SREL Reprint #0475




Ecological Energetics of Three Species of Ectothermic Vertebrates

Gary C. Smith



Comparisons were made of the energy budgets of three ectothermic vertebrates found in the Southeastern United States.  The three species studied were Elaphe guttata (corn snakes), Heterodon platyrhinos (eastern hognose snakes), and Bufo terrestris (southern toads).  Values for assimilation efficiency, ingestion, excretion, growth, shedding, metabolism, and reproduction were converted to caloric units and integrated into energy flow models for each species.

Elaphe guttata had a greater weekly ingestion rate than did the other two species in all weight classes.  Assimilation efficiencies (ingestion-egestion/ingestion X 100) for the three species were 88.92% for E. guttata, 83.92% for H. platyrhinos, and 73.70% for B. terrestris.  These values are similar to those reported for other carnivores.

Regression equations of metabolism per animal hour at 15C, 20C, 25C, and 30C for the three species were in O2 = 4.19 + 0.68 1n W + 0.10T + 0.24 for E. guttata, in O2 + -3.60 + 0.76 1n W + 0.14T + 0.36 for B. terrestris, and in O2= 5.78 + 1.04 in W + 0.10T + 0.28 for H. platyrhinos.

Reserves of fat in the fat bodies of the three species were lowest in the spring and coincided with periods of maximal reproduction suggesting that a large percentage of the energy reserves were utilized for this purpose. 

Elaphe guttata showed a much greater rate of growth than the other two species in the laboratory.  Differences in growth were directly related to amount of food ingested, since assimilation efficiency and metabolism remained constant at all feeding levels.  Shedding intervals for the two snake species at 25C averaged 40.5 days for E. guttata and 38.3 days for H. platyrhinos.  The dry shed weight:  body weight ratio increased with increasing size for hognose snakes but decreased for corn snakes.  Egg clutches comprised ~ 42% of the total caloric values of the females of all three species.  This suggests that the energy cost of reproduction would require large reserves of fat which would accumulate over a period of one or more years.

Production-assimilation ratios (production/assimilation X 100) were 86% for corn snakes, 81% for hognose snakes, and 49% for southern toads. Comparisons of energy flow in the three study species revealed that ingestion methods (A = I E) gave significantly higher and less variable results than production-respiration methods (A = P + R) for all three study species.

Key words:  Amphibia; assimilation; Bufo terrestris; Elaphe guttata; energy budgets; fat reserves; Heterodon platyrhinos; metabolism; productivity; Reptillia; shedding; southeastern United States.


SREL Reprint #0475

Smith, G.C. 1976. Ecological energetics of three species of ectothermic vertebrates. Ecology 57:252-264.

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