CONDITIONS

1
CONDITIONS RESOURCES

• Chapter 3 Organismal Ecology

2
Environmental Factors

• Factors which vary in space and time, and to
  which organisms are differentially responsive

3
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

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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

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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

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Example of a condition

• Temperature - one of the most important factors
  because of its influence on metabolism

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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

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Endotherms

• Regulate body temperature by internal heat
  production (birds, mammals)
• Regulators - 35-40C
• 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

9
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)

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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 outweigh costs

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Ectotherms

• Changes in body temperature result in changes in
  rates at which physiological processes occur
• Temperature coefficient Q10

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Q10 rule

• For every 10C 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

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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

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Other effects of temperature on ectotherms

• High temperatures can
• Inactivate/denature enzymes
• Greatly increase energy expenditures
• Dehydrate (most important for terrestrials)

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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

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Temperature can affect distributions

• Organisms generally found where temperatures are
  optimum for survival, growth, reproduction

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Temperature can affect distributions - continued

• Lethal high or low temperatures can limit
  distributions, but only need to occur
  infrequently to do so

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Saguaro cactus distribution

• Distribution limited to regions where freezing
  temps. last lt36 hours

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Temperature can affect distributions - continued

• Distributions most often limited by sub-optimal
  temperatures that reduce growth, reproduction, or
  increase mortality

20
Crayfish distribution

• Growth limited below 15C
• Toward edge of distribution, organisms occupy
  microhabitat patches where temperatures are
  nearest optimal

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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

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Trout distributions

• Warmer temperatures produce lower dissolved O2
  levels

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Temperature can affect distributions - continued

• Effects of suboptimal temperatures can be
  moderated by evolution, behavior, physiology

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Allens rule
Endotherms in cold climates have
shorter extremities than those in warm climates
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Bergmanns rule
Mammals with wide distribution are larger in
colder climates - less surface area per unit
volume
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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

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pH

• Altered pH can
• Upset osmoregulation and other processes
• Alter availability of nutrients, minerals, toxic
  metals
• Aluminum at pH lt 4.0
• Alter quality/range of available food resources
• Different organisms have different
  requirements/tolerances

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Salinity

• Organisms possess different requirements/tolerance
  s of salinity - osmoregulation
• Stenohaline - narrow limits
• Euryhaline - broad limits

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Current velocity

• Different requirements of body shape/attachment
  under different flow regimes
• Low-profile, streamlining, encrusting forms in
  higher velocities

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Current velocity - continued

• Low-profile - boundary layer
• e.g., mayfly nymphs

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Current velocity - continued

• Streamlining

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Soil structure

• Coarse versus fine
• Smooth versus rough

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Pollutants

• Differing tolerances to various pollutants

100
Species A
Species B
Percent survival
0
Concentration
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Ecological Niche

• Description of the various environmental limits
  within which a given species can
• Survive
• Grow
• Reproduce
• Maintain a viable population
• n-dimensional hypervolume

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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

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Resources

• Add more dimensions to the ecological niche

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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

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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

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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

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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)

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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

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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 -gt high LAI
• Low light intensities -gt low LAI
• Most plants have LAI optimal for average light
  intensity they receive

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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

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Solar Radiation cont.

• Efficiency of utilization
• Maximum lab values lt 5
• Maximum field values lt 3
• Tropics 1-3
• Temperate 0.6-1.2
• Temperate crops 0.6

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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

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Water

• Plants obtain moisture from ground
• Constant supply in many locations, limited in
  others

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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---gtdifferent leaf forms
• Dissociate CO2 uptake from photosynthesis
• Increase CO2 gradient into plant

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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 (cant be extracted by roots suction
  force, plant wilts and cant recover)
• Suction force causes resource depletion zone in
  vicinity of root

49
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

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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

51
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

52
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

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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

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Food Quality

• Plants - high CN ratio (401-201) because of
  high-C cellulose, other structural materials
• Heterotrophs - low CN ratios (101-81), no
  structural carbohydrate but lots of protein

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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

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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

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Defense Against Being Eaten

• Behavioral
• Flight
• Bluff (threat displays)
• Startle response (moths)
• Playing dead

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Defense Against Being Eaten

• Morphological
• Crypsis (camouflage)
• Aposematism (warning coloration)
• Mimicry (Batesian, Mullerian)

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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

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Defense Against Being Eaten

• Physical
• Spines
• Thorns
• Hard seed capsules

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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