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Competition, Predation and Symbiosis

Grade 7
Sep 9, 2022

Key Concepts

  • Differentiate between population and community in ecosystem
  • Enlist the types of community interaction
  • Competition, and how it can lead to extinction or specialization of species
  • Predation and its effect on population growth and evolution
  • Symbiosis and types of symbiotic relationship


Community interaction 

Many species share habitat in most circumstances, and their interactions are crucial in regulating population growth and abundance. 

An ecological community comprises the populations of all the diverse species that exist in a given area. 

Coral reef's ecological community

For example, if we want to describe a coral reef’s ecological community, we’d include populations of every type of organism we could find, from coral species to fish species to the single-celled, photosynthetic algae that live in the corals. That adds up to a lot of different species for a healthy reef! 

Community ecologists try to figure out what causes natural patterns of species’ coexistence, diversity, and distribution. 

Species interaction in community 

We can see in a pond that insects, fish, algae, animals, plants, and frogs all live close enough to interact. A community is the biotic component of an ecosystem in ecology. 

Pond ecosystem and community interactions

It comprises communities of various species living close and interacting with one another. 

Like abiotic elements such as climate or water depth, species interactions in communities are key biotic factors in natural selection. 

The interactions determine how the interacting species have evolved. 

Community interactions are of two types: Interspecific interactions and intraspecific interactions. 

  • Interspecific interactions are interactions between different species in a population; inter- means “between.” 
  • Intraspecific interactions are interactions between the same species in a population. 

Types of species 

Foundation species

Foundation species are the “foundation” or “bedrock” of a community, influencing its general structure the most. They are usually primary producers or organisms that provide most of the community’s energy. 


Kelp is a brown alga that makes up the foundation of the kelp forests off the coast of California. 

Foundation species: Coral reef ecosystems are built based on coral. 

The corals get their energy from photosynthetic algae, which allows them to construct reefs. 

Foundation species

Keystone species

A keystone species is one whose existence is essential for preserving biodiversity in an ecosystem and maintaining the structure of an ecological community.  

Pisaster ochraceous, a coastal sea star found in the northwest United States, is a keystone species. When this organism is removed from communities, populations of their natural prey (mussels) grow, entirely changing the species composition and lowering biodiversity.   

Another keystone species is the banded tetra, a tropical stream fish that provides virtually all of the inorganic nutrient phosphorus to the rest of the population. The community would be severely impacted if these fish became extinct. 

Keystone species

Invasive species 

Invasive species are foreign species that can harm the economy and the environment if they are introduced. 

Any non-native species that significantly alters or disrupts the ecosystems or resettles it is referred to as an invasive species, also known as an imported species, alien species, or exotic species. These species may migrate to new locations naturally, but they are frequently introduced through the activity of other species. 

Invasive species : purple loosestrife (Lythrum salicaria)

Types of community interaction 

Predation, competition, and symbiosis are the three main types of community interactions. 


Competition occurs when species compete for the same resources in the same location.  

Food, water, or space are examples of resources for which organisms compete with each other. 

Competition can be divided into two types:

  • Interspecific competition
  • Intraspecific competition

Interspecific competition 

Interspecific competition occurs when members of various species compete against each other for the same resources. 

Predators from different species, for example, may compete for the same prey. 

Interspecific competition

The lion and the hyena are on the search for prey, hence they compete with each other. 

  • Extinction and Interspecific Competition 

Competition between species frequently results in extinction.  

The less well-adapted species may receive a smaller share of the resources required by both species. As a result, members of that species have a lower chance of surviving, and the species could become extinct. 

  • Specialization and Interspecific Competition 

When competing species evolve different adaptations, specialization occurs. They may evolve modifications that allow them to eat a variety of foods. 

In tropical rainforests, many species of anole lizards prey on insects.  

Specializations have emerged as a result of their competition. Anoles feed on insects that live on the forest floor. Others collect insects in the trees. This permits different anole species to coexist in the same space without competing. 

Specialization in Anole lizard
Specialization in Anole lizard

Intraspecific competition 

Intraspecific competition occurs when members of the same species compete against each other.  

Two male birds of the same species, for example, may compete for mates in the same region. Natural selection relies heavily on this form of competition. Within a species, it leads to the evolution of greater adaptations. 

Male hartebeest lock horns and defend their territories aggressively.
Two wild Dholes fight over carcass

Two wild canines known as dholes fight over a carcass in this image. The carcass is a useful resource that both organisms require to survive. For one reason, intraspecific competition is density dependent. Each dhole gets less food as the number of dholes increases. Food is everything to the individual dhole. he most successful dholes with few natural predators (those who live and reproduce the most) are frequently simply those who eat the most. 


Predation occurs when members of one species (the predator) eat members of another species (the prey). 

This interaction is beneficial for the predator, but harmful for the prey (+/- interaction). 

Predation interactions do not always result in the death of one organism.  

Predator-prey interactions 

Herbivores often consume only a portion of the plant in herbivory. While this action may cause damage to the plant, it also has the potential to disperse seeds. 

Predation and population 

A predator-prey interaction tends to keep both species’ populations in check.  

The graph in image illustrates this. Predators get more food as the population of prey grows.  

Prey-predator interaction

As a result, the predator population grows after a short lag. As the number of predators increases, more prey is eaten. As a result, the number of preys begins to decline. 

One factor inhibits the growth of the other in the predator-prey situation. The predator population begins to decline as the prey number declines. A limiting factor is the prey population. 

A limiting factor limits an organism’s, population’s, or process’s growth or development. 

Adaptation to predation 

Natural selection has evolved adaptations to predation in both predators and prey. 

Predator adaptations help in prey capture.  

Predator detection is assisted by prey adaptations. Camouflage is a frequent predator and prey adaptation. 

Is it possible to identify where one zebra ends and another begins? 

Camouflage in Zebra

This may cause a predator to get confused, allowing the zebras to escape. 


A symbiotic connection is one in which at least one species benefits from the other. The relationship with the other species can be positive, negative, or neutral.  

Mutualism, commensalism, and parasitism are the three primary forms of symbiosis. 


Mutualism is a symbiotic partnership that benefits both sides. 

This relationship can exist either within a species or between two species. Symbionts are organisms that share this relationship. 

Goby fish and shrimp are an example of mutualism. 

The fish and the almost blind shrimp spend the majority of their time together. Both the shrimp and the fish live in a tunnel in the sand that the shrimp maintains.  

When a predator approaches, the fish warns the shrimp by touching it with its tail. The fish and shrimp will then return to their burrows until the predator has passed. The shrimp receives a warning of approaching danger as a result of their relationship. The fish is provided with a safe place and a site to lay its eggs. 

Mutualistic relationship between goby fish and shrimp

Other example is the rhino is home to the bird oxpecker, which eats all bugs and parasites on the animal’s skin. The rhino gives the bird food in exchange for the bugs being removed off the rhino’s skin. Both the rhinoceros and the oxpecker benefited. 

Mutual relationship between Oxpecker and Rhino

Plant roots and some forms of fungi create mutualistic relationships. The plant has the ability to photosynthesize and gives fixed carbon to the fungus in the form of sugars and other organic compounds. The fungus has hyphae, which are threadlike structures that allow it to collect water and nutrients from the soil and deliver them to the plant. 

Mutualistic relationships between plant roots and fungi


A symbiotic relationship in which one species benefits while the other remains unaffected is known as commensalism. (+/0 interaction).The other species is usually used for anything other than food. To receive a “free ride,” mites, for example, attach themselves to larger flying insects.  

Hermit crabs live in the shells of dead snails. The snail is unaffected, and the crab gains shelter. 

Hermit crab and snail

Commensalism is also seen in sea anemones and colorful clownfish.  

To protect themselves from predators, clownfish take refuge in a sea anemone. Clownfish develop a mucous coating around themselves during the adaptation process, allowing them to find refuge in the sea anemone without being harmed by its stings. Clownfish also feed on the remains of sea anemones’ last meal, keeping them clean. 

Relationship between sea anemones and clownfish
Cattle egrets eat the insects that the cattle stir up when grazing.


In parasitism, two species form a tight, long-term relationship that benefits the parasite while harming the host (+/- interaction). 

The species that benefit is called a parasite, and who is harmed is called a host. Some parasites reside on the host’s surface. 

Ectoparasites, including ticks, fleas, leeches, and lice—which live on the host’s body surface and do not themselves commonly cause disease in the host.  Others reside within their hosts. They are known as endoparasites. 

They can get into the host through a skin break, food, or water. Roundworms, for example, are parasitic on animals such as people, cats, and dogs. The worms lay a large number of eggs, which are released into the environment via the host’s faeces. Other people could become infected by eating or drinking contaminated food or water. Although some parasites kill their hosts, the vast bulk does not.  

 A parasite that kills its host is likely to die as well. On the other hand, parasites normally do only minimal harm to their hosts. 

Types of parasites


  • A biome is a wide area of land that is divided into different biomes based on the climate,
    vegetation, and animals that live there. Within a biome, there are multiple ecosystems.
  • Terrestrial biomes are those that are found on land. Aquatic biomes are those that are
    based on water.
  • A population is a collection of interacting organisms belonging to the same species that
    comprises individuals of all ages.
  • An ecological community is composed of all of the populations of all of the diverse species
    that inhabit a region.
  • A community is the biotic component of an ecosystem in ecology.
  • Predation, competition, and symbiosis are the three main types of community
  • Competition occurs when species compete for the same resources in the same location.
    Members of the same species compete against one another in intraspecific competition.
    helps the species adapt better. Interspecific competition occurs when members of
    different species compete against each other. It could lead to the extinction of one species
    or the specialization of both.
  • Predation occurs when members of one species (the predator) eat members of another
    species (the prey). A predator-prey interaction keeps both species’ populations in check.
  • A symbiotic relationship is one in which at least one species benefits from the other.
    Mutualism is a symbiotic partnership that benefits both parties.
  • Commensalism is a symbiotic relationship in which one species benefits while the other
    is unaffected. Parasitism is a mutualistic relationship in which one species (the parasite)
    benefits while the other (the host) suffers.
Competition, Predation and Symbiosis


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