Endemism by vimalpriya subramanian

endemism and age and area hypothesis

1. Ecology & phytogeography Endemism , age and area hypothesis Vimal priya subramanian 18MBO027 2 nd M.sc Botany PSGR.KRISHNAMMAL COLLEGE FOR WOMEN

2. Introduction Endemism  is an  ecological  word meaning that a plant or animal lives only in a particular location, such as a specific island,  habitat  type, nation or other defined zone. For example, many species of  lemur  are endemic to the island of  Madagascar .

3. Characters of Endemics They are localized in distribution because of their Narrow Ecological Amplitude and are unable to invade in fresh areas. 2. They lack potentially to migrate because of saturate genomes. 3. Real endemics never migrate while Neoendemics have the potential to migrate 4. The dispersal propagules are not able to sustain during migration to other area. It may be due to physical barriers.

4. Relic endemics The plants belong to fossil groups and are restricted to few pockets due to favourable climate, lack of competition e.g., Ginkgo biloba which is restricted to China but widely spread in the north temperate zone as a fossil, Sequoiadendron giganteum is now restricted to Californian Sierra Nevada.

5. paleoendemism   Paleoendemism  means that a species used to live in a large area but now lives only in a smaller area.  It is endemic forms of ancient origin which are restricted to a region due to the factors such as 1)physical barriers like desert, sea,mountain ,etc 2)Change in climate in the surrounding areas 3)Presence of a particular physiography / soil

6. ENDEMISM

7. Neoendemics Neoendemism  means that a species has recently appeared which is closely related to the main species or one that has formed following  hybridization  and is now classified as a separate species. This is a common process in plants especially those which exhibit  polyploidy

8. Neoendemics  On the basis of cytotaxonomic studies differentiated 3 types of neoendemics . Schizoendemics Patroendemics apoendemics

9. Schizoendemics : Derived from or having given rise to a more widespread taxon of same chromosome number   Patroendemics : Restricted diploids which have given rise to widespread polyploids . .

10. A poendemics Restricted polyploids which have arisen from widespread diploids. There is a great confusion in the terms endemic, rare, relicts etc . All endemics are not relicts as there are a larger number of Neoendemics . All endemics are not rare as some are abundantly present in the particular locality. All rare plants are not endemics. Some may occur at several places, with few representatives.

11. Psedo -endemics The endemics arise due to appearance of mutation in the local population but ultimately such forms tend to disappeat .

12. Relic endemics Neo-endemics 1.They are ancient in origin. The endemics are of recent origin. 2.Th habitats in which they grow are diverse. Neo endemics grow in uniform habitat. 3. Habitat tolerance is narrow, despite varied habitat occupation. Habitat tolerance is wide. 4.The area under a species is slowly contracting(retrogressive endemics) The area under a near neo endemics is slowly spreading (progressive endemics). 5.variability is little. Variability is plenty 6.Biotype is comparatively poor. Biotype is comparetively ricger . 7.The chromosomes are comparatively smaller but more numerous. The chromosome are larger but fewer in number 8.The propagules are able to travel only short distances. Propagules are able to travel sufficient distances.

13. Theorys of endemics The first theory believes that the last survivors of once flourishing flora which is now declining are the relics or epibiotics which are endemics. However , second theory believes that these are recent and youthful forms in course of gradual extinction . The theory is also known as Age and Area hypothesis .

14. Age and area hypothesis This hypothesis was proposed by J. W. Willis (1915) on the basis of his extensive studies of geographical distribution of certain plant species in tropics . On the basis of his findings Willis postulated that the species which evolved earlier occupy greater areas than those which appeared later in the evolutionary sequence . According to this hypothesis, the frequency of a species over an area is directly proportional to its age in scale of evolution and age of species is directly related with the area of its distribution.

15.  second theory have the examples of Primula , Impatiens Rhododendron etc. According to this theory, Area is directly proportional to its age in the sqale of evolution. So, a small area of distribution shows relatively young in age e.g., Coleus is distributed on the summit of the dry Ritigala mountains in Sri Lanka, with two species C. elongatus and C. barbatus . C. elongatus is endemic and c.barbatus is widely distriputed in tropical asia and africa willis belive that c.elongatus derived from c.barbatus

16. Factor responsiple for endemism Factors responsible for the production of endemics are Natural crossing among the closely related plants growing under favourable conditions and Mutations. If the condition of isolation is developed the effect become more pronounced.

17. Endemic Species of India Rhododendron ( Ericaceae ), Eleusine coracana ( Poaceae ), Caryota urena ( Arecaceae ), Aegle marmelos ( Rutaceae ), Crotolaria juncea ( Fabaceae ), Ficus religiosa ( Moraceae ), and  Seasamum indicum ( Pedaliaceae ).

18. Thanking you