Dispersal

1. Dispersal • Movement of species leading to range expansion • Hotly debated • Dispersalists vs. Extensionists • Continental drift changed debate • Long-distance distance dispersal vs. vicariance • Read Box 6.1

2. Diffusion Dispersal • Slow expansion from previous range into new areas • Gradual process as species acclimate to conditions and taxa at margins of range • Can follow jump dispersal (next example)

3. Cattle egret (Bubulcus ibis) • Arrived by flying from Africa in late 1800s

4. European starling (Sturnus vulgaris) • Intro to Central Park in 1896 • Wanted birds of Shakespeare

5. Oaks across Britain and Ireland

6. Jump Dispersal • Species “skips” over area outside its range to new location • Island colonization • Some species lacking from islands – limited ability to disperse (mammals, amphibians, freshwater fishes) • Also occurs across continents

7. Recolonization of Krakatau

11. Secular Dispersal • Evolutionary divergence through range expansion • Evolutionary time scale

13. Mechanisms of Dispersal • Active • Capacity to travel long distances (flight, walking, or swimming) • Best example are migratory animals

14. Migratory route of golden plover (Pluvialis dominica)

16. Mechanisms of Dispersal • Passive • Wind, water, or on animals • Plants best examples • Also animals (insects), fungi, and bacteria • Phoresy – animal hitching a ride on another animal for dispersal

19. Water Dispersal

20. Phoresy

21. Barriers • Long-distance dispersal • Encounter obstacles • Unfavorable environmental conditions • Tolerate, overcome, or dead end?

22. Physiological Barriers • Conditions fall outside range of tolerance • Not able to cross barriers • History of area may have allowed passage and distributions seen today • Freshwater lake fishes – only found in multiple locations if lakes were connected at one time • Some lakes are fishless – not because of tolerance • Marine fish vs. freshwater fish

23. v Sheephead minnow (Cyprinodon variegatus)

24. Contrast with Centrarchids

25. Differences in mountain barriers – temperate vs. tropics

26. Mammals, reptiles, etc. – aided by past vegatation

27. Temporal barriers – temperate/polar water bodies. Movement over ice

28. Ecological Barriers • Competition • Predation • Habitats – refusal to cross

29. Corridors • Allow dispersal by permitting movement • Contemporary examples • Historical – account for related of different species or even same species in widely separated regions

31. Tethyan Seaway

33. Filters • Restrictive dispersal pathway • Conditions restrictive to some species, not others • Can be biotic or abiotic

34. Two-way Filter