• T R Rao

Articles written in Resonance – Journal of Science Education

In many ecosystems, apex consumers (top predators) play acrucial role in food web dynamics. Their top-down impactsare known to spread downwards through the food webs ina cascading fashion. Trophic cascades manifest when toppredators are excluded from an ecosystem or introduced intoa system lacking them. Two such case studies are describedhere. Trophic cascades are generally more pronounced in theaquatic than in the terrestrial ecosystems, which in turn isrelated to the differences in the average body sizes of herbivoresrelative to the plant resources they feed upon andin the structure of their food webs. Scientists express concernthat human activities have been leading to planet-widetrophic downgrading (loss of apex consumers) which couldaffect vital ecological processes of the biosphere.

• Body Size Matters in the Lives of Organisms

Body size, arguably the most important attribute of all organisms in the living world, is a reliable predictor of their physiological rates and life-history attributes. Metabolic rates of all organisms ($MR$) are related directly to their body mass ($M$) as an allometric function $MR = \alpha M \frac{3}{4}$ (Kleiber’s rule). The high, mass-speciﬁc metabolic rates of small animals can be accounted for by their high surface area/volume ratios. The much-discussed ‘metabolic theory of ecology’ is essentially an expansion of Kleiber’s rule equation to include two additional metabolism-inﬂuencing factors—temperature and resource availability—with a more generalized quarter-power exponent. According to this theory, many physiological rates, life-history traits and ecological processes follow quarter-power scaling laws. Living organisms must also obey the laws of physics. The relative importance of diﬀerent physical forces to the organisms living on land or in water is also dependent on their body size.

• # Resonance – Journal of Science Education

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Volume 27 | Issue 6
June 2022

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