1.1. Interrelationships among organisms and their effects

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UNIT 1 INTERDEPENDENCE BETWEEN ORGANISMS WITHIN THEIR ENVIRONMENT Key Unit competence: Explain complex relationships between organisms within their environment. The figure below shows the mode of life in a natural park. Organisms on this interact with each other. a) Can you describe how these organisms interact? b) Are their interactions beneficial or harmful? c) How organisms on the figure above can be affected by one another in their physical environment? Introductory Activity 1 1.1. Interrelationships among organisms and their effects Activity 1.1 Read the following passage and answer related questions: No organism exists in an absolute isolation. Organisms interact with each other. If the interaction involves individuals of the same species, it is called intraspecific interaction, and interspecific interaction, when the interactions involve individuals of different species. Biological interactions can be beneficial, harmful or neutral for each of any two species. For example, the competition arises when two organisms strive for the same limited resource. Have you ever seen two bulls fighting for a female cow, or dog and cat fighting for meat? The lion cannot compete with herbivorous antelopes. Instead, the lion, king of jungle, kills and feeds on antelopes. The two species live in predation. A dog is the host ectoparasite such as fleas and endoparasites such as roundworms. The host suffers but the parasites get benefit. However, Heron birds also known as Inyange live in mutualism with the cows. Each species gets benefit from the interaction. Nevertheless, in some cases, these interactions may result into long-term ecological and evolutionary changes among the individuals participating in these interactions. For example, the intraspecific competition enables the fittest organism to improve its fitness for acquisition of resources a) Explain in your own words each of the following interaction: Intraspecific competition – Interspecific competition – Parasitism – Predation – mutualism. b) Find examples of biological interaction which can be: i). Beneficial for one individual but harmful for another ii). Beneficial for both individuals iii). Harmful for both individuals iv). Neutral for both individuals. c) Giving an example, support why biological interactions are very important in ecosystem. Interactions among organisms within a community are termed biological interactions or interrelationship among organisms. These interactions may involve individuals of the same species or different species. Thus based on these criteria, biological or population interactions may be divided into basic interactions and relationships. All the interactions are indicated by signs such as +, + or –, –, or +, –, even 0, 0. The sign (+) indicates that a particular species is benefitting from the interactions. The sign (–) indicates that a particular species in the interactions is being harmed. And sign (0) simply indicates neutral position where it is neither benefited nor harmed in the interactions. Table 1.1: Biological interaction Types of Interaction Effect on species 1 Effect on species 2 General nature of interaction Competition, direct interference type - - Direct inhibition of each species by the other or Indirect inhibition when common resource is in short supply Commensalism + 0 Population 1, the commensal, benefits, while 2, the host, is not affected Parasitism + - Population 1, the parasite, generally smaller than 2, the pray, and also harms the prey Predation (including herbivory) + - Population 1, the predator, generally larger than 2, the prey, and kills the prey Mutualism + + Interaction favorable to both and obligatory Application Activity 1.1 Analyse the photograph or watch a documentary of the wildlife provided by your teacher. Then get ready to identify main species in the documentary and their relationship. 1. Are there intraspecific or interspecific relationships among observed organisms? Why? 2. Are there useful, neutral and harmful relationships among observed organisms?