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Plant Ecology - Chapter 13 Abundance, Rarity, Invasives Abundant vs. Rare - Why? Some plants are common in many areas, and have widespread distribution Others are rare, and have restricted range Abundant vs. Rare - Why? Common plants may be dominating competitors E.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 competitors E.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 specialists Tend to have low abundances, small geographic ranges Minnesota dwarf trout lily Abundant vs. Rare - Why? Other causes of rarity might be: Lack of dispersal Historical accident Abundant vs. Rare - Why? One combination produces commonness, all other 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 range Usually exotics from from their native habitats Invasive Species What makes a plant potentially invasive? Reproduction at younger ages Smaller seeds Large seed crops produced at shorter intervals Invasive Species 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 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 speciesrich communities 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) Abundance and Community Structure Species richness may change as community productivity changes, but no clear pattern Adaptation, 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 Species richness Disturbance frequency Disturbance vs. Diversity? No relationship between disturbance and diversity is the most common observation Only 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?