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

4. 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

5. 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

6. Example of a condition
Temperature - one of the most important factors because of its influence on metabolism

7. 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

8. Endotherms
Regulate body temperature by internal heat production (birds, mammals)
Regulators °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

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)

10. 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

11. Ectotherms
Changes in body temperature result in changes in rates at which physiological processes occur
Temperature coefficient = Q10

12. 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

13. 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

14. Other effects of temperature on ectotherms
High temperatures can…
Inactivate/denature enzymes
Greatly increase energy expenditures
Dehydrate (most important for terrestrials)

15. 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

16. Temperature can affect distributions
Organisms generally found where temperatures are optimum for survival, growth, reproduction

17. Temperature can affect distributions - continued
Lethal high or low temperatures can limit distributions, but only need to occur infrequently to do so

18. Saguaro cactus distribution
Distribution limited to regions where freezing temps. last <36 hours

19. 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 15°C
Toward edge of distribution, organisms occupy microhabitat patches where temperatures are nearest optimal

21. 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

22. Trout distributions
Warmer temperatures produce lower dissolved O2 levels

23. Temperature can affect distributions - continued
Effects of suboptimal temperatures can be moderated by evolution, behavior, physiology

24. Allen’s rule Endotherms in cold climates have shorter
extremities than those in warm climates

25. Bergmann’s rule Mammals with wide distribution are
larger in colder climates - less surface area
per unit volume

26. 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

27. 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

28. Salinity
Organisms possess different requirements/tolerances of salinity - osmoregulation
Stenohaline - narrow limits
Euryhaline - broad limits

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

30. Current velocity - continued
Low-profile - boundary layer
e.g., mayfly nymphs

31. Current velocity - continued
Streamlining

32. Soil structure
Coarse versus fine
Smooth versus rough

33. Pollutants Differing tolerances to various pollutants 100 Species A
Species B
Percent
survival
Concentration

34. Ecological Niche
Description of the various environmental limits within which a given species can:
Survive
Grow
Reproduce
Maintain a viable population
n-dimensional hypervolume

35. Two Kinds of Niches Fundamental niche Realized niche
Potential limits of the species
Realized niche
Actual limits of the species as imposed on it by competitors and predators

36. Resources
Add more dimensions to the ecological niche

37. Resources Consumed or made less available to others Solar radiation
Water
Macronutrients (N, P, S, K, Ca, Mg)
Trace elements (e.g., Mn, Zn, Cu) O2
Food
Space

38. 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

39. Solar Radiation cont.
Only a portion of light spectrum is useable by plants ( nm)
Photosynthetically active radiation (PAR)
44% of total solar radiation

40. 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)

41. 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

42. 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

43. 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

44. Solar Radiation cont. Efficiency of utilization
Maximum lab values < 5%
Maximum field values < 3%
Tropics 1-3%
Temperate %
Temperate crops 0.6%

45. 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

46. Water Plants obtain moisture from ground
Constant supply in many locations, limited in others

47. 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

48. 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

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

50. 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

53. 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

54. 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

55. 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

56. 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

57. Defense Against Being Eaten
Behavioral
Flight
Bluff (threat displays)
Startle response (moths)
“Playing dead”

58. Defense Against Being Eaten
Morphological
Crypsis (camouflage)
Aposematism (warning coloration)
Mimicry (Batesian, Mullerian)

59. 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

60. Defense Against Being Eaten
Physical
Spines
Thorns
Hard seed capsules

61. 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