Plant Ecology - Chapter 13

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? • 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?