Biol. 317 - Lecture notes – Chapter 16 (Long-term change)


Long-term change


        New species take up residence

OR  Resident species disappear completely




1.    Dispersal  (drift, migrate, or be carried across oceanic barriers)

2.    Evolutionary change (new species arise by splitting of old species)

3.    Long-term shift in environmental conditions (e.g., ice ages, cooling/warming)






Rare events

        unusally broad larval dispersal (e.g.,  El Niño changed normal current patterns)

        rafting (as “benthic” juveniles or adults)

        climatic changes

        continental drift (opening of formerly isolated ocean basins)




        Ship transport (often in ballast, e.g., zebra mussel)

        Incidental to transport of commercial species (e.g., oysters)

        Other human transport


Why don’t species always survive when transported?


        unsuitable physical/chemical conditions

        inferior competitive abilities

        susceptable to predation


Are there generalities about those invasive species that do survive?

        They come from a community with more species

        They are generalists, not highly specialized

        The species invades without its normal predators/parasites/competitors

        There is an empty “niche”

        Physical/chemical conditions are similar


Examples of non-native species on West Coast


        Pacific oyster (Crassostrea gigas) – introduced from Japan

            - grow more rapidly than indigenous species

            - superior competitors

            - but most places is unable to reproduce (with exceptions)

        American lobsters – introduced from Atlantic coast

            - no lobsters present in Canadian West Coast, niche appears vacant

            - reproduction appeared normal

            - did not survive for unknown reasons


A more successful example is described: Neries diversicolor invading Caspian Sea

            - became very common without apparent impact on native species


Impact on indigenous species is hard to predict

            - Sargassum muticum and Ocenebra japonica are examples of invasive

                        species on West Coast

            - Some more damaging than others


Species tend to increase through time over evolutionary time

            - See Fig. 16.4 (Figure based on recently deceased paleontologist, Jack Sepkoski)

            - Whole communities suffered dramatic extinction events, generally due to

                        extrinsic factors, not due to being “out-competed”

            - Early communities lacked deep burrowers, etc.



Read about impact of Ice Ages up to p. 388!