Physical conditions and availability of resources

Physical conditions and availability of resources Chapter 3 - continued

Resources vs conditions • 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

Environmental Conditions • 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’

Environmental Conditions • (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)

Temperature limits the occurrence of life. • 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

Tolerance of Heat • Most life processes are dependent on water in its liquid state (0-100oC). • Typical upper limit for plants and animals is 45oC (some cyanobacteria survive to 75oC and some archaebacteria survive to 110oC). • Good: high temp -> organisms develop quicker • The bad: High temperatures: • denature proteins • accelerate chemical processes • affect properties of lipids (including membranes)

Metabolic Effectiveness • 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?

Oxygen consumption increases as a function of temperature

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

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

Metabolic theory of ecology • 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

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

WHAT ABOUT FREEZING TEMPERATURES?

Freezing temperatures… • 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

Tolerance of Freezing • 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

Tolerance of cold • Note: absolute temperature is important • Also important: timing and duration of temperature extremes • Remember: an individual need only be killed once

Environmental Conditions as stimuli

What are the stimuli for change • 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)

photoperiod • 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

Environmental conditions… • … 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

acclimatization •  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

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

Acclimation to low temperatures 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

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

Glycoproteins act as a biological antifreeze in the antarcticcodthe fish’s blood and tissues don’t freeze due to the accumulation of high concentrations of glycoproteins, which lower its freezing point to below the min temp of seawater (-1.8C) and prevent ice crystal formation

supercooling • 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

Each organism functions best… • …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

Enzymes and temperatures and swimming • 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

Compensation is possible. • 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 20oC

Irreversible developmental responses • 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

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

Phenotypic plasticity allows individuals to adapt to environmental change • Reaction norm  observed relationship between the phenotype of an individual and the environment

Phenotypic plasticity allows individuals to adapt to environmental change • 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…)

Reaction norms of populations adapted to different environments may differ

Reaction norms may be modified by evolution • May diverge when two populations of the same species exist for long periods under different conditions…

Genotype – environment interaction • 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  genotoype – environment interaction because each genotype responds differently to environmental variations • How to identify them?  reciprocal transplant experiment (remember?)

Effects of conditions on interactions between organisms • 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

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

Temperature and condition 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

Physical conditions and availability of resources