SUCCESSION

SUCCESSION

Which one defines climax community?

A climax community, in the traditional succession concept, is a relatively stable, self-perpetuating assemblage that maintains its broad composition under the prevailing climate and soil conditions. Long-lived organisms reproduce successfully within the community, nutrient cycles are comparatively tight, and small population changes do not automatically reset succession. This does not mean the community is motionless: individuals die and recruit, species abundances fluctuate, and patches are created by local disturbance. Nor must it have the highest primary productivity; mature biomass carries

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

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What determines succession pattern?

Successional patterns emerge from interactions among species, dispersal, and abiotic environmental factors. Dispersal determines which seeds, spores, larvae, or adults reach a site, creating historical contingency and priority effects. Abiotic filters such as moisture, temperature, salinity, light, soil, and disturbance decide which arrivals can survive. Species then facilitate, tolerate, inhibit, consume, compete with, or form mutualisms with one another, altering establishment and replacement. Because these processes interact, identical disturbances need not produce identical endpoints. A ni

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

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In primary succession, soil forms due to:

Soil development during primary succession begins through rock weathering combined with the activity of pioneering organisms such as lichens. Temperature fluctuations, freezing, water, and abrasion physically break rock, while carbonic and organic acids chemically dissolve minerals. Lichen fungi adhere to the surface, retain moisture, and secrete acids; their photosynthetic partners provide organic carbon. Dust and small mineral particles become trapped, and dead microbial and lichen material adds the first organic matter. This mixture gradually stores more water and nutrients, enabling mosses

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

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SUCCESSION

An example of autogenic succession is:

Grasses colonizing a sand dune can initiate autogenic succession because the organisms themselves modify the habitat and influence later community development. Grass roots bind mobile sand, while stems reduce wind speed and trap additional particles. Dead leaves and roots add organic matter, microbes release nutrients, and improved water retention makes the substrate less hostile. These changes permit herbs, shrubs, and eventually trees to establish where regional climate allows. The succession is autogenic to the extent that biological engineering drives the transition, although wind depositi

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

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Which term describes modification of environment by organisms?

Autogenic change is environmental modification caused by organisms within the community, and it can drive succession. Plants create shade, roots alter soil structure, litter adds organic matter, nitrogen-fixing microbes enrich nutrient supply, and sphagnum can acidify wetland water. These changes modify the establishment and competitive success of later species. Allogenic change originates outside the community, such as volcanic deposition, flooding, erosion, climate shifts, or altered fire regimes. “Catagenic” and “progenetic” are not the standard contrasting terms for organism-driven success

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

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SUCCESSION

Which of the following is true?

In the classic succession framework, later or climax communities commonly contain greater structural complexity and support more species than pioneer communities, making high biodiversity the best statement provided. Early colonists are usually light-demanding rather than shade-tolerant, because they exploit open habitats. Pioneer species typically grow rapidly, disperse well, and reproduce early, so low growth is not their usual syndrome. A climax community is described as relatively stable, not inherently unstable, although modern ecology recognizes continuing disturbance and multiple dynami

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

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Which factor is most important in primary succession?

Primary succession is distinguished by the initial absence of developed soil, so the keyed phrase “soil presence” is scientifically mismatched with the process as written. Soil formation, rather than pre-existing soil, is one of the most important early developments. Weathering of rock, dust deposition, microbial activity, lichens, and accumulation of dead organic matter create a substrate that stores water and nutrients and permits larger plants to establish. Temperature and light strongly affect colonists and weathering, but neither alone universally controls all primary succession. Competit

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

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Which succession occurs in an area where life previously existed?

Secondary succession occurs where a community previously existed and a disturbance removes organisms without eliminating all soil and biological legacies. Forest regrowth after fire, abandoned agriculture, storm damage, or logging are common examples. Remaining seed banks, roots, spores, microbes, soil structure, and nutrients accelerate recovery compared with primary succession. Primary succession starts on newly exposed or sterilized substrate with little or no developed soil, as on fresh lava, glacial till, or bare rock. “Autogenic” and “allogenic” describe causes of successional change rat

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

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Which ecological change is least reversible?

Extinction is effectively irreversible because it eliminates the last living members of a species and therefore its unique evolutionary lineage and gene pool. Once no viable individuals or preserved reproductive material remain, ordinary ecological processes cannot recreate that species. Evolution might eventually produce organisms with similar traits, but not the same historical lineage. Succession can reverse or restart after disturbance, invasion can sometimes be controlled or eradicated, and evolutionary change may be altered by future selection or gene flow, though none is always easily r

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

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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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Which best characterizes r-selected species in early succession?

High fecundity is characteristic of many r-selected species that dominate early succession. Disturbed habitats are open, temporary, and unpredictable, so natural selection favours organisms that reproduce quickly and produce many offspring capable of reaching new patches. Seeds or propagules are often small, dispersive, and short-generation, allowing rapid population increase when light and nutrients are abundant. Investment in numerous offspring usually trades off against large body size, prolonged parental care, durable tissues, and late reproduction. Long life span and slow maturation are m

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

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SUCCESSION

The process of succession is driven by:

Species interactions are major drivers of succession because organisms change both the physical environment and one another’s probability of establishment and survival. Pioneer plants may facilitate successors by building soil, adding nitrogen, or providing shade. Residents may instead inhibit newcomers through competition, allelopathy, or occupation of space. In tolerance pathways, later species establish independently but ultimately prevail because they survive low light or resources better. Herbivory, predation, mutualism, and decomposition also redirect trajectories. The keyed choice highl

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

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