Chapter 3

What is the difference between a resource and a condition?

An environmental condition is… A resource is consumed by organisms

for growth and reproduction Thus: organisms may compete with

each other for a share of a limited resource

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What is a ‘harsh’ or ‘benign’ or ‘extreme’ environment?

Temperature, relative humidity, and other physicochemical conditions induce a range of physiological responses in organisms – which determine whether the physical environment is habitable or not to them

Three basic types of ‘response curve’

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(a) extreme conditions are lethal but between the two extremes is a continuum of more favorable conditions. Notice range of growth and reproduction

(b) condition lethal only at high intensities. (eg: poisons) (c) conditions required by organisms at low [ ] but toxic

at high [ ] (eg: copper and sodium chloride)

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• most life processes occur within the temperature range of liquid water, 0o-100oC

• few living things survive temperatures in excess of 45oC

• freezing is generally harmful to cells and tissues

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Most life processes are dependent on water in its Most life processes are dependent on water in its liquid state (0-100liquid state (0-100ooC).C).

Typical upper limit for plants and animals is 45Typical upper limit for plants and animals is 45ooC C (some cyanobacteria survive to 75(some cyanobacteria survive to 75ooC and some C and some archaebacteria survive to 110archaebacteria survive to 110ooC).C).

Good: high temp -> organisms develop quickerGood: high temp -> organisms develop quicker

The bad: High temperatures:The bad: High temperatures: denature proteinsdenature proteins accelerate chemical processesaccelerate chemical processes affect properties of lipids (including affect properties of lipids (including

membranes)membranes)

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Temperature and Metabolism High temperature increases speed of

molecular movement High temperature speeds up chemical

reactions For each 10C rise in temperature – rate of

biological processes often roughly doubles Effects on rates of growth or development

or on final body size?

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Rate of oxygen consumption of the Colorado beetle – increases non-linearly with temperature

Doubles for every 10C rise up to 20C - increases less fast at higher temperatures

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Linear relationships between rates of growth and development and temperature for protist

Temperature has consistent effects on a range of processes important to ecology and evolution (Univ of New Mexico ecologists) Rates of metabolism Rates of development of individuals Productivity of ecosystems Rates of genetic mutation Rates of evolutionary change Rates of species formation

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Temperature has consistent effects on a range of processes important to ecology and evolution (Univ of New Mexico ecologists) Rates of metabolism Rates of development of individuals Productivity of ecosystems Rates of genetic mutation Rates of evolutionary change Rates of species formation

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Increasingly: ecologists are asked to predict consequences of say – a 2C rise in temperature

What about cold temperatures? Chilling injury: organisms may be

forced into extended periods of inactivity and cell membranes of sensitive species may begin to break down; affects many tropical fruits

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Temperatures rarely exceed 50 degrees C (except….) Note: water can supercool to temperatures

as low as -40C w/o forming ice Sudden shock allows ice to form within plant

cells this is lethal If temperatures fall slowly – ice can form

between cells dehydrated cells impact to cell like high-temperature drought

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• Freezing disrupts life processes and ice crystals can damage delicate cell structures.

• Adaptations among organisms vary:• maintain internal temperature well above freezing• activate mechanisms that resist freezing

• glycerol or glycoproteins lower freezing point effectively (the “antifreeze” solution)

• glycoproteins can also impede the development of ice crystals, permitting “supercooling”

• activate mechanisms that tolerate freezing

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Note: absolute temperature is important

Also important: timing and duration of temperature extremes

Remember: an individual need only be killed once

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Proximate factors (day length, for example) – an organism can assess the state of the environment but these factors do not directly affect its fitness

Ultimate factors (food supplies, for example) – environmental features that have direct consequences on the fitness of the organism

Photoperiod: the length of daylight: proximate factor to virtually all organisms Winter day shortens bears and other

mammals develop a thick coat; insects enter dormant phase (diapause)

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Insects may speed up development as daylength decreases (winter); and speed up development as daylength increases (spring)

Effect of daylength on larval development time in the butterfly

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… may trigger an altered response to the same or even more extreme conditions

Eg: exposure to relatively low temperatures may lead to an increased rate of metabolism at such temperatures and/or to an increased tolerance of even lower temperatures

- acclimatization

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a shfit in an individual’s range of physiological tolerances

generally useful in response to seasonal and other persistent changes in conditions

reversible But – increased tolerance of one extreme

often brings reduced tolerance of another extreme

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Photosynthetic rate as a function of leaf temperature is shown for 3 species of plants.

Blue = 20C; Red = 45C

A species’ capacity for acclimatization may reflect the range of conditions in its environment

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Samples of the Antarctic springtail were taken from field sites in the summer (5C) on a number of days and their supercooling point (pt of freezing) determined; blue circles = control; brown circles = acclimation

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One way increased tolerance is achieved: forming chemicals that as antifreeze compounds Prevent ice from forming within the cells

and protect their membrane if ice does form

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Another physical solution to freezing is the process of lowering the temperature of

a liquid or gas below its freezing point w/o it becoming a solid

Liquids can cool below the freezing point w/o ice crystals development Ice generally forms around some object (a seed) In a seed’s absence, pure water may cool more

than 20C below its freezing point w/o freezing Recorded to -8C in reptiles and to -18 in

invertebrates Glycoproteins in the blood impede ice formation

by coating developing crystals

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…under a restricted range of temperatures (but of course!)

Optimum: narrow range of environmental conditions to which organism x is best suited

Temperature! One such example. Put a tropical fish in cold water and it becomes

sluggish and soon dies; put an Antarctic fish in temperatures warmer than -5C, and it won’t tolerate it

but Many fish species from cold environments swim as

actively as fish from the tropics

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Different temperatures result in different enzyme formation (in quantity or in qualitative difference of the enzyme itself)

Rainbow trout: Low temp in its native habitat during the

winter Higher temp in the summer

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Many organisms accommodate to predictable environmental changes through their ability to “tailor” various attributes to prevailing conditions: rainbow trout are capable of producing two

forms of the enzyme, acetylcholine esterase: winter form has highest substrate affinity between

0 and 10oC summer form has highest substrate affinity

between 15 and 20oC30

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Developmental responses when conditions persist for long periods – env may influence individual development so as to modify the size or other attributes of the individual for long periods

Striking example: the African grasshopper – changes color to match the color of their environment

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Most grasshoppers complete their life cycle within a single season

So in habitats where this color progression occurs – the pigment systems in the epidermis develop in such a way that the nymphs an adult grasshoppers match the background

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Reaction norm observed relationship between the phenotype of an individual and the environment

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Some reaction norms are a simple consequence of the influence of the physical environment on life (heat energy accelerates most life processes certain caterpillars grow faster at higher temperatures … but individuals of the same butterfly species from MI and AL have different relationships between growth rate and temperature…)

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Reaction norms of populations adapted to different environments may differ

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Reaction norms may be modified by evolution

May diverge when two populations of the same species exist for long periods under different conditions…

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When the reaction norms of two genotypes cross for some aspect of performance, then individuals with each genotype perform better in one environment and worse in another environment (eg: swallowtail butterfly)

This relationship genetoype – environment interaction because each genotype responds differently to environmental variations

How to identify them? reciprocal transplant experiment (remember?)

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Temperature does not act on 1 species alone; also impacts its competitors, its predators, its prey Conditions may affect availability of a

resource (a prey, e.g.) … conditions disease

Conditions may favor spread of infection, growth of parasite, or weaken/strengthen defenses of host

…conditions competition

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Proportion of grasshoppers with observable infection with pathogen drops sharply as grasshoppers spend more of their time at high temperatures

Grasshoppers that regularly experience such temperatures effectively escape serious infection

Proportion of grasshoppers with observable infection with pathogen drops sharply as grasshoppers spend more of their time at high temperatures

Grasshoppers that regularly experience such temperatures effectively escape serious infection

Fungal pathogens of grasshopper in the US develop faster at warmer temperatures – but fail to develop at all at temperatures around 38C and higher

Fungal pathogens of grasshopper in the US develop faster at warmer temperatures – but fail to develop at all at temperatures around 38C and higher

Changing temperature reverses outcome of competition. At low temp (6C) (left) S. malma fish out survives; at 12 C (right) S. leucomaenis drives S. malma to extinction; alone, they both can live at either temperature

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Plants, aquatic invertebrates In all (except equatorial environments),

physical conditions follow a seasonal cycle

Morphological and physiological characteristics must change accordingly

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First: what is their relationship with water?

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Once water is in root cells, then what? water moving to the top of any plant must

overcome tremendous forces caused by gravity and friction in conducting elements (xylem):

opposing force is generated by evaporation of water from leaf cells to atmosphere (transpiration)

water potential of air is typically highly negative (potential of dry air at 20 oC is -1,332 atm)

force generated in leaves is transmitted to roots -- water is drawn to the top of the plant (tension-cohesion theory)

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Most water exits the plant as water vapor through leaf openings called stomates: plants of arid regions must conserve limited

water while still acquiring CO2 from the atmosphere (also via stomates) - a dilemma!

potential gradient for CO2 entering plant is substantially less than that for water exiting the plant

heat increases the differential between internal and external water potentials, making matters worse

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Numerous structural adaptations address challenges facing plants of arid regions by: reducing heat loading:

increase surface area for convective heat dissipation increase reflectivity and boundary layer effect with

dense hairs and spines reducing evaporative losses:

protect surfaces with thick, waxy cuticle recess stomates in pits, sometimes also hair-filled

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These 3 species from the Sonoran Desert in Arizona all have adaptations that help them cope w/ hot, dry conditions

Desert plants reduce heat loading in several ways – in addition to what has already been discussed. Plants may, in addition: orient leaves to minimize solar gain shed leaves and become inactive during

stressful periods

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Plants take up excessive salts along with water, especially in saline soils. plants must actively pump salts back into soil

In coastal mudflats, mangroves must acquire water while excluding salts. They: establish high root osmotic concentrations to

maintain water movement into root exclude salts at the roots and also excrete

excessive salts from specialized leaf glands

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Most species of animals are, like plants, ectotherms: rely on external sources of heat to determine their pace of metabolism Fish, amphibians and lizards

Others – endotherms: regulate their body temperature by producing heat within their body Mainly birds and mammals

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An organism’s ability to maintain constant internal conditions in the face of a varying environment is called homeostasis: homeostatic systems consist of sensors,

effectors, and a condition maintained constant

all homeostatic systems employ negative feedback -- when the system deviates from set point, various responses are activated to return system to set point

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Principal classes of regulation: homeotherms (warm-blooded animals) -

maintain relatively constant internal temperatures

poikilotherms (cold-blooded animals) - tend to conform to external temperatures

some poikilotherms can regulate internal temperatures behaviorally, and are thus considered ectotherms, while homeotherms are endotherms

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As the difference between internal and external conditions increases, the cost of maintaining constant internal conditions increases dramatically: in homeotherms, the metabolic rate

required to maintain temperature is directly proportional to the difference between ambient and internal temperatures

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Homeotherms are limited in the extent to which they can maintain conditions different from those in their surroundings: beyond some level of difference between

ambient and internal, organism’s capacity to return internal conditions to norm is exceeded

available energy may also be limiting, because regulation requires substantial energy output

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Some animals (and plants!) may only be homeothermic at certain times or in certain tissues…

pythons maintain high temperatures when incubating eggs

large fish may warm muscles or brain some moths and bees undergo pre-flight warm-

up hummingbirds may reduce body temperature

at night (torpor)

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Variability of conditions: biological challenge Seasonal cycle: can push an animal to

summer heat close to its thermal maximum and winter chill close to its thermal minimum

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