Since animals emerged on land more than 300 million years ago, they've turned to plants as a source of food. But despite deploying their best modes of attack, surprisingly, animals only manage to eat around a fifth of the vegetation that’s available to them. So why don't they eat more? In her first lecture of the series, Sue Hartley explains why animals have a harder time than we think when it comes to eating plants, whilst Adam squirm as he eats the world’s hottest chilli.
In this lecture, Sue Hartley explores the different ways plant-eating animals have evolved to adequately sustain themselves, and tackle plants' weapons of self-defence. Whilst vegetation might help fill an empty stomach, it doesn't provide animals with all the nutrients they need to live and grow. Plant material is mostly cellulose, water and carbohydrate, and has very little fat or protein which are both vital to an animal’s diet. To add to the dilemma, plants have developed all sorts of self-protection mechanisms, which make it hard for animals to feast on them at the best of times.
Plants have to make a life-threatening choice between using their energy to grow, or communicate. Just like humans and other animals, they need to communicate, particularly when they are under threat. When attacked by an animal, a plant will release lots of chemical 'signals' into the air. These signals are detected by other plants - their 'allies'. But although these chemical defence mechanisms might save them from being eaten, it uses up vital energy that could otherwise be used for growth.
In the fourth lecture from this series, Sue Hartley explores the ways we can manipulate plants to suit our own needs. In the past, human agriculture has attempted to disarm plant defences and increase their nutrient content. But advances in scientific research have allowed us to move towards cultivating plants that are bigger, healthier, and more edible. The crops on our plates now look, and taste, very different to their wild relatives.
The changes in our climate make it hard to predict whether it will be plants or animals who will win the war. A change in conditions could favour either the plants or the herbivores, breaking the balance. If one side of the war gets an advantage, their population could grow unchecked leading to an 'outbreak'. Sue Hartley's fifth and final lecture of the series looks at what effects climate change is having on plants and asks whether it might compromise their ability to defend themselves.