Food Availability Regulates Foraging Speed

Biological Strategy

Red harvester ant

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Organisms that navigate over land must avoid obstacles and find their way from one point to another. Because land lies at the interface of the ground and air, these organisms have the opportunity to use signals transmitted through both the ground or air, rather than relying on one potential source. To take advantage of this opportunity, these organisms must have strategies attuned to diverse signals, which may travel through multiple media. An example of an organism that navigates over land is a desert ant in Tunisia that senses smells from two different directions at once, forming a “mental map” of its surroundings.

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Perceiving motion is important for a living system to sense where it is in relation to a moving environment, which is critical in locating resources or wayfinding. This applies whether the environment itself is in motion (such as water movement coming from a nearby fish) or the living system is moving within a stationary environment (such as a bird flying through the air). Because motion dampens over distance and the cost of missing those motion signals is high, living systems must be quite sensitive to these signals. For example, fast-flying big brown bats have microscopic, stiff, domed hairs on their wing membranes that act as a sensor array to monitor flight speed and airflow conditions.

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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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Antennal contact behavior of harvester ants communicates food availability through feedback based on rate of coming and going.

A particular species of harvester ants (Pogonomyrmex barbatus) follows a carefully articulated algorithm to supply their colony with food. Unlike most species of insects/ants that utilize dynamical networks such as pheromone trails to regulate colony interaction, this species uses a rate-based method to monitor food foraging. These harvester ants collect food as individuals (as opposed to species that work collectively). When food is plentiful, the foragers return to the nest more quickly thus triggering more foraging ants to leave the nest. However, if food is scarce and the foragers begin returning empty-handed, the search for food slows and may even cease completely. The rate of coming and going for these ants can be observed through mathematical calculations.

Recently, Stanford researchers have related an algorithm that predicts foraging behavior based on food availability to a computer algorithm used in the Transmission Control Protocol (an internet management tool for data congestion). These ants have been utilizing a complex mathematical equation for centuries to avoid network congestion within their nests. Standford researcher, Dr. Deborah Gordon, believes that the algorithm used by the harvester ants is the first of many more complex dynamic behaviors to be uncovered and that further research on such colonies could provide insight on how to better manage complex systems such as the internet.

Learn more about communication within ant colonies and the evolution of collective behavior in this pair of iBiology video lectures by Dr. Deborah Gordon: “Local Interactions Determine Collective Behavior,” and “The Evolution of Collective Behavior.”

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Image: Bob Peterson / lickr /

Last Updated November 3, 2020

References

“Many dynamical networks, such as the ones that produce the collective behavior of social insects, operate without any central control, instead arising from local interactions among individuals. A well-studied example is the formation of recruitment trails in ant colonies, but many ant species do not use pheromone trails. We present a model of the regulation of foraging by harvester ant (Pogonomyrmex barbatus) colonies. This species forages for scattered seeds that one ant can retrieve on its own, so there is no need for spatial information such as pheromone trails that lead ants to specific locations. Previous work shows that colony foraging activity, the rate at which ants go out to search individually for seeds, is regulated in response to current food availability throughout the colony’s foraging area. Ants use the rate of brief antennal contacts inside the nest between foragers returning with food and outgoing foragers available to leave the nest on the next foraging trip. Here we present a feedback-based algorithm that captures the main features of data from field experiments in which the rate of returning foragers was manipulated. The algorithm draws on our finding that the distribution of intervals between successive ants returning to the nest is a Poisson process. We fitted the parameter that estimates the effect of each returning forager on the rate at which outgoing foragers leave the nest. We found that correlations between observed rates of returning foragers and simulated rates of outgoing foragers, using our model, were similar to those in the data. Our simple stochastic model shows how the regulation of ant colony foraging can operate without spatial information, describing a process at the level of individual ants that predicts the overall foraging activity of the colony.” (Prabhakar et al. 2012: 1)

Journal article

The Regulation of Ant Colony Foraging Activity without Spatial Information

PLoS Comput Biol | 23/08/2012 | Balaji Prabhakar, Katherine N. Dektar, Deborah M. Gordon |

Iain D. Couzin

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