Unit 5: The structure of the ecosystems                      1   2   3   4   5   6

3. Living beings relationships

Biotic factors are the relationships or interactions among the living beings of the ecosystem.

There are two types of biotic relationships:

- Intraspecific relationships that are the interactions among organisms

  of the same species.

- Interspecific relationships that are the interactions among organisms

  of different species.

a) Intraspecific relationships

The relationship among individuals of the same species can be:

- Competitive. It is a negative relationship. Individuals result harmed.

- Cooperative. It is a positive relationship. Individuals result benefited.

- Intraspecific competition

 Organisms of the same species have the same needs,

so that they will compete over resources if they become scarce.

These resources are food, territory and sexual partner.

(E. g. Male deers fight for females during the mating season)

- Cooperative relationships

In this case, organisms associate to help each other. In this way they increase the probability of survival. The main positive intraspecific relationships are:

- Gregarious association

It is a large group of individuals of the same species, not necessarily related, which live together, at least for some time.

The main gregarious associations are:

- Herds, typical of mammals (e.g. buffalo, antelopes, zebras, etc.)

- Folks, typical of birds (e.g. doves, flamingos, etc.)

- Shoals, typical of many fish species (e.g. sardines, tuna, etc.)

- Family

It is a small group of related individuals of the same species which live together to procreate and protect the young. (E.g. lions, elephants)

- Society

It is a large group of related individuals of the same species organized in a hierarchy. Within the group, different types of individuals carry out different functions. (E.g. bees, ants, termites)

- Colony

It is a group of genetically identical individuals that live together sharing

a common structure. (E. g. corals are formed by thousands of identical

 individuals that share the calcareous skeleton )

b) Interspecific relationships

When individuals of different species interact the relationship can be beneficial (+), harmful (-) or indifferent (0) for both or one of them.

According to this we can summarise the interspecific relationships in this chart:

- Interspecific competition

This relation is mutually harmful for both species.

It is established between species with similar necessities that live together in the same place.

The species fight for food or territory (E.g. gnus and zebras, giraffes and gazelles)

- Predation          

In this interaction one of the species (the predator) hunts and kills other (the prey) to feed in. (E.g. cheetahs eat gazelles)

- Parasitism

This is a relationship in which one of species (the parasite) lives at expense of another species (the host) and harms it in the process.

(E.g. ticks suck the dog’s blood)

- Commensalism 

In this case one of the implicated species (the commensal) benefits of the interaction while it is indifferent for the other. (E.g. Remora fish feeds in the rest of food that falls while sharks eat). A special type of commensalism is inquilinism, in which one organism uses the other for housing (E.g. Same species of owl lives in trees’ holes)

- Mutualism          

This relation is mutually beneficial for both species (E.g. bees pollinate flowers, cow herons eat the parasites of buffaloes, etc.). When the relationship is so narrow, that the species involved cannot survive separate the relationship is called symbiosis (e.g. Lichens are organism formed by an unicellular alga that lives within the tissues of a fungi)

3.1. Look at the pictures.

         a. Are they intra or interspecific relationships?

b. What biotic relations are represented in each one?

3.2. Competition is an interaction in which organisms fight for the same

        resources.Which type of competition is more intense intraspecific

        or interspecific one? Why?  

3.3. Indicate in the following examples what specie is beneficial and why.

a. Hyenas and vultures are scavenger animals that compete for carrion.

b. Chameleon feed in insects that they hunt with its sticky tongue.

c. Ivy grows on other plants to achieve larger amount of light.

d. Clown fish defend anemone of its predators and anemone protects the fish

    with its venom.

3.4. Listen and indicate what type of biotic relationship is been described.