Chapter 2: Populations and Sustainable Ecosystems Section 2.2: Interactions Among Species

Species Interaction In addition to resource needs and abiotic factors, the growth and size of a population can be greatly affected by interactions among the different species in an ecosystem. These interactions can have negative or positive effects. The major types of interactions are predation, competition, and symbiosis.

Ecological Niches An ecological niche is the way that an organism occupies a position in an ecosystem, including all the necessary biotic and abiotic factors. Niches can also be described as being the “role” or “job” of the organism or the “service it provides to the ecosystem.” There are millions of species on Earth, and, thus, millions of niches. Species have adapted to the ecosystem and niche they occupy. Carnivorous plants exist in ecosystems with nutrient-poor soils. These plants have adaptations for getting their nutrients from insects.

Predation and Population Size Predators are organisms that kill and consume other organisms. Prey are organisms that are eaten as food by a predator.

Reviewing Predation and Population Size Click the “Start” button to review the connection between predation and population size. Copyright © 2010 McGraw-Hill Ryerson Ltd.

Competition Competition occurs when two or more organisms compete for the same resource, such as food or space, in the same place at the same time. Competition can limit the size of a population and can also influence the ecological niche of an organism.

Competition cont’d As populations increase in an ecosystem, so does competition for resources. The more energy an organism spends competing for resources, the less energy it has for growth and reproduction.

Symbiosis Symbiosis is the interaction between two different species that live together in a close association. Mutualism is a symbiotic relationship in which both species benefit.

Mutualism Colourful coral represents a mutualistic relationship between the coral and a photosynthetic algae. The algae supplies the coral with energy, and the coral provides the algae with protection, nutrients, and CO2. If the mutualistic relationship fails, both of the species suffer or die. Without the algae, the coral bleaches (turns white) and dies.

Symbiosis - Parasitism Parasitism is a relationship in which one of the species benefits (the parasite) and the other is usually harmed (the host) The parasite is the organism whose niche depends on a close association with a larger host organism.