Lesson 2: Species Concept PDF

Bio 40 Plant Taxonomy BS ES I-A Benguet State University MODULE/ LESSON 2 Species Concept MOTIVATION In the first video presentation for the lecture part, specifically on Chapter 1, I have given you a basic definition of a species. We defined species as the basic tax...

Bio 40 Plant Taxonomy BS ES I-A Benguet State University MODULE/ LESSON 2 Species Concept MOTIVATION In the first video presentation for the lecture part, specifically on Chapter 1, I have given you a basic definition of a species. We defined species as the basic taxonomic unit of organisms, wherein if we able to classify the organism down to the species level , we are actually able to do 2 further things – we are able to identify it and give its scientific name (nomenclature). If this would be the case then that definition of species would be as simple as that. Unfortunately, it is not as simple as that because there’s a lot of controversies in defining the seemingly simple term ‘species’ - giving forth for the Species Concept. So let’s dig in! LESSON PROPER Species Concept, in simple sense, is the way one would define or describe a species. Unfortunately, scientist differs in their criteria of defining or describing species – those giving forth for the Species Concept. There are several of these but I would just be discussing 6 of the major ones here. Major Species Concept A. Morphological species concept B. Biological species concept C. Evolution species concept D. Recognition species concept E. Cohesion species concept F. Phylogenetic species concept A. Morphological species concept – otherwise known as typological species concept. The sole criterion in this concept is morphological similarity or dissimilarity – meaning similarly looking organisms would be considered as similar species and vice-versa, not similarly looking organisms would be different species. Species identified through this concept are referred to as morphospecies. However, there are 3 major problems in this concept, namely: ∙ Sibling species – morphologically similar organisms but do not breed together such as the  following: Bio 40 Plant Taxonomy BS ES I-A Benguet State University ∙ Sexual dimorphism – male and female individuals do not look alike but they breed together, say for example this birds: ∙ Polymorphism – a species that have several morphological forms like this plant Codeium variegatum B. Biological Species Concept – resulted from the limitation on morphological species concept, which argues that morphological differences is a secondary by-product of genetic divergence, thus should not be the major criterion. This concept was proposed by Mayr who defines a species as , “groups of actually or a potentially interbreeding natural populations which are reproductively isolated from other such groups”. The same idea was also proposed by Dobzhansky - “species as the largest and most inclusive reproductive community of sexual and cross-fertilizing individuals which share a common gene pool”. From these definitions, we can see that the major criteria in biological species concept are reproductive isolation and gene pool. There are 6 tenets under this concept and more self-explanatory: ∙ Species as populations ∙ Species defined by reproductive isolation ∙ Species as a reproductive community ∙ Species as ecological unit ∙ Species as genetic unit ∙ Species determination on basis of distinctiveness Bio 40 Plant Taxonomy BS ES I-A Benguet State University However, there are also limitations of this concept, such as the following: ∙ Asexual organisms – organisms that do not mate to reproduce, they can just reproduce by their own such as bacteria and others. ∙ There are also interbreeding between different species but the same family such as the cross between lion and a tiger resulting to a liger or tigon or, the cross between a llama and a camel resulting to a cama Due to the limitations of morphological and biological species concept, several other species concept arise to try answer or plug in the limitations C. Evolution Species Concept - Evolutionary species is a single lineage of ancestor-descendant populations of organisms which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate. Limitation: not mechanistic. It is purely theoretical since we cannot observe evolutionary processes in our lifetime to observe the birth of a new species from an existing one D. Recognition Species Concept – proposed by Patterson’s as, “species is the most inclusive population of individual biparental organisms which share a common fertilization system” There are 3 tenets in this concept: Bio 40 Plant Taxonomy BS ES I-A Benguet State University ∙ Organisms of a species share a common a specific mate recognition system (SMRS) ∙ SMRS is functionally adapted to the habitat ∙ New species arise upon acquiring a new SMRS E. Cohesion Species Concept – proposed by Tempeton’s: “a species is the most inclusive population of individuals having the potential for phenotypic cohesion through cohesion mechanisms The basic assumptions or tenets in this concept are the following: ∙ Mechanisms maintaining genetic cohesion such as Fertilization system and Developmental system ∙ Mechanisms reserving genetic cohesion ∙ Fundamental niche limiting genetic drift and natural selection Limitations of Recognition and Cohesion Species Concept: Both are just refinement or another idea from biological species concept and hence, share the same limitations as biological species concept F. Phylogenetic Species Concept – proposed by Cracraft’s, “a species is an irreducible cluster of organisms, diagnostically distinct from other such clusters, and within which there is a parental pattern of ancestry and descent” This concept is considered as the most comprehensive species concept as it attempts to integrate other species concept particularly morphological, biological and evolutionary species concept. EVALUATION As taxonomy students, you should be able to explain to anyone asking what are the major species concept. Say for example, you would ask me, “what is a species?”. Then if I answer you, “what concept would you want me discuss?” You should not be lost when you hear this but you should be able to further the discussion!