BIOS 3010: Ecology Lecture 2: Habitat: Resources Lecture...

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Dr. S. Malcolm BIOS 3010: Ecology Lecture 2: slide 1

BIOS 3010: Ecology Lecture 2: Habitat: Resources

•  Lecture summary: – Resources:

• Definition • Abiotic • Biotic • Space • Classification

– The niche Albrecht Dürer: A Young Hare 1502, The Large Turf 1503 (GSA, Vienna)


2. Resources and global security:

•  “The UN predicts that by 2025, two-thirds of us will experience water shortages, with severe lack of water blighting the lives and livelihoods of 1.8 billion. According to the UN World Water Assessment Programme, by 2050, 7 billion people in 60 countries may have to cope with water scarcity.” – Chenoweth, J. 2008. Water, water everywhere.

New Scientist 23 August 2008: 28-32.


3. What is a resource?:

•  All things consumed by an organism (Tilman, 1982) –  But, space is also a resource - therefore:

•  Resources are quantities that can be reduced by the activity of an organism –  Or, in the glossary to Begon et al. (1996) a resource is defined as:

•  “that which may be consumed by an organism and, as a result, becomes unavailable to another” –  e.g. food, water, nesting sites, etc. –  Thus CO2, O2, and light can be either resources or conditions - and

are more likely to be resources at high population densities and small scales.

–  Note: like conditions, resources can also act as constraints and cues.

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4. Contrast with conditions:

•  “A condition is an abiotic environmental factor which varies in space and time. Conditions are not consumed or used up by organisms or made less available to others.” – e.g. temperature, moisture or humidity, light,

chemistry (e.g. O2, pH, salinity), gravity, pressure, sound, fire, wind, stream or current flow velocity, pollutants.


5. Abiotic Resources: •  Solar radiation is a resource and not a condition when the

supply can be influenced by other organisms •  Resource supply can vary:

–  Systematically –  Unsystematically

•  Systematic Variation - e.g. globally, seasonally or diurnally when solar radiation operates more like a condition. –  Fig. 3.1, solar radiation with latitude –  Fig. 3.3, annual and diurnal variation in solar radiation with latitude –  Figs. 3.6 & 3.8 of strategic responses (rigid responses with little

tactical maneuverability) to predictable variation in the Photosynthetically Active Radiation spectrum (PAR of 380-710 nm) for plants that vary strategically in abilities to photosynthesize under different light regimes.


6. Abiotic Resources:

•  Unsystematic Variation - e.g. local, plastic or tactical responses resulting in resource depletion zones (RDZ): –  e.g. the leaves in a forest (Fig. 3.2) or plant roots

responding tactically to resource concentration with more root hairs:

•  e.g. wheat grown in sand + clay - more roots respond to available water and minerals in clay, see Figs. 3.20 & 3.21.

–  Resource depletion zones vary according to physical characteristics, e.g. nitrates are soluble but phosphates are not - hence mycorrhizae are used by all plants to aid in foraging.

•  Note: read the text (Begon et al. chapter 3) for accounts of CO2, water, mineral nutrients and O2 as resources

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7. Biotic Resources:

•  The product of autotrophic fixation of energy by plants and used by heterotrophs as consumers.

•  Produces decomposers, parasites, predators and grazers/herbivores.

•  Nutritional content of these resources varies: –  Fig. 3.23 - nutritional composition of plants versus animals

nutritional variation among and within plants: •  plants have much higher C:N ratios than animals.

–  Fig. 3.17 - the complex of herbivores on raspberry plant partition resources in space and time:

•  considered later under competition.


8. Space as a resource:

•  e.g. lizards basking on a rock compete for microsite space to bask. •  or monarch butterflies overwintering on trees require space to avoid

freezing mortality or mouse predation on the ground. •  or testosterone-manipulated red grouse territories in Fig. 3.23 (3rd ed.).


9. Tilman’s Classification of resources:

•  after Tilman 1982. •  Distinction between essential and substitutable resources to give the 5

sets of performance (growth) isoclines between 2 resources in Fig. 3.27 –  Essential –  Perfectly substitutable –  Complementary –  Antagonistic –  Inhibitory

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10. The ecological niche:

•  G. Evelyn Hutchinson (1957) defined the niche as an: –  “n-dimensional hypervolume”

•  Ecologically the niche is an abstract concept and not a fixed position in space –  (a “neesh” and not a “nitch!” …… Dr. Seuss.)

•  n-dimensions define the limits within which a species can survive and reproduce, for n environmental “factors” that will include both conditions and resources.


11. Fundamental & Realized niche:

•  Fundamental niche: –  So the zero growth isoclines of Fig. 3.27 define niche boundaries in 2

dimensions and this can be done for both lower and upper limits of either conditions or resources to define the fundamental niche of a species:

•  the space that it could occupy - its overall potential. –  These niche boundaries can be easily drawn in 1, 2 or 3-dimensions as in

Fig. 2.26, for dimensions such as those shown in Fig. 2.2, or dimensions that include resources and ecological processes. But it is difficult to visualize the niche in more dimensions and so the “n-dimensional hypervolume” is the best simple description of niche space.

•  Realized niche: –  The realized niche represents the actual niche dimensions of a species after

various ecological processes such as movement, competition and natural enemy attack have reduced the fundamental niche dimensions.


Global solar radiation absorbed annually (J·cm-2·min-1)

Fig. 3.1

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Annual & diurnal variation in solar radiation with latitude

Fig. 3.3


Photosynthetic CO2 uptake in response to radiation intensity

Fig. 3.6


Fig. 3.8

•  Annual variation in (a) PAR (☐) and leaf photosynthesis (●) and (b) CO2 exchange in the day (¢) and at night (●)

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Fig. 3.2

•  Reflection (R) and attenuation of solar radiation in:

•  (a) mixed boreal forest, (b) pine forest, (c) sunflowers, (d) corn field


Fig. 3.20

•  (a) shortgrass prairie plant roots; (b) wheat roots in sand and clay layers


Fig. 3.21

•  Radioautographs of mustard seedlings to show depletion of 32PO4- in soil

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Fig. 3.23

•  Composition of different plant and animal resources


Fig. 3.17 (3rd ed)

•  Life cycle and phenology of raspberry plant (Rubus idaeus) parts as resources for animal consumers


Fig. 2.26 (3rd ed. - see Fig 2.2)

•  Ecological niche in 1 (a), 2 (b) & 3 (c) dimensions

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Fig. 2.2

•  Various niches in (a) 1 dimension and (b) 2 dimensions


Niche theory according to Dr. Seuss

•  And NUH is the letter I use to spell Nutches,��Who live in small caves, known as Nitches, for hutches. These Nutches have troubles, the biggest of which is ��The fact there are many more Nutches than Nitches.��Each Nutch in a Nitch knows that some other Nutch ��Would like to move into his Nitch very much.��So each Nutch in a Nitch has to watch that small Nitch ��Or Nutches who haven’t got Nitches will snitch. –  Geisel, T.S. (“Dr. Seuss”) 1955. On beyond Zebra. Random House

Publishing, New York. –  http://shade.grove.iup.edu/~rgendron/Seuss.htmlx

BIOS 3010: Ecology Lecture 2: Habitat: Resources Lecture...

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