5/29 - Disturbance & Ecological Succession

week 9: be able to distinguish Primary & Secondary Succession & explain how Facilitation & Inhibition shape Successional Trajectories; Connect early & late Successional species to the r/K continuum & describe how diversity changes across successional stages, apply the Intermediate Disturbance hypothesis to explain patterns of diversity, use Niche Utilization curves to explain why Climax Communities resist Invasion

Species Succession

- the pattern of changing species composition as a result of colonization & species interactions after a disturbance

• both facilitation & inhibition influence primary & secondary succession

ecological facilitation - positive interaction where at least 1 species benefits from the presence of another, & neither is harmed (commensalism(only 1 benefits), mutualism(both benefit))

ecological inhibition - process where early colonizing species actively prevent or slow down the establishment of later species

Primary Succession

- the gradual process of life colonizing an already completely barren, lifeless environments

Secondary Succession

- the process by which an ecosystem reorganizes & repopulates after a severe disturbance (ex: wildfire, floor, deforestation); clearing existing vegetation but leaving the nutrient-rich soil & partially intact seed bank undisturbed

Characteristics of Colonist species: Pioneer Species

- the first organism to colonize barren environments or recently disturbed ecosystems

• do best only when other species are absent

• occupation by pioneer species usually means that additional pioneer colonization will be inhibited

• usually common initially then decrease in frequency

r-selected species:

• mature quickly but shorter lifespan

• small

• semelparous (reproduce once in lifetime) but produce greater # of offspring

• tolerant to harsh environment

• less competitive

EX: grasses & ferns, lichens & mosses, Nitrogen-Fixing plants

Characteristics of Colonist species: Late-Successional/Climax species

- organisms that dominate an ecosystem once it reaches a stable state of maturity

• later successional species may be facilitated, inhibited, or simply tolerate early successional species & often inhibit other species from establishing

• less common initially then increase in frequency

• better competitors than r-selected/pioneer species

k-selected species:

• longer lifespan but delayed maturity

• higher parental investment

• few offspring but iteroparous (reproduce multiple times throughout lifespan)

• larger body size

Climax Communities

- the final mature stage of ecological succession. A balanced & diverse ecosystem of plants, animals, & fungi reaches equilibrium w/ local climate & environment remaining relatively stable

• dominated by k-selected species

• invasion resistance as all niches are occupied thus preventing possibility of invaders from establishing

- > negative relationship btwn # of resident species & survival of invader

- > the greater # of resident species the less survival rate of invader