13.1: Introduction

Learning Objectives

• Observe how different populations interact with one another.
• Identify predator-prey relationships and competition amongst different species

Organisms interact with physical elements (abiotic factors) and other organisms (biotic factors) as they go about their lives. These factors make up an ecosystem, the organizational level that encompasses all living and nonliving things in a particular area. Depending on where the organism lives, changes in the environment vary in intensity. Species adapt to the characteristics of their habitat. Some adaptations result in the formation of relationships with other organisms. Organisms are not limited to one type of relationship or interaction with other populations. Organisms also form partnerships within their own species to aid in individual and population survival in an area.

Within a population, individuals of the same species may compete for habitat, food, and mates. Usually, these resources are limited and only some individuals will be successful enough to get them. The struggle to obtain a limited resource, undertaken by members of the same species, is called intraspecific competition. Sometimes organisms of different species share the same space or search for the same food. This is termed interspecific competition. In this case, less successful organisms might die or be forced to use different resources. Another type of interspecific interaction is known as predation. In a predator-prey relationship, one species (predator) feed on another species (prey).

When organisms live in close proximity to one another they often form what are referred to as symbiotic relationships. Symbiosis can come in one of three forms: mutualism occurs as both partners benefit from the relationship, commensalism occurs as one partner benefits while the other is unaffected, and finally parasitism which results in one partner profiting while the other is harmed. The costs and benefits may change as organisms evolve. In some cases, individuals possessing the physiology or behavior best suited to the symbiotic relationship will live longer and be more likely to pass on their genes. The nature of symbiotic relationships are fine-tuned by natural selection.

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