7 public questions tagged with this topic.
Succession generally leads to a stable climax community, not an unstable one.
Ref: NCERT Class 12 Biology Chapter 11: Organisms and Populations Population Interactions - Predation and Herbivory
Primary succession occurs in lifeless areas, such as newly formed volcanic islands, where no life previously existed.
Ref: NCERT Class 12 Biology Chapter 11: Organisms and Populations Life History Variations and Population Interactions - Overview
Secondary succession occurs in areas where a disturbance has removed vegetation but left the soil intact.
Ref: NCERT Class 12 Biology Chapter 11: Organisms and Populations Life History Variations and Population Interactions - Overview
Retreating ice can reveal mineral substrate with no developed soil and few biological legacies. Colonization therefore begins with microbes, lichens, mosses, and other stress-tolerant pioneers that promote weathering and organic accumulation, making this primary rather than secondary succession. 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 disturbance. Facilitation, tolerance, and inhibition are alternative mechanisms rather than mandatory universal stages; more than one may operate at the same site or at different times. The eventual assemblage also depends on climate, substrate, disturbance frequency, and the regional species pool, so a climax is better viewed as dynamic persistence than permanent equilibrium. In this context, the keyed term, Primary succession, identifies the relevant mechanism or quantitative relationship and links the observed pattern to its underlying ecological cause. The distinction is testable by measuring changes in organisms, resources, or process rates through time rather than relying on the label alone.
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 20
Succession models are interpreted from how resident species affect the arrival and replacement of later species. Facilitation occurs when an early colonist improves conditions for a successor; tolerance occurs when later species can invade regardless of earlier occupants and eventually win through traits such as shade tolerance; inhibition occurs when established organisms suppress newcomers until disturbance or death creates space. A statement that an initial species makes the environment more suitable for a later one therefore indicates facilitation. A species able to invade whether another species is present or absent, and then outcompete it, reflects tolerance rather than dependence on facilitation. The keyed response identifies the pairing “Model X: tolerance, Model Y: inhibition” as the incorrect statement, which can be coherent if Model X shows facilitation and Model Y shows tolerance. However, the defining succession diagrams are absent from the spreadsheet extract, so the model labels and key cannot be conclusively checked. The reliable method is to follow the direction and sign of each species interaction rather than infer the model from replacement alone.
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 20
Facilitation and inhibition describe opposite effects of early colonists on later species. Under facilitation, pioneer species alter a harsh habitat in ways that increase later establishment—for example, by accumulating soil, adding nitrogen, reducing temperature extremes, or creating shade. They may eventually be replaced by species that benefit from those changes. Under inhibition, early occupants make establishment harder through space pre-emption, allelopathy, shading, or resource capture; replacement occurs mainly when residents die, are damaged, or are outcompeted after a disturbance. Therefore, a diagram in which an initial species enables subsequent species represents facilitation, whereas one showing priority effects and suppression represents inhibition. The keyed interpretation assigns the first figure to facilitation and the second to inhibition, which is scientifically consistent if those arrows or replacement patterns appear in the omitted diagrams. Because the spreadsheet row does not include the figures themselves, that mapping cannot be independently verified from the text alone. The biological distinction remains clear: positive modification drives facilitation, while negative effects of residents on newcomers drive inhibition.
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 20
Late-successional forest plants usually invest in persistence and competitive ability under crowded, shaded conditions rather than rapid colonization of distant disturbances. They commonly grow slowly, live long, tolerate low light, and photosynthesize efficiently at low irradiance, with a low light-saturation point. Larger seeds provide reserves that help seedlings establish beneath a canopy, and substantial roots can support survival and resource capture. Long-distance dispersal is more characteristic of early-successional pioneers, which must reach newly disturbed patches quickly; small, numerous, easily transported seeds often provide that advantage. Long seed viability can occur in pioneers because persistent seed banks wait for disturbance, whereas many shade-tolerant forest species have shorter-lived seeds and rely on repeated local reproduction. Trait combinations vary among species, so no single syndrome is absolute. Nevertheless, the pairing of long dispersal distance with long seed viability best conflicts with the standard late-successional strategy. Slow growth, long life span, and efficient performance in dim light directly support survival as the canopy closes and resources become contested.
Ref: Ecology: Concepts and Applications, Molles, 9th Ed., Ch. 20
