Population Interactions

It is sometimes useful to think of the universe as being organized into hierarchical levels, from the universe on top to the atoms on the bottom.

Spheres of the Earth The Earth can be divided into 6 spheres: Atmosphere : The layer of gases that surrounds the planet. Lithosphere : The land, rocks, abiotic portions of the soil. Biosphere : The sum of all ecosystems, both the biotic and abiotic. Hydrophere : The Earth’s water Cryosphere : The Earth’s ice Anthrosphere : The people.

Biosphere Since it is the sum of all ecosystems, the biosphere consists of all living things, plus any non-living things that interact with those living things.

Ecosystems An ecosystem is a community of living (biotic) organisms and the non- living (abiotic) environment it inhabits. The biotic and abiotic portions of an ecosystem interact through nutrient cycling and energy flows.

Community A community is the biotic portion of an ecosystem. It includes all the living things that share an environment, including their interactions with each other.

Populations A population is a group of organisms of the same species living in the same area at the same time.

Competition A resource in an ecosystem usually occurs in a limited supply, so organisms that require that resource must “battle” each other for the resource. This battle is called competition. There are two types of competition, intraspecific and interspecific. Intraspecific Competition: Competition within the same species.

Competition Interspecific Competition: Competition between different species.

Competition Competitive Exclusion Principle : A theory first proposed by Joseph Grinnell and later formulated by Georgy Gause based on laboratory experiments. It states that two species cannot occupy a single niche at the same time without one of the species eventually crowding out the other. It is not seen very often in natural ecosystems. Surprisingly, many species find a way to live in balance with each other.

Symbiosis Definition: A close and often long-term relationship between two or more species. Most books identify three main types of symbiosis: 1)Mutualism 1)Commensalism 1)Parasitism The next few slides and videos show definitions and examples of these relationships.

Mutualism Definition : A relationship between two or more species in which both/all species benefit and no species is harmed. Example: Rhizobia bacteria in plant root nodules fix nitrogen for the plant while gaining help maintaining a suitable environment for the bacteria

Examples of Mutualism Example: Acacia ants live in acacia trees and protect the trees from plants that might steal light from the tree and from animals that wish to use the tree for food. In return, the ants get a sweet sap and other food produced by the tree.

Examples of Mutualism Example: Lichens are a symbiotic relationship between fungi and algae or other photosynthetic organisms. The fungi receive food from the photosynthesis and the algae receive other nutrients and a way to live on harsh surfaces, such as rocks.

Commensalism Definition: A relationship between species in which one species benefits and another species is neither harmed or helped..

Parasitism Definition : A relationship between two or more species in which one species gets its food from the other species. Parasitism does not usually kill the host unless numbers of parasites get too high. Still, there is a cost to the host. There are ectoparasites and endoparasites. Ectoparasites : Parasites that live on the outside of their host. For example, fleas, mites, and the cuckoo and cowbirds Endoparasites : Parasites that live on the inside of their host. For example, worms, viruses, bacteria

Predation Definition : A relationship between two or more species in which one species feeds on another, resulting in its death. Example: The owl uses finely tuned hearing/echolocation to find its prey.

Examples of Predation Example: Killer whales sometimes work together, as predators often do, to catch their prey.

Examples of Predation Example: A cuttlefish can use camouflage to hide from its prey until it attacks.

Examples of Predation Example: Big cats, such as lions, are notorious predators, as are crocodiles. Watch in this video as the two predators go to work and the prey show some of their defenses.

Herbivory Definition: The act of an animal eating a green plant

Habitat Definition: The place or ecological environment in which an organism lives. In a tree In the ocean Under a rock A deciduous forest A swamp Inside another organism Paris

Ecological Niche Definition: The way in which an organism makes its living. The habitat of the organism along with its food and any other resources or parts of the environment that the organism has a relationship.