Plant Ecology - Chapter 13

Abundance, Rarity, Invasives

Abundant vs. Rare - Why?

Some plants are common in many areas, and have widespread distributionOthers are rare, and have restricted range

Abundant vs. Rare - Why?

Common plants may be dominating competitorsE.g., removal of goldenrod increases species richness, allows less competitive species to survive

Abundant vs. Rare - Why?

Common plants may be dominant, but not strong competitorsE.g., orchard grass often dominant in old fields, but removal may affect few other plant species

Abundant vs. Rare - Why?

Rare species may be ecological specialistsTend to have low abundances, small geographic rangesMinnesota dwarf trout lily

Abundant vs. Rare - Why?

Other causes of rarity might be:

Lack of dispersalHistorical accident

Abundant vs. Rare - Why?

One combination produces commonness, allother combinations produce some form of rarity

Abundance Curves

Few common species, many rare species

Invasive Species

Species that are rapidly expanding outside of their native rangeUsually exotics from from their native habitats

Invasive Species

What makes a plant potentially invasive?Reproduction at younger agesSmaller seedsLarge seed crops produced at shorter intervals

Invasive Species

Invasive Species

“Tens Rule” on the success of invaders1 in 10 plants brought into a region will escape into the wild1 in 10 escapees will become naturalized and self-sustaining1 in 10 of these naturalized species will become invasive

Communities Susceptible to Invasion

Original ideas: disturbed communities and species-poor communities more vulnerable to invasion

Communities Susceptible to Invasion

Disturbance may hinder invasions, and invasive species often more common in species-rich communities

Communities Susceptible to Invasion

Nutrient-poor soils more resistant to invasive speciesInvasives do well in absence of native herbivores, pathogens (e.g., bladder campion)

Abundance and Community Structure

Species richness may change as community productivity changes, but no clear patternAdaptation, competition, growth rates, other explanations

More individuals, more species?

Greater environmental heterogeneity (space and time), more niches, more potential specialization, more species

Disturbance vs. Diversity?

Intermediate disturbance hypothesis - species diversity should be highest at intermediate levels of disturbance

Disturbance frequency

Speciesrichness

Disturbance vs. Diversity?

No relationship between disturbance and diversity is the most common observationOnly 16% of studies show “expected” pattern

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.

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?