Temperature and Thermal Biology: Influences, Terminology, and Heat Transfer

1. Temperature

2. Temperature • Average kinetic energy of a system • Arguably the most important aspect of the physical environment for life • Influences geographic distributions of species • Influences interspecific competition

3. Temperature Ranges • For most living, active animals: • -2 °C (polar aquatic species) to 50 ° C (desert spp.) • Few species can survive entire range

4. Terminology of Thermal Biology • Various terms used to describe thermal biology of animals: • Cold-blooded vs. Warm-blooded • Poikilothermic vs Homeothermic • Ectothermic vs. Endothermic

5. Cold-blooded vs. Warm-blooded • Description of relative body temperature • “Warm-blooded” = high body temperature • Mammals and birds • “Cold-blooded” = low body temperature • Reptiles, amphibians, fish, invertebrates • Tend to be inaccurate • Many “cold-blooded” animals have high body temperatures (e.g. desert reptiles and invertebrates) • Many “warm-blooded” animals may have low body temperatures (e.g. hibernating mammals)

6. Homeothermic vs. Poikilothermic • Description of variation in body temperature • Homeothermic – body temp. strictly regulated • Mammals and birds • Poikilothermic – body temp. may fluctuate widely • “Lower” vertebrates and invertebrates • Problems • Many “poikilotherms” normally have stable body temperatures under natural conditions • Some “homeotherms” have broad seasonal changes in body temperature (hibernation, etc.)

7. Endothermic vs. Ectothermic • Description of heat production • Endothermic – most body heat is physiologically generated (muscle contraction) • Ectothermic – most body heat derived from the environment (solar radiation, etc.) • Problems • Some animals generate lots of heat but do not use it to regulate body temperature

8. Determinants of Body Temperature • Temperature depends on the amount of heat (calories) contained per unit mass tissue • # calories contained per °C determined by the heat capacity of the tissues (~ 0.8 cal*°C-1*g-1) • Amount of heat in body depends on… • Rate of heat production • Rate of external heat gain • Rate of heat loss to the environment • Body heat = heat produced + heat transferred

9. Heat Transfer Three ways of transferring heat • Conduction – transfer of heat between objects in contact with one another • Radiation – transfer of heat by electromagnetic radiation • Evaporation – transfer of heat to water as it changes from liquid to gaseous phase

10. Conduction • Transfer of kinetic energy between two objects in contact • Heat moves from warmer region to cooler region • Rate of transfer: • H = rate of heat transfer per cross sectional area • k = thermal conductivity of the conductor • d = distance between two points • T1 and T2 = temperature at points 1 and 2

11. Conduction and Convection • Conduction rate is increased by convection • Movement of gas or liquid over the surface of transfer • Continuous replacement of fluid maximizes temperature difference and facilitates heat transfer

12. Radiation • Transfer of heat via electromagnetic emission • Objects do not require contact • Stefan-Boltzmann law: H = εσTs4 • H = rate of heat exchange per unit area • ε = emissivity (wavelengths at which EM radiation is emitted,~3-4 μm for most objects on earth) • σ = Stefan-Boltzmann constant • Ts = surface temperature of the object • Net heat exchange is from the object with the higher Ts to the one with the lower Ts

13. Evaporation • Only means by which heat can be lost to a hot environment • Vaporization of water requires heat • ~ 2400 kJ per g water absorbed from the surface of the animal • Evaporative cooling used to dissipate heat • Sweating, panting

14. Heat Storage • Animals can store heat in their bodies by moderating heat transfer to the environment • Factors Affecting Heat Transfer • Surface Area/Volume Ratio • Larger animals have proportionately lower heat flux • Temperature Gradient • Between body and environment • Lower gradient, slower heat transfer • Specific Heat Conductance • Insulation – reduces heat conductance

15. Total Body Heat Htotal = Hv + Hc + Hr + He + Hs Hv = heat produced by metabolism (+) Hc = heat loss/gain by conduction and convection (+/-) Hr = heat transfer via radiation (+/-) He = heat loss by evaporation (-) Hs = stored heat (+)

16. Effects of Body Temperature Change • Temperature affects the rate of chemical reactions • Affects chemical reactions needed to maintain homeostasis • Too low • metabolism not fast enough to maintain homeostasis • Too high • reactions in metabolic pathways uncouple, enzymes denature, etc.

17. Changes in Metabolism with Body Temperature • Temperature Coefficient (Q10) – factorial increase in a rate with a 10 °C increase in temperature Q10 = (R2/R1) 10/T2-T1 • R2 and R1 • reaction rates at temperatures T2 and T1 respectively • If T2 and T1 differ by 10 °C, Q10 = (R2/R1) • Typical Q10 values for biological rates (metabolic rate, etc) range from 2 to 3 (doubling or tripling of rate)

18. Changes in Metabolism with Temperature • Q10 values often change across a range of temperatures • Performance curves • Initial large increase, followed by smaller increases

19. Light

20. Effects of Artificial Light:- Orientation and Attraction/Repulsion- Reproduction- Communication- Competition- Predation- Ecosystem disruption

21. Complex Ecosystem

22. Effects of Artificial Light Living things respond in a variety of ways to impacts on the environment. Some examples of the effect of light at night are well known - moths gathering around a street lamp, or the harvesting of fish with spotlights. These changes can have a dramatic effect on humans - as for example the negative impact of light at night on the salmon fishery.

23. Terrestrial Mammals

24. Terrestrial Mammals Possible effects: - disruption of foraging behaviour - increased risk of predation - disruption of biological clocks, affecting mating success and group-mediated anti-predator vigilance - increased road deaths due to blinding and disorientation - disruption of dispersal movements and corridors Increased highway lighting is not effective in reducing deer-car collisions.

25. Terrestrial Mammals Many mammals (small carnivores, rodents) are nocturnal. These are affected by light at night. Night-adapted animals have a rod-based retina, which provides the necessary sensitivity for night vision but blinds the animal in bright light. Light (moonlight) increases the risk of predation, so small mammals stay hidden. A light level of 0.2 lux was sufficient to suppress melatonin production in rats and enhance tumor production.

26. Bats

27. Bats Insects are attracted to lights, bats then gather in the lights to feed on these insects. Moths evade bats by detecting their ultrasound, but moths do not use this warning in bright light, so they are an easy target.

28. Bats In several mountain valleys in switzerland, the lesser horseshoe bat became locally extinct after streetlights were installed. They were replaced by pipistrelle bats, who feed at streetlights

29. Migrating Birds

30. Migrating Birds

31. Migrating Birds Migrating birds tend to move toward light and are reluctant to leave the lighted area. - delays migration - mortality due to exhaustion and collision with structures. Floodlit structures attract and kill birds, particularly in misty weather.

32. Sea Turtles

33. Sea Turtles Hatching turtles are disoriented by artificial light, causing them to go inland instead of to the sea. Artificial light also aids predation of the hatchlings. A number of measures have been taken with some success. These include shielding of luminaires, reducing light output, installing motion detectors and light curfews, and LED lighting embedded in roadways. All coastal buildings must now have a lighting plan. However, problems continue with population growth and lighting further inland that creates sky glow. Local lighting controls are not a complete solution.

34. Reptiles Gecko

35. Reptiles Rattle snakes and water snakes hunt in the dark of the new moon. These species have declined in areas of heavy light pollution. Gecko mating is curtailed in artificial light.

36. Frogs and Toads

37. Frogs and Toads Frogs and toads have extremely sensitive night vision, and can see in light levels of 10^-6 (10000000) to 10^-5 (1000000) lux. (Moonlight is typically about 1 lux). They are nocturnal, so light at night affects them and their predator-prey relationship. Some species are attracted to light, which acts as an 'evolutionary trap'. Mating behaviour (chorusing) and fertility (in toads) are inhibited under artificial light. After exposure to bright light (along a highway, for example) frog night vision can take hours to restore to night vision sensitivity.

38. Salamanders Newt

39. Salamanders Salamanders are aquatic animals. Newts rely on the day-night transition to initiate foraging, and rely on the characteristics of natural light for navigation. Artificial light interferes with both these activities, and may be one factor in their population decline.

40. Fishes Sea Trout

41. Fishes Some fish species are attracted to light, and fishing vessels use high-intensity lamps to attract their prey. Mercury-vapour lamps have been used to attract fish into special channels around dams and power stations. Other fish species avoid light. In Scotland, lights from a tennis court eliminated sea trout from a nearby river.

42. Fishes Juvenile rainbow trout are inhibited from foraging by moonlight or artificial light. Darkness is essential for fish to avoid predation. Harbour seals have learned to use artificial light to outmigrating smolts. Salmon fry are inhibited from migration by light levels in excess of 1 lux. Several species are inhibited from spawning (laying eggs) by light at night

43. Insects and Streetlamps Insects are critically important as pollinators and members of food webs in an ecosystem. Lamp Effects on beetles, moths, flies, caddisflies: Fixation or Capture Insect cannot escape near zone of the light. Crash Barrier Flight path is interrupted so insects cannot migrate Vacuum Cleaner Insects are removed from the area local to the lamp.

44. Insects and Streetlamps

45. Insects and Streetlamps Radius of attraction: 400 to 600 metres under full darkness, 40 to 60 metres under full moon. In dark zones, the attraction has been 2000 to 11000 insects per night. In a rural village with lighting, 400 to 1600 insects per night per lamp. Approximately 1/3 of the insects are killed or incapacitated. In order, worst to best, are high-pressure mercury, high-pressure sodium and low-pressure sodium lamps. Insect attraction can be reduced with a UV filter.

46. Insects and Streetlamps Mayflies

47. Moths

48. Moths Areas around artificial lights function as bat, bird, gecko and spider feeding stations. Some bats live only a few days, so any disruption of their behaviour has an effect on the population. Light interferes with dispersal, which inhibits resistance to habitat fragmentation. Light greater than 0.05 lux inhibits mating in one species of moth.

49. Moths Lamp with ultraviolet component (mercury vapour, LED) is a strong attractant. Low pressure sodium vapour rarely attracts moths. Individual lamps attract more strongly than an aggregate of lamps. One lamp trap collected 50,000 moths in a single evening. A typical catch rate is 4 to 10,000 insects per year. Artificial light can inhibit moth parasites.

50. Fireflies Artificial light swamps the luminescent mating communications of fireflies. Continuous light (due to skyglow) may affect the timing of development from pupa to fly. Artificial light inhibits the resettlement of fragmented habitat (light barrier effect).