INTERSPECIFIC RELATIONSHIPS: TYPES AND EXAMPLES - BIOLOGY - 2025

The interspecific relationships in biology are existing partnerships between members of different species. Interactions between individuals can have different effects on the parties involved. In certain cases, both benefit, in others one benefits and another loses and in some scenarios there are agencies that are not affected. The results of the interactions allow to establish a classification of the same.

The interactions are classified into amensalism, competition, predation and herbivory, parasitism, commensalism, and mutualism. The last three categories are usually encompassed under the term of symbiosis.

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The opposite concept is that of intraspecific relationships that occur between two or more individuals of the same species - such as interaction between males and females for reproduction, competition between males for access to females, or competition for resources.

Introduction to interspecific relationships

Organisms within an ecological community are not isolated from each other. Individuals belonging to different species interact in different ways, both directly and indirectly.

The interaction that occurs between organisms is a very important property of ecosystems, as they define vital processes such as the nutrient cycle and trophic chains.

Furthermore, the long-term interaction of different species has evolutionary consequences - leading to the phenomenon of coevolution, where both parts of the interaction affect the evolutionary destiny of their partner, reciprocally and specifically.

Quantifying and analyzing the relationships between organisms is a challenge for ecologists, since this phenomenon depends on multiple variables and many times there are more than two species involved. Furthermore, the abiotic characteristics of the physical space where the interaction is taking place tend to modify it.

Some authors propose that the types of interactions that we will see below do not represent discrete categories, but rather a continuum of events dependent on many factors, both biotic and environmental.

Types and examples

Symbiosis: mutualism, commensalism and parasitism.

One of the best known - and often misinterpreted - interactions is symbiosis. This term refers to two or more species that live in direct contact that exhibit purpose and encompass a wide range of interactions. The three main types of symbiosis are mutualism, commensalism, and parasitism.

Mutualism

Mutualism is the symbiotic interaction where all parties involved benefit from contact. It should be mentioned that some authors refer to the term symbiosis as a synonym for mutualism - and not as a broad term.

Mutualism can be forced, when the species cannot live without their partners, or it can be of the facultative type when they can live separately - but not as "well" as they would as a team.

One of the most impressive examples of obligate mutualism is the relationship between leafcutter ants and the fungus they cultivate.

Ants have developed a very complex type of agriculture. They take pieces of leaves, cut them and apply the necessary treatment so that they can "sow" and cultivate the fungus in question. The food of these little ants is not the leaves they cut, it is the fungi they plant.

Commensalism

Source: Carlos Fernández San Millán, via Wikimedia Commons

Commensalism is the symbiotic interaction where one party gets a benefit from the interaction and the remaining species is not affected in any way.

This type of interaction is particularly difficult to identify in nature, since it usually involves several species and indirect effects can appear - obscuring neutrality.

Orchids establish a commensal relationship with the tree in which they grow. Orchids are epiphytic plants - which indicates that they develop on some branch of a large tree that allows access to sunlight. The tree that serves as sustenance is not affected by the presence of the orchid.

Commensalism, like the other interactions studied in this article, can be optional or compulsory.

Some carnivorous animals benefit from carcass waste that other carnivores leave behind as leftovers. The very presence of the human species represents a type of facultative commensalism for small species of mammals, such as rodents, since food waste favors their populations.

Types of commensalism

Another way to classify commensalism is according to the benefit of the parts in phoresis, tenancy and chemical commensalism. We will describe each type of relationship in detail below:

Foresis

The phoresis is the relationship between two individuals, where one of them is carrying the other. One of them receives free travel, while the other is not affected. Generally the phoresis occurs between a small individual - the transported - and a larger one.

In many cases, the benefit of forestry goes beyond transportation. Being physically anchored to a larger individual offers protection from potential predators and the transported animal can consume the food scraps that the larger animal hunts.

Tenancy

As its name implies, tenancy is the phenomenon where a species uses a cavity as a lodging site. The "cavity" can be any structure built by another animal, such as a burrow or nests.

In general, it is the use of any resource discarded by an animal. The term overlaps with thanatocresia, where the use of resources leaves a dead animal.

For example, the famous hermit crab uses the empty shells left behind by certain species of snails when they die.

Parasitism

The latter type of symbiotic relationship involves one individual who benefits from the interaction - the parasite - and another from whom it benefits and negatively affects - the host.

The parasite can be located outside the host or inside and feed on fluids. The first is called ectoparatic and the second type endoparasite.

Fleas and lice are clear examples of ectoparasites that feed on the blood of their mammalian host, which can be some domestic animals or humans.

The protozoa that cause Chagas disease, Trypanosoma cruzi, are endoparasites that develop within their human host.

Likewise, the causative agent of malaria, the different species of Plasmodium are endoparasites that affect humans. Both parasites are of clinical importance, particularly in tropical areas.

Amensalism

Amensalism occurs when an individual is negatively affected by the interaction, while his partner appears to present no harm or benefit.

For example, the presence of Penicillium negatively affects the population of bacteria that exist in the periphery, since it secretes a chemical that kills them. The bacteria, meanwhile, have no effect on the fungus.

Neutralism

Neutralism is a relationship debated in the literature. Theoretically, it raises the existence of interactions where none of its protagonists are affected by the presence of the partner.

Ecologists propose that neutralism is unlikely, since the presence of one organism must affect, to some extent, the rest.

However, there are some very specific examples of neutralism in bacteria. Apparently, the Lactobacillus and Streptococcus genera can coexist without affecting each other.

Competition

Competition is defined as the interaction that exists between individuals who pursue a limited resource in common. Competition not only involves “hand-to-hand” fights for the resource in question, it can also occur indirectly between the parties.

Competition negatively affects competitors, and the usual result comprises negative effects of greater magnitude for the weaker competitor.

Types of competition

There are two main types of competition: by interference and by exploitation. Competition for interference consists of fighting directly for the limited resource.

Competition for exploitation occurs when two or more species use a resource in common. Thus, the majority use of the resource by one species indirectly and negatively affects the other species.

For example, two hypothetical species of birds competing for the same fruit. Competition for exploitation does not only occur for food, it can also occur for territory.

Logically, competition does not only occur between individuals of different species, intraspecific competition is also a relevant aspect for the ecology and evolution of species.

Competition results

According to the mathematical models proposed for the description of competition in nature, there are several scenarios in which competition can end. The first, and most logical, is that one species displaces the other. That is, it causes the local extinction of its competitors.

In ecology, it is widely known that two species that use very similar environmental resources cannot coexist forever and one will end up displacing the other.

To avoid this, one of the parties can change some aspect of their lifestyle. If this change in the ecological niche of one of the species occurs, both parties involved in the competition will be able to coexist in nature.

These changes in life habits that decrease competition are favored by natural selection.

Examples

Lions and hyenas are a clear example of competition for the same resources, since the prey of both species overlap. When the lion decreases the population of potential prey, it indirectly affects the population of hyenas.

Predation and herbivore

What is predation?

Predation is the term used to describe one organism, called the predator, that consumes a second organism, designated as the prey. In this system of interaction, the consequences for the predator are positive, while for the prey they are negative.

Generally, the examples of predation are carried out by entities of the animal kingdom. However, in the microscopic world there are also multiple predation scenarios. Protozoans, for example, are avid eaters of bacteria.

In the plant kingdom we also find examples of predation in carnivorous plants that consume certain insects.

Typically, the interaction occurs between members of different species. When it occurs between members of the same species, it is called cannibalism - and, surprisingly enough, it is a common event in various food chains.

What is herbivory?

Similarly, when the animal consumes a plant (or specifically a primary producer), it is called herbivory.

In this event, the animal consumes parts of photosynthetic organs that affect the plant, and can kill it. This last consideration marks one of the differences between predation and herbivory: the herbivore does not always kill its prey.

Evolutionary consequences of predation and herbivory

One of the evolutionary consequences of predation and herbivory is the appearance of an arms race (or evolutionary arms race, as the event is called in Anglo-Saxon literature).

It consists of the appearance of complex adaptations that participate in the interaction. These characteristics - like sharp teeth, powerful limbs, poisons, nimble running legs - are constantly "improving" in response to changes in your "enemy."

For example, as a hypothetical prey improves its camouflage ability, the predator improves its visual acuity to detect it. The same happens in herbivory, when a plant develops a new protective toxin, the herbivore develops a new detoxification mechanism.

Examples

There are countless examples of predation, although the best known scenarios are lions in the savannah chasing deer.

In the case of herbivores, these are classified according to the zone or region of the photosynthetic organism that they cover in their menu. For example, granivores consume the seeds of plants. Many birds are fed a grain-based diet.

The frugivores, for their part, consume the fruits. Many birds and bats consume the fruits of plants, and thanks to their flying locomotion mechanism, they are important seed dispersers. That is, they are a kind of "winged gardeners."

Many mammals and insects also specialize in their diet by eating the leaves of plants - like cows, for example.

Why is it important to study relationships between organisms?

From the point of view of conservation and utility for our society, identifying the interaction networks between the organisms of the ecosystem is vital, since knowing the functioning of the ecosystem in its natural state allows us to predict how it will be affected by the action. human.

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