In today’s Academic Minute, Dr. Ian Kaplan of Purdue University explores the complex ecological and biological relationship between predators and their prey.
Ian Kaplan is an assistant professor of entomology at Purdue University where his lab seeks to apply theoretical principles from population and community ecology toward the sustainable management of crop pests. He holds a Ph.D. in entomology from the University of Maryland.
Dr. Ian Kaplan – Predation Risk and Digestion
In nature, most animals behave differently in the presence of their predators. Usually this entails feeding and moving less because predators instinctively respond to visual cues while hunting their prey. Deer, for example, take refuge and hide when foraging in a landscape that includes wolves and other large carnivores. This strategy comes with both benefits and costs. The obvious benefit is that engaging in stealthy behavior reduces the likelihood that an animal will be detected and ultimately killed by one of their enemies. The penalty, however, is that moving and feeding less should result in poor growth because of reduced food intake and missing out on activities that enhance fitness like finding mates. Consequently, anti-predator behaviors are thought to involve trade-offs between survival and growth or reproduction.
We have been studying this trade-off in hornworm caterpillars, a herbivorous insect thatfeeds on the leaves of tomato plants and serves as food for predaceous stink bugs that impale and eat them with their needle-like mouthparts. What we found through a series of field and greenhouse experiments is that hornworms eat 30-40% less leaf material when placed in a cage with stink bugs compared to when they are feeding alone. Being that hornworms are agricultural pests that damage crops, this is an effect that has important implications for using ecologically-based natural pest control methods. In other words, regardless of whether or not predators kill the caterpillars, we observe significant reductions in plant damage, an outcome that we would like to exploit in managing insects that destroy crops with biological control agents.
Interestingly, despite feeding less in the presence of stink bugs, hornworms attained the same body size as those individuals who were not exposed to predators. We documented that hornworms are more efficient in processing plant food and are better at extracting growth-limiting nutrients in their digestive tract under predation-risk. This is a species that is apparently well-adapted to physiologically compensating for carnivore-induced food limitation, at least in the short-term.