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!