|SREL Reprint #0475|
Ecological Energetics of Three Species of Ectothermic Vertebrates
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
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.
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.