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Related Concept Videos

Buffers02:56

Buffers

173.0K
A solution containing appreciable amounts of a weak conjugate acid-base pair is called a buffer solution, or a buffer. Buffer solutions resist a change in pH when small amounts of a strong acid or a strong base are added. A solution of acetic acid and sodium acetate is an example of a buffer that consists of a weak acid and its salt: CH3COOH (aq) + CH3COONa (aq). An example of a buffer that consists of a weak base and its salt is a solution of ammonia and ammonium chloride: NH3 (aq) + NH4Cl...
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Buffers: Buffer Capacity01:09

Buffers: Buffer Capacity

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Buffer capacity is the quantitative measure of a buffer to resist the change in pH. As shown in the following equation, the buffer capacity, denoted by 'beta', is expressed as the number of moles of acid or base needed to change the pH of a one-liter buffer solution by 1 unit. Here, Ca and Cb indicate the number of moles of acid and base, respectively. Note that dpH represents the change in pH.
In the graph, pH is plotted as a function of the number of moles of base (Cb) added to a weak...
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Buffer Effectiveness02:19

Buffer Effectiveness

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Buffer solutions do not have an unlimited capacity to keep the pH relatively constant . Instead, the ability of a buffer solution to resist changes in pH relies on the presence of appreciable amounts of its conjugate weak acid-base pair. When enough strong acid or base is added to substantially lower the concentration of either member of the buffer pair, the buffering action within the solution is compromised.
The buffer capacity is the amount of acid or base that can be added to a given volume...
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What is Natural Selection?01:32

What is Natural Selection?

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Natural selection is an evolutionary process in which individuals with survival-promoting traits reproduce at higher rates. These favorable traits become more common within a population or species. Naturally selected traits initially arise via random genetic mutations. In order for selection to occur, there must be variation within a population, the trait controlling the variation must be heritable, and there must be an evolutionary advantage for variation in the trait.
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Calculating pH Changes in a Buffer Solution02:45

Calculating pH Changes in a Buffer Solution

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A buffer can prevent a sudden drop or increase in the pH of a solution after the addition of a strong acid or base up to its buffering capacity; however, such addition of a strong acid or base does result in the slight pH change of the solution. The small pH change can be calculated by determining the resulting change in the concentration of buffer components, i.e., a weak acid and its conjugate base or vice versa. The concentrations obtained using these stoichiometric calculations can be used...
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Phosphate Buffer01:22

Phosphate Buffer

5.2K
The phosphate buffer system is a critical biological mechanism for maintaining pH stability in the body. This system operates primarily through two components: sodium dihydrogen phosphate (NaH2PO4), which acts as a weak acid, and sodium hydrogen phosphate (Na2HPO4), which serves as a weak base.
Sodium dihydrogen phosphate does not fully dissociate in neutral or acidic solutions. When a strong base, such as sodium hydroxide (NaOH), is introduced into the solution, sodium dihydrogen phosphate...
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Demographic buffering in natural populations: A multi-level perspective.

Gabriel Silva Santos1,2,3, Samuel J L Gascoigne3,4, André Tavares Corrêa Dias5

  • 1National Institute of the Atlantic Forest (INMA), Santa Teresa, Espírito Santo, Brazil.

The Journal of Animal Ecology
|February 3, 2026
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Summary

Demographic buffering helps populations persist despite environmental changes. However, this study found that evolutionary selection doesn't always reduce vital rate variance, even in buffered species, suggesting ecological and evolutionary signals may not align.

Keywords:
COMADRE Animal Matrix Databaseelasticityenvironmental stochasticitylife‐history evolutionnatural selectionsecond‐order derivativesensitivity

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Area of Science:

  • Ecology and Evolutionary Biology
  • Population Dynamics
  • Conservation Biology

Background:

  • Environmental variability challenges population persistence.
  • Demographic buffering, stabilizing population growth amidst fluctuations, is a proposed but empirically under-tested mechanism.
  • Existing studies on demographic buffering yield conflicting results.

Purpose of the Study:

  • To introduce an integrative demographic framework to identify demographic buffering.
  • To test if populations with low stochastic elasticities (indicating buffering) show concave selection on vital rates.
  • To assess the alignment between ecological buffering and evolutionary constraints across mammalian species.

Main Methods:

  • Developed a framework combining stochastic elasticities (sensitivity of long-term growth rate to variance) and second-order derivatives of deterministic growth (indicating selection on vital rates).
  • Applied the framework to 43 natural populations across 37 mammalian species.
  • Analyzed variance in demographic processes and identified species exhibiting buffering and concave selection.

Main Results:

  • Most primates and long-lived mammals showed evidence of demographic buffering (low stochastic elasticities).
  • Only the Columbian ground squirrel demonstrated strong buffering with key vital rates under concave selection.
  • Primates often exhibited convex or absent second-order effects, indicating a mismatch between ecological buffering and evolutionary constraint.

Conclusions:

  • Demographic buffering is more dynamic and context-dependent than previously assumed.
  • Selection does not consistently reduce vital rate variance, even in species with stable population growth.
  • Ecological and evolutionary signals of buffering may be decoupled, necessitating integrated approaches to understand population resilience.