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Interspecies relationships

Interspecies relationships

In an ecosystem, many organisms interact with each other. Sometimes they work against each other and sometimes they work with each other. Interspecies relationships describe interactions between different species in an ecosystem.

Interspecies Relationship Definition

A community includes all of the living organisms found in a specific location. All of these species interact in different ways. These are called interspecies or interspecific relationships which occur between different species.

This should not to be confused with intraspecific relationships which are between organisms of the same species.

Organisms don’t exist in isolation. Each organism interacts with many other organisms. Both of its own and of different species. Interspecies relationships always benefit one party and sometimes both.

  • Exploitation: When one party benefits from the relationship and negatively affects the other party.

  • Commensalism: When one party benefits from the relationship and the other is unaffected.

  • Symbiosis: When two organisms live together and benefit from each other. It Includes parasitism and mutualism.

  • Parasitism: When members of one species feed off another and live on or inside them.
  • Mutualism: Two species provide each other with different resources.

Interspecific relationships are very important because they affect essential processes such as food chains and nutrient cycles. Additionally, over time, coevolution can occur in response to the way species interact. It is extremely hard to quantify the relationship between organisms as there are many variables in the way organisms interact.

The word "coevolution" refers to situations in which two (or more) species have a reciprocal effect on each other's evolution. Take a plant for example. A change in its morphology may influence the morphology of a herbivore that consumes the plant, which in turn may influence the plant's evolution, which in turn may influence the herbivore's evolution and so on.

Predator-prey relationship is a common example of coevolution. The prey has a selective pressure to avoid capture and the predator must then evolve and become a better hunter.

Types of Interspecies Relationships

Interactions between species are usually classified into amensalism, competition, predation, herbivory, parasitism, commensalism, and mutualism. With the last three coming under the term symbiosis.

Symbiosis

Symbiosis refers to species that live together. It encompasses a wide range of interactions. The three main types of symbiosis are:

  • Mutualism

  • Commensalism

  • Parasitism.

Mutualism

Mutualism benefits all parties. Some species can’t live without their partners. Others can still live but not very well. Some common examples include flowers being pollinated by bees or leafcutter ants and fungus. The ants feed on the fungi they sow.

Interspecies relationships mutualism StudySmarterFig. 1 – Bee pollinating a flower. Source: unsplash.com

Both bees and flowering plants benefit from their mutualistic relationship. Bees acquire nectar and pollen (food) from flowers which worker bees use to feed their whole colony. Pollination is the process by which bees help flowers reproduce by transferring pollen (sperm cells) that gets stuck on their hairy bodies from flower to flower.

Commensalism

Commensalism is a symbiotic interaction in which one party gets a benefit from the interaction and the other species remains unaffected. This is particularly hard for ecologists to identify as indirect effects on other species can occur.

An example is orchids which grow on branches of large trees without affecting them. Humans also facilitate commensalism by leaving food waste around for rodents that feed on it.

Commensalism can be further defined as phoresis and tenancy.

Phoresis occurs when one species (usually larger) carries another (usually smaller). One receives transportation while the other is unaffected. This can also protect the smaller animals from predation and they may be able to feed on food scraps left by the larger animal.

Tenancy occurs when a species uses a structure built by another animal, such as a burrow or nest to live in. An example of this is the hermit crab inhabiting shells left by snails when they die.

Parasitism

Parasitism involves an individual who benefits from the relationship and another who is negatively impacted - the parasite and the host. An ectoparasite (eg. fleas and lice) is located outside of the host whereas an endoparasite is located inside the host (eg. tapeworm).

Isopods are an example of parasitism. Parasitic isopods adhere to the base of a fish's tongue and suck blood from it causing the tongue to atrophy. The isopod then attaches to the stub of the tongue, and replaces it. The fish will utilise the isopod as if it were its own tongue from this point forward.

Amensalism

Amensalism is a type of biological interaction where one species causes harm to another organism without any cost or benefits to itself. There are two modes of amensalism:

  • Competition: One organism deprives a smaller, weaker organism of food or habitat. E.g. Cattle trample on grass and crush it. They do not benefit from this action or are harmed in the process.

  • Antibiosis: An organism is damaged or killed by chemicals released by other organisms. E.g. Penicillium secretes penicillin which kills bacteria.

Neutralism

Neutralism is a relationship in which both species remain unaffected. Many ecologists debate that neutralism is unlikely, as the presence of one organism must affect, to some extent, the other.

However, some bacteria such as genera Lactobacillus and Streptococcus coexist without affecting each other.

Competition

Competition exists when organisms compete for the same limited resources. It negatively affects both parties, with the weaker competitor being affected to a greater extent. Examples of resources species compete for include:

  • Food

  • Light

  • Water

  • Habitat

To remind you from the previous sections, when the competition is between members of different species it is called interspecific.

The law of competitive exclusion states that 'No two species can occupy the same niche indefinitely in the same habitat.' It was created by a guy called Gauze who set up cultures of two Paramecium caudatum and Paramecium aurelia which are two closely related species from the Protozoa group (since-celled eukaryotic organisms). He found that when grown separately they flourished but when grown together, one was eliminated. He then conducted further experiments and found that by adjusting the conditions, he could change which species were eliminated.

The two main types of competition are:

  • Competition for interference (fighting directly for the limited resource).

  • Competition for exploitation (when two or more species use a resource in common).

Often, one species will displace another and the competition will end or one party may evolve to allow both species to coexist in the same niche.

An example of this is between red and grey squirrels. Grey squirrels were introduced to the UK from North America. They are able to outcompete the red squirrel. The reason grey squirrels dominate is that the grey squirrel eats a wider range of foods than the red squirrel. They also carry a disease that can kill off red squirrels but leave grey squirrels unaffected.

In areas containing lots of small seeds, for example, conifer forests, the grey squirrel can’t get enough food. This is because they are larger than red squirrels and therefore need more food to survive.

Predation

Predation occurs when one organism (the predator) consumes another organism (the prey). The consequences for the predator are positive and for the prey - negative.

In a healthy ecosystem, the numbers of predators and prey remain fairly constant.

A less balanced ecosystem would occur if there is a change in abiotic factors such as water, sunlight and temperature. Or there could be biotic factors such as a pathogen or a new predator.

In a predator-prey cycle:

  1. The number of predators increases because there is more prey.

  2. The number of prey then reduces because there are more predators.

  3. The number of predators then reduces because there is now less prey for predators so more competition for food.

Over time, prey and predators cause the evolution of each other. Predators adapt for more successful hunting and prey adapt to avoid being eaten and survive long enough to breed.

Predator adaptations

Prey adaptations

Weapons such as teeth, claws and jaws for a successful hunt.

Camouflage to avoid being seen by prey.

Built for speed to chase prey.

Eyes at the front of the head to judge speed and distance well.

Can release toxins in poison and stings.

Camouflage and mimicry to avoid being seen by predators.

Fast to get away from predators.

Eyes to the side of the head to get a wider field of view.

Table 1. Predator vs prey interactions

Interspecies relationships Predator example StudySmarterFig. 2 – A lion, which is one of the main predators in savannah ecosystems. Source: wikimedia.com

Herbivory

When an animal consumes a plant, it is called herbivory. A herbivore doesn’t always kill its prey, only if it consumes parts of photosynthetic organs that affect the plant.

You may have heard of a venus flytrap before. It is a carnivorous plant that eats insects. It is native to the subtropical wetlands of the east coast of the USA. It contains stiff and sensitive hairs that grow up to 0.5 cm on each side of the trap. When the prey lands on the trap, it triggers the head of the fly trap to snap shut and trap the bug which can then be broken down for nutrients. Two different hairs must be triggered within a 20 second period. This avoids false alarms and wasting any energy on things that aren’t food such as falling leaves or rain.

Interspecies Relationships - Key Takeaways

  • Each organism interacts with many other organisms. Both of its own and of different species.

  • Interspecies relationships are between an organism and other species. They always benefit one party.

  • Interspecies relationships are very important because they affect essential processes such as food chains and nutrient cycles.

  • Over time coevolution can occur in response to the way species interact.

  • It is extremely hard to quantify the relationship between organisms as there are so many variables in the way organisms interact.

  • Interactions between species are usually classified into amensalism, competition, predation, herbivory, parasitism, commensalism, and mutualism. With the last three coming under the term symbiosis.


References

  1. Fig. 1 - Western Honey Bee (Apis mellifera) (https://unsplash.com/photos/LPZGRIZWAHM) by Kris-Mikael Krister (https://unsplash.com/@kmkr) licensed by CC0 1.0 Universal (https://creativecommons.org/publicdomain/zero/1.0/)
  2. Fig. 2 - Panthera leo stretching (https://commons.wikimedia.org/wiki/File:Panthera_leo_stretching_(Etosha,_2012).jpg) by Yathin S Krishnappa (https://commons.wikimedia.org/wiki/User:Yathin_sk), Licensed by CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en)

Frequently Asked Questions about Interspecies relationships

The interactions between different species in an ecosystem.

They can coevolve in order to survive in the same niche.

Yes, they can form symbiotic relationships and benefit from the presence of each other.

Predation occurs when one species (the predator) hunts the other (the prey). In a predator-prey cycle: The number of predators increases because there is more prey. The number of prey then reduces because there are more predators. The number of predators then reduces because there is now less prey for predators so more competition for food.

Whichever species is not benefited (unless neither is harmed)

Final Interspecies relationships Quiz

Question

What is symbiosis?

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Answer

A relationship in which two dissimilar organisms live closely together.

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Question

What is mutualism?

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Answer

A symbiotic relationship in which both species benefit.

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Question

What is commensalism?

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Answer

A symbiotic relationship in which one partner derives all the benefits. The other partner is not harmed but does not benefit.


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Question

What is parasitism?

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Answer

A symbiotic relationship in which one partner derives benefit, other partner is harmed

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Question

Do parasites kill their hosts?

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Answer

Not usually; they require a host to use for their own benefit

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Question

What is competition?

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Answer

The struggle between organisms to survive in a habitat with limited resources.

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Question

What is predation?

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Answer

An interaction in which one organism kills another for food.

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Question

What is predation?

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Answer

An interaction in which one organism kills another for food.

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Question

What is a predator?

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Answer

An animal that hunts other animals for food.

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Question

What is prey?

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Answer

An organism that is killed and eaten by another organism

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Question

What is herbivory?

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Answer

When the animal consumes a plant.

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Question

What is the main difference between herbivory and predation?

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Answer

In herbivory, the prey isn’t always killed.

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Question

What are three types of symbiosis?

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Answer

Mutualism, commensalism, parasitism. 

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Question

What is competition for interference?

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Answer

Fighting directly for the limited resource. 

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Question

What is competition for exploitation?

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Answer

When two or more species use a resource in common. 

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Question

Why is it hard to quantify the relationship between organisms?


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Answer

As there are so many variables in the way organisms interact.

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