Foragers Respond to the Speed and Efficiency of Other Ants

Biological Strategy

Leafcutter ants

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Cooperate Within the Same Species

A species is a group of organisms capable of breeding to produce fertile offspring. When individuals within a species undertake activities that benefit one another, that cooperation benefits not just the individuals, but also local and wider populations of that species. Collaborating in activities such as finding food, controlling parasites, and protecting from predators enhances overall survival. To cooperate, there must be enough benefit to an individual, and especially to a population, to justify any risk taken by individuals. Through cooperation, risk is distributed among individuals and the benefits to the community are greater than the sum of the benefits to individuals. An example is birds that gather in flocks, a cooperative activity more beneficial than acting alone. While some birds forage, others watch for predators. When one finds food, others also feed on it. Despite potential short-term competition for an individual that finds food, over the long-term, that same individual benefits when others find different food sources.

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Respond to Signals

To interact with its environment, a living system must not only sense a variety of signals, but also respond to them. To be energy- and material-efficient, those responses must be appropriate to the signal. This generally requires sensing thresholds to trigger an appropriate level of response (for example, hiding under a shrub versus running away to avoid a predator). Response strategies are tied to a specific signal and often have a response threshold, which determines how strong a signal must be to warrant expending energy to respond. One example is a plant that lives in arid regions in South Africa. Its seed capsules remain closed until rainfall triggers them to open to release the seeds. But the plant only responds to a second rainfall, thus protecting against releasing its seeds before there is enough sustained water for them to grow.

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Distribute Solids

Solids include resources such as food, seeds, spores, and leaves, which living systems must sometimes move to accomplish various activities such as pollinating, feeding their young, or building shelters. To effectively distribute solids, living systems must use strategies appropriate to the sizes and types of solids and the media in which they exist (air, water, or another medium). This may entail strategies beyond simply holding and carrying solids. For example, some seeds are carried by the wind to new locations for germination. Others–like the burdock plant’s hooked seeds–cling to animal fur to be transported.

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Capture, Absorb, or Filter Organisms

Many living systems must secure organisms for food. But just as one living system must capture its prey to survive, its prey must escape to survive. This results in capture and avoidance strategies that include trickery, speed, poisons, constructed traps, and more. For example, a carnivorous plant called the pitcher plant has leaves formed into a tube that collect water. Long, slippery hairs within the tube face downward. When insects enter the tube seeking nectar, they lose their footing and slide inside, unable to climb out and escape being eaten and digested by the plant.

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Insects

Class Insecta (“an insect”): Flies, ants, beetles, cockroaches, fleas, dragonflies

Insects are the most abundant arthropods—they make up 90% of the animals in the phylum. They’re found everywhere on earth except the deep ocean, and scientists estimate there are millions of insects not yet described. Most live on land, but many live in freshwater or saltwater marshes for part of their life cycles. Insects have three distinct body sections: a head, which has specialized mouthparts, a thorax, which has jointed legs, and an abdomen. They have well-developed nervous and sensory systems, and are the only invertebrate that can fly, thanks to their lightweight exoskeletons and small size.

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Foragers of leafcutter ant colonies respond to the speed and efficiency of other ants by varying leaf loads in size and weight.

Introduction

Within ant colonies, each ant has a specific role. In the leaf-cutter species, foraging ants are tasked with collecting leaf fragments and bringing them back to the colony. One may think that a forager would collect the largest possible payload. However, high payloads are not shown to result in more efficient transport. Instead, foragers generally carry loads well below their maximum potential. Load size is influenced by two factors: a more manageable workload for processor ants, and the speed of other foragers.

The Strategy

When foragers return to the colony, they pass their loads to the processor ants. Processors collect the material and distribute it among the colony. There are more foragers than processors. If every forager brought large of loads to the colony, the processors would be overwhelmed by the volume of leaves coming into the colony and fall behind. As a result, materials would not be distributed throughout the colony in a timely manner.

Where Are Ants Carrying All Those Leaves?

The Potential

Foragers also carry small loads in order to maintain a consistent speed in relation to other ants. Foragers travel to and from their colony in a single file line, also referred to as unilateral transport. This is because foraging ants travel by following the chemical scent of the forager directly in front of them. It’s as if ants travel down a one lane highway, where passing is illegal. Because smaller loads mean faster foraging and bigger loads mean slower foraging, if one ant chooses to take a larger than average load it will slow down the entire group. This can have a serious effect on the colony as a whole.

This summary was contributed by Allie Miller.

Last Updated January 13, 2017

References

Journal article

HEAVY LOADS SLOW TRUCK DRIVERS AND ANTS

Journal of Experimental Biology | 08/06/2011 | C. J. Klok

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Reference

Journal article

The ‘truck-driver’ effect in leaf-cutting ants: how individual load influences the walking speed of nest-mates

Physiological Entomology | 28/12/2010 | ALEJANDRO G. FARJI-BRENER, FEDERICO A. CHINCHILLA, SETH RIFKIN, ANA M. SÁNCHEZ CUERVO, EMILIA TRIANA, VERÓNICA QUIROGA, PAOLA GIRALDO

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