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Asymptotic prey profitability drives star-nosed moles to the foraging speed limit

Abstract

Foraging theory provides models for predicting predator diet choices assuming natural selection has favoured predators that maximize their rate of energy intake during foraging1,2,3,4,5,6. Prey profitability (energy gained divided by prey handling time) is an essential variable for estimating the optimal diet. Time constraints of capturing and consuming prey generally result in handling times ranging from minutes to seconds, yet profitability increases dramatically as handling time approaches zero, providing the potential for strong directional selection for increasing predator speed at high encounter rates (tiny increments in speed increase profitability markedly, allowing expanded diets of smaller prey). We provide evidence that the unusual anatomical and behavioural specializations characterizing star-nosed moles resulted from progressively stronger selection for speed, allowing the progressive addition of small prey to their diet. Here we report handling times as short as 120 ms (mean 227 ms) for moles identifying and eating prey. ‘Double takes’ during prey identification suggest that star-nosed moles have reached the speed limit for processing tactile information. The exceptional speed of star-nosed moles, coupled with unusual specializations for finding and eating tiny prey, provide new support for optimal foraging theory.

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Figure 1: Star-nosed mole foraging.
Figure 2: Prey profitability and energy intake for different handling times and prey densities.
Figure 3: The unusual dentition and nose of star-nosed moles.
Figure 4: A double take illustrating initial movement in the wrong direction, followed by a sudden correction that brings the foveal region into contact with the prey.

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Acknowledgements

We thank D. McCauley, M. Leal, P. Abbot and E. Haldeman for comments on the manuscript. Research was supported by an NSF Career Award to K.C.C.

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Correspondence to Kenneth C. Catania.

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The authors declare that they have no competing financial interests.

Supplementary information

Supplementary Video 1

This movie shows a star-nosed mole filmed from below as it detects and eats a small prey item (piece of an earthworm, approximately 10 joules) in under 150 milliseconds. (MOV 1682 kb)

Supplementary Video 2

This movie shows a short-tailed shrew (a species commonly found in star-nosed mole tunnels) eating a cricket (approximately 1400 joules) in 30 seconds. (MOV 4339 kb)

Supplementary Video 3

This movie show a star-nosed mole eating an earthworm segment containing approximately 1100 joules of energy. (MOV 1638 kb)

Supplementary Video 4

This movie shows an Eastern American mole encountering a series of small (10J) prey items. (MOV 500 kb)

Supplementary Video 5

This video shows a star-nosed mole's first encounter with a multiple prey item array. (MOV 6601 kb)

Supplementary Video 6

This movie shows a "double-take" during which a star-nosed mole exhibits a time lag before returning to contacted prey. (MOV 2108 kb)

Supplementary Figure 1

A summary of our hypothesis regarding the evolution of short handling times in star-nosed moles. (PDF 3037 kb)

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Catania, K., Remple, F. Asymptotic prey profitability drives star-nosed moles to the foraging speed limit. Nature 433, 519–522 (2005). https://doi.org/10.1038/nature03250

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