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

 

Long-term change

 

        New species take up residence

OR  Resident species disappear completely

 

Mechanisms:

 

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)

 

Dispersal

 

Pre-human:

 

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)

 

Human-aided

 

        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!