Environmental Controls on Life

1
Environmental Controls on Life

• Light
• Temperature
• Moisture

Picea glauca 10C July isotherm
2
Light

• Heliophytes
• sun loving (shade intolerant)
• C4, CAM
• Sciophytes
• shade loving (shade tolerant)
• C3

3
Photosynthesis and Light

• PS increases until maximum, then declines
• Hyperbolic shape
• Compensation point
• Saturation point
• Photoinhibition

4
Physical Adaptations to High Light Environment

• Small and thick leaves,
• Thick cuticle (covering)
• Curled, less surface area
• Reflective surface layer
• High number of stomata
• Leaf orientation
• (heliotropic)

5
Physical Adaptations to Low Light Environment

• Large, soft leaves
• High amounts of chlorophyll
• Long-lived leaves
• Heliotropic leaves!

6
Life History Adaptations to Light

• Annuals versus perennials
• Canopy trees flower more
• Seeds require light to germinate
• Loblolly pine (Pinus taeda)

7
Physiological Adaptations to Light

• Phenology timing of changes in growth
• Flowering
• Leaf shedding
• Leaf burst

8
Temperature - Plants

• Poikilothermic
• Optimum temperature for photosynthesis - varies
• EX. Circumarctic treeline
• Cold stress, freezing damage

9
Black spruce (Picea glauca) limits and July temps
10
Plant Adaptations to Temperature

• Dormancy deciduous
• How do needleleaved plants survive?
• Frost hardening
• Chemical alteration of liquids (antifreeze)
• Less water in cells
• Cell walls deformed

11
Plant Adaptations to Temperature

• Saguaro
• CAM photosynthesis
• Palo Verde nurse shrubs

12
Plant Adaptations to Temperature

• Palm distribution
• Why cant palms be cultivated at higher
  latitudes?

13
Temperature - Animals

• Poikilotherms
• cold-blooded
• -1.9C body temp OK for Antarctic icefish, 6C
  lethal
• Homeotherms
• generate heat through metabolism
• 37-47C (10C higher than core temps.) lethal

14
Northern Limits of the Eastern Pheobe
15
Adaptations to Temperature in Animals

• Metabolic rates
• Sweating, panting, licking
• Ratio of body mass to surface area
• Behavioral adaptations

• Shivering
• Super-cooling (gylcerol)
• Hybernation
• Insulation

16
Allens Rule
Latitude and Body Shapes

• Low latitude high surface areavolume
• High latitude low surface area volume

• Low latitude long extremities
• High latitude short extremities

17
Adaptations to Moisture - Plants

• Photosynthesis
• Turgor (rigidity)
• Movement of nutrients (vascular plants)
• Xerophytes dry loving
• Mesophytes moist loving
• Hydrophytes water loving

18
Transpiration

• Release of water to atmosphere by plants
• Generally through stomata
• Evapotranspiration transpiration evaporation

19
Water Stress and Range

• Moisture deficit
• evaporative demand gt root absorbtion
• Creosote (Larrea tridentata)
• -2.0- -2.9 Mpa
• Alder (Alnus spp)
• -1 Mpa

20
Lower Treeline

• High elevations
• Lower evaporative demand
• Higher rainfall (orographic)
• Seedlings have highest sensitivity
• Fig 3.9

21
Plant Adaptations Moisture Stress

• Water stress escapees
• Annual plants
• Water stress avoiders
• Cacti
• Drought deciduous (Fouquieria splendens
  ocotillo)
• Water stress tolerators
• Selaginella lepidophylla resurrection plants

22
Cactus Family - avoiders

• Fine surface root systems
• Enlarged stems to store water
• Light colored thorns reflect light
• CAM ps pathway (stomota open at night)
• Slow growth rates

23
Moisture - Excess

• Diffusion of O2 through water is slow!!
• Plantanus occidentalis (sycamore) growth declines
  at gt50 soil moisture saturation

24
Moisture - Animals

• 2/3 water by weight
• Mammal losses 15-20 water fatal
• Water loss lower in arid dwellers
• Ex. Kangaroo rat (Dipodomys spectabilis)
• Dry urine, feces
• No sweat
• Nocturnal
• Water from dry food!

25
Other Physical Factors

• Chemical nutrients/environment
• Nitrate, phosphorous, potassium in plants
• Salinity, oxygen for aquatic orgs.
• Combinations of factors

26
Geographical Range vs. Density

• Range Area where species is found
• Density Abundance per unit area (rare versus
  common)
• Highest densities in range center

27
Gaussian Curve and Environmental Gradients

• Physiological functioning
• Density

28
What is a niche?

• Ecological concept
• Species exist in a multi-dimensional space
  defined by various limiting factors that affect
  physiological functioning and abundance

29
Generalist vs. Specialist

• Generalist wide ranges of environmental
  tolerances
• Specialist restricted gradient distributions

30
Correlation Caveat

• If the geographic range of a species and some
  climatic variable overlap, does that mean that
  this variable controls the range of this species?
  
• What other factors might affect a species range?