Environmental Controls on Life

• Light

• Temperature

• Moisture

Picea glauca & 10°C July isotherm

Light

• Heliophytes – – sun loving (shade intolerant)

– C4, CAM

• Sciophytes – – shade loving (shade tolerant)

– C3

Photosynthesis and Light• PS increases until maximum, then

declines

• Hyperbolic shape

• Compensation point

• Saturation point

• Photoinhibition

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)

• Large, soft leaves

• High amounts of chlorophyll

• Long-lived leaves

• Heliotropic leaves!

Physical Adaptations to Low Light Environment

Life History Adaptations to Light

• Annuals versus perennials

• Canopy trees flower more

• Seeds require light to germinate– Loblolly pine (Pinus taeda)

Physiological Adaptations to Light

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

Temperature - Plants

• Poikilothermic

• Optimum temperature for photosynthesis - varies

• EX. Circumarctic treeline – Cold stress, freezing

damage

Black spruce (Picea glauca) limits and July temps

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

• Saguaro – CAM photosynthesis– Palo Verde nurse shrubs

Plant Adaptations to Temperature

Plant Adaptations to Temperature

• Palm distribution

Why can’t palms be cultivated at higher latitudes?

Temperature - Animals

• Poikilotherms– “cold-blooded”-1.9°C body temp OK for

Antarctic icefish, 6°C lethal

• Homeotherms– generate heat through

metabolism– 37-47°C (10°C higher than core

temps.) lethal

Northern Limits of the Eastern Pheobe

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

Allen’s Rule

• Low latitude = high surface area:volume

• High latitude = low surface area: volume

• Low latitude = long extremities

• High latitude = short extremities

Latitude and Body Shapes

Adaptations to Moisture - Plants

• Photosynthesis

• Turgor (rigidity)

• Movement of nutrients (vascular plants)

• Xerophytes – dry loving

• Mesophytes – moist loving

• Hydrophytes – water loving

Transpiration

Release of water to atmosphere by plants

Generally through stomata

Evapotranspiration = transpiration + evaporation

Water Stress and Range• Moisture deficit =

evaporative demand > root absorbtion

• Creosote (Larrea tridentata)

= -2.0- -2.9 Mpa

• Alder (Alnus spp)

= -1 Mpa

Lower Treeline• High elevations:

– Lower evaporative demand– Higher rainfall (orographic)

• Seedlings have highest sensitivity

• Fig 3.9

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”

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

Moisture - Excess• Diffusion of O2 through

water is slow!!

• Plantanus occidentalis (sycamore) growth declines at >50% soil moisture saturation

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!

Other Physical Factors

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

• Combinations of factors

Geographical Range vs. Density

• Range: Area where species is found

• Density : Abundance per unit area (rare versus common)

• Highest densities in range center

Gaussian Curve and Environmental Gradients

• Physiological functioning

• Density

What is a niche?

• Ecological concept

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

Generalist vs. Specialist

• Generalist: wide ranges of environmental tolerances

• Specialist: restricted gradient distributions

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?