Living Planet 2010

2. Living Planet 2010

6. Responses by sedentary organisms • Plants, aquatic invertebrates • In all (except equatorial environments), physical conditions follow a seasonal cycle • Morphological and physiological characteristics must change accordingly

7. Animal responses to environmental temperatures • 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

8. Organisms maintain a constant internal environment. • 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

9. Negative feedback system

10. Temperature Regulation: an Example of Homeostasis • 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

11. Homeostasis is costly. • 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

12. Limits to Homeothermy • 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

13. Partial Homeostasis • 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)

14. Hummingbirds maintain a constant low body temp when in torpor

15. Plant resources

16. Resources may be either biotic or abiotic components of the environment • Organisms that are fixed and ‘rooted’ in position cannot search for food; must grow toward their resources – like a shoot or a root – or catch resources that move to them • Green plants depend on: • Energy that radiates to them • Atmospheric carbon dioxide that diffuses to them • Mineral cations that they obtain from soil colloids in exchange for hydrogen ions • Water and dissolved anions that the roots absorb from the soil

17. Solar radiation • Green plants use only ~ 44% of that narrow part of the spectrum of solar radiation that is visible to us between infrared and ultraviolet • Rate of photosynthesis increases with intensity of radiation that a leaf receives – but with diminishing returns. What does that mean?

18. Response of photosynthesis by leaves of various types of green plants

19. Solar radiation • Sun and shade plants and sun and shade leaves • Photoinhibition of photosynthesis – rate of fixation of carbon decreases with increasing radiation intensity • High radiation  overheating • Solar radiation – dynamic • Angle and intensity change – diurnally; cloud cover; leaf shadowing

21. water • Most plant parts are largely composed of water; as much as 98% of soft leaves; minute fraction of water that passes through plant • Wilting  if rate of uptake falls below rate of release, body of plant starts to dry out; cells lose turgidity; plant wilts

22. Moving Water from Roots to Leaves • 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)

23. Water potential that moves water from the roots to the leaves of a plant is generated by transpiration

24. Plants and water • Species of green plants differ in who they survive dry environments • Avoiders: desert annuals, annual weeds, and most crop plants • Short lifespan; photosynethetic activity [ ] during periods when + balance; otherwise dormant as seeds or shed their leaves • Tolerators: produce long-lived leaves that transpire slowly • Tolerate drought; slower photosynthesis

25. Adaptations to Arid Environments • 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

26. Adaptations to Arid Environments • 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

27. Spines and hairs help plants adapt to heat and drought. (a) cross section; (b) surface view of the leaf of the desert perennial herb

28. This drought-resistant plant reduces water loss by placing its stomates in hair-filled pits on the leaf’s undersurface

29. Leaves of desert plants: adaptations These 3 species from the Sonoran Desert in Arizona all have adaptations that help them cope w/ hot, dry conditions

30. Plants and heat • Evaporation of water lowers temperature of body • If plants are prevented from transpiring – they may overheat; die from heat • Example: desert honeysweet – grows strongly; leaves killed if temp reaches 50C; • Transpiration cools leaf surface to a 40-45C • How?

31. Water and Salt Balance in Terrestrial Plants • 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

32. Mangrove plants have adaptations for coping with a high salt load. (a) roots immersed in salt water at high tide; (b) specialized glands in the leaves excrete salt

33. Plants and Mineral nutrients • Roots: extract water and minerals from soil • N, P, S, K, Ca, Mg, and Fe • Traces of Mn, Zn, Cu, and B • All from the soil • Root architecture • Foraging efficiency

34. Plants and carbon dioxide • Variations beneath a canopy • Carbon dioxide [ ] is highest very close to the ground in the summer – where it is released rapidly from decomposing organic matter in the soil • Daytime photosynthesizing plants: actively remove CO2 from the air; night [ ] increase as plants respire • Winter: low temperatures  rates of photosynthesis, respiration, and decomposition – all slow • Aquatic environments: variations in CO [ ] highest when water mixing is limited • Summer: layers of warm water towards the surface and colder, carbon-dioxide rich layers beneath

35. Carbon cycle