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Competition and parasitism

Source: Gilles San Martin, http://commons.wikimedia.org, licencja: CC BY-SA 3.0.

Link to the lesson

Before you start you should know
  • parasites are bacteria, fungi and pathogenic protozoa; some species of flatworms, nematodes, ringworms, arthropods and some vascular plants.

You will learn
  • to explain what inter‑species competition is using examples;

  • to distinguish between intra‑species and inter‑species competition;

  • to discuss what parasitism is using examples;

  • to describe the adaptation of organisms to parasitism;

  • to explain the influence of parasitism on the number of specimens in host population.

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Nagranie dźwiękowe abstraktu

Competition

When two different species with similar life requirements live close to each other, they tend to compete for access to resources. Inter‑species competitionInter‑species competitionInter‑species competition is unfavourable to the organisms involved. It always ends in elimination of the weaker competitor: it either changes its place of residence, the manner of using the environment, or dies. For this reason, it's considered to be an antagonistic relationship. The effects of inter‑species competition might be the following: reducing the number of specimens in one species, its migration to less competitive areas, or a change in its needs.

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Ilustracja interaktywna. Na spalonej słońcem trawie hiena pożywiająca się padliną - rozkładającym się ciałem gnu, z którego pozostała już tylko głowa z zakrzywionymi rogami i żebra z resztkami zakrwawionego mięsa. Wyświetla się napis: 1. Hyena eats wildebeest. Nieco dalej, przy kępie wysokich, zielonych traw, stado sępów. Wyświetla się napis: 2. Vultures wait for their turn
Inter-species competition
Source: Marcel Oosterwijk, licencja: CC BY-SA 3.0.

Inter‑species competition takes place, for example, between hollow‑nesting species. An example of such species is black woodpecker. Due to the fact that a pair of woodpeckers usually prepares several hollows and uses only one of them for breeding, other bird species, such as owls, jackdaws and rollers, also find shelter in the tree trunks. These birds compete for hollows with each other, but also with bats, martens and even wasps.

Beech trees are strong competitors in the forest. Their roots emit substances into the soil, which make it impossible for other plants to germinate. For this reason, there is not much understory and ground cover vegetation in the beech forest. A similar mechanism is observed in the case of some fungi. The Penicillium fungi produces an antibiotic that prevents the development of bacterial colonies in their vicinity. This way, they protect their food supply.

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Beech forest
Source: Jonas Löwgren, www.flickr.com, licencja: CC BY 2.0.

In fields and in garden plant beds there is competition for space, light, water and mineral salts between the cultivated and wild plants, known as weeds. In neglected crops, weeds that grow intensively and produce huge quantities of seeds quickly overgrow and drown out their competitors.

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Competition in the cultivated field
Source: Dwight Sipler, Tomorrow Sp. z o.o., www.flickr.com, licencja: CC BY 2.0.

Competition is the most intense among the specimens of the same species. Intra‑species competitionIntra‑species competitionIntra‑species competition is usually associated with animals. They get into fierce fights to gain access to females and having offspring. In the herds, the so‑called pecking order is established - the most important individuals in the herd satisfy their hunger first, and for the weaker ones there might not be enough food left. The competitors that have lost may leave their herd (living area) and look for better conditions elsewhere. If they fail there too, they die and leave no offspring that would also have the genes ensuring defeat rather than victory.

It is easiest to see the intra‑species competition in the forest, where same age spruce seedlings have been planted densely and at equal distances from each other. They are planted close together to limit the appearance of self‑crops from other trees and shrubs in between. It can be expected that around 500‑800 individuals, out of a total of around 4 000 individuals planted per hectare, will live to harvest. In production forests, plantings are protected against herbivores and pests, so the loss of trees will mainly be the result of intra‑species competition.

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Animacja przedstawiająca konkurencję wewnątrzgatunkową. Na animacji pokazano pięć drzew iglastych - rosną, rozrasta się ich system korzeniowy, który łączy się z sąsiadującymi drzewami. Niższe drzewa usychają w cieniu wyższych, dominujących drzew.

Parasitism

One of the antagonistic relationships between species is parasitismparasitismparasitism. A parasite lives permanently or temporarily at the expense of the victim, called a host. The victim of a parasite is its place of life and his source of food, so most parasites do not seek to kill the host. The death of a victim would be detrimental for the parasite. A parasite without food source either dies or needs to search for a new host. The effectiveness of parasitic lifestyle is proven by the fact that parasites are found in all groups of organisms.

External parasites of animals usually feed on blood, epidermis or feathers. They may be attached (permanently or temporarily) to the body of the host (e.g. a tick, a leech) or move freely (like lice and fleas). They are in constant contact with the outside world and can find a new host after the death of the current one. The parasites which feed on individuals of numerous and highly concentrated populations have the best living conditions. Some human parasites transmit diseases: anopheles - malaria, ticks - borreliosis or tick‑borne meningitis.

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A tick on a dog's skin
Source: Doug Beckers, Steven Lilley, Tomorrow Sp. z o.o., www.flickr.com, licencja: CC BY-SA 2.0.
Task 1

Prove that tuberculosis bacterium is a parasite, which living conditions are fostered by the high density of the human population.

Internal parasites of animals may be present in different parts of the body. They are often found in the digestive system (e.g. pinworms, armed and unarmed tapeworm, human roundworm), where they feed mainly on the digestive content. However, some of them may live in internal organs - e.g. liver (liver fluke), duodenum, lungs, brain, skeletal muscles. Some internal parasites feed on blood or epithelium.

Internal parasites are much more host‑dependent than external parasites. The host suffers damage not only through loss of nutrient content or disruption of tissue continuity, but also through poisoning with harmful metabolic products of the parasite. Usually, when the host dies, his parasites die with him.

Many parasites feed on plants or inside them, e.g. pathogenic bacteria, soil nematodes, fungi and insects, stem rust, polypore, beetle larvae (grubs) and white cabbage butterfly larvae as well as larvae and adult aphids. There are also plants that are parasites themselves.

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Common toothwort - a tree parasite
Source: Andrzej Bogusz, licencja: CC BY 3.0.
Task 2

Explain why the mistletoe is described as a semi‑parasite. List the adaptations to its lifestyle.

Adaptations to parasitism

Parasites, like other organisms, have special adaptations necessary to lead their lifestyles and to gain food. In the case of animals that are external parasites, these may be specially converted organs for cutting or pricking the skin and drinking blood. In addition, some parasites, such as leeches, have chemicals that disable blot clotting in their saliva as well as anaesthetics that prevent the host from noticing the unwelcome guest immediately. Other parasites, such as head lice, have hooked legs that allow them to stay on the surface of the host's body even during very rapid movements. They have a solid body structure, thanks to which they are able to survive even scratching with claws or rubbing against bark of trees.

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Removal of parasites
Source: David Dennis, www.flickr.com, licencja: CC BY-SA 2.0.

Internal parasites are provided with stable and safe living conditions. Their bodies are usually soft and elongated. They have no legs, but some have prehensile organs (e.g. hooks on the head of an armed tapeworm) to attach to the intestinal wall. In this way, the intestinal movements do not move the parasites towards the rectum, from where they can be removed along with the faeces.

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Exercise 1
Match the following terms with their explanations. inter-species competition Możliwe odpowiedzi: 1. competition between specimens of the same species for access to the same natural resource, 2. interaction between organisms in which the host organism is a victim of a parasite that feeds on it, 3. competition between populations of different species for access to the same natural resource, 4. a type of interspecies relationship that is unfavourable to both or one of the populations. intra-species competition Możliwe odpowiedzi: 1. competition between specimens of the same species for access to the same natural resource, 2. interaction between organisms in which the host organism is a victim of a parasite that feeds on it, 3. competition between populations of different species for access to the same natural resource, 4. a type of interspecies relationship that is unfavourable to both or one of the populations. antagonistic relationship Możliwe odpowiedzi: 1. competition between specimens of the same species for access to the same natural resource, 2. interaction between organisms in which the host organism is a victim of a parasite that feeds on it, 3. competition between populations of different species for access to the same natural resource, 4. a type of interspecies relationship that is unfavourable to both or one of the populations. parasitism Możliwe odpowiedzi: 1. competition between specimens of the same species for access to the same natural resource, 2. interaction between organisms in which the host organism is a victim of a parasite that feeds on it, 3. competition between populations of different species for access to the same natural resource, 4. a type of interspecies relationship that is unfavourable to both or one of the populations

Summary

  • Inter‑species competition takes place between species that inhabit the same environment and have similar life needs.

  • Inter‑species competition may result in the reduction of the number of specimens in one species, its migration to less competitive areas or a change in its needs.

  • Parasites developed many specialized adaptations to their lifestyle and to their manner of obtaining food;

  • Parasites cause and transmit many diseases and thus affect the number of specimens in the host population.

Keywords

competition, parasitism, internal parasite, external parasite

Glossary

inter‑species competition
inter‑species competition
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Nagranie dźwiękowe słówka interspecies competition

konkurencja międzygatunkowa – antagonistyczne oddziaływanie między populacjami różnych gatunków; polega na tym, że populacje o podobnych wymaganiach współzawodniczą ze sobą o dostęp do tego samego zasobu środowiska, na przykład pokarmu lub światła

intra‑species competition
intra‑species competition
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Nagranie dźwiękowe słówka intraspecies competition

konkurencja wewnątrzgatunkowa – antagonistyczne oddziaływanie między osobnikami jednego gatunku; sposród zwykle bardzo licznego potomstwa jednego osobnika pozwala zachować przy życiu tylko kilka osobników najlepiej przystosowanych do środowiska

parasitism
parasitism
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Nagranie dźwiękowe słówka parasitism

pasożytnictwo – oddziaływanie między organizmami, w którym organizm żywicielski (gospodarz) jest ofiarą żerującego na nim pasożyta; pasożyt nie uśmierca gospodarza, ale żywi się jego kosztem