • Lighter skin individuals protect against excessive UV-B, while also facilitating vitamin D synthesis.

    • Darker skin individuals maximize UV-B absorption to produce sufficient vitamin D.

Species Concept Definitions

Phenetic Characters:

  • Species are often recognized and defined by observable phenetic characters.

  • However, these characters may not uniformly appear in all members of a species.

  • Variation alone does not justify defining separate species.

Types of Species Concepts:

Biological Species Concept: 

  • Defines species as groups of organisms that can interbreed among each other and are reproductively isolated from other groups.

  • Emphasize sexual reproduction, creating uniform genetic traits through recombination, while promoting isolation as a barrier to gene flow. (Defined by Dobzhansky, 1937)

Recognition Species Concept:

  • Defines species as a set of organisms that recognize each other as mates, sharing a mate recognition system.

Cladistic (Phylogenetic) Species Concept:

  • Defines species as lineages of populations between two phylogenetic branch points or speciation events, increasingly leveraging DNA analysis.

Variability within Species Concepts

  • Species concepts can be understood both horizontally and vertically:

  • Horizontal Species Concept:

  • Attempts to define species at a specific time point.

  • Vertical Species Concept:

  • Attempts to define species through evolutionary time, considering their historical development.

Hybrid Speciation

  • Definition: The formation of a third species from the mating of two distinct species, leading to a reproductively isolated group from both parental species.

    • Process:

    • Two separate species exist.

    • Hybrid individuals emerge from mating.

    • Reproductive isolation leads to speciation.

Example and Diagram of Hybrid Speciation

Isolating Barriers

  • Definition: Mechanisms that prevent interbreeding between species.

  • Barriers include: