Biotic interaction – Definition, Types, Examples

What is Biotic interaction?

• Biotic interactions refer to the various relationships and interactions that occur between living organisms within an ecosystem. These interactions are critical in shaping the survival, behavior, growth, and overall dynamics of organisms in their environment. They can occur between organisms of the same species, known as intraspecific interactions, or between different species, termed interspecific interactions. Each type of interaction has a unique impact on the organisms involved, influencing their fitness, reproduction, and population sizes.
• Intraspecific interactions happen within a single species. Examples include competition for resources like food, territory, or mates. These interactions can influence natural selection within a population, favoring individuals with advantageous traits. On the other hand, interspecific interactions occur between different species and can manifest in several forms, such as predation, mutualism, competition, commensalism, and amensalism.
• Predation involves one organism (the predator) consuming another organism (the prey). This interaction is crucial for regulating populations and maintaining ecological balance. Mutualism is a beneficial interaction where both species involved gain from the relationship, such as bees pollinating flowers while feeding on their nectar. Competition arises when species vie for the same resources, often limiting their growth and reproduction. In commensalism, one species benefits while the other remains unaffected, and in amensalism, one species is harmed while the other is unaffected.
• These biotic interactions, whether beneficial, neutral, or harmful, are vital in regulating population sizes, influencing species distribution, and maintaining the health of ecosystems. While abiotic factors like temperature and rainfall also play roles in shaping ecosystems, biotic factors tend to have a more direct and intense influence on the population dynamics of living organisms.

Types of Biotic Interactions

Based on the nature of these effects, biotic interactions can be categorized into three main types: positive, neutral, and negative. Below are the types of interactions, along with detailed descriptions:

• Positive Interactions
  These types of interactions result in one or both species benefiting from the relationship without causing harm.
  • Commensalism
    In commensalism, one species benefits while the other species is neither helped nor harmed. This interaction is common in ecosystems where one organism can gain resources or protection without impacting the other species involved.
  • Mutualism
    In mutualism, both species benefit from the interaction. This is often essential for the survival or reproduction of the organisms involved. Each species contributes something that the other needs, such as nutrients, shelter, or protection.
  • Protocooperation
    Protocooperation is a form of mutualism where both species benefit from the interaction, but the relationship is not essential for their survival. This type of interaction is less obligatory, meaning that both organisms can thrive independently, but their relationship provides added advantages.
• Neutral Interactions
  These interactions have no significant impact on either species involved.
  • Neutralism
    In neutralism, neither species affects the other. Both species coexist in the same habitat, but their presence or absence has no measurable influence on each other’s survival, growth, or behavior.
• Negative Interactions
  Negative interactions occur when one or both species experience harmful effects as a result of the relationship.
  • Amensalism
    Amensalism occurs when one species is negatively impacted while the other remains unaffected. Typically, this interaction happens when one organism inadvertently harms another, such as by releasing chemicals that inhibit the growth of other species without benefiting itself.
  • Predation
    In predation, one species (the predator) hunts, kills, and consumes another species (the prey). This interaction directly benefits the predator while leading to the death or reduction of the prey population. Predation plays a significant role in controlling population sizes and maintaining balance within ecosystems.
  • Parasitism
    Parasitism involves one species (the parasite) benefiting at the expense of another (the host). Unlike predators, parasites typically do not kill their hosts, instead living off them for an extended period, which may weaken or harm the host.
  • Competition
    In competition, two or more species compete for the same limited resources, such as food, shelter, or territory. This interaction negatively affects all species involved, as the availability of essential resources is reduced for everyone.

A. Positive Interactions

1. Mutualism

Mutualism is a type of biotic interaction where two species engage in a relationship that is mutually beneficial. In this form of interaction, both organisms derive advantages from each other, enhancing their survival and reproductive success. Mutualism can be either compulsory (obligatory) or optional (facultative) based on the nature of the interaction. Below are examples of both types:

1. Compulsory Mutualism
   In compulsory mutualism, the relationship is obligatory, meaning both species depend on each other for survival and are in continuous contact. These interactions are essential for the life processes of both organisms involved.
   • Lichens (Algae and Fungi)
     Lichens are a classic example of mutualism, where algae and fungi live in close, permanent association. The fungal component provides moisture, minerals, and protection to the algae, while the algae manufacture food through photosynthesis, supplying energy to the fungus. Neither organism can survive independently in nature, making this relationship obligatory.
   • Symbiotic Nitrogen Fixers (Rhizobium and Leguminous Plants)
     This mutualistic relationship involves the bacterium Rhizobium, which forms nodules on the roots of leguminous plants. The bacteria fix atmospheric nitrogen, making it available to the plant, while the plant provides carbohydrates and a habitat for the bacteria. Both the plant and bacterium benefit, with the plant gaining essential nutrients and the bacteria receiving food.
   • Association Between Zoochlorellae and Paramecium
     Zoochlorellae, a type of unicellular algae, live symbiotically within the body of Paramecium. The algae synthesize food through photosynthesis, which is shared with the Paramecium, while the Paramecium provides protection to the algae. This mutualistic relationship is also seen in other organisms like sponges, mollusks, and worms, where algae live within the tissues of their animal hosts.
   • Cycas and Blue-Green Algae (Nostoc and Anabaena)
     The coralloid roots of Cycas are inhabited by nitrogen-fixing blue-green algae like Nostoc and Anabaena. These algae fix atmospheric nitrogen, benefiting the Cycas, while receiving nutrients and protection in return. This interaction enhances the nitrogen availability for the plant, aiding its growth.
   • Pinus and Ectotrophic Mycorrhiza
     In this mutualistic relationship, the fungal mycelium is attached to the roots of Pinus trees. The fungus aids in absorbing water and nutrients from the soil, enhancing the tree’s growth. In return, the fungus receives carbohydrates and nutrients from the tree. The fungal hyphae act as natural substitutes for root hairs in this relationship.
   • Termite and Flagellate Protozoans (Trichonympha)
     Termites feed on wood, but they rely on the protozoans, Trichonympha, living in their guts to digest cellulose. The protozoans secrete enzymes that break down cellulose, allowing termites to derive nutrients from the wood. In return, the protozoans receive food and a stable habitat within the termite’s digestive system.
2. Facultative Mutualism
   In facultative mutualism, the relationship is not obligatory, meaning the organisms can survive independently, but the interaction provides additional benefits. These relationships are more flexible, and the organisms do not have to be in continuous contact.
   • Crocodile Bird and Crocodile
     The crocodile bird enters the mouth of the crocodile to feed on leeches and other parasites lodged between the crocodile’s teeth. In this process, the bird fulfills its nutritional needs while cleaning the crocodile’s teeth, benefiting both parties. This relationship is an example of cleaning symbiosis, where both organisms gain from the interaction but can live independently.
   • Neon Gobis and Grouper Fish
     In this relationship, the small neon gobis fish cleans the mouth of the larger grouper fish by feeding on food particles. The grouper benefits from having its mouth cleaned, while the neon gobis gains a steady food source. This interaction is another form of cleaning symbiosis.
   • Sea Anemone and Hermit Crab
     The sea anemone attaches itself to the shell of a hermit crab, receiving transportation to different locations. In return, the hermit crab benefits from the sea anemone’s stinging cells (nematocysts), which provide protection against predators. This mutualistic relationship allows both organisms to thrive by offering mobility and defense.

2. Commensalism

Commensalism is a type of biotic interaction where one species, known as the commensal, benefits from the relationship while the other species is neither helped nor harmed. The unaffected species can be referred to as the host. Commensalism is commonly observed in nature, and it can occur in various forms, either externally on the host’s body (ectocommensalism) or internally (endocommensalism). Below are detailed examples of both types:

• Ectocommensalism
  In ectocommensalism, the commensal lives on the surface or body of the host, benefiting from support, protection, or transportation without affecting the host. The host species provides a platform or habitat, but it does not suffer any loss from the relationship.
  • Epiphytes on Trees (e.g., Orchids)
    Epiphytes, such as orchids like Vanda, grow on the branches of large trees. These plants use the trees solely for physical support, without extracting nutrients or water from the host tree. The epiphytes gain a favorable position for sunlight, while the tree remains unaffected.
  • Epiphytes on Animals (e.g., Algae on Sloths)
    Some species of green algae grow on the fur of sloths, giving the animals a greenish appearance. The algae benefit from a habitat that provides them with light, moisture, and nutrients. Meanwhile, the sloth is unaffected by the algae growing on its body.
  • Staphylinid Beetle and Termites
    The staphylinid beetle lives within termite colonies as a scavenger. It feeds on the debris and waste material found in the colony and often rides on the heads of termites for transportation. The termite colony provides the beetle with food and shelter, while the termites remain unaffected by the beetle’s presence.
  • Suckerfish (Remora) and Sharks
    The suckerfish, or Remora, has a modified dorsal fin that functions as a suction disc, allowing it to attach to larger fish such as sharks. The suckerfish benefits by receiving free transportation, moving with the shark through the ocean without expending energy. It detaches itself when it needs to feed, and this interaction does not harm the shark.
  • Clownfish and Sea Anemone
    Clownfish live among the tentacles of sea anemones, which protect the fish from predators due to their stinging cells. The clownfish, immune to the stings, gains protection and a safe habitat. In this interaction, the sea anemone is neither harmed nor directly benefited by the clownfish’s presence.
• Endocommensalism
  In endocommensalism, the commensal lives inside the body or tissues of the host, deriving shelter or nutrients from the environment created by the host, without negatively impacting it.
  • Tropical Fish and Sea Cucumber
    The tropical marine fish Fierasfer lives inside the cloacal chamber of sea cucumbers (holothurians), where it finds protection from predators. The fish leaves the cloacal chamber occasionally to feed and re-enters by touching the opening of the cloaca with its snout, positioning itself to enter tail-first. The sea cucumber remains unaffected by this commensal interaction.
  • Saprophytic Bacteria and Fungi
    A variety of microorganisms, including saprophytic bacteria, fungi, and protozoa, live inside the tissues or cavities of higher plants and animals. These microorganisms often reside in the digestive systems of animals, where they feed on undigested food. For example, Escherichia coli (E. coli) lives in the intestines of humans, utilizing leftover nutrients without causing harm to the host.

3. Protocooperation

Protocooperation is a form of mutualism where two species benefit from their interaction but do not depend on each other for survival. Unlike obligatory mutualism, the relationship in protocooperation is non-essential for the life of either species. However, both species involved experience improved growth, health, or well-being due to the interaction. This biological relationship occurs in various ecosystems, playing a role in enhancing species interactions without imposing absolute dependence. Below are examples and explanations of protocooperation in different biological contexts:

• Soil Bacteria, Fungi, and Plants
  In the soil ecosystem, bacteria and fungi engage in protocooperation with higher plants. While neither the plants nor the microorganisms require each other for survival, they form a mutually beneficial relationship. Bacteria and fungi help shape soil composition by breaking down organic matter, which in turn enhances soil fertility. These organisms interrelate by forming nutrients essential to plant growth. For instance, bacteria in root nodules fix nitrogen, while fungi decompose organic matter, releasing nutrients. Plants benefit by absorbing these nutrients, including essential minerals and carbon dioxide. Although these nutrients are not crucial for plant survival, they contribute significantly to the plants’ enhanced growth.
• Ants and Aphids
  A well-known example of protocooperation is the relationship between ants and aphids. Ants feed on the sugary honeydew secreted by aphids, mealybugs, and scale insects, which reside on trees and shrubs. In return, ants often protect these honeydew-secreting insects from predators, ensuring their safety. Ants even stimulate aphids to secrete honeydew directly into their mouths. This relationship benefits the ants by providing them with food and helps the aphids by reducing predation. However, the plants involved may experience negative effects due to the increased presence of aphids.
• Flowers and Insects
  Protocooperation also occurs between flowering plants and insects. Insects such as bees, butterflies, and birds, particularly those attracted to brightly colored, nectar-rich flowers, act as pollinators. The flowers benefit from this interaction as it increases their chances of successful pollination, aiding in reproduction. In return, the insects receive food in the form of nectar and pollen. Although neither species relies on the other for survival, this relationship enhances the reproductive success of plants and provides nourishment for the insects.
• Birds and Large Mammals
  Protocooperation in birds can be observed through species like the Egyptian plover and the cattle egret. The Egyptian plover removes insect pests from large animals like buffalo, antelope, giraffes, and rhinos. Similarly, the cattle egret in the Americas performs the same function, feeding on insects and parasites that would otherwise harm these large mammals. This interaction benefits the birds by providing them with food, while the mammals benefit from the removal of pests that may cause irritation or disease.
• Cleaning Fish
  In aquatic environments, certain fish species engage in protocooperation by cleaning other fish. These cleaner fish remove ectoparasites, clean wounds, and consume dead flesh from larger fish, including predatory species. The fish being cleaned adopt a passive stance during this process, allowing the cleaning fish to perform their task without interference. This interaction occurs at specific locations known as “cleansing stations,” where fish gather to be cleaned. The cleaner fish benefit by gaining a food source, while the larger fish benefit from improved health through parasite removal.

B. Negative interaction

These interactions include association where one or both individuals are harmed. The harm may e caused by eating other organism, competition for food, excretion of harmful wastes, etc, Where memen of one population may eat members of the other population, compete for food, excrete harmful wasies, otherwise interfere with the other population. These have been sub-divided into (1) Exploitation. (2) Competition and (3) Antibiosis . The various relationship in respect of food may belong to;

1. Exploitation

Exploitation is a biological interaction where one species benefits at the expense of another. This interaction often involves the consumption of biomass from one organism by another, leading to harm or even death of the exploited organism. Predation and parasitism are common forms of exploitation, and they occur across different levels of the food chain, from herbivores feeding on plants to predators hunting prey. While both parasites and predators derive nourishment from other organisms, the impact on the exploited species varies significantly between the two. Below are various types and examples of exploitation:

• Parasitism
  In parasitism, one organism (the parasite) benefits by deriving food or other resources from another living organism (the host). Unlike predation, the host is not immediately killed by the parasite, though the relationship may weaken or harm the host over time. Parasitism occurs widely among both plants and animals.
  • Total Parasites: These parasites, such as Cuscuta (dodder), depend entirely on their host for water, minerals, and food. They lack chlorophyll and cannot perform photosynthesis, making them completely reliant on their host for survival.
  • Partial Parasites: Some parasites, such as Viscum (mistletoe) and Loranthus, can photosynthesize their own food but rely on the host for water and minerals.
  • Animal Parasites: External parasites, or ectoparasites, like ticks, mites, and lice, attach to the outside of their host. Internal parasites, or endoparasites, like the malarial parasite and roundworms, live inside the host’s body.
  • Microbial Parasites: Microorganisms such as bacteria, fungi, and protozoans often live as parasites, causing diseases in their hosts. For example, Corynebacterium diphtheriae causes diphtheria, and fungal parasites like Erysiphe cause crop diseases.
• Predation
  Unlike parasites, predators kill their prey to obtain nourishment. Predators are usually free-living organisms that hunt other animals for food. Predation is a direct food relationship between two individuals, where the predator catches and consumes the prey.
  • Animal Predators: Examples of animal predation include tigers hunting deer, frogs eating insects, and owls feeding on rats. In each case, the predator must capture and kill its prey to survive.
  • Carnivorous Plants: Some plants, such as Drosera (sundew), Nepenthes (pitcher plants), and Utricularia (bladderworts), have adapted to trap and digest insects. These insectivorous plants are often found in nutrient-poor environments and use their specialized structures to capture prey, supplementing their nitrogen intake.
  • Herbivory: Herbivores, such as cattle, camels, and goats, exploit plants by feeding on them. This exploitation can lead to significant changes in vegetation, particularly when grazing removes competitive grasses, allowing shrubs to dominate. Grazing animals can cause more damage to annual plants than perennials due to their feeding habits.
  • Seed and Seedling Destruction: Insects, rodents, and other animals consume seeds and young plants, often trampling and damaging them. This form of predation can severely affect plant populations by reducing their reproductive success.
• Browsing and Grazing
  Herbivores that feed on plant material without necessarily killing the plant are engaging in browsing or grazing. This form of exploitation may lead to varying degrees of harm depending on the intensity of feeding.
  • Aquatic Plant Exploitation: Herbivory also occurs in aquatic ecosystems. Ducks, fish, and other animals feed on aquatic plants, often creating challenges for the management of water bodies. Filter-feeding organisms exploit diatoms, flagellates, and algae, removing them from aquatic environments.
• Carnivorous Plants
  Some plants have evolved remarkable mechanisms to exploit small animals as a source of nutrients. These carnivorous plants produce proteolytic enzymes that digest their prey, allowing them to absorb the nutrients. Although these plants are capable of photosynthesis, they have adapted to trap and digest insects in nutrient-poor soils where nitrogen is limited. While not entirely dependent on this prey for survival, these plants benefit from the additional nutrients provided by their insectivorous habits.

2. Competition

Competition is a biological interaction in which organisms or species vie for the same limited resources, resulting in harm to both parties. This interaction plays a vital role in shaping community structure, influencing both species’ survival and ecological balance. Competition occurs within a species (intraspecific) and between different species (interspecific), affecting the availability of essential resources like food, water, and territory. The outcomes of competition can vary, with some species adapting or disappearing, and it is an essential mechanism in natural selection and evolutionary processes. Below are the various types, mechanisms, and dynamics of competition:

• By Mechanism
  Competition occurs through two primary mechanisms—interference and exploitative competition. Both mechanisms apply to intraspecific and interspecific competition.
  • Interference Competition: This occurs when organisms directly interact, often aggressively, to secure resources. An example is male-male competition in red deer during the rut, where males physically battle for mating opportunities. Similarly, Novomessor cockerelli ants interfere with harvester ants by blocking their colony entrances with rocks, thus preventing them from foraging.
  • Exploitative Competition: This is an indirect form of competition where organisms vie for resources by consuming them, leaving fewer available for others. For instance, plants that absorb nitrogen from the soil reduce its availability for nearby plants, often leading to the death of those unable to access the resource.
  • Apparent Competition: This occurs indirectly when two species are preyed upon by the same predator. For example, an increase in species A may lead to a higher population of predator C, which will then hunt more of species B, causing its decline.
• By Size Asymmetry
  Competition can also be classified based on the size and resource acquisition abilities of the competing individuals.
  • Symmetric Competition: All individuals in a population receive the same amount of resources, regardless of size.
  • Size-Asymmetric Competition: Larger individuals exploit resources more effectively than smaller ones, often monopolizing the available resources. This phenomenon is particularly notable in plant communities, where larger plants outcompete smaller ones for light, significantly influencing biodiversity and community structure.
• By Taxonomic Relationship
  Competition is often distinguished by whether it occurs between members of the same species (intraspecific) or between different species (interspecific).
  • Intraspecific Competition: Members of the same species compete for identical resources, such as food, space, or mates. This competition often regulates population dynamics, as overcrowding leads to resource scarcity. For example, Paramecium aurelia and Paramecium caudatum, two protozoan species, cannot coexist in the same environment when resources overlap, a phenomenon described by Georgy Gause’s competitive exclusion principle. Smaller or weaker individuals, especially juveniles, are typically the first to be affected by resource limitations, often leading to death or failure to reproduce, reducing population growth.
  • Interspecific Competition: This occurs when different species compete for the same limited resource. A classic example involves cheetahs and lions, both of which hunt similar prey. The presence of one species reduces the available food for the other, though both species persist despite competition. Sometimes, competition leads to behaviors like “intraguild predation,” where potential competitors kill each other. For instance, in southern California, coyotes kill and eat gray foxes and bobcats, all of which compete for small mammals as prey.
• Competitive Exclusion Principle
  According to this principle, when two species compete for the same resource, one species will inevitably outcompete the other, leading to the extinction of the less competitive species in that environment. However, in nature, this strict exclusion is rarely observed, as species may adapt or occupy different ecological niches to coexist. Nonetheless, competition remains a significant evolutionary force, influencing species’ survival and adaptation.
• Evolutionary Impact
  Competition has been a driving force in the evolution of species. For example, mammals lived alongside reptiles for millions of years but did not dominate until the dinosaurs were devastated by the Cretaceous-Paleogene extinction event. This shows that large-scale competition between groups can shape the evolutionary trajectories of entire clades, favoring the emergence of new species when opportunities arise.

3. Antibiosis

Antibiosis is a biological interaction in which one organism is either completely or partially inhibited by another through the secretion of a harmful substance or by altering the environment in a way that is detrimental to the other organism. This interaction is common among microorganisms, particularly bacteria, actinomycetes, and fungi, which produce antimicrobial substances that can suppress the growth of other organisms. These substances, often referred to as antibiotics, are widespread in nature and play a significant role in controlling microbial populations.

• Microbial Antibiosis
  • Bacteria, actinomycetes, and fungi are well-known for their ability to produce antimicrobial substances, which are often referred to as antibiotics. These substances inhibit the growth of competing microorganisms in their environment.
  • Antibiosis is particularly evident in soil ecosystems, where microorganisms such as Streptomyces (an actinomycete) release antibiotics that suppress the growth of bacteria or fungi in the surrounding soil.
  • This type of interaction ensures that organisms that produce antimicrobial compounds can outcompete others for nutrients and space, enhancing their survival in competitive environments.
• Plant-Associated Antibiosis
  • Many higher plants and lichens also participate in antibiosis by producing chemicals that inhibit the growth of molds and bacteria.
  • For example, certain plants release substances into the soil that prevent the growth of pathogenic fungi or bacteria, protecting the plant from infection and competition. This defensive strategy not only shields the plant but also influences the composition of the surrounding microbial community.
• Antibiosis in Algae
  • Antagonistic interactions have also been observed in some algae. For instance, in cultures of Chlorella vulgaris, a substance accumulates that inhibits the growth of the diatom Nitzschia frustulum.
  • This type of interaction demonstrates how even simple, photosynthetic organisms can engage in chemical warfare to secure their ecological niche, highlighting the broad spectrum of organisms that employ antibiosis as a survival strategy.
• Hypersensitive Reactions
  • Antibiosis also encompasses hypersensitive reactions, which occur during interactions between pathogenic microorganisms. These reactions are often harmful to one or both organisms involved.
  • In such cases, the host organism responds to the presence of a pathogen by rapidly producing substances or altering conditions that inhibit the pathogen’s growth, thereby preventing the spread of infection.

C. Neutral Interactions

1. Neutralism

Neutralism in ecology describes a biological relationship between two species where their population densities do not exert any noticeable effect on one another. This concept underscores the idea that certain species can coexist within the same habitat without directly impacting each other’s growth, survival, or reproduction. Although instances of neutralism can be observed across various ecological scenarios, the true nature of this interaction is often debated among ecologists.

• Examples of Neutralism
  • Neutralism is frequently illustrated through various ecological interactions. For instance, pelicans and cormorants may be seen feeding together in ocean waters without competing for resources, as they target different types of prey or occupy distinct feeding niches.
  • In another example, spiders and mantises may coexist in the same bush, both preying on insects but typically targeting different species or using different hunting strategies.
  • Similarly, diverse songbird species may feed and nest in a woodland area simultaneously, utilizing different resources such as insects, seeds, or nesting sites, thereby maintaining their population dynamics without significant interference with one another.
  • Additionally, numerous microorganisms inhabit various organs in the human body, including the skin, nose, and mouth, where they can exist alongside one another without directly affecting each other’s populations.
• Challenges in Establishing True Neutralism
  • While these examples suggest a form of neutrality, establishing true neutralism remains a contentious topic. Ecologists argue that determining whether a relationship is genuinely neutral is challenging due to the complexities inherent in ecological systems.
  • The intricate interdependencies among species often complicate efforts to confirm the absence of influence or interaction. Factors such as competition for resources, disease transmission, and mutualistic relationships can subtly influence populations, making it difficult to declare a relationship as neutral.
  • As a result, rigorous studies aimed at understanding these interactions often reveal that, while species may appear to coexist without effects on each other, underlying ecological dynamics may still be at play, leading to subtle influences that challenge the notion of complete neutrality.