Energetics of burrowing, running, and free-living in the Namib Desert golden mole (Eremitalpa namibensis)

Abstract

The Namib Desert golden mole (Eremitalpa granti namibensis) is a small (c. 20 g), blind, sand-swimming, chrysochlorid insectivore that inhabits the sand dunes of one of the driest and least productive areas of the world. Its food, largely termites, is sparse and occurs in widely distributed patches, and free water is unavailable. The moles forage by running on the surface and burrowing below the sand. We estimated their daily energy expenditure in the ®eld to be 11.8 kJ d -1 by constructing a`distance-energy budget' based on measurements of tracks in the sand and the energy cost of running (4.2 kJ d -1 ), burrowing (3.2 kJ d -1 ), and resting (4.4 kJ d -1 ). We also measured ®eld metabolic rate (12.5 kJ d -1 ) and water turnover (2.3 ml d -1 ) independently with doubly-labelled water. The resting metabolic rate (0.5 ml O 2 g -1 h -1 at 35 8C) is about a ®fth of that predicted for a normal insectivorous mammal, and the daily ®eld energy expenditure and water turnover are about a half. The low daily energy expenditure stems mainly from the low resting metabolic rate, which is associated with low body temperatures and metabolic depression. Moles save more energy during foraging by running on the surface of the sand, rather than burrowing under it. The gross energy cost of sand-swimming (80 J m -1 ) is 26 times more expensive than running on the surface (3.0 J m -1 ), but is less than a tenth of the energy required by mammals that tunnel through compact soil. Nevertheless, it would be energetically impossible for the moles to obtain enough food by foraging only underground at our study site. The mean track length was 1.4 km, but only 16 m of it was below the surface. There is evidence that the track length and fraction underground depend on food abundance which is in¯uenced by rainfall.

Energetics of burrowing by the cirratulid polychaeteCirriformia moorei

“…The costs of transport calculated from these three efficiencies still span a broad range but seem to indicate that burrowing may be more energetically costly per distance traveled than other forms of locomotion (Fig.8). This result is consistent with direct comparisons showing much higher costs of burrowing through desert sands than running for the Namib desert golden mole (Seymour et al, 1998) and the northwestern marsupial mole (Withers et al, 2000) (Fig.8). The cost of burrowing by C. moorei is comparable to the cost per distance of burrowing through desert sands by moles and less than that of burrowing by mice (White et al, 2006) or scorpions (White, 2001) (Fig.8).…”

“…postural costs (Full, 1991)]. Our calculated GCT can, however, be compared with the GCT for maggots, calculated from Berrigan and Lighton (Berrigan and Lighton, 1993), and that for burrowing by desert moles in sand (Seymour et al, 1998) and the values are very similar (Fig.8). Although not comparable to many values in the literature for other species, GCT provides an upper bound for the metabolic cost of transport.…”

Energetics of burrowing by the cirratulid polychaeteCirriformia moorei

“…The costs of transport calculated from these three efficiencies still span a broad range but seem to indicate that burrowing may be more energetically costly per distance traveled than other forms of locomotion (Fig.8). This result is consistent with direct comparisons showing much higher costs of burrowing through desert sands than running for the Namib desert golden mole (Seymour et al, 1998) and the northwestern marsupial mole (Withers et al, 2000) (Fig.8). The cost of burrowing by C. moorei is comparable to the cost per distance of burrowing through desert sands by moles and less than that of burrowing by mice (White et al, 2006) or scorpions (White, 2001) (Fig.8).…”

“…postural costs (Full, 1991)]. Our calculated GCT can, however, be compared with the GCT for maggots, calculated from Berrigan and Lighton (Berrigan and Lighton, 1993), and that for burrowing by desert moles in sand (Seymour et al, 1998) and the values are very similar (Fig.8). Although not comparable to many values in the literature for other species, GCT provides an upper bound for the metabolic cost of transport.…”

Balancing the competing requirements of saltatorial and fossorial specialisation: burrowing costs in the spinifex hopping mouse, Notomys alexis

“…Furthermore, the ecological consequences associated with fossorial specialisation are likely to be detrimental for hopping mice. Although the energetic costs of terrestrial locomotion of specialised burrowers (Eremitalpa granti namibensis and Notoryctes caurinus) are similar to allometric predictions (Seymour et al, 1998;Withers et al, 2000), maximum running speeds of fossorial moles (Talpa europaea and Scalopus aquaticus) are significantly lower than those of non-fossorial species (Fig.·7). Hopping mice forage in open areas in arid environments , so their capacity to escape predation is probably related to maximum running speed, and species from open habitats have higher maximum running speeds than species from less open habitats (Fig.·8).…”

Termite Digestibility and Water and Energy Contents Determine the Water Economy Index of Numbats ( Myrmecobius fasciatus ) and Other Myrmecophages

“…The compositions of Coptotermes and Nasutitermes termites examined in this study (Table 1) are typical of values for termites in general. Water contents (76.7% and 78.0%) were similar to those for other termite species (66%-80%; Redford and Dorea 1984;Abensperg-Traun and de Boer 1992;Oyarzun et al 1996;Williams et al 1997;Seymour et al 1998), ants (40%-80%; Griffiths 1965;Withers and Dickman 1995), and a generalised insect (70%-75%; Bell 1990). The total energy contents (23.1 kJ and 22.7 kJ ) were typical of most bio-…”

Energetics of burrowing by the cirratulid polychaeteCirriformia moorei

“…The costs of transport calculated from these three efficiencies still span a broad range but seem to indicate that burrowing may be more energetically costly per distance traveled than other forms of locomotion (Fig.8). This result is consistent with direct comparisons showing much higher costs of burrowing through desert sands than running for the Namib desert golden mole (Seymour et al, 1998) and the northwestern marsupial mole (Withers et al, 2000) (Fig.8). The cost of burrowing by C. moorei is comparable to the cost per distance of burrowing through desert sands by moles and less than that of burrowing by mice (White et al, 2006) or scorpions (White, 2001) (Fig.8).…”

“…postural costs (Full, 1991)]. Our calculated GCT can, however, be compared with the GCT for maggots, calculated from Berrigan and Lighton (Berrigan and Lighton, 1993), and that for burrowing by desert moles in sand (Seymour et al, 1998) and the values are very similar (Fig.8). Although not comparable to many values in the literature for other species, GCT provides an upper bound for the metabolic cost of transport.…”

Balancing the competing requirements of saltatorial and fossorial specialisation: burrowing costs in the spinifex hopping mouse, Notomys alexis

“…Furthermore, the ecological consequences associated with fossorial specialisation are likely to be detrimental for hopping mice. Although the energetic costs of terrestrial locomotion of specialised burrowers (Eremitalpa granti namibensis and Notoryctes caurinus) are similar to allometric predictions (Seymour et al, 1998;Withers et al, 2000), maximum running speeds of fossorial moles (Talpa europaea and Scalopus aquaticus) are significantly lower than those of non-fossorial species (Fig.·7). Hopping mice forage in open areas in arid environments , so their capacity to escape predation is probably related to maximum running speed, and species from open habitats have higher maximum running speeds than species from less open habitats (Fig.·8).…”

Termite Digestibility and Water and Energy Contents Determine the Water Economy Index of Numbats ( Myrmecobius fasciatus ) and Other Myrmecophages

“…The compositions of Coptotermes and Nasutitermes termites examined in this study (Table 1) are typical of values for termites in general. Water contents (76.7% and 78.0%) were similar to those for other termite species (66%-80%; Redford and Dorea 1984;Abensperg-Traun and de Boer 1992;Oyarzun et al 1996;Williams et al 1997;Seymour et al 1998), ants (40%-80%; Griffiths 1965;Withers and Dickman 1995), and a generalised insect (70%-75%; Bell 1990). The total energy contents (23.1 kJ and 22.7 kJ ) were typical of most bio-…”

Energetics of burrowing by the cirratulid polychaeteCirriformia moorei

“…The costs of transport calculated from these three efficiencies still span a broad range but seem to indicate that burrowing may be more energetically costly per distance traveled than other forms of locomotion (Fig.8). This result is consistent with direct comparisons showing much higher costs of burrowing through desert sands than running for the Namib desert golden mole (Seymour et al, 1998) and the northwestern marsupial mole (Withers et al, 2000) (Fig.8). The cost of burrowing by C. moorei is comparable to the cost per distance of burrowing through desert sands by moles and less than that of burrowing by mice (White et al, 2006) or scorpions (White, 2001) (Fig.8).…”

“…postural costs (Full, 1991)]. Our calculated GCT can, however, be compared with the GCT for maggots, calculated from Berrigan and Lighton (Berrigan and Lighton, 1993), and that for burrowing by desert moles in sand (Seymour et al, 1998) and the values are very similar (Fig.8). Although not comparable to many values in the literature for other species, GCT provides an upper bound for the metabolic cost of transport.…”

Balancing the competing requirements of saltatorial and fossorial specialisation: burrowing costs in the spinifex hopping mouse, Notomys alexis

“…Furthermore, the ecological consequences associated with fossorial specialisation are likely to be detrimental for hopping mice. Although the energetic costs of terrestrial locomotion of specialised burrowers (Eremitalpa granti namibensis and Notoryctes caurinus) are similar to allometric predictions (Seymour et al, 1998;Withers et al, 2000), maximum running speeds of fossorial moles (Talpa europaea and Scalopus aquaticus) are significantly lower than those of non-fossorial species (Fig.·7). Hopping mice forage in open areas in arid environments , so their capacity to escape predation is probably related to maximum running speed, and species from open habitats have higher maximum running speeds than species from less open habitats (Fig.·8).…”

Termite Digestibility and Water and Energy Contents Determine the Water Economy Index of Numbats ( Myrmecobius fasciatus ) and Other Myrmecophages

“…The compositions of Coptotermes and Nasutitermes termites examined in this study (Table 1) are typical of values for termites in general. Water contents (76.7% and 78.0%) were similar to those for other termite species (66%-80%; Redford and Dorea 1984;Abensperg-Traun and de Boer 1992;Oyarzun et al 1996;Williams et al 1997;Seymour et al 1998), ants (40%-80%; Griffiths 1965;Withers and Dickman 1995), and a generalised insect (70%-75%; Bell 1990). The total energy contents (23.1 kJ and 22.7 kJ ) were typical of most bio-…”