1 Open ocean
How do you track down prey in a vast, seemingly featureless ‘blue desert’?
Just 10 per cent of marine species occupy the ‘big blue’. It is the biggest, yet most sparsely occupied, of Earth’s major biomes. As a result, in these vast seascapes many large predators have evolved to excel at two things: first, ensuring that potential prey, when spotted, has no chance of escape; and second, minimising energy loss as they travel through the seawater.
In sailfish, marlin, tuna and mako sharks (pictured above), all wide-ranging in their habits, speed is of the essence. Their large eyes detect prey at a distance and they make their move with lightning rapidity. Makos, for instance, may swim at nearly 80kph for short bursts in pursuit of fish and squid, which they track unawares from deeper waters below.
Makos and tuna have a circulatory heat-exchange system that allows their body temperature to be far warmer than their surroundings, so they can maintain higher levels of activity in cold water than their prey. Sailfish and marlin possess a similar heat-exchange system that warms the eyes and brain, keeping them primed for action at all times – vital for tracking down scarce food.
Locating prey in such a complex habitat requires patience and an eagle eye.
Far from being relatively featureless like the open ocean, rainforest biomes have a rich three-dimensional structure and possess incredible niche complexity. Here there is only one game in town: hide-and-seek. In response to this, rainforest predators have evolved to become either sit-and-wait specialists, such as canopy-dwelling chameleons and snakes, or master detectives, such as soil-snuffling armadillos. But harpy eagles (pictured above) deserve credit for mastering both of these skills, and then some.
First, they wait. Harpies often sit it out near the places that attract mammalian prey, such as salt-licks and freshwater openings, lunging when the opportunity arises at species including capybaras, anteaters, coatis and, sometimes, small deer. But when they are done with sitting and waiting, harpies work the forest canopy. Moving from branch to branch, they ‘perch-hunt’, scanning the canopy around them as they go, alert for the movements of nearby monkeys or sloths.
Interestingly, like goshawks and sparrowhawks, harpies are also able to hunt fleeing birds through the canopy. They dodge and weave through leaves and branches in the chase – not bad for one of the biggest and heaviest species of eagle in the world. In such a complicated habitat, adaptability is key to survival.
3 Polar regions
Dramatic shifts in seasonal food availability need flexible hunting strategies.
Polar landscapes are among the most changeable on Earth. Periods of intense seasonal productivity quickly give way to long months of nothingness, where few things grow and only a handful of species manage to hang on. However, many polar bears are still able to hunt provided they can locate the air-holes required by their chief prey – ringed and bearded seals.
They do this mainly through smell. Once a breathing hole is located, the polar bear sits and waits. When a seal appears it is quickly snatched by the bear, for whom the blubber consumed is literally a lifesaver. To hide their scent from polar bears arctic seals rarely defecate above the water, and they maintain a selection of local breathing holes to keep their predators guessing – though in Antarctica, where there are no surface predators, seals aren’t nearly so wary.
For many populations of polar bears, the seasonal change in the availability of sea-ice is becoming increasingly erratic. The seals migrate locally, constantly seeking out the newest and best feeding grounds, and the polar bears have no choice but to follow, even if it means swimming long distances.
4 Tidal pools
Predators have to move quickly to take advantage of the calm after the waves.
The spoils left in rockpools after the waves recede are rich, provided predators can master weathering the turbulent tides. Here sticking power is key. Nudibranchs – a colourful group of gastropods that shed their shells early in life – are among those predators to make this strange way of life their own. As the waves retreat some species hide beneath rocks and in cracks between boulders, before emerging in the now tranquil rockpools where they hunt for sea anemones by touch and smell.
And then there are the octopuses. Octopuses are like Swiss army knives in the variety of hunting adaptations they employ during low tide. They force shelled molluscs such as clams open with their tentacles, drill through harder-shelled molluscs with their beaks, and use their venomous bite to subdue more mobile crustacean prey like shrimp and crabs.
And octopuses aren’t limited to water, either. There have been many observations of intertidal octopus species climbing between rockpools during low tides via land bridges. Since they are largely nocturnal, most of their movement probably takes place at night, without us ever knowing.