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Lecture 19

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Shawn Lehman

ANT333 Lecture #19 – Effects of Body Size Size and Shape  Gould (1974) “Yet, however much we celebrate diversity and revel in the peculiarities of animals, we must also acknowledge a striking “lawfulness” in the basic design of organisms. This regularity is most strongly evident in the correlation of size and shape.”  Uniform body size in all mammals Shape  Above a certain size, large terrestrial oganisms look basically alike - they have thick legs and relatively short, stout bodies  An organism assumes a form best adapted to its size  In other words, point here is, that size may influence morphology, ecology, physiology and evolution of an organism Small vs. Large Organisms  Under identical physical forces but they are differentially affected.  Cohesion – force that holds things together  Gravity – pulling down force  Kinetic – energy of motion Modes of growth  Relative weakness of gravitational forces also permits a mode of growth that large animals could not maintain  Insects discard their external skeleton & secrete a new one  A large mammal without any supporting structures would collapse to a formless mass under influence of gravitational forces during a molt The Effects of Size  There are 2 factors to consider with respect to body size: o Surface area (length x width) & o Volume (length x width x height) The Effects of Size  As body size increases, surface area changes as function of square of linear dimensions (L2).  Two (2) dimensions that change in size: length x width. The Effects of Size  As body size increases, body volume changes as function of cube of linear dimensions (L3).  Volume changes in three (3) dimensions: length x width x height.  If an animal were to double in length, breadth, and width, its cross-sectional dimensions would increase 4x, and its volume would increase 8x Size and Weight  Strength of bones is function of cross-sectional area of bone.  Animal whose linear dimensions doubled would weigh 8x as much 1  But structural supports would be only 4x as strong  So animals of different size will not be similarly proportioned (see femurs)  Allometry: study of size-related differences in biology of an organism  Intraspecific allometry: size-related differences in adults of the same species  Interspecific allometry: size-related differences across a wide range of species for broader principles of scaling)  Growth allometry: study of shape changes associated with size changes in ontogeny (growing older) Four (4) Aspects of Size: 1. Size and diet 2. Size and locomotion 3. Size and life history 4. Size and ecology 1. Size and Diet  Organisms who live off leaves are usually over 1 kg  Most primates eat fruit  Insectivore are usually small, lose a lot of heat 2. Size and Locomotion  Terrestrial primates larger than arboreal primates.  Smaller primates tend to leap more than larger-bodied primates.  Suspensory behavior more common among larger bodied primates.  Quadrupedalism does not seem to be related to body size. 3. Size and life history  Many characteristics of animals, including basal metabolic rate, brain size, heart size and rate of blood circulation, litter size and size of offspring at birth, etc., scale linearly over most body sizes when plotted on logarithmic axes  E.g., body size scales: (+) positively to average adult lifespan & age of maturity & (-) negatively to yearly litter size. 4. Size and Primate Ecology  Smaller primates usually more susceptible to predation than large species.  Home range size positively correlated with primate body mass.  Group size increases with body size, particularly in frugivores, but not folivores. Introduction  Fundamental issue in evolutionary ecology is understanding intraspecific & interspecific variations in body mass.  Why? Because body mass correlates with important traits (e.g., density & extinction risk).  Body mass and energy implicit in this pattern.  Goal: Discuss some aspects of evolutionary ecology of lemur body mass. 2 Energetic Equivalent Rule (EER)  Inverse relationship between density (D) and body mass (M), such that D:M–0.75 relationship.  Why? Because body mass and metabol
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