Temperature Relations

Transcription

1 Temperature Relations Reading: Molles & Cahill 2008 Chapter 5 Ecophysiology (Physiological Ecology): considers physiological responses of individual organisms to environmental conditions. Today we will consider individual responses to temperature. Note that this topic is often related to water (our next topic.)

2 Temperature responses have both genetic and environmental components Acclimation physiological adjustment to environmental conditions over an individual s life. Adaptation evolutionary adjustment (via genetic traits) to environmental conditions over the long term. Key terms: Adaptation - evolutionary response - Genetically fixed Long-term response Acclimation physiological adjustment Behavioral responses ( strategies ) Controlled by organism Short term response These terms differ according to the time frame and mechanism of response.

3 Key terms (continued) Macroclimate what affects biome distributions, and what we measure with weather stations (affected by altitude, season, etc.) Microclimate what individual organisms experience (affected by slope, aspect, albedo, height off the ground, proximity to water, behavior, etc.) Macroclimate and microclimate are inter-related (e.g. microclimate is partly determined by macroclimate) Temperature and moisture are two factors that vary dramatically with macro/microclimate Examples of factors influencing microclimate Slope and aspect Proximity to neighbors ( nurse plants ) Albedo (reflectivity) Proximity to water (thermal mass)

4 Slope (steepness) & aspect (direction of slope) affect temperature and moisture Fig. 5.2, Molles & Cahill 2008 Proximity to neighbors e.g. Nurse plant effect affects microclimate The presence of a nurse plant often enables germination and survival of younger plants, particularly in hot climates. Molles 2008

5 Albedo (reflectivity) affects microclimate White vs. black sands Snow vs. soil background Fig. 5.4, Molles & Cahill 2008 Proximity to water affects microclimate Large water bodies with their high thermal mass (heat capacity) tend to buffer temperatures Fig. 5.7, Molles & Cahill, 2008

6 Note the thermal stability of water, compared to air Thermal tolerance Molles 2008 Some organisms must exist within a narrow temperature range in order to function this temperature range defines their thermal tolerance ) Understanding tolerance limits and how they affect fitness and distributions of organisms have been central topics in physiological ecology.

7 Temperature response curves of bacteria Psychrophilic bacteria from Antarctica Thermophilic bacteria from hot springs Adaptation or acclimation? How can we tell? Figs & 5.15, Molles & Cahill, 2008 Temperature response curves in plants Plants from contrasting biomes but is this a genetic adaptation or phyiological acclimation? Transplant experiments reveal physiological acclimation Figs & 5.13, Molles & Cahill 2008

8 Evidence for acclimation in fish Further evidence for physiological acclimation at a biochemical level Fig. 5.10, Molles & Cahill 2008 Energy Balance A quantitative analysis of an organism s response to microclimate. Derived from the First Law of Thermodynamics (conservation of energy) Provides a formal, mathematical way to understand temperature responses.

9 One version of the energy balance equation Where: (Molles 2008) Hs = heat storage by organism Hm = heat gained by metabolism Hcd = heat gained or lost via conduction Hcv = heat gained or lost via convection Hr = heat transferred through radiation/re-radiation (radiative transfer) He = heat lost via evaporation (vaporization) Organisms control their energy balance through adaptation, acclimation, and behavioral responses Terminology related to temperature: Endotherms metabolic control over body temperature. (e.g. homeotherms must maintain constant body temperature e.g. mammals) formerly called warmblooded Ectotherms body temperature controlled by environment (poikilotherms e.g. most reptiles & plants) formerly called coldblooded

10 Terminology related to temperature: Endotherms metabolic control over body temperature. (e.g. homeotherms must maintain constant body temperature e.g. mammals) formerly called warmblooded Ectotherms body temperature controlled by environment (poikilotherms e.g. most reptiles & plants) formerly called coldblooded Endotherms vary metabolic rate to maintain a constant temperature Note how the thermal neutral zone defines the optimal temperature for an endotherm Fig. 5.25, Molles & Cahill 2008

11 Thermal neutral zones for arctic and tropical mammals Fig. 5.26, Molles & Cahill 2008 Manduca sexta (moth) an example of an endotherm Fig. 5.30, Molles & Cahill 2008

12 Plants are normally ectotherms, but some plants can be endotherms! (use metabolically generated heat to warm the plant body) Figs & Molles & Cahill, 2008 Terminology related to temperature: Endotherms metabolic control over body temperature. (e.g. homeotherms must maintain constant body temperature e.g. mammals) formerly called warmblooded Ectotherms body temperature controlled by environment (poikilotherms e.g. most reptiles & plants) formerly called coldblooded

13 Lizards are a good example of ectotherms use external energy to regulate body temperature. Lizards exhibit behavioral responses to maintain an optimal temperature Fig. 5.21, Molles & Cahill 2008 Molles 2008 Evidence of genetic constraints on optimal temperature in lizards Fig. 5.11, Molles & Cahill 2008

14 Like lizards, many plants use behavior to adjust their energy balance Darwin, C. (1880) The Power of Movement in Plants Some plant organs (leaves and flowers) can alter their temperature through heliotropism (solar tracking - following or avoiding the sun). These arctic flowers act as solar-tracking parabolic reflectors, directing the heat to the ovaries and hastening seed production. Papaver radicatum - Arctic poppy Dryas integrifolia (Images from Wikipedia)

15 Plants adjust their temperature by a variety of responses (adaptation, acclimation, and behavior) Fig. 5.16, Molles & Cahill 2008 Fig. 5.19, Molles & Cahill 2008

16 What do organisms do when temperatures exceed their range of thermal tolerance? Get dressed! Escape! Die! Certain mammals hibernate to avoid temperature or moisture extremes Molles 2008

17 Limits to thermal tolerance: extinction of local snail populations in Switzerland with warming Molles 2008