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Transcript
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