Dispersal

1. GEOG2202 – The Biosphere Dispersal Robert Kinlocke Department of Geography and Geology UWI, Mona

2. Introduction • Species evolve in specific areas • As the number of individuals increase the resources necessary to sustain them diminish • Species respond by expanding their boundaries by moving altogether or by sending out propagules • [Propagules: The stages in an organism’s life cycle (e.g.: a plant seed), parts of an organism (e.g.: plant cuttings), or groups of organisms (e.g.:a male and female rabbit of mating age) that can form a new colony (Hugget, 2004).]

3. Dispersal is the process of moving away from the parent stock. • At the end of this session you should be able to : • Explain the types of dispersal • Describe the agents of dispersal • Describe the major dispersal routes

4. Types of Dispersal • Secular migration: Extremely slow movement of organisms which is usually characterized by evolution during the process of movement. • By the time the organism arrives in its new location it is different from its ancestor • e.g.: The Isthmus of Panama became dry land between 3 and 3.5 million years ago and facilitated and even known as the Great American Interchange . Animals such as camels, horses, tapir and deer moved southward. During the period of migration, camels evolved into various members of the South American Camel family (alpaca, llama and vicuna). Movement also occurred in the opposite direction as the porcupine which is today found in forests as far north as Canada and Alaska belong to a family of rodents which evolved in South America

5. Examples of migrant species in both Americas. Olive green silhouettes denote North American species with South American ancestors; blue silhouettes denote South American species of North American origin. The Great American Interchange

7. Diffusion: This process is faster than secular migration but still slow. • Species gradually extend their range and over several generations, the limits to their distribution undergo outward expansion. • e.g.: The Japanese beetle was introduced to New Jersey, USA in 1911 and covered less than one acre in the first year. By 1923, it covered nearly 2,500 square miles and by 1960 they were found throughout the USA

8. The Nine-banded Armadillo • Kingdom: AnimaliaPhylum: ChordataClass: MammaliaOrder: CingulataFamily: DasypodidaeSubfamily: DasypodinaeGenus: DasypusSpecies: D. novemcinctus

9. Map of Distribution: • Useful link: http://bss.sfsu.edu/geog/bholzman/courses/fall99projects/armadillo.htm

11. Jump Dispersal: The most rapid form of dispersal and usually takes less time than the life-span of the individual involved. • Usually involves traversing large distances and inhospitable ecological barriers • e.g.: An insect carries across the sea by wind

12. Range Shift • Organisms expand to one front but experience extinction in their former range.

13. Agents and Mechanisms of Dispersal • Active dispersal (vagility): This is mainly a feature of mobile animals as they can walk, swim or fly away from their source area. • Differential dispersal capacity among animals • The dispersal capacity of large mammals is low. • The spread of plants by means of rhizomes or stolons may be considered a form of active dispersal but this occurs only over short distances Stolons: underground runners that take root at joints or tips forming new plants e.g.: Grasses. Rhizomes: underground horizontal stems that send out roots and shoots from nodes

14. Rhizomes Ginger Euphorbia Stolon Lipstick Strawberry

15. Passive dispersal (pagility): This is mainly a feature of organisms with limited capacity for movement. • Agents include wind, water and mobile animals • Sometimes it is difficult to distinguish between active and passive dispersal as organisms capable of voluntary movement may be transported by wind or water • For example, after Hurricane Hugo, some locusts were found in the Eastern Caribbean

17. Hydrochore: • e.g.: seeds dispersed by water. The distribution of rubber in the Amazon basin has been associated with this agent and fishsometimes assist in dispersal. • Anemochore: • Winged and light seeds and spores dispersed by air currents. • e.g.: dandelion • Thalassochore: • e.g.: coconut palm dispersed by sea with the help of its 3 layered structure. • Anemohydrochore: • e.g.: tiny plumed seeds of the Aspen are dispersed by both wind and water. • Biochore: • Fruits dispersed by birds and other animals • Eg: drupes, fleshy fruits with single seed. • Undergo physical changes such as colour or smell to attract agents. • Anthropochores

19. Dandelion Seeds

20. Dispersal Routes • Corridors: This route traverses terrain that is generally hospitable and characterized by a variety of habitats. • Organisms found on both ends of the corridor have no difficulty in moving to the other side. • Corridors allow taxonomically balanced assemblages of plants and animals to cross from one source area into another. • In time organisms found on both sides would be identical.

21. Filters: These routes are more restrictive than corridors. It selectively blocks the passage of certain forms while allowing those able to tolerate the conditions of intervening environments to migrate freely.

22. Sweepstake Routes: Barriers that are crossed by rare, chance interchanges. Dispersal depends on a combination of circumstances. • Some species on true or ecological islands are cut off and may survive crossing barriers to colonize new areas. • Unlike the filter route, organisms cannot survive the intervening environment but they possess features which allow them to negotiate the barrier. • e.g.: The Sea Bean (hydrochorethalassochorebiochore)

23. Done!