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Background

Considering just the "Kingdom Animalia" branch of organisms. It is clear that bigger does not necessarily mean better - there is large variation in body size...

From the 94 µm long Tantulocarid arthropod (Stygotantulus stocki)

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To the 25.5 m long Blue Whale (Balaenoptera musculus)

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Questions

  • What trade-offs exist between having a particular body size (very large, very small) to other traits and factors?

  • Alternatively, What are the evolutionary/ecological advantages/disadvantages are there to having a large or small body size?

Thank you!

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I saw something recently that claimed that, in general, lineages evolved to become larger more often / more consistently then to become smaller. It seems like it might be relevant to this question, but I can't seem to find the citation - maybe someone else can? –  Oreotrephes Dec 2 '13 at 3:37
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Ah, apparently it's Cope's Rule, and it's still a pretty hot topic of debate for and against. –  Oreotrephes Dec 2 '13 at 3:44
    
You should quote or summarize this rule as an answer! –  hello_there_andy Dec 2 '13 at 8:36
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Have you read the book WHY SIZE MATTERS by Bonner? It's an excellent book covering every aspect of size in an easy to read manner. –  biogirl Dec 5 '13 at 12:00

1 Answer 1

up vote 6 down vote accepted

I don't think one can fully answer to such a broad question. It depends on the population, the environment (presence of predators for example), the genetic background (having a big stomach is good but only if the intestin is big too), the population's social relations, .. Many traits are correlated and one might want to say that a given trait is beneficial but it is not because this trait is correlated (because of genetic, physical or social constraints). Here is a list of possible advantages/disadvantages.

  • visibility to predators
  • ability to hunt bigger preys or to manipulate smaller preys
  • running faster
  • be more impressive
  • fighting ability
  • energy consumption for maintaining a body
  • Quantity/quality of food to be found
  • homothermy (heat loss)
  • sustaining its own weight
  • Rooms for the organs
  • Attractiveness to the other sex
  • being more able to move freely (in viscous environment (water))
  • mechansisms for bringing nutrients and air to the tissues
  • density of the body (water)
  • excretion of wastes
  • moving in small habitats
  • Hiding in small areas
  • bearing big and complex structures
  • Parental care
  • flying better
  • etc...

You might be interested in life-history traits, to allometric relations. Maybe you can be interested by this article as well.

You might also be interested in the philosophical discussion of adaptation, optimality, cost and benefit like this book (which I haven't read!) for example.

Concerning the relation between heat loss and size, you might be willing to have a look to the Kleiber's law. This law has been extensively debated and is today thought (or known) to be wrong.

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cheers for this, I now realize the issues you've raised. What do you think of me re-wording it so that I ask for "general and commonly observed" advantages/disadvantages? E.g. there may be some evolutionary reasons that hold true to all clades? E.g. the surface area to volume ratio effect for heat retention. –  hello_there_andy Dec 1 '13 at 22:08

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