#succession models

ECOLOGICAL SUCCESSION

The model where early colonizers have no effect on later species is:

In the tolerance model, early colonists have little direct effect on recruitment of later species. Different species may enter the site, but those able to tolerate progressively lower resources or altered conditions survive and eventually dominate; replacement does not require facilitation by pioneers. Classical succession terminology divides community development into site exposure, arrival, establishment, interaction, environmental reaction, and relative stabilization. Modern ecology treats these as useful descriptions rather than a rigid deterministic program. Local resource conditions, dis

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 20

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ECOLOGICAL SUCCESSION

Tolerance model suggests:

The tolerance model allows early and late successional species to arrive independently; pioneers neither strongly facilitate nor inhibit later colonists. Species that tolerate lower resource levels or other conditions developing over time eventually persist and grow better, so their life-history traits drive replacement. A disturbance changes the availability of space, resources, and biological legacies, creating opportunities for colonization. Whether succession is primary or secondary depends chiefly on the starting substrate and survival of soil, not simply on the identity of the disturbanc

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 20

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ECOLOGICAL SUCCESSION

Which model states that early species hinder the establishment of later ones?

Under the inhibition model, established early colonists suppress recruitment or growth of later arrivals through preemption of space, resource capture, allelopathy, or other antagonistic effects. Replacement occurs chiefly when residents die or are damaged, releasing occupied sites rather than because they prepare the habitat for successors. Successional trajectories emerge from dispersal, establishment, species interactions, and organism-driven environmental change. Priority effects can make arrival order important, while retained soil and propagules strongly accelerate recovery after disturb

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 20

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ECOLOGICAL SUCCESSION

The classical model of succession is:

The classical facilitation model proposes that early colonists modify a harsh environment in ways that improve establishment by later species. Soil stabilization, organic-matter accumulation, nitrogen fixation, and shelter from physical stress can make pioneers necessary precursors even though successors may eventually replace them. Organisms can drive succession autogenically by changing their own habitat, while floods, erosion, sedimentation, or climate can drive allogenic change. Biological agents such as grazers and pathogens may also redirect succession by altering competitive relationshi

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 20

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SUCCESSION

In inhibition model of succession:

The inhibition model gives early occupants a negative effect on later colonists. Once pioneers establish, they monopolize space, light, nutrients, or attachment sites, or they release inhibitory chemicals, thereby preventing other species from recruiting successfully. Succession proceeds mainly when residents die, are damaged, or are removed by consumers or disturbance, creating openings that another species can occupy. The first colonist need not prepare the site for its successor and may even be a long-lived species, so the sequence depends strongly on arrival order and priority effects. In

Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 20

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