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Unit 1: Basic Ecological Concepts and Principles Related to Agricultural Systems

Assessing Ecosystem Structure: Interactions. In addition to diversity, another important aspect of the second ecological principle is how species and populations relate to or depend upon each other. In an ecosystem, no organism is an autonomous entity, isolated from its surroundings. In agroecosystems, crop plants, animals, weeds, insects and microorganisms interact with each other to varying degrees and with different impacts. Understanding these interactions allows farmers to develop production strategies that are cost effective and in keeping with sustainability goals.
The different relationships or interactions among different species within an ecosystem (based on the need for energy and nutrients to survive and reproduce) can be classified as follows. Click each item for a brief description:
    Competition

    Commensalism

    Symbiosis/mutualism

    Parasitism

    Predation

Competition: direct inhibition of both organisms due to limited resources such as energy, nutrients, water. Competition among members of the same species is known as intraspecific competition, while competition between individuals of different species is known as interspecific competition.

Commensalism: one organism benefits while the other organism is not significantly harmed or helped.

Symbiosis/mutualism: relationships from which both organisms benefit for different reasons.

Parasitism: parasites feed on living organisms while taking up residence in or on their prey; this relationship may or may not lead to the death of the prey or host; parasitism occurs in both animal and plant systems.

Predation:  predators feed on other living organisms, the prey, but never take residence in or on them. Predation results in the death of the organism.

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