BIOLOGY 403 PRINCIPLES OF ECOLOGY Regulatory Limiting Factors

BIOLOGY 403: PRINCIPLES OF ECOLOGY (Regulatory / Limiting Factors)

LIMITING / REGULATING FACTORS • 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 stage of 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’ soils species 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) + Na. NO 3 --- 10% increase in yield + K 2 SO 4 --- 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 (o. C): -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 40 o. WHY?

TEMPERATURE (II) • Highest temp. in some ecosystems • 36 o in normal seawater • Land shade temp. often reaches 46 o for a month or more; sometimes 55 o • High or low temp. may be regulating but seasonal fluctuations are often regulating; Midcontinental areas (Minnesota) may have 35 o (some areas of Tibet reported to be 80 o) • Maritime equatorial area may be as little as 0. 5 o

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. 5 o. C for every 1, 000 m (3 o. F 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 fogbelt to s. Oregon (temp. ) --- freezing of seedlings c. coastal California (moisture) • Pedicularis groenlandica (Colorado rockies) not above 10, 000 ft. not altitude directly temp. --- but not directly on the plant obligate 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 O 2 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 effective WHY?

LIGHT (I) • Important for animals as well as plants • Can have too much as well as too little • Light and temp. often related WHY / 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 socalled short or long day plants) • Some plant and animal tropisms • Some organism processes / activities

LIGHT (III) • Intensity effects: • Plant (auxin responses) and animal tropisms • Photosynthesis compensation 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 • SO 2 --- important in acid precipitation • O 2 and CO 2 are the main gases • Rarely are O 2 and CO 2 overly regulating in terrestrial situations (sometimes in very highly organic soils, waterlogged soils or at high elevations)

ATMOSPHERIC GASES (II) • O 2 and CO 2 often regulating in aquatic systems • Water holds only about 5% the amount of O 2 found in an equal volume of air • CO 2 is quite soluble and can alter p. H (currently affecting marine ecosystems)

CURRENTS & PRESSURES (I) • Especially important in aquatic situations WHY? • 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 situations WHY? • 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. )