Biological Invasions

Question 1

Invasive alien species (IAS)

Answer 1

„Invasive alien species: an alien species whose establishment and spread threaten ecosystems, habitats or species with economic or environmental harm“ (IUCN 2001)

IAS are

• of ecological significance (threaten biodiversity, „environmental weeds“)
• of economic significance (yield loss, weeds, pest organisms)

Question 2

Reasons for species loss

Answer 2

Habitat fragmentation, invasive species, pollution, urbanization

Question 3

Acheophytes

Answer 3

Exotic species introduced before 1500. Neophytes: introduces after 1500.

Question 4

Invasive vs. alien

Answer 4

Invasive species make only a small proportion of all naturalized alien species in a region. Alien/exotic plants grow in the wild but were originally introduced by man. They do not cause species loss.

Question 5

Vectors and pathways of introductions

Answer 5

Intentional introduction
Accidental introduction
• Weed seeds as contaminants of cereals, wool, packing materials • Seeds or vegetative parts in soil of pot plants • Seeds in the fur of animals, cloths • Seeds on car tires and agricultural machine

Question 6

Do invasive species share certain traits? Which habitats are prone to invasion?

Answer 6

Habitat properties: no general rules, but disturbances often facilitate the establishment of invasive species
Species properties: no general rules (no key traits), but often observed:
• fast growth, high competitive ability
• clonal growth and vegetative spread
• broad ecological tolerance
• absence of natural enemies
• high seed output

Question 7

What do invasive plant species do? Ecological impacts

Answer 7

They can …
• change ecosystem functions (water and nutrient cycling)
• change natural disturbance regimes (fire, insect outbreaks)
• promote soil erosion
• outcompete native species
• change food web structures
• slow down natural successions
• change vegetation structures
• degrade wildlife habitat
• displace species rich plant communities with monocultures
… often in combination

Question 8

Transformer species

Answer 8

Invasive species, whose impacts affect whole ecosystems at several trophic levels: species richness, vegetation and food web structure, abiotic conditions