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

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