BIOLOGY 403: PRINCIPLES OF ECOLOGY

(Regulatory / Limiting Factors)

LIMITING / REGULATINGFACTORS

• Limiting Factor ???Is Regulatory Factor a better term?

• Virtually anything can be Limiting / Regulating .

• Nutrients (or other minerals), Temperature, Light, Water, Atmospheric Gases, Currents and Pressures, Soil, Fire, Biotic Factors (just to name some)

LIEBIG’S LAW OF THE MINIMUM

• Justus Liebig (1830’s-1840’s, agronomist)

• From his work we get what some call Liebig’s Law of the Minimum

• The size of a crop is determined by the essential nutrient that is present in minimal amount.

• PARAPHRASED: the weakest link determines the strength of the chain

WEAKNESSES IN LIEBIG’S LAW

• he was only interested in nutrients

• interested only in the effects from nutrient deficiency

• did not take into account + and – synergisms

• SYNERGISM –-- result of an interaction of two or more factors so that the combined effect is greater (+ or -) than the sum of their separate effects

SHELFORD’S LAW OF TOLERANCE

• the absence or poor performance of a species may be controlled by the qualitative or quantitative deficiency or excess of any factor that approaches the limit of tolerance

• much more general

• just an ‘extension’ of Liebig’s ideas ???

• lower limit, optimum, upper limit

SOME RIDERS / AFTERTHOUGHTS• relatively large variations in factor intensity are of

relatively small consequence in the region of the optimum

• a particular organism may have narrow ranges of tolerance for some factors, medium for others and wide for yet others

• these ranges / limits may vary seasonally, geographically (ecotypes), and/or with the stageof the life cycle (age)

• when conditions are not optimal for one factor this may influence other factors (? domino effect ?)

MORE RIDERS / AFTERTHOUGHTS • organisms rarely (IF EVER!) live under optimal

conditions for all (or even most) factors

• organisms live where an acceptable ‘ecologic sum’ exists, that is, where a multitude of factors are at their ‘relative best’

• an acceptable ‘ecologic sum’ can be arrived at in more than one way

• in ‘real’ systems it is often difficult (and unrealistic) to single out ONE thing as the major regulatory factor (WHY ?????)

SOME IMPORTANT PREFIXES

• Steno

• (narrow range)

• Meso

• (middle or a bit wider range)

• Eury

• (wide range)

SOME IMPORTANT SUFFIXES

• thermal

• hydric

• haline

• phagic

• oecious or ecious

STENO ORGANISMS

• They are specialists.

• Advantage ???

• Disadvantage ???

EURY ORGANISMS

• They are generalists (“jack of all trades”)

• Advantage ???

• Disadvantage ???

WHICH REGUALTORY FACTOR IS HAVING THE EFFECT ????

• shrub genus Emmeranthe

• species A grows on ‘normal’ soilsspecies B grows on serpentine soils (high in Mg, Fe and low in Ca, P, N)

• transplant them to the other’s habitat and they die?

• Why ?????

WHICH REGUALTORY FACTOR IS HAVING THE EFFECT ????• Sp. A cannot tolerate the unusual nutrient

conditions in the serpentine soils

• Sp. B doesn’t need (as such) the unusual nutrient conditions in the serpentine soils

• Sp. B does well in ‘normal’ soils that have been autoclaved

• bacterial toxins from bacteria that live only in the ‘normal’ soils inhibit Sp. B

NUTRIENTS

• most material covered previously

• too much of a nutrient as well as too little can be harmful

• Too little (???)

• Too much (???)

• Synergisms and extrapolation (fertilizer experiment)

• + NaNO3 --- 10% increase in yield

• + K2SO4 --- 10% increase in yield

• + both --- doubled the yield

TEMPERATURE (I)• Sometimes difficult to determine if this is the major

factor --- WHY?

• Often interacts with moisture

• Temps on the earth (oC): -70 to +100 or more

• Some spores can tolerate these conditions (and even worse in laboratory studies)

• Some living organisms can be active at the upper natural extremes but few anywhere near the lower

• Majority are found active between 0 o and 40o. WHY?

TEMPERATURE (II)

• Highest temp. in some ecosystems

• 36o in normal seawater

• Land shade temp. often reaches 46o for a month or more; sometimes 55o

• High or low temp. may be regulating but seasonal fluctuations are often regulating; Midcontinental areas (Minnesota) may have 35o (some areas of Tibet reported to be 80o)

• Maritime equatorial area may be as little as 0.5o

TEMPERATURE (III)

• Regulating temp. may vary depending on other abiotic environmental factors or with the stage in the life cycle

• Temp. varies with altitude and latitude; it is temp. rather than these factors which is REALLY regulating

• Temp. decreases 5.5oC for every 1,000 m (3oF for every 1,000 ft.)

TEMPERATURE (IV)(Is it altitude and latitude?)

TEMPERATURE (V)• North / South temp. cline similar to the Altitudinal

temp. cline

• Limiting effect of temp. --- Sequoia sempervirens (the coast redwood)pacific coast fogbeltto s. Oregon (temp.) --- freezing of seedlingsc. coastal California (moisture)

• Pedicularis groenlandica (Colorado rockies)not above 10,000 ft.not altitude directlytemp. --- but not directly on the plantobligate outcrosser --- temp. on its pollinator (bee)

WATER (I)

• Essential for all life forms

• Some organisms never ingest ‘free’ water

• Too little water (drought) – directly regulating

• Too much water – more of an indirect effect• Leaching of nutrients

• Too little O2 in waterlogged soils

WATER (II)

• Total yearly precipitation not as important as ‘EFFECTIVE PRECIPITATION’

• One area with 45 in. (114 cm.) could support deciduous forest while another at the same latitude could be grassland or even desert

• WHY?

WATER (III)• ‘EFFECTIVE PRECIPITATION’ depends on:

• Total precipitation• Seasonal distribution• Temp.• Wind• Relative humidity• Soil

• Precipitation may become more effective with increasing elevation and then less effectiveWHY?

LIGHT (I)

• Important for animals as well as plants

• Can have too much as well as too little

• Light and temp. often relatedWHY / HOW ?

• 3 factors / aspects we are concerned with:

• Quality (= wavelength)

• Intensity

• Duration

LIGHT (II)

• Quality (= wavelength) effects:

• photosynthesis

• Flowering initiation (red/far red light in so-called short or long day plants)

• Some plant and animal tropisms

• Some organism processes / activities

LIGHT (III)

• Intensity effects:

• Plant (auxin responses) and animal tropisms

• Photosynthesiscompensation point (~100 fc)saturation point (~2,000 fc, about 1/5 of full sunlight)

• Humans (SAD)

LIGHT (IV)

• Duration effects:

• May interact with quality and/or intensity

• Plant flowering

• Metamorphosis in some insects; resting stages in many plants and animals

• Humans (SAD)

ATMOSPHERIC GASES (I)• Already discussed water vapor

• Already discussed nitrogen as a nutrient

• NOX --- important in acid precipitation

• SO2 --- important in acid precipitation

• O2 and CO2 are the main gases

• Rarely are O2 and CO2 overly regulating in terrestrial situations (sometimes in very highly organic soils, waterlogged soils or at high elevations)

ATMOSPHERIC GASES (II)

• O2 and CO2 often regulating in aquatic systems

• Water holds only about 5% the amount of O2

found in an equal volume of air

• CO2 is quite soluble and can alter pH (currently affecting marine ecosystems)

CURRENTS & PRESSURES (I)

• Especially important in aquatic situationsWHY?

• Directly on organisms in aquatic situations - HOW?

• Indirectly on aquatic organisms - HOW?

• Winds (direct and indirect), more often important at higher elevations

CURRENTS & PRESSURES (II)

• Especially important in aquatic situationsWHY?

• Generally not very important in terrestrial situations WHY?

SOIL (I)

• More concerned with texture, structure and mode of formation

• Terrestrial soils can be delimited on mode of formation:

• Residual (in place)

• Colluvial (talus)

• Alluvial (deltas, etc.)

• Glacial (till)

• Wind (eolian) --- dune and loess

SOIL (II)• Soil texture

• Parent material usually 90% or more of the soil solids; texture usually refers to this constituent

• One system of classification:• Coarse gravel --- 5.0 mm and larger

• Fine gravel --- 2.0 mm to 5.0- mm

• Coarse sand --- 0.2 mm to 2.0- mm

• Fine sand --- 0.02 mm to 0.2- mm

• Silt --- 0.002 mm to 0.02- mm

• Clay --- less than 0.002 mm (colloidal size particles)

SOIL (III)

• Soil particle size influences:

• Moisture holding capacity

• Aeration

• Fertility

• Root and animal penetration / burrowing ability

• Freezing and thawing patterns

SOIL (V)

SOIL (VI)

FIRE

• Helps maintain some grasslands

• Helps maintain some pine forests

• Surface fires often temporarily increase productivity

BIOTIC FACTORS

• Some animals may help maintain vegetation in an area

• Pollinator specificity

• Seed dissemination by animals

• Effects of humans

• Other interactions (predation, etc.)