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Chapter 2

The Organism and its Environment

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Interaction with the environment

Plant absorbs CO2 , excrete oxygen

Animals consume plants and other animals

discharge wastes

No resources - animals die

Homogeneous - constant in space and time

single problem

inhabit entire planet

not the case

Environment varies, organism’s needs vary


2.1 Environmental conditions vary both in time and space

Varying temperature, moisture, light, and nutrients

Differ - latitude, region, and locality

varies with time - yearly, seasonally, and daily

Solar radiation reaching Earth

directly influences - air temperature, atmospheric moisture, and light

Microclimate differences


2.2 Organisms need a fairly constant internal environment

Homeostasis - the maintenance of conditions within the range that the organism can tolerate.

water, acidity, salinity

consume and digest food to adjust metabolism

excrete wastes from chemical process



Feedback mechanism

Temperature regulation

Negative feedback - e.g. lowering temperatures

heat stroke

death by freezing

Positive feedback - reinforces change, driving the system to higher and higher or lower and lower values


2.3 Homeostasis is possible only within a limited range of conditions

Leibig’s law of the minimum - the performance ( survival, growth, and reproduction ) of an organism will be the function of the most limiting environmental factor.

Law of tolerance - maximum and minimum conditions limit the presence and success of an organism


2.4 An organism cannot do equally well in differing environments

Physical characteristics -

doing well

limiting performance

tall basketball player

short jockey

Distinctive mouthparts = different food types

a. Baleen whale - filter krill

b. Killer whale - large teeth, larger prey

c. Huymmingbird - long beak, nector feeder

d. Cardinal - short beak, seed eater

e. Grasshopper - vegetation, chewing

f. Misquito - piercing to penetrate drawing blood


2.5 The distribution of organisms reflects environmental variations

Distribution - presence or absence

Abundance - numbers or population size

physical environment


range of tolerance

Red Maple (Acer rubrum)

next slide


Red Maple

High degree of tolerance = widespread geographic distribution

SE Canada - 40 C --> Gulf Coast + Southern Florida

Not to West = too dry

Various soil types

Soil moisture



Wood swamps top dry ridges

Min. + max. temperature tolerance = limits of species distribution


Carolina wren (Thryothorus ludovicianus)

Strongly related to temperature

absent when avg. Jan. temperature drops below - 12 C

Regular when avg. min. temperature is - 7 C


2.6 An organism live in a habitat

Habitat - actual location or place where an organism lives.

Horned lark - open grassland

continental wide

optimum area = midwest prairie

narrowed habitat

doesn’t like tallgrass

small grass limited colonization


2.7 Constraints and trade-offs in habitats use define an organism’s niche

Joseph Grinnell - Calif. Ornithologist

1917 coined " niche "

Niche - the ultimate distributional unit within which a species is restrained by the limitations of its physical structures and its physiology = species habitat.


Other Scientists

1958 G.E.Hutchinson


current definition

Niche - includes all physical and biological variables that affect an organism’s well being


multidimensional response

fig. 2.10, page 18

Generalists: organisms with a wide range of tolerances occupy a large niche


Specialists: organisms with a narrow range of tolerance occupy a smaller niche.


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