optimal foraging theory - the shark

When you see, hear, or read about the idea of optimal foraging theory, it may be intimidating or even seem irrelevant. In reality, it’s something as humans that we consider unconsciously every day. While many human beings don’t forage or hunt in the classical sense anymore, we do decide what we are going to eat and when we are going to eat it. Just like our wild animal counterparts, we subconsciously consider the energy our next meal will cost us and if the energy we gain from it will be worth it.

We all have asked ourselves at one point or another if we should make a fresh dinner at home with chicken and vegetables or instead go through the fast-food drive-through on the way home from work. You may not have ever thought of it this way, but you are making an energy cost decision just like every consumer on the planet must do.

With that in mind, let’s take a closer look at what the optimal foraging theory entails.

 

What Is the Optimal Foraging Theory?

Optimal foraging theory is a biological model that allows scientists to make predictions about how an animal will eat and hunt its food. This is critical to the survival of every animal because while eating provides the consumer with energy, it is important that the energy required for foraging does not exceed the energy consumed. The goal is to create a balance or better yet an ideal formula for an optimal foraging strategy for each and every animal on earth. This is important because successful foragers save more energy which increases aspects of their fitness, such as reproduction and being able to pass more of their genes into the gene pool of the next generation.

Each consumer has a range and limitations to the types of foods it consumes and/or hunts. These limitations can be simply biological and have to do with their morphology or physiology. They can also be tied to geographical range as well as energy costs associated with the consumption of their meal. While these factors are all logical reasons why animals eat certain things and not others, it is not uncommon to see animals only consume a small portion of the variety of food they are capable of eating. We can use optimal foraging theory to take a closer look at an animal’s diet range and the energy costs associated with each diet choice.

There are many different kinds of consumers in nature. One type of strategy for a consumer is a generalist, which just as its name suggests, these consumers have a broad variety in their diet. This often means they will eat or prey upon any food choices in their range that they come in contact with. Generalists often are omnivores and can survive in many different environments. An excellent example that most people can relate to is the raccoon. Raccoons can flourish on nearly any edible item they can find, and for that reason, they thrive in North and Central America.

On the opposite end of the strategy spectrum, another type of consumer is a specialist. Specialists have very specific or narrow ranges of food. They are preferential foragers and only eat or prey upon a very specific food item. These types of animals are even known to ignore possible prey because it is not precise enough to their diet preference. These specialists often require unique ranges and are limited in terms of habitat. Specialists often have a more difficult time adapting to change in short term situations if prey, food, or habitat become unavailable to them. This leaves many specialist consumer types vulnerable to extinction. A famous and excellent example of a specialist would be the Giant panda. Giant pandas eat 99.5 percent bamboo in the wild, just about as exact as a diet gets. Due to specific habitat loss in the bamboo forests where they live, these animals are listed as an endangered species.

OFT Formula

optimal foraging theory formula

Formula 1. Optimal Conditions for OFT

 

Optimal foraging theory has four variables to its equation. E, which stands for the energy content of a prey item, h, which is the handling time for a prey item, i, which is the next most profitable item, and finally, s, which is search time for a given prey item. The variable i determines which item is the most energy-efficient or profitable item. In specialists, this should be very clear, and in generalists, this may be difficult to pinpoint or may change throughout time, ranges, and/or seasons. Keeping this in mind, the condition where the ith item is the best or most profitable strategy would be as seen the formula image.

 

Applying OFT

optimal foraging theory in actionOptimal foraging theory can be applied to any type of consumer. Sharks are consumers that show great variation just between species alone. Shark species, like the whale shark, are very much specialists eating nearly only on microscopic organisms, such as plankton and krill. Many sharks are thought of as generalists or being able to prey on a wide variety of organisms. This is also why sharks are so incorrectly thought of as mindless predators. The species at the pinnacle of this incorrect misconception is the great white shark. While it is true white sharks have exposure to a broad diet range, including bony fish, crabs, rays, sea birds, snails, squid, turtles, and even other sharks, it is also true that they have a preferential prey choice in seals or sea lions.

Great white sharks live in primarily cool, temperate oceans throughout the world. Impressively, the white shark is able to keep its brain, muscles, and stomach about 25 degrees Fahrenheit above the water temperature it lives in. While this allows the shark to hunt in prey-rich cold waters, it is costly and requires a very high metabolic rate. Therefore, great whites must eat a great deal of calories to keep up with their exceptional metabolism. Being an apex predator, it is no wonder that the great white shark has its choosing of a wide variety of prey throughout the ocean. Even so, great whites nearly only eat marine mammals, such as seals and sea lions, when available. Applying what we know about optimal foraging theory, it is no wonder that white sharks prefer seals, sea lions, and even whales over fish, birds, and other prey when they get the chance.

Seals and sea lions have a very high amount of fat or blubber that allows them to stay warm in cold waters. Fat has twice as many calories as protein and thus, twice the energy benefit. Eating such high calorie foods allows the shark to feed less frequently and save the energy it would otherwise use to hunt every day or even multiple times a day. Great white sharks are built for this type of feeding as they are able to store up to 10 percent of their body mass. This enables them to gorge when they have the opportunity. By rejecting low-calorie foods, such as fish or birds, white sharks are able to max out their energy intake which allows them to hunt less frequently. Since many seal or sea lion species are fantastic, fierce predators in their own right, it often requires extra energy for them to be caught. While this is true, as long as the energy gained is more than the energy used, the great white shark has foraged successfully and has increased fitness.

Wrapping Up

Optimal foraging theory is very fascinating once you get into it and start to discover how it works in nature. You may even start to see how it works in your daily life. What food choices do you make to save energy? Are your food choices making the best use of energy used versus energy gained? You may be surprised by what you find when you start applying OFT to your own eating habits.