Why Do Animals Need Feeding Strategies?

All animals need a source of organic nutrients and energy.

Unlike plants, animals cannot manufacture all of their own organic food from simple inorganic substances. They obtain nutrients by consuming other organisms or materials produced by organisms.

However, animals do not all obtain food in the same way.

Different species have evolved different feeding strategies depending on:

• The food available in their habitat.
• Their body structure.
• Their size.
• Their movement and behaviour.
• Competition with other organisms.
• The nutritional value of available food.
• The risks involved in obtaining food.

A feeding strategy is the combination of structures and behaviours an animal uses to locate, obtain, consume, and process food.

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Major Feeding Strategies

Animals can be grouped in several ways according to what and how they eat.

Four useful categories are:

• Herbivores – mainly consume plants or algae.
• Carnivores – mainly consume other animals.
• Omnivores – consume both plant and animal material.
• Filter feeders – remove small organisms or food particles suspended in water.

These categories describe general feeding patterns. Nature is not always divided into perfectly separate groups, and some animals change their diets depending on age, season, or food availability.

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Herbivores

A herbivore is an animal that obtains most of its food by consuming plants or algae.

Examples include:

• Cattle
• Horses
• Rabbits
• Deer
• Elephants
• Giraffes
• Many insects

Plant material can provide large amounts of food, but it presents an important challenge.

Plant cell walls contain cellulose, which most animals cannot digest using their own digestive enzymes.

Many herbivores therefore depend on microorganisms living within their digestive systems to help break down plant material.

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Herbivore Teeth

Many mammalian herbivores have teeth adapted for cutting and grinding vegetation.

Common adaptations include:

• Incisors for cutting or cropping vegetation.
• Broad premolars and molars for crushing and grinding.
• Large grinding surfaces.
• Jaw movements that allow food to be ground thoroughly.

Grinding breaks plant material into smaller pieces.

This increases its surface area and makes digestion more efficient.

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Herbivore Digestive Systems

Some herbivores have long and specialised digestive systems.

This provides time and space for microorganisms to help digest plant material.

Cattle and other ruminants, for example, have a specialised multi-compartment stomach.

Microorganisms ferment plant material and help the animal obtain nutrients from food that would otherwise be difficult to digest.

Horses and rabbits use a somewhat different strategy, with substantial microbial fermentation occurring farther along the digestive tract.

Different digestive structures can therefore solve the same basic problem in different ways.

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Carnivores

A carnivore obtains most of its food by eating other animals.

Examples include:

• Lions
• Wolves
• Sharks
• Eagles
• Many snakes
• Spiders

Carnivores may hunt living prey or consume animals that are already dead.

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Carnivore Teeth

Many mammalian carnivores have teeth adapted for catching and processing animal tissue.

Common features include:

• Large canine teeth for gripping or puncturing.
• Sharp incisors.
• Sharp-edged premolars and molars.
• Teeth capable of cutting or shearing flesh.

These structures differ considerably from the broad grinding teeth common in many herbivores.

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Other Carnivore Adaptations

Not all carnivores use teeth.

Different predators have evolved very different feeding structures.

Eagles

Eagles use:

• Strong talons to capture prey.
• A hooked beak to tear flesh.
• Excellent vision to locate prey.

Snakes

Many snakes can:

• Capture prey using their jaws.
• Swallow prey whole.
• Separate parts of the skull and move the jaws in ways that allow relatively large prey to be swallowed.

Spiders

Many spiders use:

• Fangs to immobilise prey.
• Venom.
• Digestive enzymes that begin digestion outside the body before liquefied material is consumed.

Feeding structures therefore depend strongly on the type of prey and how it is captured.

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Predator Behaviour

Carnivores also show important behavioural adaptations.

A predator may:

• Chase prey.
• Ambush prey.
• Hunt in groups.
• Use camouflage.
• Construct traps.
• Use venom.
• Wait motionless for prey to approach.

A cheetah and a crocodile are both carnivores, but they use very different strategies.

A cheetah can pursue prey at high speed.

A crocodile may remain almost motionless before launching a sudden attack.

Both strategies solve the same problem: obtaining animal food.

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Omnivores

An omnivore regularly consumes both plant and animal material.

Examples include:

• Humans
• Bears
• Pigs
• Crows
• Many rodents

Omnivory can provide an important advantage.

An omnivore may be able to switch between different food sources depending on what is available.

For example, an omnivore might consume:

• Fruits
• Seeds
• Roots
• Insects
• Eggs
• Small animals

This dietary flexibility can be particularly useful in environments where food availability changes seasonally.

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Omnivore Teeth

Many mammalian omnivores have a combination of tooth types.

For example, they may have:

• Incisors for cutting.
• Canines for gripping and tearing.
• Premolars and molars for crushing and grinding.

Their teeth often show less extreme specialisation than those of strict herbivores or carnivores.

This reflects their varied diet.

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Filter Feeding

Some animals do not hunt individual prey or bite pieces from large food sources.

Instead, they collect large numbers of small food particles from water.

This is called filter feeding.

Filter feeders include:

• Baleen whales
• Many bivalves such as mussels
• Some fish
• Flamingos
• Some crustaceans
• Many aquatic invertebrates

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How Filter Feeding Works

A filter feeder moves water past specialised structures.

Food particles are trapped while much of the water passes through.

A simplified sequence is:

Water containing food enters → filtering structure traps food → water leaves → food is swallowed

This strategy works particularly well when large numbers of small organisms or food particles are suspended in water.

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Baleen Whales

Baleen whales provide a dramatic example of filter feeding.

Instead of teeth, they possess plates called baleen.

A whale takes water containing small organisms such as krill into its mouth.

The whale then pushes water outward through the baleen.

The water passes through, while food becomes trapped.

This allows an enormous animal to survive by consuming organisms that are individually extremely small.

The strategy works because the whale processes a very large volume of food-containing water.

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Filter Feeding in Bivalves

Animals such as mussels and oysters use a different type of filter feeding.

Water passes across specialised structures, including the gills.

Small food particles can be trapped and transported toward the mouth.

Filter feeding allows these animals to obtain food while remaining attached to a surface or moving very little.

This feeding strategy therefore fits their relatively sedentary lifestyle.

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Structure and Function

Feeding strategies provide excellent examples of the relationship between structure and function.

An animal's feeding structures provide clues about how it obtains food.

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Feeding Strategies and Habitat

Feeding strategies are closely connected to habitat.

Different environments provide different food resources.

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Grasslands

Grasslands contain large quantities of grasses and other vegetation.

Many grazing herbivores have adaptations such as:

• Broad grinding teeth.
• Digestive systems capable of processing cellulose.
• Behaviour that allows long periods of feeding.

Examples include cattle, antelope, and zebras.

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Forests

Forests contain food at many different heights and locations.

Animals may feed on:

• Leaves
• Fruits
• Seeds
• Bark
• Insects
• Other animals

A giraffe's long neck, for example, allows it to reach vegetation that many other herbivores cannot easily access.

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Oceans

Marine environments contain organisms ranging from microscopic plankton to enormous animals.

Feeding strategies include:

• Filter feeding.
• Grazing on algae.
• Hunting fish.
• Crushing shellfish.
• Scavenging.
• Feeding on plankton.

The diversity of marine food sources has produced an equally large diversity of feeding adaptations.

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Feeding Behaviour and Survival

Obtaining food involves both benefits and costs.

Animals must gain enough energy and nutrients to survive, but obtaining food itself requires energy and can involve risk.

An animal's feeding behaviour can therefore affect its chances of survival.

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Energy Gained vs Energy Used

Imagine a predator that uses a very large amount of energy chasing prey.

If most hunts fail, the predator may spend more energy searching and chasing than it gains from successful feeding.

Natural selection therefore favours behaviours that can improve the balance between:

Energy gained from food

and

Energy spent obtaining food

This idea is sometimes studied as optimal foraging.

Animals do not perform mathematical calculations before feeding, but behaviours that improve feeding efficiency can provide an evolutionary advantage.

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Group Hunting

Some predators hunt cooperatively.

Examples include:

• Wolves
• Lions
• Orcas
• Some dolphins

Group hunting can provide advantages such as:

• Capturing larger prey.
• Surrounding prey.
• Increasing the probability of a successful hunt.
• Sharing tasks during the hunt.

However, captured food may also need to be shared among group members.

There are therefore both costs and benefits to cooperative feeding.

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Feeding Alone

Other predators hunt alone.

Solitary hunting may reduce competition over captured food.

It may also be effective for:

• Ambush predators.
• Animals hunting small prey.
• Predators living where prey is widely scattered.

Whether group or solitary hunting is advantageous depends on the ecological situation.

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Camouflage and Feeding

Camouflage can be a feeding adaptation as well as a defence against predators.

An ambush predator that blends into its surroundings may approach prey more easily.

Examples include:

• Crocodiles
• Praying mantises
• Some snakes
• Many spiders
• Some predatory fish

Camouflage can reduce the distance a predator must chase prey, potentially reducing energy expenditure.

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Specialised Feeding Structures

Some animals have extremely specialised feeding structures.

Hummingbirds

Hummingbirds have long bills and specialised tongues that allow them to obtain nectar from flowers.

Their ability to hover allows them to feed while remaining in front of a flower.

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Woodpeckers

Woodpeckers have strong beaks for drilling into wood.

Many species also have long specialised tongues that help extract insects from holes and crevices.

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Anteaters

Anteaters have:

• Long snouts.
• Very long tongues.
• Sticky saliva.
• Strong claws for opening insect nests.

These structures allow them to specialise in feeding on ants and termites.

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Generalists and Specialists

Animals can also be compared according to how broad their diets are.

A specialist feeder relies on a relatively narrow range of foods.

A generalist feeder can consume a wider variety.

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Specialist Feeders

Specialisation can be highly efficient when a particular food is reliably available.

Advantages may include:

• Reduced competition.
• Highly efficient feeding structures.
• Ability to exploit resources other animals cannot use easily.

However, specialists can be vulnerable if their food source disappears.

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Generalist Feeders

Generalists can use many different food sources.

Advantages include:

• Flexibility when conditions change.
• Ability to switch foods seasonally.
• Greater ability to exploit new environments.

However, generalists may be less efficient at exploiting a particular food than a highly specialised species.

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Worked Example: Comparing a Cow and a Lion

Consider two mammals living in a grassland ecosystem.

Cow

The cow primarily eats vegetation.

Useful adaptations include:

• Broad grinding teeth.
• Powerful jaw muscles.
• A specialised digestive system.
• Microorganisms that help digest cellulose.
• Behaviour involving long periods of grazing.

Lion

The lion primarily eats other animals.

Useful adaptations include:

• Sharp canine teeth.
• Cutting teeth.
• Strong jaws.
• Claws.
• Forward-facing eyes that assist depth perception.
• Hunting behaviour.

Both animals require nutrients and energy, but they obtain them through very different strategies.

Their structures reflect the foods they consume.

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Worked Example: Identifying a Feeding Strategy from Evidence

Imagine scientists discover an unfamiliar aquatic animal.

They observe that it:

• Has no large teeth.
• Has comb-like structures around its mouth.
• Regularly swims through areas containing dense plankton.
• Takes large quantities of water into its mouth.
• Expels the water through the comb-like structures.

The evidence strongly suggests filter feeding.

The comb-like structures are adapted to trap food particles while allowing water to escape.

This illustrates how scientists can infer an animal's feeding strategy from its structure and behaviour.

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Feeding Strategies and Competition

Different feeding strategies can reduce competition between species.

Imagine several bird species living in the same forest.

One feeds on seeds on the ground.

Another catches insects in tree bark.

Another feeds on nectar.

Another catches insects while flying.

Although all four species live in the same habitat, they use different food resources.

This helps reduce direct competition.

The role of an organism within its ecosystem, including how it obtains resources, forms part of its ecological niche.

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Feeding Strategies Can Change

An animal's feeding strategy is not necessarily identical throughout its life.

Diet can change because of:

• Age
• Season
• Migration
• Reproduction
• Food availability
• Habitat changes

For example, some animals consume different foods as juveniles and adults.

Others switch between food sources as seasons change.

Feeding behaviour therefore has both structural and behavioural components.

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Common Mistakes

Thinking Herbivores Eat Only Plants Under Every Circumstance

Feeding categories describe general dietary patterns. Real animal diets can be more complex.

Thinking All Carnivores Chase Their Prey

Carnivores can use pursuit, ambush, traps, venom, scavenging, or other strategies.

Thinking Omnivores Simply Eat "Anything"

Omnivores consume both plant and animal material, but individual species still have particular dietary preferences and adaptations.

Thinking Filter Feeders Must Be Small

Some of the world's largest animals, including baleen whales, are filter feeders.

Thinking Teeth Are the Only Feeding Adaptation

Feeding adaptations can include:

• Beaks
• Tongues
• Claws
• Talons
• Digestive structures
• Baleen
• Filtering structures
• Venom
• Behaviour

Assuming Similar Diets Require Identical Structures

Different species can evolve different structures that perform similar functions.

Assuming Feeding Is Only About Getting Maximum Food

Animals must balance energy gained against energy used, competition, predation risk, and other costs.

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Check Your Understanding

1. What is a feeding strategy?

2. Define herbivore.

3. Describe two feeding adaptations commonly found in herbivorous mammals.

4. Why is cellulose difficult for many animals to digest?

5. Explain how microorganisms help some herbivores obtain nutrients.

6. Define carnivore and give two structural adaptations used by carnivores.

7. Explain how an ambush predator's feeding behaviour differs from a pursuit predator's behaviour.

8. What is an omnivore?

9. Explain one potential advantage of omnivory.

10. Describe how filter feeding works.

11. Explain how baleen helps a whale obtain food.

12. Give one example showing how feeding strategy is related to habitat.

13. Explain how feeding behaviour can affect an animal's energy balance.

14. Compare specialist and generalist feeding strategies.

15. An aquatic animal has fine filtering structures, lacks large teeth, and regularly processes large volumes of plankton-rich water. Predict its feeding strategy and explain the evidence supporting your conclusion.

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Key Terms

• Feeding strategy – the combination of structures and behaviours used by an animal to obtain and process food.
• Herbivore – an animal that obtains most of its food from plants or algae.
• Carnivore – an animal that obtains most of its food by consuming other animals.
• Omnivore – an animal that regularly consumes both plant and animal material.
• Filter feeder – an animal that removes suspended food particles or organisms from water.
• Predator – an organism that captures and consumes other organisms.
• Prey – an organism captured and eaten by a predator.
• Baleen – filtering plates found in the mouths of baleen whales.
• Cellulose – a structural carbohydrate found in plant cell walls.
• Ruminant – a herbivorous mammal with a specialised digestive system that supports microbial fermentation.
• Adaptation – an inherited characteristic that improves survival or reproduction in a particular environment.
• Structural adaptation – a physical feature that contributes to survival or reproduction.
• Behavioural adaptation – a pattern of behaviour that contributes to survival or reproduction.
• Specialist feeder – an animal that relies on a relatively narrow range of food sources.
• Generalist feeder – an animal capable of using a relatively wide range of food sources.
• Foraging – searching for and obtaining food.
• Ecological niche – the role of an organism in its ecosystem, including how it uses resources.

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Key Takeaways

• Animals use a wide variety of feeding strategies to obtain nutrients and energy.
• Herbivores mainly consume plant material and often have adaptations for grinding and digesting vegetation.
• Many herbivores depend on microorganisms to help digest cellulose.
• Carnivores mainly consume other animals and may have structures such as sharp teeth, claws, talons, or hooked beaks.
• Predators can use behaviours such as pursuit, ambush, group hunting, camouflage, and trapping.
• Omnivores consume both plant and animal material, giving many species considerable dietary flexibility.
• Filter feeders remove small organisms or food particles from water.
• Baleen whales demonstrate how extremely large animals can survive by filter feeding on very small organisms.
• Feeding structures are closely related to function.
• Feeding strategies are influenced by an animal's habitat and lifestyle.
• Structural adaptations and behavioural adaptations often work together.
• Animals must balance the energy obtained from food against the energy and risks involved in obtaining it.
• Specialist feeders can exploit particular resources efficiently but may be vulnerable to changes in food availability.
• Generalist feeders can use a wider variety of resources and may adapt more easily to changing conditions.
• Feeding behaviour is an important part of an animal's ecological niche and can directly influence its survival and reproductive success.