Species Concept

Species Concept

v  A framework to define and categorize species, reflecting different perspectives on biological diversity and evolutionary relationships.

v  Importance: Guides taxonomy, conservation, and evolutionary studies, with various concepts addressing morphological, genetic, ecological, phylogenetic, and reproductive criteria.

Genetic Species Concept (Lotsy)

v  Proposed by Johannes Paulus Lotsy, this concept defines a species as a group of genetically identical or highly similar individuals.

v  Basis: Emphasizes genetic uniformity or close relatedness as the criterion for species membership.

v  Example: Populations of bacteria with nearly identical DNA sequences are classified as the same species.

v  Strength: Reflects genetic coherence, especially in asexual organisms.

v  Limitation: Difficult to apply to sexually reproducing species with natural genetic variation; overlooks ecological or behavioral factors.

Ecological Species Concept (Van Valen)

v  Proposed by Leigh Van Valen, a species is a lineage occupying an adaptive zone minimally distinct from others in its range, evolving separately from lineages outside its range.

v  Basis: Focuses on the ecological niche and competitive interactions that define a species' role.

v  Example: Darwin's finches, where each species occupies a unique feeding niche (e.g., seed size preference) on the Galápagos Islands.

v  Strength: Highlights ecological adaptation and isolation as drivers of speciation.

v  Limitation: Challenging to apply when niches overlap or change over time.

Ecological Species Concept (Colinvaux)

v  Proposed by Paul Colinvaux, a species comprises related populations whose members compete more with each other than with members of other species.

v  Basis: Centers on intra-specific competition as a defining feature.

v  Example: Lions and hyenas in the same habitat compete less with each other than lions do within their own prides for resources.

v  Strength: Emphasizes ecological interactions and resource partitioning.

v  Limitation: May not account for species with minimal competition or those in diverse ecosystems.

Phylogenetic Species Concept (Eldredge and Cracraft)

v  Devised by Niles Eldredge and Joel Cracraft, this concept identifies a species as a group of individuals sharing a common ancestor, distinguished by unique morphological or molecular characters.

v  Basis: Uses evolutionary history and diagnostic traits (e.g., DNA sequences, anatomical features) to delineate species.

v  Example: Separate bird species identified by distinct mitochondrial DNA and beak morphology.

v  Strength: Integrates evolutionary relationships with observable traits, applicable across diverse taxa.

v  Limitation: Requires detailed phylogenetic data, which may be unavailable for some groups.

Recognition Species Concept (Paterson)

v  Proposed by Hugh E. Paterson, this concept defines a species as a group of organisms that recognize each other's mating signals.

v  Basis: Focuses on specific mate recognition systems (e.g., calls, pheromones) as the basis for species boundaries.

v  Example: Cricket species distinguished by unique mating songs that attract only conspecifics.

v  Strength: Highlights reproductive behavior as a key isolating mechanism.

v  Limitation: Less applicable to asexual species or those with limited signaling.

Evolutionary Species Concept (Wiley)

v  Proposed by E.O. Wiley, an evolutionary species is a single lineage of ancestral-descendant populations that maintains its identity, with its own evolutionary tendencies and historical fate.

v  Basis: Emphasizes long-term evolutionary continuity and divergence from other lineages.

v  Example: The lineage of modern horses (Equus caballus) evolving from Hyracotherium with distinct historical adaptations.

v  Strength: Accounts for evolutionary processes over deep time, including extinction risks.

v  Limitation: Difficult to apply to contemporary populations without extensive fossil or genetic records.

Phenetic Species Concept (Ridley)

v  Proposed by Mark Ridley, a species is a set of organisms that look similar to each other and distinctly different from others.

v  Basis: Relies on overall phenotypic similarity, often measured by quantitative traits.

v  Example: Butterflies of the genus Heliconius grouped by wing color patterns.

v  Strength: Simple and practical for field identification.

v  Limitation: Ignores genetic or evolutionary relationships; similar appearances may not reflect common ancestry.

Biological Species Concept (Mayr)

v  Proposed by Ernst Mayr in 1942, a species consists of organisms that interbreed freely in nature, producing viable, fertile offspring, and are reproductively isolated from other groups (e.g. behavioral, temporal, geographic barriers).

v  Basis: Centers on reproductive compatibility and isolation mechanisms.

v  Example: Lions (Panthera leo) and tigers (Panthera tigris) are separate species as they do not interbreed in the wild, despite producing hybrids (ligers) in captivity.

v  Limitations:

         Asexual/Vegetative Reproduction: Excludes organisms like bacteria or plants that reproduce asexually.

           Fossils: Cannot assess interbreeding potential in extinct species.

Sibling Species:

v  Morphological same but reproductively isolated.

v  Result to sympatric speciation example - Insect of rainy reason.

Sub – Species:

v  Morphological different but can interbreed (as they started to live under different environment).

v  Result of Allopatric Speciation.

v  According to morphological species concept - same.

v  According to biological species concept - same.

Clines:

v  Cline is a group of members of same species in which a measurable gradient in a single character (biological trait) is present across its geographical range. Result of parapatric speciation.