1. How does a species become invasive?
Invasive Species
How does a species become invasive?

2. Invasion ecology
‘ We must make no mistake, we are seeing one of the great historical convulsions in the world’s fauna and flora.’ Elton, 1958

3. DEFINITIONS indigenous = native to a particular place
biogeography = the branch of biology that studies the geographical distribution of organisms
Biogeographical studies = native and introduced populations of the same species are compared
community studies = non-indigenous species (NIS) are compared with native counterparts

4. Threats to biodiversity (Earth, 2018)
Current rate of species extinction is 1000X to 10,000X the natural rate over the past several billion years
Most serious threats to biodiversity stem from human population growth, consumption levels, and mobility
HIPPO

5. Threats to biodiversity (Earth, 2018)
Habitat Loss
Industrial activities
Agriculture
Aquaculture
Mining/resource extraction
Deforestation
Water extraction
Settlement patterns

6. Threats to biodiversity (Earth, 2018)
Invasive Species
Predation
Parasitism
Diseases
Competition
Modify habitat
Disrupt important interactions

7. Threats to biodiversity (Earth, 2018)
Pollution
Toxic chemicals
Eutrophication—too much of a good thing
Dead zones
Bioaccumulation
POPs—persistent organic pollutants
Plastics

8. Threats to biodiversity (Earth, 2018)
Population, human
1800 < 1 billion
Today almost 7.5 billion
Increased Land use, resource use, pollution

9. Threats to biodiversity (Earth, 2018)
Overharvesting
Hunting
Gathering
Fishing, including bycatch

10. What’s the problem with invasive species???
Causes of Global Species Endangerment
What’s the problem with invasive species???
All Species
Marine Species
Lawler et al. (2006), Frontiers in Ecology & the Environment

11. Negative Impacts of Invasive Species
Ecosystem Level Impacts
Disturbance Regimes
Hydrology: Alterations of Water Regimes
Geomorphological processes (erosion, sedimentation)
Soil chemistry
Community or Population Level Impacts
Habitat structure
Community composition
Resource competition
Population reductions, eliminations
Genetic Impacts

12. Economic Impacts
Along with irreplaceable losses to biodiversity - Billions $$$ per year from
Lost agricultural productivity
Lost forest productivity
Lost recreational opportunity
Pimental et al Ecological Economics 52:

13. How do they get here? Intentional
Exotic plant species for ornamental/agricultural uses
Accidental
Ship’s ballast
Contaminants in crop seed
Stow-aways on ships/airplanes
Release
pets

14. The Enemy Release Hypothesis (ERH)
Relates the success of non-indigenous species (NIS) to reduced control by enemies
Pathogens
Parasites
Predators
Studies are split
Biogeographical analyses show a reduction in the diversity of enemies in the introduced range compared with the native range
Community studies imply no significant enemy differences between natives and invasives
Too simple to describe processes at work?

15. Evolution of Increased Competitive Ability hypothesis (EICA)
Blossey & Nötzold (1995)
Observations
Usually a lag period between time of introduction & point at which it is considered invasive
Invasive plants seem to be more virulent in habitats into which they have been introduced (as compared with their native habitats)
Presumed a sort of naturalization through modification
Predicts that much of the invasive potential of an invasive species is derived from its ability to evolve to reallocate its resources

16. Evolution of Increased Competitive Ability Hypothesis (EICA)
As applied to plants –
Under identical growing conditions, species will produce more biomass in an area where it has been introduced vs. in its native range.
Invasive species will exhibit lower herbivore defense rates in introduced range than in native range.
A species is not as fit (in its native habitat) at the time of introduction vs. when it becomes invasive.
Blossey and Notzold Journal of Ecology 83(5):

17. Novel Weapon Hypothesis
Suggests that the success of some invaders is due to the novelty of their competitive, defensive, or predatory traits (Callaway & Ridenour, 2004).
Native species may have no evolutionary experience with, and therefore may be extremely susceptible to, allelopathic or defensive compounds produced by invaders

18. So…which is it??? Very different species as invaders
Very different native habitats
Cause of invasiveness varies depending on individual factors