Lessons from Israel's desert woodlice

Unlike terrorists, animals that are not herbivores and don’t subsist exclusively on grain, berries, and vegetables, kill only to survive: Not to murder. In the pecking order, larger and stronger animals hunt and feed on smaller, less powerful ones.

In a world filled with potential threats, animals that are preyed upon have to find safe breeding sites for themselves and their young. 

A recent study led by ecologists Dr. Viraj Torsekar and Prof. Dror Hawlena from the ecology, evolution, and behavior department at the Hebrew University of Jerusalem (HU) investigated the complicated dynamics of burrow-site selection while animals are endangered by predators.

Focusing on the fascinating behavior of desert isopods (woodlice) that live close to scorpion burrows, their research discovered how these prey animals make decisions. The study, say the researchers, paves the way for a deeper understanding of the intricate ecological interactions between predators and prey, underscoring the significance of examining the subtleties of animal behavior within the delicate balance of nature.

Isopods are vital components of ecosystems, contributing to the decomposition of organic matter in various terrestrial and aquatic environments. Woodlice are a crustacean belonging to the suborder Oniscidea that got their name from often being found in old wood and from "louse," a parasitic insect.

Woodlice, however, are neither parasitic nor insects.

The researchers conducted their field experiment at the Avdat Research Station in the Negev in March 2021. The peak of the isopods’ daily dispersal activity was between 1 and 2 p.m.

At the end of day one between 4 and 5 p.m., the experiment was temporarily halted due to reduced isopod activity. All burrows were then covered with lids to ensure that animals inside would not escape and to prevent new hole occupancy.

At the end of the second day, all isopods still inside burrows were collected, measured, and released.

The study has just been published in the Royal Society’s journal, Biology Letters under the title “Prudent Burrow-Site Selection in a Landscape of Fear,” aimed at investigating whether prey animals prefer safer breeding sites over riskier ones when presented with a choice.

It also explored how the preference for safety might differ among those with varying competitive abilities – especially when the costs of competing within their species outweigh the benefits of securing a safer breeding site.

They found that size matters. Larger female desert isopods showed a greater tendency to occupy burrows, whether located near or far away from scorpion burrows. This shows the significant role of size in their selection of burrow sites.

Safety also matters to the woodlice. Larger females spent more time in safer burrows, helping them to raise their young in a safer environment.

Choosing abundance over safety

In contrast, smaller females tended to prefer riskier sites where there was little direct competition. This indicated a prudent choice where the potential benefits of safety might be outweighed by the costs of intraspecific competition (competition between individuals from the same species.)

These findings challenge conventional assumptions about burrow-site selection and underscore the necessity of considering intraspecific competition when investigating how predators influence the behavior of their prey.

Torsekar explained that their findings showed that "the landscape of fear, shaped by the presence of predators, influences the behavior of prey animals in intricate ways. It’s not solely about safety; it’s about carefully weighing the costs and benefits of every decision, even when it pertains to fundamental choices like selecting a breeding site.” 

Summarizing, the team wrote that “we showed that larger female isopods were more likely to occupy new burrows regardless of whether or not the burrow sites were safe. We also found that larger females stayed longer in safer sites while smaller females tended to stay longer in riskier sites, implying a prudent burrow selection by small female isopods.

"Male isopods show a preference for larger females in safer sites – raising the question of why smaller females, despite the excessive fitness costs of not finding a mate or mating with a lower-quality male, still use prudent behavior," they said. "Future work should explore this conundrum by comparing the probabilities of smaller females to pair in risky and safer habitats.”

The Environment and Climate Change portal is produced in cooperation with the Goldman Sonnenfeldt School of Sustainability and Climate Change at Ben-Gurion University of the Negev. The Jerusalem Post maintains all editorial decisions related to the content.

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