CONDITIONS & RESOURCES

Chapter 3: Organismal Ecology

Environmental Factors Factors which vary in space and time, and

to which organisms are differentially responsive

Conditions (abiotic factors) Physicochemical features of the environment that

may be altered by the activities of living organisms, but not consumed Temperature Relative humidity pH Salinity Current velocity Soil structure Pollutant concentration

Resources Quantities of something that can reduced by the

activities of a living organism during its growth and development

Made less available or unavailable to other organisms Solar radiation Inorganic materials - CO2, water, oxygen, mineral

nutrients (macro-, micronutrients) Food Space

Effects of conditions For each species, there is some

level/concentration/intensity of a factor at which it does best - its optimum for that factor

Optimum conditions result in individuals with the highest fitness

Higher or lower levels of a factor result in reduced fitness or non-survival

Example of a condition Temperature - one of the most important

factors because of its influence on metabolism

Temperature Homeotherms - maintain constant body

temp. as environmental temp. varies Poikilotherms - body temp. varies with

environmental temp. Endotherms - regulate body temp. by

internal heat production Ectotherms - depend on external heat

sources

Endotherms Regulate body temperature by internal heat

production (birds, mammals) Regulators - 35-40°C Constancy of performance over wide range of

temperatures Large expenditure of energy to maintain internal

heat (large food requirements) (cost) At higher temps., they alter insulation, shunt blood

flow to surface, pant, seek out cool habitats

Ectotherms Depend on external heat sources Conformers Can moderate or modify heat exchange with

environment by: Developing various body coverings (reflective) Simple or complex behaviors Complex physiological process (bee shivering)

Body temp. still varies with environment because… Regulatory powers limited (esp. plants) Dependent on external source of heat (not

always available) Costs associated with temp. regulation

(energy, predator exposure) - benefits must outway costs

Ectotherms Changes in body temperature result in

changes in rates at which physiological processes occur

Temperature coefficient = Q10

Q10 rule For every 10°C increase in temperature, a

reaction rate (e.g., metabolism, development) increases two times Q10 = 2

May be higher or lower in some organisms for some reactions

Other effects of temperature on ectotherms Can become acclimatized to different temperature

regimes Some physiological processes adjust over time to

different temperatures

Temperature may serve as stimulus to begin some process Initiate development in some plants Diapause

Other effects of temperature on ectotherms High temperatures can…

Inactivate/denature enzymes Greatly increase energy expenditures Dehydrate (most important for terrestrials)

Other effects of temperature on ectotherms Low temperatures can…

Reduce energy expenditures (also cease maintenance, repair activities)

Induce “hardening” in plants (acclimatization to low temps.)

Produce chilling injury - disruption of membrane structure that interferes with water uptake or retention

Produce freezing injury/death - ice crystal formation within cells

Temperature can affect distributions Organisms generally found where

temperatures are optimum for survival, growth, reproduction

Temperature can affect distributions - continued Lethal high or low temperatures can limit

distributions, but only need to occur infrequently to do so

Saguaro cactus distribution Distribution limited

to regions where freezing temps. last <36 hours

Temperature can affect distributions - continued Distributions most often limited by sub-

optimal temperatures that reduce growth, reproduction, or increase mortality

Crayfish distribution Growth limited below

15°C Toward edge of

distribution, organisms occupy microhabitat patches where temperatures are nearest optimal

Temperature can affect distributions - continued Sub-optimal temperatures may affect

distributions by altering competitive interactions between species, or by interacting with other factors (i.e., O2) that more strongly affect organisms

Trout distributions Warmer temperatures

produce lower dissolved O2 levels

Temperature can affect distributions - continued Effects of suboptimal temperatures can be

moderated by evolution, behavior, physiology

Allen’s ruleEndotherms in cold climates have shorterextremities than those in warm climates

Bergmann’s ruleMammals with wide distribution arelarger in colder climates - less surface areaper unit volume

Other conditions Relative humidity Rate of water loss from evaporation and

respiration by terrestrials is dependent on relative humidity Higher humidity lower rate of loss Organisms differ in abilities to reduce or counteract

losses Require different relative humidities Often difficult to separate from temperature and wind

speed

pH Altered pH can:

Upset osmoregulation and other processes Alter availability of nutrients, minerals, toxic

metals Aluminum at pH < 4.0

Alter quality/range of available food resources

Different organisms have different requirements/tolerances

Salinity Organisms possess different

requirements/tolerances of salinity - osmoregulation Stenohaline - narrow limits Euryhaline - broad limits

Current velocity Different requirements of body

shape/attachment under different flow regimes

Low-profile, streamlining, encrusting forms in higher velocities

Current velocity - continued Low-profile - boundary layer

e.g., mayfly nymphs

Current velocity - continued Streamlining

Soil structure Coarse versus fine Smooth versus rough

Pollutants Differing tolerances to various pollutants

Concentration

Percentsurvival

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Species A Species B

Ecological Niche Description of the various environmental

limits within which a given species can: Survive Grow Reproduce Maintain a viable population

n-dimensional hypervolume

Two Kinds of Niches Fundamental niche

Potential limits of the species

Realized niche Actual limits of the species as imposed on it

by competitors and predators

Resources Consumed or made less available to others

Solar radiation CO2

Water Macronutrients (N, P, S, K, Ca, Mg) Trace elements (e.g., Mn, Zn, Cu) O2

Food Space

Solar Radiation Source of energy used by plants for

photosynthesis Not equally distributed worldwide

Equator - most Poles - least

Results from tilt of earth on axis relative to sun and thickness of atmosphere penetrated by light

Solar Radiation cont. Only a portion of light spectrum is useable by

plants (380-710 nm)

Photosynthetically active radiation (PAR) 44% of total solar radiation

Solar Radiation cont. Rate of photosynthesis depends on light

intensity Zero in darkness Compensation point - level where

photosynthesis equals respiration Saturation - maximal (achieved only if

products of photosynthesis are withdrawn rapidly for growth or storage)

Solar Radiation cont. Low intensities used more efficiently by

“shade” species

“Shade” species reach maximum photosynthesis rates at much lower light intensities than do sun species

Solar Radiation cont. Light intensity determines optimal leaf area

index (LAI) for a plant population LAI is surface area of leaves borne above

area of ground High light intensities -> high LAI Low light intensities -> low LAI

Most plants have LAI optimal for average light intensity they receive

Solar Radiation cont. Angle of leaves have strong effect on rate

of photosynthesis Perpendicular to sun, absorb most light Angled to sun, reflect some light

Angle changes throughout day, seasons

Solar Radiation cont. Efficiency of utilization

Maximum lab values < 5% Maximum field values < 3%

Tropics 1-3% Temperate 0.6-1.2%

Temperate crops 0.6%

Water Terrestrial organisms continually lose

water to environment Animals replenish it by:

Drinking water Obtaining it from their food (metabolism)

Availability can limit distribution and abundance

Water Plants obtain moisture from ground

Constant supply in many locations, limited in others

Water Plants mechanisms for reducing water loss

Rhythmic opening/closing of stomata

Leaf surface to reduce water loss Thicker cuticle, waxy or hairy (lower temp)

Modified stomata (reduce water gradient) Different conditions--->different leaf forms Dissociate CO2 uptake from photosynthesis Increase CO2 gradient into plant

Water Limits placed on plant roots’ abilities to

obtain water from soil Field capacity - maximum amount soil can

contain (held by soil pores against gravity) Permanent wilting point - minimum amount

needed by plants (can’t be extracted by root’s suction force, plant wilts and can’t recover)

Suction force causes resource depletion zone in vicinity of root

Water Root growth to water

Elongate first, then branch (develop laterals) Reduces competition between root hairs for same

water Branch more in soils that contain more water, or

where water moves less freely Clay versus sand

Early pattern of growth determines success Heavy rains, waterlogged soil, drought

Macronutrients, trace elements Animals get them from food Plants get them from soil

Require the same, but in different quantities or proportions Limits distributions of certain plants to certain soil

types Each nutrient enters soil independently of

others, has different properties of absorption, diffusion

Macronutrients, trace elements Nitrates, calcium, sodium move freely

through soil with water Often delivered to roots faster than can be

taken up by plant Resource depletion zones may be wide

because of ease of movement through soil

Macronutrients, trace elements Phosphate and potassium bound on soil

colloids by surfaces with calcium, aluminum, ferric ions Rate at which they move to plant depends

primarily on how rapidly they are released from colloids (tightly adsorbed)

Resource depletion zones usually narrow

Food Heterotrophs, consumers

Predators - kill and eat part or whole Parasites - eat on living Decomposers - eat on dead

Polyphagous - generalists - have preferences but are adaptable

Monophagous - specialists - not very adaptable

Food Quality Plants - high C:N ratio (40:1-20:1) because

of high-C cellulose, other structural materials

Heterotrophs - low C:N ratios (10:1-8:1), no structural carbohydrate but lots of protein

Food Most organisms lack cellulase to break

down cellulose Herbivores physically rupture cell walls to

gain access to contents, or use microbes Detritivores may get much nutrition from

bacteria, fungi colonizing dead materials

Food Herbivores may be selective on certain

plant parts Parts often have less cellulose and more:

Nitrogen - growing tips Carbohydrate (starch, sugar) - tubers Fats (oils) - seeds

Defense Against Being Eaten Behavioral

Flight Bluff (threat displays) Startle response (moths) “Playing dead”

Defense Against Being Eaten Morphological

Crypsis (camouflage) Aposematism (warning coloration)

Mimicry (Batesian, Mullerian)

Defense Against Being Eaten Plant chemical defense

Cyanide, acids, glycosides, tannins, alkaloids Secondary chemicals that play no role in normal

plant physiology Released by chewing, make plant taste bad, make

organism sick

Defense Against Being Eaten Physical

Spines Thorns Hard seed capsules

Defense Against Being Eaten All defenses reduce likelihood of being

consumed One or more “predators” capable of

overcoming the defense Defense costs energy that could have been

used in other activities

Resources Add more dimensions to the ecological

niche