Introduced species

• Lecture Outline

– How introduced species affect native fish assemblages

– Testing prediction of species invasions

Introduced Species: The Problem

1) Globally, > 160 species of exotic fishes have been listed by FAO in 120 countries (Allan and Flecker 1993)

2) Of the 27 species of N. American fishes that have gone extinct, introduced species were cited as a causal factor in 18 of these extinctions (Miller et al. 1989)

Where do introduced species come from?

How do introduced species affect native fish communities

1) Predation

a) Nile Perch

2) Competition

a) Silversides

3) Hybridization

a) Gila trout x Rainbow trout

4) Habitat modification

a) Common carp

b) Bighead carp

Predictions regarding fish invasions

1) Most successful invaders are those adapted to the local hydrologic regime

a) Species with a very different origins have invaded Kansas and Oklahoma streams

b) Local species tend to be most abundant

2) A wider range of species can invade systems with high levels of human disturbance

a) Relationship among human population size, reservoir distance and the number of introduced species

3) Native species are capable of adjusting to new invaders: extinctions following invasions are rare

a) The number of native species has remained constant in OK/KS, but introduced species have increased

b) Abundance of native species has declined

c) Generally more invasions than extinctions

4) All fish assemblages are invasible, regardless of diversity of resident fishes

a) At large scales, it appears that high diversity “constrains” the number of introduced species

b) No significant relationship between native and introduced species richness at smaller scales