1. Plant Ecology - Chapter 13
Abundance, Rarity, Invasives

2. Abundant vs. Rare - Why?
Some plants are common in many areas, and have widespread distribution
Others are rare, and have restricted range

3. Abundant vs. Rare - Why? Common plants may be dominating competitors
E.g., removal of goldenrod increases species richness, allows less competitive species to survive

4. Abundant vs. Rare - Why?
Common plants may be dominant, but not strong competitors
E.g., orchard grass often dominant in old fields, but removal may affect few other plant species

5. Abundant vs. Rare - Why? Rare species may be ecological specialists
Tend to have low abundances, small geographic ranges
Minnesota dwarf trout lily

6. Abundant vs. Rare - Why? Lack of dispersal Historical accident
Other causes of rarity might be:
Lack of dispersal
Historical accident

7. Abundant vs. Rare - Why? One combination produces commonness, all
other combinations produce some form of rarity

8. Abundance Curves
Few common species, many rare species

9. Invasive Species
Species that are rapidly expanding outside of their native range
Usually exotics from from their native habitats

10. Invasive Species What makes a plant potentially invasive?
Reproduction at younger ages
Smaller seeds
Large seed crops produced at shorter intervals

11. Invasive Species

12. Invasive Species “Tens Rule” on the success of invaders
1 in 10 plants brought into a region will escape into the wild
1 in 10 escapees will become naturalized and self-sustaining
1 in 10 of these naturalized species will become invasive

13. Communities Susceptible to Invasion
Original ideas: disturbed communities and species-poor communities more vulnerable to invasion

14. Communities Susceptible to Invasion
Disturbance may hinder invasions, and invasive species often more common in species-rich communities

15. Communities Susceptible to Invasion
Nutrient-poor soils more resistant to invasive species
Invasives do well in absence of native herbivores, pathogens (e.g., bladder campion)

16. Abundance and Community Structure
Species richness may change as community productivity changes, but no clear pattern
Adaptation, competition, growth rates, other explanations

17. More individuals, more species?
Greater environmental heterogeneity (space and time), more niches, more potential specialization, more species

18. Disturbance vs. Diversity?
Intermediate disturbance hypothesis - species diversity should be highest at intermediate levels of disturbance
Species
richness
Disturbance frequency

19. Disturbance vs. Diversity?
No relationship between disturbance and diversity is the most common observation
Only 16% of studies show “expected” pattern

20. Diversity Concerns
Will reduction in plant species diversity (failure to conserve species adequately) lead to decrease in primary productivity?
Potential to reverberate through food chain, leading to extinctions of consumers.

21. Diversity Concerns
Are more diverse plant communities less stable, or less likely to return to their original state after disturbance?
Do more diverse communities have less year-to-year variation in productivity than less diverse communities?