B. Habitat and Niche: Concept of habitat and niche; Niche width and overlap; Fundamental and Realized niche; Resource partitioning; Character displacement. Concept of Habitat and Niche • Habitat: The kind of place under which an individual or species is biologically adapted to live. Each habitat provides numerous niches. Competitors can coexist in the same habitat, but have separate niches. • Microhabitat: Small area of intensive use within the habitat of an organism; dead logs for salamanders, nest sites for birds • Niche: Role or function of an organism in the biotic community; includes trophic level (feeding level), foraging location (forest, pasture, etc.), where it feeds (canopy, mid-story, ground, etc.), what it eats (insects, seed, etc.), what size food it eats (large or small seeds), when it eats, where it finds shelter, how it responds to abiotic factors, where it nests etc. By analogy, the habitat is the organism's "address", and the niche is its "profession“. Ecologically, nature tends to fill all niches with communities. Niche The term Niche was used for the first time by Grinnel (1971). The ecological niche of an organism is the position it fills in its environment, comprising the conditions (the biotic and abiotic factors) under which it is found, the resources it utilizes and the time it occurs there, thus is the sum of all adaptations, use of resources and lifestyle for a positive population growth. The Eltonian Niche - The ecological role of a species in a community (its ‘job/profession’) The Hutchinsonian Niche -The range of conditions and resource availabilities within which an individual or a species persists. Niches are very tough to define due to high dimensionality. Species have evolved to occupy their own ecological niche. Organisms that have evolved together for very long periods of time seem to reduce competition (fill other niches) The three aspects of ecological niche are: o Spatial/Habitat niche: Physical space occupied by an organism. o Trophic niche: functional role i.e. trophic position GYAN BINDU ACADEMY PVT. LTD. www.gyanbinduacademy.com (9313033399, 9350172220) 1 CSIR NET JRF LIFE SCIENCES PART – B & C (AS A NEW PATTERN)
Transcript
B. Habitat and Niche: Concept of habitat and niche; Niche width and overlap; Fundamental and Realized niche; Resource partitioning; Character displacement.
Concept of Habitat and Niche• Habitat: The kind of place under which an individual or species is biologically adapted to live.
Each habitat provides numerous niches. Competitors can coexist in the same habitat, but have separate niches.
• Microhabitat: Small area of intensive use within the habitat of an organism; dead logs for salamanders, nest sites for birds
• Niche: Role or function of an organism in the biotic community; includes trophic level (feeding level), foraging location (forest, pasture, etc.), where it feeds (canopy, mid-story, ground, etc.), what it eats (insects, seed, etc.), what size food it eats (large or small seeds), when it eats, where it finds shelter, how it responds to abiotic factors, where it nests etc.
By analogy, the habitat is the organism's "address", and the niche is its "profession“. Ecologically, nature tends to fill all niches with communities.
Niche The term Niche was used for the first time by Grinnel (1971). The ecological niche of an organism is the position it fills in its environment, comprising the
conditions (the biotic and abiotic factors) under which it is found, the resources it utilizes and the time it occurs there, thus is the sum of all adaptations, use of resources and lifestyle for a positive population growth.
The Eltonian Niche - The ecological role of a species in a community (its ‘job/profession’) The Hutchinsonian Niche -The range of conditions and resource availabilities within which an
individual or a species persists. Niches are very tough to define due to high dimensionality. Species have evolved to occupy their own ecological niche. Organisms that have evolved together for very long periods of time seem to reduce
competition (fill other niches) The three aspects of ecological niche are:
o Spatial/Habitat niche: Physical space occupied by an organism.o Trophic niche: functional role i.e. trophic positiono Multidimensional/Hypervolume niche: Position in environmental gradients
Multifactor/ Hypervolume/ Hutchinsonian niche• Developed by Hutchinson (1965)• An N-dimensional hypervolume of
suitable resources and conditions.• The niche is the set of biotic and
abiotic parameters that determine where a species can and cannot exist.
• It is the fundamental niche.• Multidimensional niche space: each condition or resource which defines the niche of an organism contributes one dimension to the space in which the organism can occur. Considering all dimensions together defines fully the organism’s niche and the multidimensional niche space.
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Niche construction: the process whereby organisms, through their activities and choices, modify their own and each other's niches. Niche segregation: the differentiation of niches that enables two similar species to coexist in a community.As a result, species can overlap on several niche dimensions and still not have competition.Ecological release: The expansion of habitat and resource usage by populations into areas of lower species diversity and it results from lower levels of interspecific competition.
Niche and Convergent evolution• The more similar the requirements of two species are, the more their niches overlap.• If the niches of two species overlap, they are expected to compete.• Interspecific competition leads to Niche Diversification• Organisms adapt to fill open niches• Niches that are separated by geographic barriers may be filled by different species (1
species, 1 niche, 1 location)• Unrelated species who fill a similar niche and display similar form or function exemplify
convergent evolution
Expression” of the costs of interspecfic competition includes:• Competitive exclusion • Resource partitioning• Character displacement• Fundamental vs. Realized Ecological Niche
Fundamental vs. Realized niche• Fundamental niche: All possible environmental (biotic and abiotic) range of conditions in
which an organism can live.• Thus it is that space/hypervolume which a population can fill in the absence of competition or
predation.• Realized niche: The actual environmental conditions in which an organism lives.• It is thus a smaller range of particular niche dimensions occupied by an organism when
competition & predation occur, being always a subset of the fundamental niche.• The fundamental niche is the "set of resources and physical factors required for survival and
reproduction of individuals of a species" and the realized niche is the "set of resources and physical habitats actually used by individuals of a species in an area “
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Environmental gradient, e.g. pH., distance from disturbance, salinity…
Generalists and Specialists • Generalist: wide ranges of environmental tolerances• Specialist: restricted gradient distributions• A Generalist has a very wide fundamental niche, and can exist in many different local
environments. • Generalists make great opportunistic species, as their widely dispersed eggs can settle and
succeed in many of the new environments they may reach. • A Specialist has a narrow fundamental niche and the number of environments a specialist can
occupy is much lower than that of a generalist. • Specialists are often equilibrium species; a long period without environmental disasters allows
them to become very well adapted to a particular environment, which can enable them to out-compete the generalists in resource allocation as long as the environmental conditions remain constant.
Gause principle/ Competitive exclusion principle Gause principle was restated by Hardin (1960) as competitive exclusion principle. When two species have the same requirements, they both cannot occupy the same niche
indefinitely, one would out-compete other and drive it to extinction. The one that can more efficiently gather resources will eventually prevail.
Experiments by Gause (Paramecium), Peter Frank (Daphnia), and Thomas Park (Triboleum) have confirmed it for simple laboratory scenarios.
If they do occur in the same places, they frequently use different resources or are active at different times to reduce competition and permit coexistence i.e. they are ecologically segregated as a result of niche differentiation.
In natural, undisturbed systems, niche partitioning has been worked out by co-evolution.Example: yellow and red-winged blackbirds will partition nesting sites when using the same area of a marsh.
`Resource partitioning
• Resource partitioning prevents competitive exclusion, allowing the coexistence of several species using the same limiting resource.
• Two or more competing species subdivide same resources in different areas, ways and/or times so that they do not come into direct competition for at least part of the limiting resource
• Example, hawks (diurnal) and owls (nocturnal) have somewhat similar niches in terms of prey, but divide up the resources by foraging at different times (day vs. night)
Resource partitioning by warblers in a New England forest
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• Evolution of morphological divergence in places where two otherwise similar species occur together
• Darwin’s finches, Geospiza fortis and G. fuliginosa occurred on large islands together, they could be distinguished unequivocally by beak size. When either one occurred by itself on a smaller island, however, the beak size was intermediate in size relative to when the two co-occurred.
• Anolis lizard on isolated islands diverge to occupy separate ecological niches, mostly in terms of the location within the vegetation where they forage (such as in the crown of trees vs. the trunk vs. underlying shrubs). These divergences in habitat are accompanied by morphological changes primarily related to moving on the substrate diameter they most frequently encounter, with twig ecomorphs having short limbs while trunk ecomorphs have long limbs.
• Species DIFFER more in sympatry (together) than in allopatry (separate)
Darwin’s Finches and Character Displacement
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