Transcript Dispersal and Immigration

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
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)
• Cattle egret (Bubulcus ibis)
• Arrived by flying from Africa in
late 1800s
• European starling (Sturnus vulgaris)
• Intro to Central Park in 1896
• Wanted birds of Shakespeare
• Oaks across Britain and Ireland
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
Recolonization of Krakatau
Secular Dispersal
• Evolutionary divergence through range
expansion
• Evolutionary time scale
Mechanisms of Dispersal
• Active
• Capacity to travel long distances (flight,
walking, or swimming)
• Best example are migratory animals
Migratory route of golden plover (Pluvialis dominica)
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
Water Dispersal
Phoresy
Barriers
•
•
•
•
Long-distance dispersal
Encounter obstacles
Unfavorable environmental conditions
Tolerate, overcome, or dead end?
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
v
Sheephead minnow (Cyprinodon variegatus)
Contrast with Centrarchids
Differences in mountain barriers – temperate vs.
tropics
Mammals,
reptiles, etc. –
aided by past
vegatation
Temporal barriers – temperate/polar water bodies.
Movement over ice
Ecological Barriers
• Competition
• Predation
• Habitats – refusal to cross
Corridors
• Allow dispersal by permitting movement
• Contemporary examples
• Historical – account for related of different
species or even same species in widely
separated regions
Tethyan Seaway
Filters
• Restrictive dispersal pathway
• Conditions restrictive to some species, not
others
• Can be biotic or abiotic
Two-way Filter