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Related Concept Videos

Mass Spectrometry: Isotope Effect01:13

Mass Spectrometry: Isotope Effect

Most elements exist in nature as a mixture of isotopes. The isotopes differ in weight due to their respective number of neutrons. The molecular weight of a molecule is different depending on the specific isotope of its elements involved. As a result, the mass spectrum of the molecule exhibits peaks from the same fragment at multiple positions. The positions of these mass signals depend on the mass differences between isotopes. Furthermore, the intensity of these signals is dependent on the...
Molar Mass01:54

Molar Mass

The identity of a substance is defined not only by the types of atoms or ions it contains but by the quantity of each type of atom or ion. For example, water, H2O, and hydrogen peroxide, H2O2, are alike in that their respective molecules are composed of hydrogen and oxygen atoms. However, because a hydrogen peroxide molecule contains two oxygen atoms, as opposed to the water molecule, which has only one, the two substances exhibit very different properties.
Mass Spectrum01:23

Mass Spectrum

A mass spectrum is the graphical representation of the relative abundance of the charged fragments in an analyte plotted against their mass-to-charge ratio (m/z). The plot's x-axis represents the ratio of the mass of the charged fragment to the number of charges it carries. The y axis of the plot represents the relative abundance of each charged species. The relative abundance is calculated from the signal intensity of each charged species recorded at the detector. The most intense signal (the...
Mass and Weight01:19

Mass and Weight

Mass and weight are often used interchangeably in everyday conversation. For example,  medical records often show our weight in kilograms, but never in the correct units of newtons. In physics, however, there is an important distinction. Weight is the pull of the Earth on an object. It depends on the distance from the center of the Earth. Weight dramatically varies if we leave the Earth's surface, unlike mass, which does not vary with location. On the Moon, for example, the acceleration due to...
Mass and Weight01:19

Mass and Weight

Mass and weight are often used interchangeably in everyday conversation. For example,  medical records often show our weight in kilograms, but never in the correct units of newtons. In physics, however, there is an important distinction. Weight is the pull of the Earth on an object. It depends on the distance from the center of the Earth. Weight dramatically varies if we leave the Earth's surface, unlike mass, which does not vary with location. On the Moon, for example, the acceleration due to...
High-Resolution Mass Spectrometry (HRMS)01:15

High-Resolution Mass Spectrometry (HRMS)

The resolution of a mass spectrometer depends on the efficiency of separating ions with different ion masses. The mass of an atom is approximated to the sum of the masses of protons and neutrons inside, considering the masses of protons and neutrons as equal. However, the masses of the proton (1.6726 × 10−24 g) and neutron (1.6749 × 10−24 g) are not truly equal. There is a minor error in the expression of atomic masses relative to the simplest atom of hydrogen. For example, the mass of helium...

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Related Experiment Video

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Modeling the Size Spectrum for Macroinvertebrates and Fishes in Stream Ecosystems
07:41

Modeling the Size Spectrum for Macroinvertebrates and Fishes in Stream Ecosystems

Published on: July 30, 2019

How many species have mass M?

Aaron Clauset1, David J Schwab, Sidney Redner

  • 1Santa Fe Institute, Santa Fe, New Mexico 87501, USA. aaronc@santafe.edu

The American Naturalist
|December 19, 2008
PubMed
Summary

Species body mass distributions are shaped by evolutionary processes. A new model explains these patterns in mammals and birds, highlighting a balance between growth trends and extinction risks.

Area of Science:

  • Evolutionary biology
  • Macroevolutionary patterns
  • Biophysics

Background:

  • Species body mass distributions are broadly asymmetric, with large outliers.
  • Existing theories struggle to fully explain these canonical shapes.

Purpose of the Study:

  • To introduce and solve a simplified cladogenetic diffusion model for species body mass.
  • To test the model's predictions against empirical data for mammals and birds.
  • To investigate the interplay between evolutionary trends and extinction risks.

Main Methods:

  • Analytical solution of a simplified cladogenetic diffusion-reaction equation.
  • Parameterization of the model using empirical data.
  • Comparison of model predictions with body mass data from 4,002 terrestrial mammals and 8,617 extant bird species.

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Main Results:

  • The diffusion-reaction model accurately predicts observed body mass distributions for mammals and birds.
  • A critical trade-off between within-lineage drift (Cope's rule) and mass-dependent extinction risk is identified.
  • The model suggests specific evolutionary pressures shaping species mass.

Conclusions:

  • Cladogenetic diffusion, bounded by physiological limits and extinction risks, explains species body mass distributions.
  • The balance between evolutionary drivers and extinction is key to macroevolutionary patterns.
  • The model provides a framework for predicting future evolutionary trajectories of species masses.