1. CHAPTER 3 Factors Affecting Distribution and Abundance : 1)DISPERSAL

2. Learning Outcome To define and describe the concepts of dispersal
To describe the colonization process
To acquire knowledge on fugitive species
To explain the Lidicker’s Hypothesize
- pre-saturation and saturation dispersal

3. Dispersal
Dispersal = Movement of individuals away from their place of birth
Ecological process that affects distribution
Disperse and colonize new area
Dispersal into or out of some area
Increase/decrease population density
Expanding population/response to climate change/changing in food supply

4. If dispersal is successful it results in gene flow (Darwinian fitness)
If colonization is successful, dispersal will result in gene flow and thus affect the genetic structure of a population.

5. Example of dispersal: Gypsy Moth (Lymantria dispar)
an introduced sp. - silk industry (purposely introduced)
Purpose: to make a caterpillar hybrid, that could resist diseases.
Escaped - found suitable habitat - multiply
Negative impact: initially in Europe only but now in US – destroy timber trees.
Overcome the spread: use of pheromone traps

7. Chestnut blight fungus (Cryphonectria parasitica)
Example of dispersal :
Chestnut blight fungus (Cryphonectria parasitica)
Attack American chestnut tree (Castanea dentate)
Eliminated chestnut in 40 years only. The fungus kills only the above ground biomass - roots of trunks killed after 60 years still send out shoots.
Resulted in replacement by codominant trees such as oak, beech, red maple
Chestnut infection caused the tree trunk to split

8. Sea Otter (Enhydra lutris )
Example of Dispersal:
Sea Otter (Enhydra lutris )
- Hunted to near extinction by fur traders.
Protective laws since 1914: Range of the otters widened
Other example of Dispersal : African honey bee & zebra mussel
Since there were safe, then they can disperse further and expand their range

9. Modes of Dispersal
Diffusion
Jump Dispersal
Secular Dispersal

10. Modes of Dispersal 1) Diffusion
gradual/slow spread or movement of populations across hospitable terrains for a period of several generations
Sea otter, Gypsy moth & Chestnut blight

11. Modes of Dispersal 2) Jump Dispersal
quick movement of individual organisms across large distances - successful establishment in the new area
occurs in a short time during the life span
usually across unsuitable terrain
E.g. island colonization – Bird Bonasa umbellus, African Honey Bees and Fire Ant

12. Modes of Dispersal 3) Secular Dispersal Occurs over geologic time.
Although the geographic range is expanding, natural selection is causing migrants to diverge from the ancestral population.

13. All forms of dispersal are affected by barriers such as……..

14. Water as barrier
Example of barriers in jump dispersal – water as a barrier for birds
Islands closer to mainland are colonized but further islands are not.
The ruffed grouse (Bonasa umbellus) are found on islands that are 800 m or closer to the mainland shore of the great lakes in US because this birds cannot fly for more than 800m.

15. Impact on native species :
dispersal may not limit distribution because introduced sp may not be able to survive local environments
Only 4 out of 50 introduced bird species have survived in US
Only 13 out of 85 introduced bird sp were successful in Europe
Only 15 out of 50 bird sp. introduced in Sydney survived
Generally the survival of introduced sp. is about 10 – 30%
1 in 10 imported species to a country becomes introduced, 1 in 10 of introduced species becomes established, 1 in 10 of the established species becomes a pest
1 in 10 imported species to a country becomes introduced, 1 in 10 of introduced species becomes established, 1 in 10 of the established species becomes a pest

16. Dispersal : Who? Why? Juvenile – to find or colonize new areas
Adult - Escape from deteriorating situation
Why?
Natural selection will favor individuals that leave a relatively crowded habitat and colonize an empty one in which it can leave many descendents – to maximize fitness
Dispersers increase chances of encountering new individuals to mate, thus reduces in-breeding, and increases fitness of offspring due to heterogeneity

17. When do they disperse? How far? The rule: the pre-reproductive period
when population increases
How far?
Depends on density of surrounding population and availability of suitable unoccupied habitats (new area)
The rule:
move to the first uncontested (open) available site
disperse in a straight line from their natal area or make exploratory surveys
settle in the first empty site

18. Monk parakeets
move to the first uncontested (open) available site
disperse in a straight line from their natal area or make exploratory surveys
settle in the first empty site
Red squirrels

19. Nearly all studies show very local dispersal
Most tree seeds fall within a few meters of parent.
Only a few seeds make it to further distance.
Haphazard-random

20. White crowned sparrow Deermouse
Expected dispersal
Observed dispersal
Proportion of the dispersing
juvenile Mountain White-crowned Sparrows began to move away from the natal site.
By the time they reached full independence from parental care (about 30 days of age), they had often crossed through several neighbouring territories and were 200 m or more from the nest.

21. Dispersal for expanding population

22. What are the motivation to disperse?
Intra-specific competition – population increase, aggression increase, resources are less, breeding partners decreases
Aggressive individual force subdominants to move
Dispersal usually occurs before peak density of populations/ before reproductive period
Asocial members disperse – have no ties.

23. 2 options :
Stay at home and be happy
– living in crowded conditions (very dense, scarce food stock, low quality of habitat, less individual to mate - leave few offsprings. OR
Disperse & take a chance
– find a new place – colonize it – and leave many descendents (good habitat, ample food resources, meeting new individuals to mate, reduces inbreeding - increases fitness of offspring due to heterogeneity.

25. Colonization
Colonization occurs whenever any one or more species populate an area

26. Colonization E.g Krakatau Explosion
1883 Krakatau erupted and caused total extinction of all species on the island and the remaining land became sterile.
2 nearby islands were completely covered by ash and this caused total extinction of species.
Nearest island not destroyed was 40 km away.

27. Colonization process…
….one or more species populate an area
Time Since
Explosion
Species found
9 months
Single Spider
3 years
Blue-green algae; 11 fern species; 15 flowering plant species
10 years
Coconut trees growing
25 years
263 species of animals; dense forest

28. Birds dependent on plant colonization
Most plants and animals probably colonized by wind
Large vertebrates may have arrived by floating on driftwood rafts or possibly swam.

29. Colonization milestone
Where there is vacant space organisms will find it – mostly by chance (exploratory survey) and adaptive ability

30. Fugitive Species
Devote most of their effort to dispersal (extreme disperser)
‘Weeds’ of plant (dandelion) and animal (water boatman) kingdoms
Colonize temporary habitats.
Grow almost predominately on disturbed areas.
Water boatman- aquatic bugs

31. Characteristics of fugitive species: - Colonize temporary habitats.
Reproduce and leave before the habitat disappear or competition with other organisms increases.
These fugitive sp usually found in disturbed habitats.
They produce large number of seeds.
Adapted for long distance dispersal by wind or animals – Taraxacum officinale a fugitive weedy sp.
Dung beetle loves to be at dung area that lots of waste and excretion of living organism. They will make a dung ball from the waste as their food. They feed partly or exclusively on feces.

32. Dispersal is advantageous when habitats are patchy and unstable.
Organisms living in stable or uniform habitats also disperse as long as there are potential sites away from parents
Species that live in more permanent habitats generally disperse less.

33. Lidicker’s (1975)* Hypothesis
Presaturation Dispersal
During the increase phase of pop before reaching peak/maximum or before resources get depleted
Dispersers are in good condition and are of any sex or age group- enough energy/fit
Have a good chance of survival and settling into a new area
*Lidicker, W.Z (1975). The role of dispersal in the demography of small mammals. In: F.B. Golley, E. Petrusewicz & L. Ryszkowski (eds.). Small Mammals, Their Productivity and Population Dynamics. Cam bridge Univ. Press, Cambridge, England. p

34. Lidicker’s Hypothesis
Saturation dispersal
When population reach/exceed its carrying capacity
Mostly juveniles
Have 2 choices
Stay, perish and do not breed
Or leave
Survival is low (less energy/ unfit)
Not in good condition.

35. Conclusion
Dispersal ability has been molded by natural selection to maximize the chance of colonizing vacant areas
Dispersal requires:
a source
a sink (empty and unfilled, marginal and unsuitable habitat)