Animals reduce their use of costly defence against their predators when living in groups

Background

Lots of animals live in groups, despite the disadvantages of competing for food and other resources. The main advantage is usually thought to be ‘safety in numbers’: that individuals are safer from predators when with their kind. However, whenever researchers measure mortality in groups of animals there is no effect of group size. An explanation for this apparent paradox may lie in understanding how behaviour responds to group size.

Findings

We kept caterpillars of the large cabbage white (Pieris brassicae) alone and in groups, and simulated predator attacks on them when they were either 11 or 18 days old (they metamorphose from around 25 days old). These caterpillars, like many those of many other species, regurgitate the contents of their stomach as defense against predators. We found that caterpillars living alone more quickly defended themselves and produced more vomit than those in groups. We made a simple mathematical model that showed that this change in behaviour will mean mortality rates in groups and when alone will be roughly equal.

Implications

We kept caterpillars of the large cabbage white (Pieris brassicae) alone and in groups, and simulated predator attacks on them when they were either 11 or 18 days old (they metamorphose from around 25 days old). These caterpillars, like many those of many other species, regurgitate the contents of their stomach as defense against predators. We found that caterpillars living alone more quickly defended themselves and produced more vomit than those in groups. We made a simple mathematical model that showed that this change in behaviour will mean mortality rates in groups and when alone will be roughly equal.

Subject

Behavioural ecology


Subject Group

Zoology and Ecology


Keywords

Predation

Antipredator defence

Gregarious caterpillars

Regurgitation


Posted by

Andrew Higginson

on Fri Sep 01 2017


Article ID

PKKCEC7BZ


Details of original research article:

Daly D, Higginson AD, Dong C, Ruxton GD, Speed MP. Density-dependent investment in costly antipredator defences: an explanation for the weak survival benefit of group living. Ecol Lett. 2012;15:576-583.

Preceded by:

Adult size and egg number are reduced when Large Cabbage White caterpillars use their defence against predators

Posted by: Andrew Higginson Posted Fri Sep 01 2017


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