Niches

"The concept of the ecological niche is almost inseparable from the concept of interspecific competition, but is difficult to define rigorously. The ecological niche is the sum total of the organism's use of the biotic and abiotic resources in its environment. One way to grasp the concept is through and analogy made by (world-reknowned) ecologist Eugene Odum: If an organism's habitat is its address, the niche is its occupation. Put another way, an organism's niche is its ecological role - how it "fits into" an ecosystem. The niche of a population of tropical tree lizards (see figure 53-3 below), for example, consists of, among many other variables, the temperature range it tolerates, the size of trees upon which is perches, the time of day in which it is active, and the size and type of insects it eats."

The term fundamental niche refers to the set of resources a population is theoretically capable of using under ideal circumstances. In reality, each population is embedded in a web of interactions with populations of other species, and biological constraints, such as competition, predation, or the absence of some usable resources, may force the population to use only a subset of its fundamental niche. The resources a population actually uses are collectively called its realized niche." See figure 53-2 below for an example of fundamental vs. realized niches.

SOURCE: Campbell, N.A., Reece, J.B. and L.G. Mitchell. 1999. Biology, 5th ed. Benjamin Cummings, Menlo Park, CA. p. 1115.

Fig 53-3a. Resource partitioning in a group of sympatric lizards. Seven species of Anolis lizards live in close proximity in the Dominican Republic. Each species perches in a characteristic microhabitat, distinguished by the amount of sun it receives and the size of the vegetation. Such patterns of resource partitioning probably reduce interspecific competition among members of a community, enabling them to coexist within a small geographic area. / © Pearson Education, Inc.	Fig 53-3b. Anolis distichus, for example, perches on fenceposts and other sunny surfaces (such as this leaf).
	Fig 53-3c. A. insolitus usually perches on shady branches.
Fig 53-2. Testing a competitive exclusion hypothesis in the field. Balanus balanoides and Chthamalus stellatus are two species of barnacles that grow on rocks exposed during low tide along the Scottish coast. The barnacles have a stratified distribution, with Balanus most concentrated on the lower portions of the rocks and Chthamalus on the higher portions. The swimming larvae of the barnacles may settle randomly on the rocks and begin to develop into sessile adults, but Balanus fails to survive high on the rocks because it is unable to resist desiccation when these areas are exposed to air for several hours during low tides. Its fundamental niche (potential niche) and its realized niche (actual niche) are similar. Even though Chthamalus is concentrated primarily on the upper strata of rocks, when ecologist Joseph Connell removed Balanus from the lower strata, the Chthamalus population spread into that area. Thus, Chthamalus could survive lower on the rocks than where it is generally found, were it not for competition from Balanus . Its realized niche is only a fraction of its fundamental niche. / © Pearson Education, Inc.

Links:

• Whole-earth mentor: a conversation with Eugene P. Odum.
• Caribbean Lizards Evolve Independently - remarkably similar lizard communities have evolved independently on different islands.
• Biologists Find Unexpected Rapid Evolution In Caribbean Lizards.
• Jonathan Losos and his research team study lizards to understand the origins of diversification and how organisms survive.
• Losos' Lab at Washington University, St. Louis.

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