Geometrical aspects of the energetic effectivenes of huddling in small mammals

Abstract

Canals M., Rosenmann M. and Bozinovic F. 1997. Geometrical aspects o f the energetic effectiveness of huddling in small mammals. Acta Theriologica 42: 321-328.Reduced energy expenditure resulting from huddling in small mammals is mainly attributed to the reduced surface area/volume ratio of the huddling group. Here we propose a model to account for the reduction of the relative exposed area of grouped animals and for the diminution of metabolic rate during huddling. We attempt to explain mechanistically how changes in energy savings may operate. We applied our model to results obtained by grouping deformable bodies, and also laboratory meas urements o f oxygen consumption on huddling small mammals of four species. We found a small amount of diversity in the energetic efficiency of huddling. We estimate that the average relative area lost during huddling ranged between 28.7 and 39.1%. The average huddling effectiveness in the studied species was 42%, which is a significant fraction of the energy/matter budget of a small mammal, especially under winter conditions.

Modulating factors of the energetic effectiveness of huddling in small mammals

“…From the total of the fitted models, including our results and data from the literature, only in four cases R 2 was lower than 66.67% (see Tables). Previous studies reported a percentage of observed energy saving attributed to the reduced surface effect ranged from 58 to 94% (Canals et al 1997). …”

“…This parameter was called deformation coefficient because it represents twice the average surface lost by the huddled individuals and determines the effectiveness of animals in reducing the metabolic rate of the group from huddling (HE -huddling effectiveness) (Canals et al 1997). The f(rc) parameter is affected by the number of grouped individuals (n) and by the temperature gradient between body (Tb) and ambient (T a ), that is (Tb -T a ).…”

A reanalysis of apparent survival rates of Indiana myotis (Myotis sodalis)

“…Each individual in the model enters winter with a unique body and fat mass and arouses with a unique pattern throughout winter. All individuals in a population are subjected to the same winter length, number and pattern of disturbances (see below), and each population either clusters in groups of greater than 5 individuals (Canals et al 1997) or does not cluster.…”

“…Most cavernicolous species cluster to some extent, and even small clusters (5 individuals) significantly reduce heat loss by individuals (Canals et al 1997;Kurta 1985). To estimate the energetic benefit of clustering, we ran all simulations with and without clustering.…”

“…To estimate the energetic benefit of clustering, we ran all simulations with and without clustering. Based on theoretical estimates of Canals et al (1997), we assumed that clustering lowered energy expenditure during euthermy to 41.1% of that expended when solitary. This assumes that most individuals in a cluster arouse synchronously, and are euthermic for the same period.…”