Invasive Species in Nova Scotia

A Primer

Native Species

Any animal or plant that was here when we got here

Brook Trout

Red Spruce

Black Duck

Canada GoldenrodBumblebee

Mussel

Red Squirrel

Introduced Species(Non-Native, Exotic, Alien, Naturalized)

Any animal or plant that humans brought here

Rainbow Trout

Scots Pine

Ring-Necked Pheasant

Queen-Anne’s Lace Gypsy Moth Norway Rat

Invasive Species

An introduced species that displaces native species

• Tend to establish large populations Eurasian Watermilfoil

Spiny-CheekCrayfish

• Out-compete native species for space or other resources

• Sometimes also consume native species (e.g., fish larvae)

Pest Species

• An organism that does things we don’t like

• Becoming too numerous

• Competing with preferred species

• Causing or carrying disease

• Growing where we don’t want it

• Being ugly

• May be native or introduced

• May or may not be invasive

How do introduced species get here?

Accidental introductions

Species transported incidentally by human

traffic and transport

Dandelion Zebra Mussel WoodlouseDutch Elm Disease

How do introduced species get here?

Deliberate Introductions

Species brought here to provide food, sport,

beauty or other amenities

Wild Apple

Honey BeeEuropean Starling

Purple Loosestrife

What kinds of species are introduced?

ALL KINDS

Smallmouth Bass

Green Crab

Codium fragile

Didymosphenia geminata

BurdockNorway Maple Asian Ladybird Beetle

Why are invasive species a problem?

1. Reduce populations of native species

(sometimes to extinction)

2. Reduce natural diversity and compromise ecosystem function

3. Interfere with important commercial

enterprises (fishing, farming, forestry)

4. Reduce aesthetic appeal of invaded areas

What makes a species invasive?

• No single feature unites all invasives• Tend to be tolerant of physical conditions• Tend to be fast-growing• Tend to reproduce quickly and abundantly• Tend to be competitive or aggressive• Tend to disperse easily• Tend to show phenotypic plasticity• Tend to tolerate or welcome disturbance

Natural Advantage Hypothesis

What makes a species invasive?

• Invasive species may be controlled in native range by a predator or disease

• Predator or pathogen absent in new range• Predators may be grazing mammals, insects,

fungi, viruses• Specialist enemies most important• Generalist enemies create biotic resistance

Enemy Release Hypothesis

Evidence for Enemy Release

Based on 473 plant species naturalized in the U.S.A.(Mitchell , C.E. and Power, A.G. 2003. Nature 421: 625-627)

What makes a species invasive?

• Invasive species may fill an unused niche• Using different resources• Acquiring resources in a different way• A form of natural advantage• Most likely in species-poor communities• Supported by Island Biogeography Theory

Empty Niche Hypothesis

What makes a species invasive?

• Disturbance removes competitors and predators (reduces biotic resistance)

• Fewer competitors means unused resources• Invasive species may exploit new niche• Widespread human disturbance creates

many invasion opportunities• Addition of resources (fertilizer, CO2) creates

even more invasion opportunities

Anthropogenic Disturbance Hypothesis

What to do about invasive species?

1. Prevention• Keep the invasive organism out• If it does get in, prevent or slow

its spread

2. Eradication • Remove populations that are already established

JapaneseKnotweedGood luck with that

Common Reed