Effects of trail gradient on leaf tissue transport and load size selection in leaf-cutter ants

Lewis, Owen T.; Martin, Mark T.; Czaczkes, Tomer J.

doi:10.1093/beheco/arn032

Cited by 25 publications

(33 citation statements)

References 30 publications

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“…For leafcutter ants, trail building and maintenance are a major energy cost for resource acquisition (Lugo et al 1973;Lewis et al 2008;Farji-Brener et al 2014). The energy invested into resource acquisition is generally balanced against the nutrient value of a resource (optimal diet theory; Rockwood & Hubbell 1987), and thus the trade-off between trail-building costs and resource nutritional value has been hypothesized to partially govern foraging in leafcutter ants (Shepherd 1985;Rockwood & Hubbell 1987).…”

Section: Discussionmentioning

confidence: 99%

“…Email: mewinsto@uchicago.edu Studies on Neotropical Fauna and Environment, 2015http://dx.doi.org/10.1080/01650521.2015 colonies (Vasconcelos et al 2006). In light of research that has estimated trail maintenance as 75% of the total energetic costs of the colony (Lugo et al 1973), and other work that has shown leafcutters respond to specific environmental conditions to optimize performance (Lewis et al 2008;Farji-Brener et al 2014), it is possible that leafcutter foraging in disturbed habitat differs from that in undisturbed, old growth forest. Conversely, estimation of foraging costs by Howard (2001) suggests the costs of trail maintenance to be minimal relative to the number of available workers and the rates of mass harvest.…”

Section: Introductionmentioning

confidence: 99%

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Unpaved roads alter foraging patterns of the leafcutter antAtta colombica

Winston

Herz

2015

Studies on Neotropical Fauna and Environment

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Leaf cutting ants are dominant herbivores and influential ecosystem engineers in the Neotropics. It has been suggested that habitat disturbances alter the architecture of foraging trail systems for colonies in their vicinity; however, the evidence remains scarce. In this study we investigated the effect of unpaved roads dissecting tropical lowland forest habitat on the structure of leafcutter foraging trail systems and foraging effort. We mapped trail systems for 16 mature Atta colombica colonies located at different distances from unpaved roads. Our results suggest exploitation of unpaved roads by leafcutters provides favorable foraging conditions, causing significant differences in foraging trail structure.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Unpaved roads alter foraging patterns of the leafcutter antAtta colombica

Winston

Herz

2015

Studies on Neotropical Fauna and Environment

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“…Running speeds in leaf-cutting ants have been shown to depend on such environmental conditions (trail gradients [25], [26], height constraints [27]), and it is likely that these effects are based on the ants’ need to maintain stability. We previously demonstrated that grass-cutting ants can maintain stability by adjusting the fragment angle by head movements on trails with inclines (+20°) or declines (−20°), but this re-orientation did not fully compensate the predicted shift of the centre of mass [19].…”

Section: Discussionmentioning

confidence: 99%

How Load-Carrying Ants Avoid Falling Over: Mechanical Stability during Foraging in Atta vollenweideri Grass-Cutting Ants

2013

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BackgroundForaging workers of grass-cutting ants (Atta vollenweideri) regularly carry grass fragments larger than their own body. Fragment length has been shown to influence the ants’ running speed and thereby the colony’s food intake rate. We investigated whether and how grass-cutting ants maintain stability when carrying fragments of two different lengths but identical mass.Principal FindingsAnts carried all fragments in an upright, backwards-tilted position, but held long fragments more vertically than short ones. All carrying ants used an alternating tripod gait, where mechanical stability was increased by overlapping stance phases of consecutive steps. The overlap was greatest for ants carrying long fragments, resulting in more legs contacting the ground simultaneously. For all ants, the projection of the total centre of mass (ant and fragment) was often outside the supporting tripod, i.e. the three feet that would be in stance for a non-overlapping tripod gait. Stability was only achieved through additional legs in ground contact. Tripod stability (quantified as the minimum distance of the centre of mass to the edge of the supporting tripod) was significantly smaller for ants with long fragments. Here, tripod stability was lowest at the beginning of each step, when the center of mass was near the posterior margin of the supporting tripod. By contrast, tripod stability was lowest at the end of each step for ants carrying short fragments. Consistently, ants with long fragments mainly fell backwards, whereas ants carrying short fragments mainly fell forwards or to the side. Assuming that transporting ants adjust neither the fragment angle nor the gait, they would be less stable and more likely to fall over.ConclusionsIn grass-cutting ants, the need to maintain static stability when carrying long grass fragments has led to multiple kinematic adjustments at the expense of a reduced material transport rate.

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“…It has been argued that the selection of smaller leaf fragments was favored during evolution because of the underground processing rates of the fragments after their delivery, which are maximal for fragments of intermediate size (Burd and Howard, 2005) (but see Roces and Bollazzi, 2009). Load transport rates may also depend on environmental conditions, such as trail gradients (Lewis et al, 2008), height constraints (Dussutour et al, 2009) and fallen branches (Farji-Brener et al, 2007). The relationship between load size and transport rates is likely to be affected by these factors and hence may influence the ants' decisions.…”

Section: Discussionmentioning

confidence: 99%

The energetics of running stability: costs of transport in grass-cutting ants depend on fragment shape

Moll

Federle

Roces

2012

Journal of Experimental Biology

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SUMMARYGrass-cutting ants (Atta vollenweideri) carry fragments that can be many times heavier and longer than the ants themselves and it is important for them to avoid falling over during load transport. To investigate whether the energetic costs of transport are affected by the need to maintain stability, the rate of CO 2 production was measured in both unladen workers and workers carrying standardized paper fragments of different size and shape. We tested: (1) the effect of mass by comparing workers carrying either light or heavy fragments of the same size, and (2) the effect of shape by comparing short and long fragments of the same mass. Consistent with previous studies, metabolic rate increased but running speed remained constant when ants carried heavier fragments. The net cost of transport (normalized to the total mass of ant and fragment) was the same for heavy and light fragments, and did not differ from the costs of carrying a unit body mass. Ants carrying long fragments showed similar metabolic rates but ran significantly slower than ants carrying short fragments. As a consequence, net cost of transport was significantly higher for long fragments than for short ones, and higher than the costs of carrying a unit body mass. The observed reduction in running speed is likely a result of the antsʼ need to maintain stability. When the absolute costs of transport were compared, smaller ants required more energy to carry heavier and longer fragments than larger workers, but the opposite was found for lighter and shorter fragments. The absolute costs of transport per unit fragment mass suggest that it is energetically advantageous for a colony to allocate smaller workers for the transport of small fragments and larger workers for large fragments. The present results underline the importance of biomechanical factors for the understanding of leaf-cutting ant foraging strategies.

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Effects of trail gradient on leaf tissue transport and load size selection in leaf-cutter ants

Cited by 25 publications

References 30 publications

Unpaved roads alter foraging patterns of the leafcutter antAtta colombica

Unpaved roads alter foraging patterns of the leafcutter antAtta colombica

How Load-Carrying Ants Avoid Falling Over: Mechanical Stability during Foraging in Atta vollenweideri Grass-Cutting Ants

The energetics of running stability: costs of transport in grass-cutting ants depend on fragment shape

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