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Ecological Energetics of a Homeothermic Predator, The Short‐Tailed Shrew
Author(s) -
Randloph J. Collier
Publication year - 1973
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1935587
Subject(s) - shrew , predator , predation , homeothermy , biology , ecology , energetics , range (aeronautics) , population , thermoregulation , materials science , demography , sociology , composite material
A detailed examination of the thermal and chemical energy fluxes of an individual predator is used in estimating seasonal energy transfer from prey populations to predator populations. The short—tailed shrew, Blarina brevicauda, was selected as the predator because it is a homeotherm that is active during the entire year. Blarina has a combination of metabolic, insulative, and behavioral adaptations permitting survival through a wider range of environmental temperatures than usually occur in its typical habitat. Both insulative and metabolic modifications occur seasonally. Within the range of 0 degrees to 25 degrees C, Blarina metabolism is inversely porportional to ambient temperature. At any given ambient temperature heat loss is lower from winter shrews than from summer shrews. Winter shrews at winter temperatures have a higher metabolic rate than do summer shrews at summer temperatures. Blarina has a digestive efficiency of about 0.90, which is not affected by seasonal temperature changes. Changes in the thermal environnemt have a more pronounced effect on a shrew's energy requirement than do changes in the daily level of locomotor activity. Blarina's metabolic rate during normal exploring locomotor activity is approximately double that during sleep. Existing models of assimilation and heat transfer in animals were used as subsystem components in a deterministic model. The model estimated that the winter food requirement of the predator population is about 43% higher than the summer food requirement. A population of 20 Blarina in a 6.47—acre deciduous woodlot near Manotick, Ontario, would require only about 3% of the total prey energy base during the summer and about 37% of the prey energy base during the winter. The prey energy available per square meter of forest floor during the summer is estimated to be about eight times that available during the winter. A population of 20 adult Blarina should experience little difficulty in obtaining sufficient food both during summer and winter.